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SECTION II
INDUSTRY CHARACTERIZATION
This document presents an analysis of the available
technologies for the control of water pollution from the
concrete products industry, and will provide guidance in
determining permit requirements issued under the National
Pollutant Discharge Elimination System (NPDES).
The products covered in this report are listed below with
their SIC designations:
a. Concrete Block and Brick (3271)
b. Concrete Products, N.B.C. (3272)
c. Ready-Mixed Concrete (3273)
The data for identification and analyses were derived from a
number of sources. These sources included EPA NPDES permit
information, published literature, technical consultants,
on-site visits, verification sampling at manufacturing
plants throughout the U.S.,, and interviews and meetings with
various trade associations, manufacturers, and regional EPA
personnel. The references used in developing the guidelines
reported herein are included in Section XIII of this report.
Table 3 summarizes the data base for the plants studied in
this volume. In addition to those plants visited and
sampled, some additional data was collected through a survey
of 658 plants.
11
-------
TABLE 3
Summary of Data Base
Plant. Type
Total Number of
Plants in US
Plants
Surveyed
Visited
Sampled
By EPA.
Census/Industry
Concrete block and)
brick, autoclave )
curing ) 1388 1560
Concrete block and)
brick, low pressure)
steam curing )
Concrete Pipe )
Precast Concrete )
products ) 3595
Prestressed and )
Precast )
Prestressed , )
Concrete products)
Ready-Mixed )
Concrete Permanent)
Plants )
Ready-Mixed )
Concrete Portable)4915
Plants )
Ready-Mixed )
Concrete Mobile )
Plants )
390
app.2500
8000
Total
9898
12,496
7
153
12
12
11
437
21
1
658
7
9.
7
3
5
54
2
1 ,
94
1
3
2
1
3
15
0
0
27
CONCRETE BLOCK AND BRICK
The U.S. Bureau of the Census shows that in 1972 there were
1300 companies operating 1,388 establishments engaged in the
manufacture of concrete building block and brick with 416
establishments having 20 employees or more.
Concrete block and brick are classified into the following
products: structural block produced with lightweight
aggregate such as cinder, expanded shale, pumice or other
materials; structural block produced with heavyweight
aggregate such as sand, gravel, crushed stone or other
materials; decorative block - such as screen block, split
block, slump block and shadowal block; and concrete brick.
12
-------
The 1972 production for each product is given below:
Lightweight block
Heavyweight block
Decorative block
Concrete brick
1,814.7 million block equivalents*
833.1 million block equivalents*
90.2 million block equivalents*
420.7 million block equivalents*
Total 3,158.7
*Block equivalents are 20 cm x 20 cm x 41 cm (8 in. x 8 in. x 16 in.)
Industry sources indicate that 62 million kkg (69 million
tons) of concrete block and brick were produced in the U.S.
in 1972.
The process for the manufacture of concrete block and brick
consists of mixing, forming and curing. The raw materials
for the block and brick, aggregate and cement, are shipped
to the plant by rail or by truck. The aggregates are
normally stored outside and kept moist until they are
transferred to the batch plant by belt or screw conveyor
into distribution bins. The cement is usually received in
bulk form and transferred to a storage silo by screw or air
conveyor. Typically, the aggregate, cement and water are
weighed and batched into a three cubic meter (four cubic
yard) rotary mixer. The concrete mix used for production of
block and brick contains less water than ready-mixed
concrete. The mixed concrete is then fed into an automatic
block molding machine, where the moist mix is rammed,
pressed or vibrated into the desired shape. The product is
then stacked onto iron framework cars and allowed to cure at
50°C (120°F) for four hours. The quantity of water^ in the
mix is critical, as too much will cause severe shrinkage,
and too little will reduce block strength and produce
friable corners. Colors may be added to the mix to produce
decorative block. Occasionally the block may be split to
expose a rough decorative surface or may be sawed to a
particular shape.
The production of a structural high-strength block, within a
reasonable time period, necessitates curing the block under
moist conditions,- One of two methods is generally used in
the block industry: low pressure steam (75-85% of total
production); and autoclaves, high pressure steam, (15-25%).
In the low pressure steam process, the loaded curing cars
are placed into a chamber or kiln where low pressure steam
less than 9.7 atm (150 psi) is injected from perforated
pipes for approximately 8-10 hours. The length of curing is
dependent on mix conditions, user specifications, and
ambient temperature. Waste water from this curing method
13
-------
consists, primarily f of steam condensate which contains some
suspended solids, dissolved solids, and a high pH (10-11)
due to the calcium oxide content of the cement. The low
pressure steam is generated by a boiler which' requires
periodic blowdown.
The autoclave curing method produces a higher strength block
in a shorter time period with less shrinkage than the low
pressure steam curing process. The cars containing preset
blocks are loaded into a large horizontal, cylindrically
shaped autoclave where high pressure steam is injected or
convected. After a curing cycle of about 8 hours the steam
is released to the atmosphere and the blocks are removed and
prepared for storage. One special form of steam production
utilizes a hot oil convection method, where water is placed
in a trough in the autoclave, and hot oil heats the water
into steam. After completing this cycle, the autoclave is
cooled, and a portion of the steam condenses back to the
trough as water. Periodically, this water is discharged
because the alkalinity is corrosive to the steel racks.
CONCRETE PRODUCTS, NOT ELSEWHERE CLASSIFIED
Concrete products, not elsewhere classified are comprised of
three basic types of products: concrete pipe, precast
concrete products and prestressed concrete products.
According to the U.S. Bureau of the Census, 3,199 companies
operated 3595 plants in the concrete products (N.E.C.)
industry in 1972.
I
CONCRETE PIPE
' - y I r (- - e
From the 1972 Census of Manufacturers, the following is a
compilation of concrete pipe products and their prod'uction.
-------
product
kkg
production
tons
Culvert pipe
' reinforced
non-reinforced
Storm Sewer Pipe
reinforced
non-reinforced
Sanitary Sewer Pipe
reinforced
non-reinforced
Pressure Pipe
reinforced
prestressed
pretensioned
other pressure pipe
Irrigation Pipe and Drain
Tile
Other Concrete Pipe
(e.g., manholes and conduits)
2/691,000
228,000
3,321,000
150,000
1,738,000
279,000
meters
396,000
701,000
884,000
withheld
kkg
446,000
1,867,000
2,965,000
251,000
3,660,000
165,000
1,915,000
307,000
feet
1,300,000
2,300,000
2,900,000
tons
491,000
2,058,000
The basic raw materials of concrete pipe manufacture are
Portland cement, aggregate, and water. For reinforced pipe,
a steel wire cage is added to provide increased strength.
The proportions of these materials vary, depending on the
manufacturing process and strength requirement.
Concrete pipe is generally produced by three methods. The
vertical packerhead (tamping) method involves the use ' of a
moist concrete mix which is compacted and vibrated into a
steel form by a machine called a packerhead. This method is
generally used to produce pipe up to 1.5 meters (5 ft) in
diameter. The vertical cast method can be used to produce
any size of reinforced pipe, but it is generally limited to
diameters over 1.5 meters (5 ft) due to the high cost of
labor and time required. A wet concrete mix is produced in
a central mixer and transported to a vertical steel form
with transport buckets. The concrete is allowed to set,
then the forms are stripped. The spin casting production
method is generally used to produce reinforced pipe up to
1.2 meters (4 ft) in diameter. A reinforcing cage is
fabricated and positioned in a form which is then placed
horizontally on a high speed roller drive mechanism. The
form is rotated at a high rate, while the concrete is
directed evenly by a reciprocating nozzle on the inside of
the form. The spinning action densities the concrete on the
inside of the form and dewaters it. Water flows off the
inside surface of the pipe, and the concrete surface is
finished by a mechanical roller. Reinforced' concrete
15
-------
pressure pipe, produced by spin casting, uses a permanent
form, i.e., remains with the pipe. A sheet steel cylinder
is fabricated, hydraulicly tested, then placed on the spin
cast machine, and concrete is poured inside as with
reinforced pipe.
In all methods, when the concrete pipe has reached a certain
green (uncured) strength, it is cured by the application of
low pressure steam either in a kiln or in a chamber
constructed around the pipe. For pipe produced by the
tamping method, the forms are generally stripped before
steam curing, while the spin cast and vertical cast pipe
forms are generally left on the pipe during curing. All of
the pipe forms are coated with a form release oil to
facilitate the separation of the pipe and form.
The production of reinforced pipe other than pressure pipe
uses a welded wire cage for the reinforcing member which is
embedded in the circumference of the pipe. The reinforcing
cage is usually fabricated from the wire coils in an
automatic machine which cuts and welds the wire into a
cylinder.
Pressure pipe production may include the following operations;
(1) fabrication of a steel cylinder;
(2) hydraulic testing of the cylinder;
(3) insertion of the cylinder into a vertical casting form
or spin cast machine;
(4) batch mixing cement, aggregate and water;
(5) pouring, or placing and compacting, the concrete within
the pipe form;
(6) stripping the pipe forms; ;-'
(7) curing the pipe with low pressure steam;
(8) circumferentially wrapping the cured pipe with high
strength steel wire;
(9) coating the steel wire wrap with concrete grout, and
(10) inspection and storage.
The production of pressure pipe involves several more manu-
facturing steps than required for other concrete pipe
including prestressing with high strength wire. These
additional operations make the pressure pipe more expensive
to produce with a resultant increase in selling price.
16
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PRECAST CONCRETE PRODUCTS
Precast concrete products include:
product
Roof and floor units
slabs and tile
joints and beams
Architectural wall panels
Pilings, posts and poles
Cast stone (products for
architectural purposes)
Prefabricated building systems
Other precast construction prod.
Burial vaults and boxes
Silo staves
Septic tanks
Dry-mixed concrete materials
(e.g., Sakrete)
Other precast (e.g., laundry
tubs)
Estimated Total
Estimated Total {less dry mixed
concrete)
1972 production
kkq tons
370,000
110,000
694,000
84,000
unknown
148,000
unknown
235,000
139,000
1,050,000
1,748,000
unknown
4,578,000
2,830,000
408,000
121,000
765,000
93,000
unknown
163,000
unknown
259,000
153,000
1,157,000
1,926,000
Unknown
5,045,000
3,119,000
The raw materials of precast concrete products are cement,
aggregate and water. Reinforced .concrete products contain
steel structural members to provide increased strength. The
production of simple precast concrete products (i.e.,
transformer pads, meter boxes, pilings, utility vaults,
steps, cattleguards, and balconies) involves mixing the
cement, aggregate and water in a central mixer,, pouring the
concrete into forms and allowing it to cure overnight. The
forms are removed the following morning and the cure is
completed under ambient conditions.
17
-------
Precast architectural wall panels are generally finished to
produce a decorative surface of exposed aggregate. Although
there are several methods of production, the one frequently
used involves spreading a retarder in the bottom of a form,
placing reinforcing steel in the form, and casting the
concrete mix. The concrete is allowed to set, the form is
removed and the surface with the retarder added is either
washed with a weak solution of acid, sandblasted, or washed
with high pressure water. Since the retarder prevents the
setting of the surface cement, washing exposes the coarse
aggregate. The panel then cures completely in a storage
yard.
PRESTRESSED CONCRETE PRODUCTS
Prestressed concrete products are chiefly used as structural
and architectural components and include:
product
Single tees, double tees, and
channels
Piling, bearing piles, and sheet
piles
Bridge beams
Solid and hollow cored slabs
and panels
Other prestressed products
(e.g., arches)
Joist, girders, and beams
(other than bridge beams)
Total
production
kkg
14,402,000
1,470,000
470,000
2,238,000
740,000
44,000
19,364,000
tons
15,871,000
1,620,000
518,000
2,466,000
815,000
48,000
21,338,000
The raw materials of prestressed concrete products are
cement, aggregate, water, and steel tendons. Prestressed
concrete products are manufactured by:
(1) inserting the steel tendons in a metal form,
(2) stressing the steel tendons,
(3) batch mixing in a central mixer,
(4) pouring the concrete into the form,
(5) overnight curing of the product using low pressure
steam. '
(6) removal of the metal form and release of the external
stress on the steel tendons,,
(7) for certain prestressed products, end-sawing or finishing, and
(8) product testing and storage™
18
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Pros-tressed and precast products are produced similarly
except that prestressed products utilize steel cables
(tendons) in tension in place of steel rods for
reinforcement. Prestressing also prevents tension cracks in
a structural member under design loads. This normally
allows the use of a structural member with a smaller cross
sectional area and lighter in weight. Prestressed concrete
products may be either pretensioned or post-tensioned.
Prestressed pretensioned products are made by placing the
steel cables in tension in the form before concrete is
added. Once the concrete is set, cured and the forms are
removed, the external tension is released from the steel
cables. The cable remains stressed due to the compression
of the concrete around the cable. This method of
prestressing predominates in the industry.
Prestressed post-tensioned products are made by placing
cables in the form, casting the concrete, allowing it to set
and cure to a certain strength, then placing the steel
tendons under tension. Cables must be protected with a
steel or plastic tube or mastic coating to prevent bonding
with the concrete prior to tensioning. Cables may or may
not be grouted while under tension and are locked under
tension by appropriate end anchorage or clamps. An
alternate method of post-tensioning involves casting the
concrete member with a tube or slot for future insertion of
the steel tendon.
READY-MIXED CONCRETE ..";.-. . '
The ready-mixed concrete establishments engage' in
manufacturing portland cement concrete produced and
delivered to the purchaser in a plastic (unhardened) state.
Ready-mixed concrete represents the largest category of
Portland cement concrete used in the United States.
According to U.S. Bureau of Census figures, 159.4 million
cu m (208.5 million cu yd) were produced in 1972. This
total quantity of ready-mixed concrete was produced by 3978
companies operating 4,915 total establishments, of which
1,328 establishments utilized 20 employees or more.
However, the National Ready-Mixed Concrete Association
(NMRCA) puts the number of plants at approimately 8,000.
NRMCA data indicate there were 5,266 companies in 1971. A
state-by-state listing of the number of companies in this
industry in 1971 provided by NRMCA is presented in Table 4.
The two processes used for ready-mixed concrete are batching
Land1 mixing. At a, batch plant, the concrete is mixed in the
truck mixer, while at a central mix plant, the concrete is
prepared in a plant, mixer then transferred to a truck mixer
or agitator for delivery.
19
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Location of U.S.
States
Alabama
Alaska
Arizona
Arkansas
California
Colorado
Connecticut
D. C.
Delaware
Florida
Georgia
Hawaii
Idaho
Illinois
Indiana
Iowa
Kansas
Kentucky
Louisiana
Maine
Maryland
Massachusetts
Michigan
Minnesota
Mississippi
Missouri
# 1971 NRMCA
111
2
70
93
356
91
44
3
14
142
108
4
43
282
171
221
139
128
115
19
40
48
217
163
86
229
TABLE 4
Concrete Operators*
States No.
Montana 4 3
Nebraska 101
Nevada 27
New Hampshire 20
New Jersey 76
New Mexico 58
New York 207
North Carolina 98
North Dakota 43
Ohio 216
Oklahoma 163
Oregon 95
Pennsylvania 195
Rhode Island 8
South Carolina 69
South Dakota 67
Tennessee 84
Texas 290
Utah 6 2
Vermont 11
Virginia 78
Washington 78
West Virginia 52
Wisconsin 150
Wyoming 36
TOTAL 5,26^
20
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The batching and mixing equipment used at ready-mixed
concrete plants ranges in size and complexity from small
portable mixers to automated permanent plants with central
mixers capable of producing several hundred cubic meters of
concrete per hour.
The raw materials for the concrete, coarse and fine
aggregate and cement are usually shipped to the plant via
rail or truck. However, at some 300 ready-mixed
establishments according to Census figures, the coarse or
fine aggregate is mined or quarried at the plant site. The
coarse and fine aggregates are generally stockpiled in the
open, where they are kept saturated with moisture. The
aggregates are transferred to the plant by conveyor, front
end loader or crane, to distribution bins. The portland
cement is usually received in bulk form either by rail or by
truck, transferred to a cement hopper, and then conveyed to
a storage silo or to the central batch bin. The aggregates
and cement are weighed and blended into a mixer with a
premeasured quantity of water and the goncrete is mixed for
specified length of time. At a batch plant, the mixing is
accomplished in the truck mixer, while in a central mix
plant, a central mixer is used which then transfers the
concrete to an agitator truck.
Ready mix concrete plants can also be differentiated by the
location of the batching and mixing operations. The three
types of facilities are:
(1) Permanent — This type of plant uses ready-mixed trucks
which deliver various types of concrete to numerous
customers from a central plant. At a permanent plant
the concrete may be centrally mixed and hauled in
agit,ator trucks or may be dry batched into mixer trucks
and"mixed in the truck on the way to the job.
(2) Portable - This is the type of plant used on large
highway and airport paving jobs. The concrete may be
produced in a portable central mixer and hauled in
agitator trucks or it may be dry batched into trucks and
hauled to a portable mixer at the construction site.
The latter is the older method.
(3) Mobile - The mobile concrete plant utilizes trucks
capable of measuring and mixing the aggregate, cement,
and water at the job site. The raw materials are
transported separately on the mobile truck, proportioned
and mixed in the truck-mounted mixer at the job site.
Mobile ready-mixed concrete is primarily used for small
21
-------
jobs that can be economically serviced without returning
to the base plant after each job.
The permanent ready-mixed concrete plant may operate either
as a dry batch plant or a central mixer plant. In a dry
batch plant, the mix of aggregate and cement is weighed and
transferred in a dry state to the ready-mixed trucks along
with a proportioned amount of water, then mixed in the
truck. This type of operation is found in approximately
three-fourths of the plants in the permanent segment of the
ready-mixed industry. The other one-fourth of these plants
uses a central mixer with an average capacity of 4 cu m
(5 cu yd) .
A general practice in the construction industry is to order
slightly more concrete than necessary to complete the job to
prevent running short. This practice results in an excess
of concrete in the truck which must be either dumped or
reused. In some cases, the unused concrete is dumped on the
job site, however, in most cases, it returns to the plant in
the ready-mixed truck and either used for paving the plant
yard, or flushed out as waste material. The disposal of the
unused concrete depends on the amount left in the truck, the
length of time since batching, the formulation of the
following order, and other factors. The amount of returned
waste concrete varies but averages between 1 to 4 percent of
average daily production. Ready-mixed concrete plants use
water primarily in the batching of concrete, and for washing
out the ready-mixed trucks and central mixer. The washout
is an essential part of the daily operations of all concrete
plants to prevent hardening of the concrete in the equipment
and consequent lost time and maintenance costs.
•-•A:!/:.
The concrete produced by ready-mixed plants can be
considered to be made of two major components, aggregates
and paste. The aggregates generally occupy 60 to 80 percent
of the volume of concrete. The most commonly used
aggregates (sand, gravel, crushed stone, and air- cooled
blast furnace slag) produce a normal weight concrete having
a density in the range of 2,166 to 2,568 kg/cu m (135 to
160 Ib/cu ft). Structural lightweight concretes use
aggregates such as expanded shale, clay, slate and slag.
The lightweight concretes have densities ranging from 1,361
to 1,846 kg/cu m (85 to 115 Ib/cu ft). Other lightweight
materials such as pumice, scoria, perlite, vermiculite, and
diatomite are used to produce insulating concretes weighing
241 to 1,445 kg/cu m (15 to 90 Ib/cu ft) . Heavyweight
concrete is produced primarily for nuclear applications and
uses heavy aggregates such as barite, limonite, magnetite,
ilmenite, and iron or steel particles.
22
-------
In normal-weight concrete, -the aggregates are generally
classified into two size groups, fine and coarse. Fine
aggregates consist usually of sand with particle sizes
smaller than a number 4 standard sieve or approximately
0.6 cm (1/4 inch). The coarse aggregates are usually
crushed stone and gravel with particle sizes retained on a
number 4 standard sieve.
The paste component of the concrete is composed of cement,
water, admixtures and sometimes entrained air. The cement
paste ordinarily constitutes 20 to 40 percent of the total
volume of concrete and consists in volume of between 7 and
15 percent cement - 284 to 567 kg/cu m (375 to 750 Ib/cu yd)
and 14 to 21 percent - 174 to 265 kg/cu m water (230 to
350 Ib/cu yd). Air content in air-entrained concrete range
up to about 7.5 percent of the volume of the concrete. A
typical formulation for normal-weight air entrained concrete
is shown as follows:
Fine aggregate
Coarse aggregate
Cement
Water
Air Entrainment Agent
Air
kq/cu m
410
625
174
104
0.26-0.28
6% by volume
Ib/cu yd
1,180 :
1,800
(max. 3/4 in.)
500
300
0.75-0.80
6% by volume
Ideally each particle of aggregate is completely coated with
paste, and all Of the space between aggregate particles is
completely filled with paste. The quality of the concrete
is greatly dependent upon the quality of the paste which in
turn i£ dependent upon the ratio of water to cement used,
and the extent Of curing. The cementing properties of the
paste are due to the chemical reaction between cement and
water called hydration, which requires time and favorable
conditions.
A notable advance in concrete technology in recent years was
the development of air entrainment. The use of entrained
air is recommended in concrete for nearly all purposes, but
the principal reason is to improve resistance to freezing
and thawing exposure. Air entrained concrete is produced by
using either an air entraining cement or an air entraining
admixture added during the mixing of the concrete. An air
entraining cement contains material interground with
Portland cement during the process of manufacture. One of
these materials has been described as a mixture of
triethanolamine and a calcium salt of modified lignosulfonic
23
-------
acid. An air entraining admixture, on the other hand, is
added directly to the concrete materials either before or
during mixing. Typical agents consist of the following: a
saponified natural resin or stabilized wood resin derived
from pulp and paper production, such as Vinsol; a
combination of a primary alkylolamide plus alkyl aryl
sulfonate; a saponin or keratin compound; or generically a
triethanolamine salt of a sulfonated hydrocarbon or fatty
acid glyceride. Some more recently developed agents include
vinyl acetate or a styrene copolymer of vinyl acetate. Many
of these agents contain combinations of air entrainment
agents, wetting agents and dispersing agents.
Other admixtures which may be added to the concrete before
or during mixing include water reducing agents, retarders,
accelerators, and others. A water reducing admixture is a
material used for the purpose of reducing the quantity of
mixing water required to produce concrete of a given
consistency. Some water reducing admixtures such as
lignosulfonic acids and their salts, also can be used for
air entrainment. Other water reducers act as set retarders.
A retarding admixture is a material that is used for the
purpose of increasing the setting time of concrete.
Retarders are sometimes used in concrete to (1) offset the
accelerating effect of hot weather on the setting of the
concrete, or (2) delay the initial set of the concrete where
difficult or unusual situations occur or where desired to
produce special effects on concrete products. Because most
retarders also function as water reducers, they are
frequently referred to as water-redueing retarders.
Hydroxylated carboxylic acids and their salts are ofter used
for this purpose.
An accelerating admixture is used to accelerate the setting
and strength development of the concrete. The most commonly
used accelerating admixture is calcium chloride. There are
many commercial admixtures sold which combine various
functions under one trade name,
PRODUCTION OF CONCRETE PRODUCTS
The 1972 production and employment figures for the concrete
products category was derived from the Bureau of the Census
(U.S. Department of Commerce) publications and from data
developed from other sources during this study. These
figures are tabulated as follow in Table 5:
-------
TABLE 5
Production of Concrete Products
SIC
3271
3272
3273
Product
Concrete block &
brick, total
1972 Production
kkq (tons)
62,000,000
(69,000,000)
Autoclave Curing 14,000,000
(15,500,000)
Low Pressure Steam 48,000,000
Curing (53,500,000)
Concrete Products, 35,100,000
NEC, total (38,600,000)
Concrete Pipe 10,700,000
(excluding pressure (11,800,000)
pipe)
Precast and Pre-
stressed Concrete
Products
Ready-Mixed
Concrete, total
21,400,000
(23,500,000)
378,000,000**
(417,000,000)**
*Pr0duetion workers only
1.8 kkg per cubic meter of concrete
Employment
No. of Employees*
15,200
53,500
56,900
25
-------
aaor.
-------
SECTION III
INDUSTRY CATEGORIZATION
The concrete products industry was subcategorized on a
general product basis. This was done because of the
differences between manufacturing processes and the
resultant pollutants. The following lists the subcategories
discussed in this report.
TABLE 6
Industry Subcategorization
Subcategory
Concrete Block and
Brick
Concrete Pipe
Precast & Prestressed
Products
Ready-Mixed
Concrete
FACTORS CONSIDERED
Manufacturing Processes
The processes generally used in the concrete products
industry include mixing aggregates, cement and water and
transporting the mixture to the job site in the case of
ready-mixed concrete or casting and curing the product in
the case of block and brick and concrete products. Upon
examination of the various processes and wastes generated
Subcategorization was consistent with the type of
manufacturing process.
Raw Materials
The raw materials for all commodities used are principally
cement, aggregates and water which vary only in proportion
in a given product. Raw materials are therefore not a
suitable basis for Subcategorization.
27
-------
Waste Water Pollutants
The principal pollutants from this industry are pH, total
suspended solids and oil and grease. There are occasional
limited instances of deleterious materials such as the many
different types of admixtures that may be used in a concrete
mix.
Although suspended solids are ubiquitous, the treatability
of the effluents varies widely depending heavily, among
other things, upon the other constituents present in the raw
materials. Concrete pipe and precast and prestressed
concrete products could have oil and grease in their
effluent and deserve to be considered separately from the
other commodities.
Water Use Volume
Water use is determined by the needs of the individual
concrete manufacturing facility and varies greatly depending
mainly on the operational factors. For the manufacturing
processes studied herein, water use varies from a negligible
amount to 10,000 liters per kkg of product.
Differences in water use fall along the lines of product
differences which were already a basis for
subcategoriz ation.
Plant Size
In the plants from which EPA obtained information, capacity
varied from as little as 1,360 kkg per year to 540,0:00 kkg
per year. Based on the data obtained it appears t'fisTt the
amount of wastes generated is directly related to amoun€ of
product; therefore subcategorization based on plant size is
not necessary.
Plant Age
The newest plant studied was less than a year old and the
oldest was 50 years old. Often the equipment and
manufacturing practices at new and old plants are identical.
There is no correlation between plant age and the ability to
treat process waste water to acceptable pollutant levels.
Therefore, plant age was not an acceptable criterion for
subcategorization.
28
-------
SECTION IV
WATER USE AND WASTE CHARACTERIZATION
The quantity of water use at facilities in the concrete
products industry ranges from zero to 2,830,000 liter per
day (0 to 730,000 gallons per day). Plants using large
quantities of water are those producing pipe by the
spincasting method and ready-mixed concrete plants which
have extensive equipment washings.
Waste water in the concrete products industry originates
from the following sources:
(1) Process water - mix water
wash water
miscellaneous water
(2) Non-process water .
(3) Contaminated storm runoff '
WATER USE -
Process Water
Process water is defined as that water which, during the
manufacturing process, comes into direct contact with any
raw jiMte rial* intermediate product, by-product or product
use
-------
washing conveyor belts. Other uses include washing the
surface of wall panels with a weak acid solution or water
under high pressure to expose aggregate for decorative
purposes. Production of concrete pressure pipe requires
additional process water for hydrostatic testing of steel
reinforcing cylinders and the prewetting of reinforced
pressure pipe before outside coating of concrete is applied.
Miscellaneous water uses include spraying stockpiles to keep
aggregates in the saturated, surface-dry condition. This
water is usually low volume and may be either evaporated or
absorbed in the raw material.
Miscellaneous water uses vary widely among the facilities.
It is generally used for floor washing, clean-up and
sanitary purposes. There is also miscellaneous process
water used for yard dust control, aggregate moisture
control, chute rinse-off and equipment clean-up, which in
most plants becomes yard runoff.
Significant quantities of water may be used to control dust
on plant yards, the amount varying seasonally. This water
in many instances evaporates or percolates.
Relatively small amounts of contact water are used for saw
blade cooling in the manufacture of concrete products.
Non-process Water
Non-process water is defined as that used for auxiliary
operations necessary for the manufacture of a product but
not contacting the process materials. For example, boiler
water and water treatment regeneration are auxiliary
operations. The volume of water used for these purposes^."is
minimal. pn,
The largest use of non-process water is as non-contact
cooling water for equipment such as pumps and air
compressors.
PROCESS WASTE CHARACTERIZATION
CONCRETE BLOCK AND BRICK
Concrete block and brick may be lightweight or heavyweight
depending on the type of aggregate used. The methods of
forming block and brick are similar at most plants.
However, two different curing methods are used. Concrete
block and brick manufacture was subcategorized based on
curing method, i.e., low pressure steam and autoclave
30
-------
curing. Low pressure steam curing is predominant in the
industry. Live steam at low pressure is injected into a
kiln in which uncured block -has been stacked. Process waste
water generated by this operation consists of steam
condensate, which has a pH greater than nine and contains
suspended solids. This is caused by direct contact with the
product. Autoclave curing utilizes high pressure steam at
9.7 atm (150 psi) and above in autoclaves which have been
loaded with uncured block. Waste water from this process
includes autoclave blowdown condensate and autoclave purge,
both having pH greater than nine and containing suspended
solids from product contact.
In this study 13 plants were visited and 3 plants were
sampled. Plant ages in this study range from 2 to 35 years,
LOW PEESSURE STEAM CURING
The production of concrete block and brick with low pressure
steam curing includes: batch mixing of cement, water and
aggregates; forming the block in a machine which presses,
rams or vibrates the moist mix into blocks; curing of the
block with low pressure steam in a kiln; and visual
inspection, stacking and loading for delivery. Low pressure
steam is produced in a boiler and is injected into the
kilns. Plant 7103 produces part of its block by atmospheric
curing and the remainder by low pressure steam curing. In
the atmospheric curing process, the formed block is stacked
in the plant yard and cured by ambient heat and humidity
plus the internal effects of the heat of hydration. Plant
7104 cures block by stacking them in an enclosure after they
are formed and allowing them to cure with their heat of
hydration and ambient heat and humidity. A flow diagram for
concrete" block and brick produced by the low pressure steam
curing process is shown in Figure 1. Annual production of
concrete block and brick by this process for the 7 plants
contacted ranges from 26,600 to 79,800 kkg (29,300 to
88,000 tons) .
The principal process water uses are mixing the concrete and
curing the block and brick. Miscellaneous process water
uses include conveyor belt washing at plant 7104, yard dust
control at plant 7109, aggregate moisture control and
delivery truck washoff at plant 7110. Non-process water
uses include make-up water for boilers, water treatment
regeneration, non-contact cooling of bearings and
compressors and boiler blowdown.
31
-------
i
§ \
o
m
t
I
3:
fc — ^
,
UJ
CJCO
mo
X
ll|g
GC ^^
Q.
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5
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8
}
SQo
g<<
t
X
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f
t!>C3 P
[0^5
;K m
s 1 T^i
i
0
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8
^
Q
/v*
£
il
^: cc
O !D
o o
-1
QQ ^>
^Sl
w 0 O LJ
c 2: oc
O CO
o£
~^Bfe pi
^^gi oci »i..
=*• _J ":.xrlo™ • •
Q ?foo
Q.
- -
p UJS^
fcj ^mS
^ IS K [$; "
§£
-------
Total water use varies with production and duration of
curing. For the plants contacted water use ranges from 24
to 35 liters/kkg (5.7 "to 8. 1 gallons/ton) . Mix water use
per unit weight of production varies from 24 to
30 liters/kkg (5.7 to 7.1 gallons/ton) and becomes part of
the product. Process hydraulic loads at selected plants are
shown below:
Plant
7102
7103
7104
7106
7108
7109
7110
Amounts, 'liters/kkg (gal/ton) of
Low Pressure
-.Steam
Mix Water Condensate
unknown
24 (5.8)
24 (5.8)
(5.8)
(7.1)
(6.0)
(5.8)
24
30
26
24
.10.6 (2.5)
0.2 (0.04)
none
unknown
unknown
8.9 (2.1)
unknown
Conveyor
Belt Washoff
none
none ,
5.2 (1-3)
none
none
none
none
Waste water pollutants from low pressure steam curing are
suspended solids, COD, oil and grease and high pH. Self-
monitoring data supplied by plant 7109 showed 0.0005 kg/kkg
(0.0010 Ib/ton) TSS, 0.0002 kg/kkg (0.0004 Ib/ton) COD, and
a pH of 11.;1. Plant 7111 showed 0.005 kg/kkg of oil and
grease in a concentration of 35 mg/1. The concentrations of
the other pollutants were 64 mg/liter TSS and 26 mg/liter
COD. All plants but 7104 had steam condensate containing
these pollutants.
Solid wastes from these plants include cement dust from
batching, waste concrete from mixer clean out, and scrap
block and brick from forming, stacking and loading
operations. In most cases cement dust is collected in a
baghouse and returned to the cement storage silos. Solid
wastes are used as fill in all plants,contacted.
Miscellaneous wastes come from equipment washoff, accidental
spill washdown and aggregate moisture control. Non-process
waste water includes boiler blowdown water and influent
water treatment regeneration wastes.
Raw waste loads vary with production. The, waste concrete
and scrap block for plants studied are shown below.
33
-------
Plant
7102
7103
7104
7106
7108
7109
7110
Waste Concrete and Scrap Block kq/kkg (Ib/lOOOlb)
26
10
4
19
13
2
9
AUTOCLAVE CURING
The production of autoclave-cured concrete block and brick
includes: batch mixing of cement, water and aggregates;
forming of the block in a block machine where the moist mix
is rammed, pressed, or vibrated into shape; curing of the
block with high pressure steam in an autoclave; and stacking
and loading for delivery. High pressure steam is generated
by two methods. Plants 7100 and 7101 use a hot oil
convection process in which oil is heated and piped through
a water trough at the bottom of the autoclave, forming steam
inside the autoclave. Plants 7105 and 7107 produce high
pressure steam" in an external boiler and inject it into the
autoclave. This latter method is used in most plants. A
flow diagram for concrete block and brick produced by the
autoclave curing process is shown in Figure 2. Annual
production of concrete block and brick by this process for
the six plants studied ranged from 63,500 to 250,000 kkg
(70,000 to 275,000 tons).
The principal process water uses at these plants occur
during the mixing of the concrete and curing the block and
brick. Miscellaneous process water is used for equipment
clean-up and housekeeping within the plant, and aggregate
moisture control. Non-process water use includes boiler
blowdown and non-contact cooling of bearings and
compressors. Water use varies with operating factors,
duration of curing, the number of autoclave purges in the
convected steam plants. For these reasons, daily water use
for the plants contacted ranges from 71 to 227 liters/kkg
(17 to 54 gal/ton). The use of mix water, which becomes
part of the product, when measui-ed per unit weight of
production is relatively constant. Process hydraulic loads
at selected plants are shown below:
34
-------
Ill*
fe
UJ
o
CD
T
n:
tu
a.
z>
•
LU
fc
o
i
Ul
3
LU
< UJ
Bl
HO
0
8
ce
IU
I
Ul
X
35
-------
Quantity in liters/kkg of product (gal/ton)
7100 7101 71057107
mix water
autoclave
blowdown
condensate
autoclave
purge
22 (5)
19 (5)
30 (7)
22 (5)
part of
autoclave
purge
13 (3) 17 (H)
214 (51) 77 (19)
90 (22) none
none
Pollutants include suspended solids, COD, oil and grease,
and high pH, resulting from autoclave blowdown condensate
and in the convection process, autoclave purae.
Miscellaneous wastes include equipment washoff, aggregate
moisture control and accidental spill clean-up. Solid
wastes from plants which cure with autoclaves are cement
dust from concrete batching, concrete from mixer clean-out,
and scrap from block forming, stacking and loading. Cement
dust is usually collected in a baghouse and returned to the
cement storage silo. Waste solids are typically landfilled,
however, plant 7100 crushes broken block for reuse as
aggregate.
Raw waste loads vary from day to day due to operating
factors such as housekeeping, ambient temperature and
humidity. The amount of autoclave purge is highly variable
which affects the amount of raw wastes contained in this
purge. The estimated average raw waste loads for some
plants contacted in this study follow.
36
-------
Source
autoclave
blowdown
Parameter
TSS
Raw Wastes, kg/kkg of product (lb/1,000 Ib)
7100 7101 7105 7107 7113
combined
autoclave
and other
waste water
unknown unknown 0.035
0.02
0.012
condensate
autoclave
purge
PH
COD
Oil and
grease
TSS
pH> • .
COD
Oil and
grease
unknown
unknown
unknown
0.005*
.1.1.3
0.0024
unknown
unknown
unknown
unknown
0.007
11.5
0.004
unknown
11.5
0.018
unknown
"
none
N.A.
none
none
11.3
unknown
unknown
none
N.A.
none
hone
12.3
0.001 (BOD)
unknown
none
N.A.
none
none
TSS
pH
BOD
Oil and
grease
*EPA measured data
N.A. not applicable
none
N.A.
none
none
none
N. A.
none
none
none
N.A.
none
none
none
N.A.
none
none
0.016
11.6
0.011
unknown
37
-------
CONCRETE PIPE
The production of concrete pipe includes batch mixing,
fabricating, inserting steel reinforcing, pouring concrete
into a pipe form, curing and finishing. Batch mixing
involves blending cement, aggregates and water in a central
mixer. There are three methods for curing pipe - low
pressure steam curing, atmospheric curing or spray curing.
Atmospheric curing uses ambient heat and humidity to cure
the product. Steam curing involves placing the product in
an enclosure into which steam is injected. Water spray
curing involves spraying the uncured product with a mist of
water to assist curing. There is no waste water from
atmospheric curing. Waste water from steam curing and spray
curing contains suspended solids, oil and grease and has a
high pH. Finishing may include endsawing or application of
grout. Pressure pipe production is similar but may also
include prestressing with steel wire, fabricating and
hydrostatic testing a steel liner, applying a layer of
grout, and curing a second time using low pressure steam.
Figure 3 is a process flow diagram for the production of
culvert, storm sewer, and sanitary sewer pipe. Figure 4 is
a process flow diagram for the production of pressure pipe.
Annual production of concrete pipe for the 9 plants visited
ranges from 16,000 to 106,000 kkg (18,000 to 117,000 tons).
Process water is used for mixing concrete, washing out
central mixers, transport buckets and forms for vertical
cast pipe, curing and prewetting imbedded pressure pipe.
Forms are washed off at 50 per cent of the plants studied.
The water used for curing is either in the form of low
pressure steam or a fine mist. Miscellaneous procesis water
uses include hydrostatic testing of the steel cylinders for
pressure pipe, yard dust control, and equipment washoff.
Non-process water uses include boiler blowdown and non-
contact cooling of bearings and compressors.
Water use is variable and depends on operating factors, the
number of central mixer and transport bucket washouts, and
the duration and type of curing. Because of these
variables, hydraulic loads in liters/kkg of product
(gal/ton) show a wide range. Mix water becomes part of the
product and therefore remains relatively constant when
expressed as liters/kkg of product.
38
-------
39
-------
%
r^-i
(2?
HYDROSTATIC
TESTING
f
11-*
|
TRANSPORTING
(BUCKET)
ft!
Q_
LJ
01
CO
o
5
G*.
40
-------
Quantity, liters/kkg of product faal/toni
7201 T>nc l*\*\i. -. ~_ J *
Mix water
42 (10)
Central mixer 7 (1.7)
and transport
bucket washout
7205
56 (13)
none
Steam
condensate
Spray cure
water
Form washout
Pre-wetting
Hydrostatic
testing
28 (7) 31 (7)
none
1.7
(0.4)
none
none
none
none
none
none
7224
30 (7)
11 (2.6)
134 (32)
36 (9)
7229
42 (10)
unknown
7233
38 (9)
5 (1.2)
unknown none
none
included none
in c/m
washout
none
13 (3)
none
none
none
included
in c/m
washout
none
none
Quantity, liters/kkg of product (gal/ton)
7239 -70/11 -7i»i-7* ;=.^.';L.— -*-
Mix water
Central mixer
and transport
bucket wa shout
25 (6)
none
SteamiQSondensate 1
Spray cure water
Form washout ,
Pre-wetting
Hydrostatic
testing
(0.25)
none
1.3
(0.3)
none
none
7241
74 (18)
0.9
(0.2)
unknown
none
0.9
(0.2)
none
none
7247*
42 (10)
334
(80)
113
(27)
none
none
150 (36)
75 (18)
7248*
42 (10)
21
(5)
83
(20)
none
none
unknown
unknown
*Pressure Pipe Plant
41
-------
Additional water use data were obtained from 142 plants
through a survey conducted by the American Concrete Pipe
Association. These data, collected by the association, are
summarized as follows. Figure 5 shows the distribution of
noneonsumptive water use from 138 of these plants.
Maximum Minimum Average
Production of plants, kkg/day
Mix water, liters/kkg of product
Form washout water, liters/kkg
of product
Curing water, liters/kkg of
product
Other water, liters/kkg of
product
Steam condensate, liters/kkg
of product
Total waste water generated,
liters/kkg of product
772
417
235
698
8,258
8,785
8,995
1.9
2.1
0.2
0.5
0.6
0.1
0.2
135
58
21
80
300
147
174
The pollutants in the waste water include suspended solids,
oil and grease, pH and COD. These pollutants result from
central mixer and transport bucket washout, spincast waste
water, condensate from steam curing, spray curing waste
water, and form washout. Waste solids also originate from
the pre-wetting of imbedded pressure pipe.
Solid wastes include cement dust from concrete batching,
solids from mixer clean-out and broken pipe. The cement
dust is usually collected in a baghouse and returned to the
cement storage silo. Waste solids from mixer cleanout,
broken pipe and waste concrete are usually landfilled.
Waste solids from central mixer and transport buckets
average 35 kg/cu m (100 Ib/cu yd) of central mixer and
transport bucket capacity for each washout. In most cases,
the plants are unable to quantify raw waste loads. Efforts
to obtain samples and thereby directly obtain raw waste data
were unsuccessful in most cases because of rapid
solidification of the samples.
Raw waste loads vary from day to day and depend on operating
factors, the number of central mixer and bucket washouts,
duration of curing, and the amount of waste concrete.
42
-------
1
I
o
cc
in
5,000
2,000
1,000
500
200
100
50
20
IO
TOTAL OF:
FORM WASHOUT
CURING WATER
BOILER SLOWDOWN
STEAM CONDENSATE AND OTHER
12 5 10 20 40 60 80 90S5 SB99
CUMULATIVE PERCENT CF PLANTS
LESS THAN
FIGURE 5
DISTRIBUTION OF ^CONSUMPTIVE WATER USE
AT CONCRETE PIPE PLANTS
(DATA FROM !38 PLANTS)
-------
PRECAST AND PRESTRESSED CONCRETE PRODUCTS
The production of precast concrete products includes:
preparation of a mold or form; fabrication of steel
reinforcement cages; mixing cement, aggregate and water in a
central mixer; placing the concrete mixture into the form;
initial curing either under atmospheric conditions, with low
pressure steam, or with a water spray; removal of the form;
completion of curing, usually at atmospheric conditions;
and, for special products, a finishing step which may
include sawing, washing, etching, or sand blasting.
Prestressed concrete products are manufactured similarly
with the additional step of pretensioning or prestressing
the steel reinforcing rods, prior to pouring the concrete
into the form. Prestressed concrete products are typically
cured with low pressure steam. Product finishing, similar
to precast products, is common practice. A. process flow
diagram for precast and prestressed concrete products is
shown in Figure 6.. Annual production of precast and
prestressed concrete products for the 15 plants visited
varies from 1,800 to 227,000 kkg (2,000 to 250,000 tons).
About 50 percent of the plants surveyed produce both precast
and prestressed products. Because of the similarities in
these manufacturing processes, only one subcategory was
deemed necessary.
Process water is used for mixing concrete; washing central
mixer, transport bucket and forms; curing (low pressure
steam and spray curing); and product finishing.
Miscellaneous process water uses include yard dust control
and equipment washoff. Non-process water uses include
boiler blowdown and non-contact cooling of bearings and
compressors. In this study 15 plants were visited and 6
were sampled.
Water use varies from day to day and depends on production,
number of central mixer and transport bucket washouts,
duration of curing, and the type of product finishing.
Because of these variables, water use in liters/kkg of
product for the plants studied shows a wide range.
Process hydraulic loads at selected plants are shown below in
liters per kkg of product (gal/ton):
Plants '
Mix water
7200
63
(15)
7203
63
(15)
7204
54
(13)
7206
54
(13)
-------
u_
tt
U.CO
1
j£
-------
Central mixer
and bucket
washout
Curing
Product
finishing
2
(0.4)
none*
none
8.2
(2)
none*
15
(3.5)
14
(3.4)
24
(5.8)
none
10
(2.4)
unknown
none
Plants
Mix water
Cental mixer
and bucket
washout
Curing
Product
finishing
Mix water
Central mixer
and bucket
washout
Curing
Product
finishing
Other (truck
washout)
7207
42
(10)
87
(21)
none*
521
(125) .
7235
63
(15)
14
(3)
none*
61
(15)
none
7230
54
(13)
139
(33)
35
(8.4)
75
(18)
Plants
7238
54
(13)
63
(15)
none
unknown
none
7231
54
(13)
8.3
(2)
none*
none
7240
54
(13)
25
(6)
none
unknown
5
(1)
7232
58
(14)
8.7
(2)
unknown
none
7244
63
(15)
10
<2-£>
none*
17
(4.1)
none
7234
63
(15)
104
(25)
209
(50)
none
*atmospheric curing
46
-------
Waterborne wastes result from central mixer and transport
bucket cleanout, form washoff, low pressure steam and spray
curing, product finishing and miscellaneous equipment
washoff. Pollutants in the waste water are suspended
solids, high pH, COD, and oil and grease. Concrete batching
produces cement dust, a solid waste which is usually
collected in a baghouse and returned to the cement storage
silo.
The waste concrete left over at the end of a working day
creates a waterborne waste if washed out, or a solid waste,
if scraped out and landfilled. Most plants landfill waste
concrete.
Raw waste loads vary from day to day and depend on operating
factors, number of "pours", number of central mixer and
transport bucket washouts per day, duration of curing,
number of products finished, and the amount of waste
concrete. Estimated raw waste loads for selected plants are
shown in kg/kkg of product (lb/1000 Ib) together with pH
values measured by EPA:
Plant
Source
Central
mixer and
transport
bucket
washout
Curing
w
• ~3 ("
Product" ,
Finishing
Waste
concrete
Parameter
TSS
pH
TSS
TSS
PH
TSS
7200
7203
0.5 2.5
unknown unknown
7206
8
unknown
7207
16
unknown
none
none
unknown
1.7
none
0.005
11.7
none
unknown
none
unknown
10
none
.unknown
unknown
unknown
-------
Source
Parameter
7230
7231
7232
7234
Central TSS
mixer and pH
transport
bucket
washout
Curing TSS
8 9
unknown unknown
47
11.7
unknown
1.5
none
unknown unknown
Product
finishing
Waste
concrete
TSS
pH
TSS
7
unknown
none
none
N.A.
1
none
N.A.
5
none
N.A.
5
* unknown
**not applicable
Source
Central
mixer and
transport
bucket
washout
Curing
Product
finishing
Waste
concrete
Parameter
TSS
pH
TSS
TSS
pH
TSS
7235
36
unknown
none
13
unknown
35
7238
0.011
unknown
none
unknown
unknown
0.012
7244
1
unknown
none
8
unknown
8
N.A. not applicable
Waste solids from central mixer and transport bucket washout
average 35 kg/cu m (100 Ib/cu yd) of central mixer and
transport bucket capacity for each washout. This value was
used for the estimation of total suspended solids in the raw
waste loads given above.
In most cases, the plants are unable to quantify raw waste
loads. Efforts to obtain samples and determine meaningful
raw waste data were unsuccessul. It is impracticable to
process raw waste samples from the industry due to rapid
solidification of the samples.
48
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Plants 7200, 7203, 7207, 7231, 7235, and 7244 use
atmospheric curing and have no curing wastes. Plant 7238
uses dry electric heat for during. ? ;
I '
READY-MIXED CONCRETE
The three types of ready-mixed concrete plants — permanent,
portable and mobile — differ markedly in their waste water
problems. Permanent ready-mixed concrete plants often have
extensive waste water treatment facilities or room for such.
Their plant yards may be paved., Portable ready-mixed plants
are designed to be moved to locations that are near the
sole, short-term user of their product (highway paving,
building construction, dam construction, etc.). Their plant
sites are generally leased, yards are riot paved and space
for waste water treatment is limited. Strict quality
control requirements are placed on concrete used for paving,
thus more waste concrete may be generated. Mix ratios are
not changed often, therefore, there are fewer truck washout
operations. Mobile concrete plants use trucks capable of
measuring and mixing aggregate, cement and water at the job
site. Truck washout is not usually done at the plant site.
Mobile plants represent a small part of the total volume and
most of their sales are to private individuals for small
jobs such as sidewalks and patios.
Major sources of waste water in the ready-mixed concrete
manufacturing are truck washout and washoff and central
mixer washout.
PERMANENT READY-MIXED CONCRETE PLANTS
Ready-mixed concrete is manufactured by one of three
methods: centrally-mixed concrete made in a stationary mixer
and is delivered either in a truck agitator, a truck mixer
operating at agitating speed, or a special non-agitating
truck; shrink-mixed concrete mixed partially in a stationary
central mixer and completed in a truck mixer; and completely
truck-mixed concrete.
At a permanent ready^-mixed concrete plant, the raw materials
— cement, fine and coarse aggregate, mix water and special
admixtures — are weighed or metered into either a central
mixer and discharged into a mixer truck, or dry-batched
directly into a ready-mixed truck, which serves as the
mixer. The unhardened concrete is then delivered to the job
site to be pouredi Afterward, the mixer truck returns to
the batching plant for another load of concrete. If the mix
recipe is different, the truck is washed out prior to
-------
receiving a fresh load.
Figure 7.
A process flow diagram is shown in
Annual production of ready-mixed concrete for the 437 plants
contacted or visited ranges from 1,530 to 230,000 cu m
(2,000 to 300,000 cu yd). Approximately 25 percent of the
plants use central mixers.
Process water consists of mix water, central mixer washout,
and mixer truck washout and washoff. There is also
miscellaneous process water used for yard dust control,
aggregate moisture control, chute rinse-off and equipment
clean-up which, in most plants becomes yard runoff. Non-
process water includes boiler blowdown and non-contact
cooling of bearings and compressors.
Water use varies from day to day depending on such operating
factors as number of mixer trucks operating, number of truck
and central mixer washout and washoffs, and amounts of other
miscellaneous water uses. Because of these variables,
hydraulic loads at those plants contacted have a wide range
of liters/cu m of product (gallons/cu yd) . The amount of
water used for mixing concrete ranges from 129 to
188 liters/cu m of product (26 to 38 gallons/cu yd). The
plant-by-plant breakdown of process hydraulic loads is given
below. One-fourth of the plants contacted reuse mixer truck
washout water for the same purpose. in addition,
seven plants studied reuse clarified mixer truck washout
water for a percentage of mix water make-up. Some plants
with mechanical aggregate separators use additional water
for aggregate separation. This water use is included in the
mixer truck weshout in the following table.
50
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51
-------
Process Hydraulic Loads for Ready-Mixed
Concrete (Permanent), liters/cu m (gal/cu yd)
Plant
Mix
Water
Truck
Washout
Truck
Washoff
7305
7363 *
7365
7385
7441
7451
7452
7487 *
7542
7543
7544
7545
7699
7729 *
7731
7732 *
7736 *
7750
7755
7757 *
139
139
139
149
149
173
173
129
168
168
168
168
188
139
139
139
144
139
149
149
(28)
(28)
(28)
(30)
(30)
(35)
(35)
(26)
(34)
(34)
(34)
(34)
(38)
(28)
(28)
(28)
(29)
(28)
(30)
(30)
99 (20)
25 (5)
15 (3)
50 (10)
89 (18)
149 (30)
124 (25)
50 (10)
35 (7)
25 (5)
25 (5)
20 (4)
25 (5)
282 (57)
84 (17)
317 (64)
45 (9)
74 (15)
64 (13)
139 (28)
15 (3)
15 (3)
5 (1)
2 (0.4)
20 (4)
25 (5)
25 (5)
15 (3)
64 (13)
64 (13)
69 (14)
54 (11)
1 (0.2)
35 (7)
10 (2)
40 (8)
15 (3)
20 (4)
5 (1)
10 (2)
Central
Mixer
Washout
none
2 (0.4)
none
3 (0.6)
10 (2)
none
none
none
none
none
none
5 (1)
none
none
none
none
none
none
5 (1)
none
Miscellaneous
15 (3)
unknown
unknown
248 (50)
unknown
unknown
unknown
unknown
unknown
25 (5)
20 (4)
129 (26)
15 (3)
unknown
unknown
unknown
unknown
unknown
unknown
unknown
* These plants reuse clarified mixer truck washout water
for a percentage of mix water make-up.
The raw wastes for all plants consist of solid wastes, from
concrete batching and waterborne solids from cleanfup of
mixer trucks and central mixers. Concrete batching wastes
include cement dust and aggregate fines which are usually
collected in a baghouse and recycled to the storage silo.
Waste solids from washout of the central mixer and mixer
trucks average 59 kg/cu m (100 Ibs/cu yd) of central mixer
and mixer truck capacity for each washout. Average mixer
truck volume is 6.9 cu m (9 cu yd); average central mixer
volume is 3.8 cu m (5 cu yd).
Excess concrete is returned to> the plant in the mixer truck
either to be incorporated in the following load or
discharged from the truck as waste. This returned concrete
may generate a waterborne waste if discharged to the waste
water treatment system or a solid waste if landfilled. At
some plants, returned concrete is molded into useful items
such as splash blocks or patio blocks.
52
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Mix water spillage, mixer truck chute rinse-off and rainfall
contribute to yard runoff. The raw waste loads vary from
day to day depending on operational.factors such as number
of trucks operating, number of washouts and washoffs per
truck, and the amount of returned concrete. Most of those
raw wastes are usually generated over a short period of time
near the end of the working day. Consequently, large
amounts of waste require treatment or temporary storage
during these times.
It was found to be impracticable to analyze raw waste
samples from the industry due to rapid solidification of
collected samples.
The piant-supplied pH data obtained for raw waste streams
was limited to measurements from two truck washout streams.
At plant 7363 the pH of this stream was 12.3 while at plant
7365 it was 12.5. Yard runoff at plant 7385 was reported to
have a pH of 11.2.
PORTABLE READY-MIXED CONCRETE PLANTS
Portable ready-mixed concrete plants use the same
manufacturing process as permanent plants with the following
exceptions:
(1)
(2)
(3)
Mixing is predominantly done in central mixers (95 per
cent of those contacted) rather than in truck mixers.
Only 29 percent of the plants contacted wash off mixer
trucks on a daily schedule.
Mi^er trucks make more trips in a day due to proximity
gf "the plant to the job site.
Annual production of ready-mixed concrete for the 21
portable, plants contacted ranges from 13,000 to 153,000 cu m
(17,000 to 200,000 cu yd).
Process water is primarily used in mixing, central mixer
washout, and mixer truck washout and washoff . Miscellaneous
process water is used for mixer truck chute rinse-off, yard
dust control, and for spraying stockpiles to moisten the
exterior of the : pile to keep aggregate at the "saturated,
surface-dry (s.s.d.) condition". Non-process water is used
for boiler feed and non- contact cooling of bearings and
compressors. Water use varies from day to day and depends
on operational factors such as number of mixer trucks
operating, and the number of mixer truck washouts and
washoffs.
53
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Water use at portable plants is similar to that described
for permanent plants. The amount of water used for mixing
varies depending on the fineness of aggregates, desired
slump of the concrete, amount of cement in the mix and
amount of entrained air. Average amounts of mix water used
at the plants range from 124 to 198 liters/cu m (25 to
40 gal/cu yd). The process water use at several plants is
shown as follows:
Process Water Use for Portable Ready-Mixed
Concrete Plants, liters/cu m (gal/cu yd)
Plant
Mix
7362
7601
7602
7603
7604
7609
7627 *
7633
7641
7649
7691
7706 *
7707
7753
7758
198 (40)
124 (25)
149 (30)
149 (30)
173 (35)
129 (26)
124 (25)
173 (35)
unknown
149 (30)
124 (25)
149 (30)
124 (25)
134 (27)
unknown
Truck
Washout
none
15 (3.0)
14 (2.8)
25 (5.0)
7 (1.4)
54 (10.8)
2 (0.4)
30 (6.0)
99 (19.8)
14 (2.8)
2 (0.4)
50 (10.0)
89 (17.8)
36 (7,2)
none
Truck
Washoff
8 (1.6)
none
none
none
none
3 (0.6)
none
none
12 (2.4)
0.8 (0.2)
none
none
9 (1.8)
18 (3.6)
none
Central
Mixer
Washout
none
1.5 (0.3)
7.4 (1.5)
12.4 (2.5)
1.8 (0.4)
7.0 (1.4)
3.0 (0.6)
1.5 (0.3)
25 (5.0)
2.0 (0.4)
0.4 (0.1)
4.0 (0.8)
9.0 (1.8)
6.0 (1.2)
none
* average of four plants
Recycle of mixer truck washout water is a fairly common
practice at portable ready-mixed plants. Reuse of clarified
mixer truck washout water as part of mix water make-up is
not practiced because of strict standards for mix water
quality adopted by regulatory agencies and industry
technical committees.
Raw wastes result from concrete batching and mixer washout
and truck washoff. Cement dust from concrete batching is
usually collected in baghouses located on the storage silos.
Collected dust is usually recycled to the storage silos.
Pollutants include suspended solids, pH and COD from central
mixer washout and mixer truck v?ashout and washoff.
54
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Returned concrete at port .able plants usually is due to
quality control rejection at the job site. The waste
concrete is either landfilled or converted to a waterborne
waste if discharged to a treatment system. Most portable
plants do not make by-products from their returned concrete.
Raw wastes from miscellaneous sources come from mix water
spillage and mixer truck chute rinse-off. Raw waste loads
vary from day to day depending on operational factors such
as number of operating mixer trucks, number of mixer truck
washouts and washoffs and the amount of returned concrete.
MOBILE READY-MIXED CONCRETE PLANTS
Mobile ready-mixed concrete trucks, "concrete-mobiles", are
miniature batch plants on wheels* Aggregate, cement, water
and admixtures are loaded in separate compartments on the
concrete-mobile at the batch building. The concrete-mobile
then travels to the job site, where the ingredients are
mixed together in the. concrete-mobile mixer as they are
dispensed. In this manner, only the amount of concrete
needed for the job is mixed. Normally, no returned or waste
concrete results. Average capacity of a concrete-mobile is
5.3 cu m (7 cu yd) .
There are approximately 1,800 mobile ready-mixed plants in
the U.S. ranging in annual production from 2,865 to
57,300 cum (3,750 to 75,000 cu yd). Most firms use the
concrete-mobile for small, homeowner type jobs, where rapid
mixing and dispensing of concrete is not critical.
Approximately 30 permanent ready-mixed concrete firms have
added a concrete-mobile to their fleet for these type jobs.
Figure 8 illustrates the production of mobile ready-mixed
concrete.
Process water is primarily used in mixing, concrete-mobile
mixer washout, and concrete-mobile washoff. Miscellaneous
process water is used for yard dust control and for moisture
control of aggregate stockpiles. Non-process water uses
include non-contact cooling of bearings and compressors.
Water use varies from day to day and depends on operational
factors such as number of operating concrete-mobiles, the
number of mixer washouts and the number of washoffs. The
amount of water used for mixing varies depending on the
fineness of aggregates, desired slump of the concrete,
amount of cement in the mix and amount of entrained air.
The process water use at two plants is shown as follows:
55
-------
Ui
s
o
56
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Process Water Use for Mobile Ready-Mixed Concrete
Plants, liters/cu m (gal/cu yd)
Plant Mix Mixer Washout Concrete-Mobile Washoff
7759 139 (28) 7.4 (1.5) 3.5 (0.7)
7760 139 (28) 5.0 (1.0) 5.0 (1.0)
Raw wastes result from loading the ingredients into the
concrete-mobile, mixer washout and truck washoff. Cement
dust from loading is usually collected in baghouses located
on the storage silos. Collected dust is usually recycled to
the storage silos.
Waterborne pollutants include suspended solids, pH and COD
resulting from concrete-mobile mixer washout and concrete-
mobile washoff.
57
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SECTION V
SELECTION OF POLLUTANT PARAMETERS
Total suspended solids, oil and grease and pH were found to
be- the major waste water pollutant parameters. The
rationale for inclusion of these parameters and exclusion of
other parameters is discussed in this section.
Oil and Grease
Oil and grease may be present in the waste waters from
concrete block and brick, concrete products (NEC) and ready-
mixed concrete production. Based on the data available,
concentrations of oil and grease vary from 0.0 to 376 mg/1.
Because of. widespread use, oil and grease occur often in
waste water streams. These oily wastes may be classified as
follows:
2.
Light Hydrocarbons - These include light fuels such
as gasoline, kerosene, and jet fuel, and
miscellaneous solvents used for industrial
processing, degreasing, or cleaning purposes. The
presence of these light hydrocarbons may make the
removal of other heavier oily wastes more
difficult.
Heavy Hydrocarbons, Fuels, and Tars - These include
the crude oils, diesel oils, #6 fuel oil, residual
oils, slop oils, and in some cases, asphalt and
road tar.
3. Lubricants and Cutting Fluids - These generally
fall into two classes: non-emulsifiable oils such
as lubricating oils and greases and emulsifiable
oils such as water soluble oils, rolling oils,
cutting oils, and drawing compounds. Emulsifiable
oils may contain fat soap or various other
additives.
4. Vegetable and animal fats and Oils - These
originate primarily from processing of foods and
natural products.
These compounds can settle or float and may exist as
solids or liquids depending upon factors such as method
59
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of use, production process,
water.
and temperature of waste
Oils and grease even in small quantities cause troublesome
taste and odor problems. Scum lines from these agents are
produced on water treatment basin walls and other
containers. Fish and water fowl are adversely affected by
oils in their habitat. Oil emulsions may adhere to the
gills of fish causing suffocation, and the flesh of fish is
tainted when microorganisms that were exposed to waste oil
are eaten. Deposition of oil in the bottom sediments of
water can serve to inhibit normal benthic growth. Oil and
grease exhibit an oxygen demand.
Levels of oil and grease which are toxic to aquatic
organisms vary greatly, depending on the type and the
species susceptibility. However, it has been reported that
crude oil in concentrations as low as 0.3 mg/1 is extremely
toxic to fresh-water fish. It has been recommended that
public water supply sources be essentially free from oil and
grease.
Oil and grease in quantities of 100 1/sq km (10 gallons/sq
mile) show up as a sheen on the surface of a body of water.
The presence of oil slicks prevent the full aesthetic
enjoyment of water. The presence of oil in water can also
increase the toxicity of other substances being discharged
into the receiving bodies of water. Municipalities
frequently limit the quantity of oil and grease that can be
discharged to their waste water treatment systems by
industry.
pH ' :>•;.-.
Although not a specific pollutant, pH is related to the
acidity or alkalinity of a waste water stream. It is not a
linear or direct measure of either, however, it may properly
be used as a surrogate to control both excess acidity and
excess alkalinity in water. The term pH is used to describe
the hydrogen ion - hydroxyl ion balance in water.
Technically, pH is a function of the hydrogen ion
concentration or activity present in a given solution. pH
numbers are the negative logarithm of the hydrogen ion
concentration. A pH of 7 generally indicates neutrality or
a balance between free hydrogen and free hydroxyl ions.
Solutions with a pH above 7 indicate that the solution is
basic while a pH below 7 indicates that the solution is
acidic.
60
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Knowledge of the pH of water or waste water is useful in
determining necessary measures for corrosion control,
pollution control, and disinfection. Waters with a pH below
6.0 are corrosive to water works structures, distribution
lines, and household plumbing fixtures and such corrosion
can add constituents to %rinkings water such as iron,
copper, zinc, cadmium, and lead. Low pH waters not only
tend to dissolve metals from structures and fixtures but
also tend to redissolve or leach metals from sludges and
bottom sediments. The hydrogen ion concentration can affect
the "taste" of the water and at a low pH, water tastes
"sour".
Extreme values of pH or rapid pH changes can exert stress
conditions or kill aquatic life outright. Even moderate
changes from "acceptable" criteria limits of pH are
deleterious to some species. The relative toxicity* to
aquatic life of many materials is increased by changes in
the water pH. For example, metalocyanide ' complexes can
increase a thousand-fold in toxicity with a drop of 1.5 pH
units. Similarly, the toxicity of ammonia is a function of
pH. The bactericidal effect of chlorine in most cases is
less as the pH increases, and it is economically
advantageous to keep the pH close to 7. Based on the
available data, the pH of waste waters from the concrete
products industry varies from 5,7 to 12.5.
Total Suspended Solids •
Suspended solids include both organic and inorganic
materials. The inorganic compounds include sand, silt, and
clay. The organic fraction includes such materials as
grease, oil, tar, and animal and vegetable waste products.
These solids may settle out rapidly and bottom deposits are
often a mixture of both organic and inorganic solids.
Solids" may be suspended in water for a time, and then settle
to the bed of the stream or lake. These solids discharged
with man's wastes may be inert, slowly biodegradable
materials, or rapidly decomposable substances. While in
suspension, they increase the turbidity of the water, reduce
light penetration and impair the photosynthetic activity of.
aquatic plants.
Suspended solids in water interfere with many industrial
processes, cause foaming in boilers and incrustations on
equipment exposed to such water, especially as the
temperature rises. They are undesirable in process water
*The term toxic or toxicity is used herein in the normal
scientific sense of the word and not as a specialized
term referring to section 307(a) of P.L. 92-500.
61
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used in the manufacture of steel, in the textile industry,
in laundries, in dyeing^ and in cooling systems.
Solids in suspension are aesthetically displeasing. When
they settle to form sludge deposits on the stream or lake
bed, they are often damaging to the life in water. Solids,
when transformed to sludge deposits, may do a variety of
damaging things, including blanketing the stream or lake bed
and thereby destroying the living spaces for those benthic
organisms that would otherwise occupy the habitat. When of
an organic nature, solids use a portion or all of the
dissolved oxygen available in the area. Organic materials
also serve as a food source for sludgeworms and associated
organisms.
Disregarding any toxic effect attributable to substances
leached out by water, suspended solids may kill fish and
shellfish by causing abrasive injuries and by clogging the
gills and respiratory passages of various aquatic fauna.
Indirectly, suspended solids are inimical to aquatic life
because they screen out light, and they promote and maintain
the development of noxious conditions through oxygen
depletion. This results in
food organisms. Suspended
the killing of fish and fish
solids also reduce the
recreational value of the water. Based on the available
data, suspended solids from the concrete products industry
varies from 4 to 837 mg/1.
SIGNIFICANCE AND RATIONALE FOR REJECTION OF POLLUTION
PARAMETERS
A number of pollution parameters other than those selected
were considered, but had to be rejected for one or several
of the following reasons:
(1) Not harmful when selected paramters are controlled
(2) Not present in significant quantities
(3) Control substitutes a more harmful pollutant
(4) Insufficient data available
(5) Indirectly controlled when selected parameters are
controlled
(6) Not controllable
Dissolved solids
Dissolved solids may be present in significant amounts in
the waste water from this industry, but there is no treat-
ment other than no discharge to practicably reduce them.
62
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Temperature
Excess thermal load even with condensate from steam curing
has not been and is not expected to be a significant problem
in this industry. The holding time involved in the waste
water treatment systems should be adequate to dissipate
temperature increases.
Chemical Oxygen Demand (COD)
For the concrete products industry COD is chiefly
attributable to chemicals which are measured by the oil and
grease test i.e. form release oils. By controlling oil and
grease adequate control of COD should result. Some
admixtures may contribute to COD but not to oil and grease.
The data available however is insufficient to indicate that
specific control of COD is necessary because of admixtures.
63
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SECTION VI
CONTROL AND TREATMENT TECHNOLOGY
Waste water from the concrete products industry may contain
suspended solids and oil, and have a high pH. The general
treatment practices are similar for all subcategories.
Suspended solids are removed in settling basins, tanks or
ponds; pH is adjusted with sulfuric acid; and oil is removed
by skimming from pond or tank surfaces. Ready-mixed
concrete differs from the rest of the industry in that the
untreated waste water contains a significantly heavier load
of suspended solids. Handling and disposal of the resulting
solid wastes is a more severe problem. Oil and grease are
not usually found in waste water from ready-mixed or block
and brick plants, but have been found in the pipe and
prestressed and precast concrete product subcategories.
Many concrete producing facilities are located in urban or
suburban areas, where land may be scarce and expensivei
Fortunately, the suspended solids generated settle rapidly
so that tanks and small ponds may still be effective even
when space is at a premium.
Waste water discharges from plants manufacturing concrete
products are relatively small. The maximum reported values
of waste water handled in these plants (but not necessarily
discharged) are: ready-mixed concrete plants
568,000 liters/day (150,000 gallons/day); block and brick
plants 60vOOO liters/day (15,000 gallons/day); concrete pipe
400,000^1i*ers/day (100,000 gallons/day); and prestressed
and pressiafst products 57,000 liters/day (14,000 gallons/day).
Since some recycle is practiced and the use of evaporation/
percolation ponds is wide-spread, discharge volumes are
often significantly less than total waste water volumes
reported.
Based on the plants surveyed by EPA, an estimated *}0 per
cent of the concrete products plants usually have no
discharge because of evaporation/percolation ponds, recycle,
on-site ground seepage, or no generation of waste water:
65
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Treatment/Disposal Technology Percent, of Total Plants
Recycle ponds, evap/percolating 30
ponds plus ground seepage
Recycle from clarifiers 7
(ready-mixed only)
No waste water . 3
Plants which normally discharge waste water do so by
disposal either to surface waters or to sewers. Of the 30
plants surveyed which discharge, 17 discharge to surface
water and 13 to storm sewers. Waste water is generally
discharged after treatment by the concrete block and brick,
concrete pipe, and precast and prestressed concrete products
subcategories. Many ready-mixed concrete plants practice
some recycle and treatment.
Treatment and control practices for waste water of the
concrete products industry are discussed below in three
areas:
1) separation and control of waste water
2) treatment technology
3) monitoring
The treatment technologies currently used in this industry
for waste water consist of settling of suspended solids,
neutralization of high pH discharges, and separation of oil
and grease. >•-; -
to
The aggregate components of concrete wastes settle rapidly.
The cement component also settles fairly rapidly in an
undisturbed settling environment. Many treatment systems
are not designed to provide this quiescent settling and
cement fines are often carried over in the discharge. A
detailed discussion on cement settling rates is given later
in this section.
The settled solids usually must be removed from the settling
pond or tank. Handling and disposal methods include:
(1) Pumping the cement slurry into tank trucks
to a landfill
and hauling
66
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(2) Removing the settled sludge from tanks or ponds with
front-end loaders, backhoes, ora cranes, and dumping
nearby to dry prior to a second loading and hauling
operation of dried solids for land disposal
(3) Filling of pits with the settled solids, followed by pit
abandonment
(4) Separation of coarse aggregate by means of clarification
equipment with fine aggregate and cement components sent
for land disposal
(5) Separation of fine aggregate and coarse aggregate
components by means of clarification equipment or sloped
slab basin. Aggregate may be used or sold; cement sent
for land disposal
(6) Separation of fine aggregate, coarse aggregate
cement followed by reuse of all components
and
Except for the last, all these methods involve major solid
waste disposal on land.
The clarified waste water contains sufficient lime to raise
the pH to 11 to 12. Acid treatment is required to adjust
the pH to between 6 and 9. This acid treatment is practiced
by only one or two per cent of the plants studied.
There is potential for reuse of recovered aggregate, cement
and clarified water. Reuse is limited by regulatory
restrictions and quality uncertainties of concrete produced
with reused materials. Most specifications for concrete
call for potable water to be used in the mix. This prevents
the use of clarified recycle water for this portion of the
business. However, several companies were found that use
treated waste water where possible with no discernible
difference in physical properties of the resultant concrete.
Once the coarse and fine aggregate have been separated, the
cement can be retained in suspension and used in preparation
of new batches. At least one company has successfully
followed this approach.
Oil wastes are not usually present in the manufacture of
ready-mixed concrete- .However, the manufacture of cast
concrete products involves the use of oil as a form release
agent. Oil removal from waste water is not generally
practiced
67
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Waste water streams were found to contain COD up to
200 mg/liter. The amounts do not appear to correlate
consistently with any process variable. It is likely that
COD arises partially from the use of air entrainment agents
in concrete production. These agents are generally organic
materials and their amount arid composition vary according to
individual plant formulations. . Treatment of COD not
associated with oil and grease is not practiced in the
concrete products industry.
WASTEWATER TREATMENT FOR SPECIFIC CONCRETE PRODUCTS
Although all concrete plants use the same basic waste water
treatment technologies, there are significant differences
among the different subcategories as to amount of waste
waters treated.
CONCRETE BLOCK AND BRICK
The concrete block and brick manufacturing consists of
plants utilizing autoclave curing and low pressure steam
curing. Below are summarized the treatments used by
fourteen plants of either type:
Plant Curing Process
7100 high pressure autoclave
7101 high pressure autoclave
7102 low pressure steam
7103 low pressure steam
7104 low pressure steam
7105 high pressure autoclave
7106 low pressure steam
7107 high pressure autoclave
7108 low pressure steam
7109 low pressure steam
7110 low pressure steam
7113 high pressure autoclave
Treatment Used
no treatment
no treatment
evaporation/percolation
pond (no discharge)
evaporation/percolation
pond (no discharge)
evaporation/percolation
pond (no discharge)
settling pond (discharge
to storm sewer)
evaporation/percolation
no treatment
evaporation/percolation
no treatment
evaporation/percolation
settling basin and pH control
Waste water results from steeim condensate and miscellaneous
washdowns. Waste water quantities are small enough at most
plants so that evaporation or percolation on plant property
is feasible. Waste water quantities vary with production
and duration of curing. For example, steam condensate is
generated only during the 8 to 10 hour curing cycle.
68
-------
Based upon NPDES Application data (1971), some
characteristics of the effluent stream from plants that
discharge are:
Flow, liters/kkg
PH . _ .
Parameter Concentration,
mcf/liter
, TSS
COD
Oil and Grease
6H_
26
none
Plant
10
56
35
570
unknown
Parameter Amounts,
kg/kkq
TSS
COD
Oil and Grease
0.0005
0.0002,
none
0.001 a
0.0080
0.005
0.0002
0.025
unknown
*Plant 7111 manufactures both concrete block and
concrete pipe.
Waste water results from autoclave blowdown condensate and a
periodic discharge (purge) of the water used in the
convection process of steam generation at plants 7100 and
7101. Blowdown condensate results when the autoclave is
vented at the end of a curing cycle (8-10 hours). For this
reason, blowdown condensate is only produced approximately
1-2 hours/day at the plants visited. The discharge of
autoclave, 6 purge at plant 7100 occurs once a week resulting
in an intermittent waste water flow. Plant 7101 discharges
autoclave purge after each curing cycle. Plant 7100 settles
out suspended solids from autoclave blowdown condensate and
autoclave purge in an earthen settling pond. Plant 7105
removes suspended solids from autoclave blowdown condensate
in a concrete settling basin* Plant 7107 treats suspended
solids in an evaporation/percolation pond. Plant 7101 is
installing a waste water treatment system to settle
suspended solids from blowdown condensate and autoclave
purge using a settling basin. The clarified decant may be
used for aggregate stock pile dust control, thereby
eliminating discharge.
1 • '' .':.-'. , ' " • . • ; . • . > •-
No additional waste water, treatment methods were found in
the U.S. plants contacted, however, a Canadian concrete
block plant (plant 7113) visited had an automatically
69
-------
controlled acid-neutralization system. This installation
consisted of a 500 gallon acid-proof tank, with a pH sensor
that actuated a solenoid valve controlling the addition of
hydrochloric acid. The pH control was set to maintain a pH
level*of 9.0-9.5, but effluent analyses were not available.
Plants 71,00 and 7101 currently discharge their treated
effluent to a waterway, plants 7105 and 7113 to a municipal
storm ! sewer, and plant 7107 to an evaporation/percolation
pond. Constituents of the treated effluents from plants
7100 and 7105 are:
Plant
7100
7105
Flow, 1/kkg
(gal/ton)
50 (12)
214 (51)*
Constituents
TSS
pH
COD
Oil and grease
TSS
pH
COD
Oil and grease
Concentration Amount, kg/kkg
mg/liter (lb/1000 Ib)
20
11.3
48
2
54
11.5
unknown
unknown
0.001
0.0024
0.0001
0.01
unknown
unknown
*Plant-supplied datum
Low pressure steam curing processes as practiced by plants
7102, 7103, and 7104 have such small waste water flow that
they can often dispose of the water in on-site
evaporation/percolation ponds without treatment. When
discharge is necessary, treatment would be similar to that
for the high pressure autoclave system-settling of suspended
solids in a small pit, sump or tank and adjustment of pH to
6 to 9. c
CONCRETE PIPE
Waste water comes from central mixer and transport bucket
washout, spincasting, low pressure steam condensate, spray
curing, form washoff, prewetting of imbedded pressure pipe
and miscellaneous sources such as hydrostatic testing.
Central mixer and transport bucket washout are approximately
25 per cent of the waste water volume.
i I
Waste water volumes generated by 3 plants sampled range from
28 to 1,000 liters/kkg of product (6.7-240 gal/ton).
Typical waste water treatment involves only the removal of
suspended solids. All of the plants studied use settling
basins or ponds to remove suspended solids from central
70
-------
mixer and' transport bucket washout and spincast waste water.
Plants 7224 and 7247 treat low pressure steam condensate,
while plants 7201, 7205, 7229, 7233, 7239, 7241, and 7248 do
not. Plant 7224 collects spray curing waste water, settles
out suspended solids, and reuses the clarified water for
spray curing. Plant 7247, a pressure pip^e plant, combines
all waste water streams, settles out: suspended solids,
removes oil and grease by skimming and sorbant booms, and
adjusts 'the pH of the clarified decant with sulfuric .acid.
Table 7 summarizes that waste water volumes generated and
treatment utilized in several pipe plants. Those plants
•with untreated or partially treated waste water may need to
settle solids in small pits, tanks or ponds, to adjust pH
with acid addition, and to skim; off floating oil with belt
units or small API-type separators or to adsorb it in straw
or other adsorbents.
Information on discharged waste water at concrete pipe
plants based upon EPA measurements is given below.
7201
Flow, liters/kkg 28
(gal/ton) (7)
pH ,11.5
Parameter amounts,
kq/kkg (lb/1000 lb>
TSS 0.002
COD '"'"::'" 0.003
Oil and grease
0.01
Parameter concentra-
tions, mg/liter
TSS 70
COD 115
Oil and grease 376
Plants
7224
161
(39)
9.0
0.13
0.08
0.04
837
466
264
7247
1 , 000
(240)
7.4
0.006
0.16
0.003
6
161
2.9
Permit application (NPDES) data for additional concrete pipe
plants were reviewed. Usable discharge data were obtained
from six plants. These are summarized:
71
-------
TABLE 7 , TOTAL WASTEWATER GENERATED FROM CONCRETE PIPE PLANTS
Wastewater Origin
Plant
Code
7201
7205
7212
7223
7224
7229
7233
7239
7241
7247
7248
Treatment
settling pond
e/P
none
settling pond
settling pond
e/P
e/p
none
none
settling pond;
oil removal;
pH adjust
settling pond
L.
X
fi ^
i- X
c"s
(0 O
X
X
X
X
X
X
X
X
c*.
'o
§ "&.
X
X
X
X
X
X
X
X
X
X
&
> ^
S 'a.
(J V*l
X
L-
.*-
0
X
X
Total
Wastewater
Quantity
liters/day
760
8,370
760
3,200
66,600
unknown
320
184
320
302,800
75,700
e/p - evaporation/percolation.
72
-------
7224
7247
7249
7250
7251
7252
Flow, liters/kkg 1,070 743
(gal/ton) (256) (178)
pH 11 7.5
Parameter amounts,
kg/kkg (lb/1000 lb)
TSS 0-35
COD 0.1
Oil and grease
Parameter concen-
trations, mg/liter
TSS
COD
Oil and grease
0,013
not mea-
sured
not given 0,004
327 17
93 not mea-
sured
not given 5.5
1,202
(288)
9.5
0.12
0.12
0.03
100
103
26
235
(56)
8.0
0.002
0.005
0.003
8
20
•11
278
(67)
9.6
0.009
0.004
0.017
32
15
64
Figures 9 and 10 illustrate typical belt and API-type oil-
skimming units. For the usual waste water volumes from pipe
operations, the belt-type skimmer would be more appropriate.
Adsorbent materials can also be used conveniently to remove
small amounts of oil.
PRESTRESSED AND PRECAST CONCRETE PRODUCTS
Waste water results from central mixer and transport bucket
washout; form washoff; curing(low pressure steam condensate
and runoff from, spray curing); product finishing; and mis-
cellaneous contributions such as waste water from equipment
clean-up, and any spills that may occur. Central mixer and
transport bucket washout constitute approximately 50 per
cent of the daily waste water volume. Mix water is
incorporated into the concrete and does not become a source
of waste water. Form washoff may 'be used but was not
observed. Total reported daily waste water volumes
generated by the plants contacted ranges from 7 to
608 liters/kkg (2 to 145 gallons/ton) as shown in Figure 11.
Waste water treatment is principally the removal of
suspended solids by sedimentation prior to reuse' or
discharge. Plant 7238 adjusts pH as part of its treatment
method. Approximately 30 per cent of the plants contacted
have no waste water treatment. Suspended solids are removed
either by settling in ponds or basins or by mechanical
clarification. At most plants the removed solids are
landfilled. Where pH is generally adjusted, it is done with
sulfuric acid in a holding or mixing tank.
329
(79)
8.8
0.03
0.013
0.004
92
39,
11
73
-------
OIL
SCRAPER
' BLADE
(2)
OIL
CATCH
PAN
(2)
OIL COATED
(BOTH SIDES)
MOTOR
DRIVE CHAIN
BELT
OIL LAYER
FIGURE 9
BELT OIL SKIMMER
74
-------
75
-------
o
I-
o
DC
o.
P
o
DC
b
CO
DC
LU
DC
UJ
fe
3
1,000
500
200
100
50
20
10
2 -
I
JL
.L
J I ! I I I
JL
J
I 2 5 10 20 40 60 80 90 95 98
CUMULATIVE PERCENT OF PLANTS LESS THAN
FIGURE 11
DISTRIBUTION OF WASTMTEP GFNEM1B) AT PRECAST
AND PRESTRESSED CONCRETE PRODUCTS PLANTS
(DATA FROM 32 PLANTS)
76
-------
Waste water from prestressed and precast concrete plants is
usually treated in a similar manner to that of the pipe
subcategory. Ponds or basins are used for removing
suspended solids in this subcategory. One plant studied
controls pH by addition of acid. Amounts of waste water
generated and types of treatment are summarized in Table 8.
Effluent information on discharged waste water at plants
studied follows. Plant 7238 verification data was obtained
during startup and is possibly atypical. The oil found by
EPA measurement in this plant's effluent is used for
mosquito control not from the manufacture of precast and
prestressed cement products.
Plants
7203
24
(6)
7207
87
(21)
7230
139
(33)
7232
8.7
(2.1)
Flow, liter/kkg
(gal/ton)
pH 11.5 11.4 10.9 11.7
Parameter amounts
kg/kkg (lb/1000 Ib)
TSS 0.002 0.02 0.07 0.003
COD 0.0009 0.0014 0.05 0.009
Oil and grease 0.00002 0.0003 0.0002 7 x 1
Parameter Concentration
mg/liter
TSS
COD
Oil and grease
97
57
0.8
230
16
4
488
335
1.4
353
101
0.08
77
_
-------
TABLE 8
TOTAL WASTCWATER GENERATED FROM PRESTRESSED AND
PRECASTE CONCRETE PLANTS
Wastewater Origin
Plant
Code
7200
7203
7204
7206
7207
7208
7209
7210
7211
7213
7214
7215
7216
7217
7218
7219
7220
7221
7222
7225
7226
7228
7230
7231
7232
7234
7235
7236
7238
7240
7242
7243
7244
7245
Treatment
settling pond
settling pond
e/p
settling pond
•settling pond
none
none
not given
none
settling pond
none
none
e/p
none
none
settling pond
settling pond
settling pond;
e/P
settling pond
none
settling pond;
e/p
settling pond
settling pond
e/p
e/p
e/p
settling pond;
e/p
e/p
mechanical
clarification;
settling pond;
pH adjustment
none
settling pond
none
e/p
none
o
j<
5
"e §
4) J®
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
0)
•6
trt
c:
11
**" t \
X
X
X
X
tt
o
£ ~8
l°--£
o
"5;
*- 4:
It
£ -g
£ CO
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
c
1 '°
"§ "o
O- 5
X
X
X
X
X
X
X
X
^
j=
6
X
X
X
X
X
Total
Quantity
liters/day
190
2,080
8,900
3,800
14,600
80
0
1,900
1,200
1,140
5,300
9,500
15,100
400
49,200
11,360
9,460
5,690
3,800
11,400
490
7,600
1:13,600
SO
3,800
17,000
12,100
27,400
56,800
8,000
3,800
1,500
6,100
29,700
78
-------
7238
Flow, liter/kkg 201
(gal/ton) (48)
pH 9.8
Parameter amounts
kg/kkg (lb/1000 Ib)
TSS 0.002
COD 0.003
Oil and grease 0.013
Parameter concent.rat.ion
mg/liter
TSS 12
COD 14
Oil and grease 64
Plant
7238*
249
(60)
7.5
0.013
unknown
unknown
88
unknown
unknown
7253**
371
(89)
9.1
0,098
0 . 046
0.015
264
125
41
#Plaht supplied information - -
**Permit application(NPDES) data.
READY-MIXED CONCRETE
Permanent Plants
Waste wiater comes from mixer truck washout and Washoff,
central mixer washout, and miscellaneous sources' such as
yard dust control, mixer truck chute rinse-off, and
equipment clean-up. Mixer truck washout and washoff
constitute approximately 80 percent of the waste water
volume. Mix water is incorporated into the concrete and
does not become a source of waste water.
The plants contacted reported waste water volumes generated
ranging from 20 to 287 liters/cu m (4 to 57 gallons/cu yd),
with 4 of the plants having more than 248 liters/cu m
(50 gallons/cu yd) of waste water. Only a small portion of
the waste water generated is normally discharged at these
plants as shown in Figures 12, 13 and 14.
79
-------
fe
tr
P
bJ
O
CO
O
CO
£
1,000
500
200
100
50
20
10
_L
_L
_L
J_
TOTAL OF:
CENTRAL MIXER WASHOUT
TRUCK V/ASHOUT
TRUCK WASHOFF AND
MISCELLANEOUS WASH
_L
JL
J
5 10 20 50 70 80 90 95 99
CUMULATIVE PERCENT OF PLANTS LESS THAN
FIGURE 12
DISTRIBUTION OF WASTEWATER GENERATED
AT PERMANENT READY-MIXED CONCRETE PLANTS
(DATA BASED ON 385 PLANTS)
80
-------
500
cc
Q.
U-
O
021
LU
O
O
•v.
CD
cc
UJ
200
100
50
20
10
_L
J_
5 SO 20 4O 60 80 90 95
CUMULATIVE PERCENT OF PLANTS LESS THAN
FIGURE 13
DISTRIBUTION OF PROCESS \mSTEWATER GENERATED
AND DISCHARGED AT READY-MIXED CONCRETE PLANTS
(VERSAR MEASUREMENTS OF 5 PLANTS)
81
-------
Waste water treatment generally involves sedimentation to
remove suspended solids. Two percent of the plants adjust
the pH of the waste water for discharge as part of their
treatment. six percent of the plants contacted have no
waste water treatment. The sedimentation techniques usually
used in this industry are:
1) earthen ponds
2) concrete tanks or ponds
3) sloped slab basins
4) mechanical clarification units
Where pH is adjusted, sulfuric acid is typically the
chemical used. The waste water treatment methods used at
plants visited are given in the following table:
Waste water Treatment Practices at Selected
Ready-Mixed Concrete Plants
Plant
7305
7363
7365
7385
7441
7451
7452
7487
7542
7543
7544
7545
7699
7729
7731
7732
7736
7750
7755
7757
Settling Sloped
Pond Slab
Treatment Practiced
x
x
x
X
X
X
X
X
X
X
X
X
X
X
Mechanical
Clarifier
x
x
X
X
X
X
X
X
X
X
X
X
X
X
pH
Adjust
Reuse of
Waste water
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
X
X
The clarified waste water may be reused for truck washout,
added to mix water, or discharged. in most plants the
solids removed from a sloped slab or a mechanical
clarification system are either sold as basefill material,
reused for batching concrete, or landfilled.
82
-------
Specific information on waste water disposal methods used at
some plants is presented as follows:
Plant
7305
7363
7365
7441
7451
7452
7487
7542
7543
7544
7545
7699
7729
7731
7732
7736
7750
7755
7757
Total
Containment
x
- - *.' -4
Evaporation/
Waterway Percolation
x
x
x
x
x
X
X
X
X
X
Comments
Except during
heavy rainfall
Yard runoff dis-
charged during
heavy rainfall
Yard runoff dis-
charged during
heavy rainfall
Yard runoff dis-
charged to waterway
Yard runoff dis-
charged to waterway
Yard runoff dis-
charged to waterway
Landfilled
Discharge to
storm sewer
Yard runoff dis-
charged to waterway
Discharges to
municipal sewer
Yard runoff dis-
charged to waterway
Mixer truck washout and washoff are reused at many of the
plants reducing the requirements for disposal.
Twelve plants were found in this study which treat yard
runoff. Eight of- the twelve plants combine and treat yard
runoff with other process waste water.
Effluent information measured by EPA is as follows:
83
-------
Plant
7305*
7365
7542
7543**
Flow, liter/cu m
(gal/cu yd) 40 (8) 20 (4) 248 (50) 25 (5)
PH 12.1 11.8 5.7 10.1
Parameter Amounts,
kg/cu m (Ib/cu yd)
TSS 0.005
(0.008)
Parameter Con-
centration,
mg/liter
TSS 125
* Plant supplied data
** Yard runoff data
0.002 0.001 0.0001
(0.003) (0.0017) (0.00017)
89
Plant
7544**
Flow, liter/cu m
(gal/cu yd) 20 (4)
pH 12.5
Parameter Amounts,
kg/cu m (Ib/cu yd)
TSS 0.0008
(0.003)
Parameter Con-
centration,
mg/liter
TSS 38
7545
163 (33)
6.5
7545**
129 (26)
10.8
7731
69 (14)
11.5
0.0015 0.008 0.001
(0.0025) (0.013) (0.002)
61
15
** Yard runoff
PORTABLE PLANTS
The sources of waste water in portable plants are idential
to those in permanent plants. The distribution of waste
water;generated at the plants studied is shown in Figure 14.
Because of recycle of mixer truck washout and washoff for
truck washout is practiced in the industry, the quantity of
waste water discharged is reduced. Mixer truck washout, and
washoff constitute approximately 80 percent of the waste
water volume.
84
-------
lOOr
g
Q
I
fe
ffi
UJ
O
m
3
*»v
UJ
50
20
10
TOTAL OF:
CENTRAL MIXER WASHOUT
TRUCK WASHOUT
TRUCK WASHOFF '
J J I I I I
-L
J
2 5 10 20 40 60 80 90 95
CUMULATIVE PERCENT OF PLANTS. LESS THAN
FIGURE 14
DISTRiBUTiON OF .WASTEVWTER-GENERATED
AT PORTABLE READY-MIXED PLANTS
(DATA FROM 18 PLANTS)
85
-------
Typical waste water treatment at portable plants involves
the removal of suspended solids in a settling pond. There
may be no effluent from the pond because of evaporation and
percolation. None of the plants contacted adjust pH as part
of waste water treatment. Ten percent of the plants
contacted had no system for recovery of wash water and hence
no treatment of waste water.
Facilities to remove suspended solids vary
plant to plant but are of the following:
in detail from
(1) earthen settling ponds,
(2) earthen settling ponds with filtered overflow,
(3) mechanical clarification systems.
Mechanical clarification systems are designed to settle and
separate suspended solids in a more compact space than
ponds. Plant 7753, which uses a mechanical clarification
system, uses the aggregate removed from the system for fill
material.
The methods of waste water treatment used at several plants
are:
Settling
Plant Pond
7362 '•
7601
7602
7603
7604
,7609
7627
(4 plants)
7633
7641 '
7649
7691
7706
(4 plants)
7707
7753
7758
x
x
X
X
X
X
X
X
X
X
X
Mechanical
Clarification
& Discharge
Reuse of
Waste water
x
X
Other
no treatment,
no discharge
' a :•
no treatment
filter pond
x
x
no treatment,
no discharge
86
-------
At some of the plants, recycle mixer truck washout and
washoff reduces the total volume of disposed waste water.
The methods of waste water disposal practiced at the plants
studied ,is presented below. ,
Plant
7362
Total ,
Containment
Disposal
to Waterway
7601
7602 x
7603 x
7604 x
7609
7627 x
(4 plants)
7633 x
7641
7649
7691 x
7706 x
(4 plants)
7707
7753 x
7758
x
Other
Disposal
e vaporati on-percolation
on yard
yard dust control
no treatment
x
storm sewer
water used only to spray
stockpiles at plant site
Data qn the quality of the effluents is not available from
portable plants but it should be similar to that of
permanent ready-mixed plants.
MOBILE PLANTS ,
Waste water from these plants comes from mixer washout and
concrete-mobile washoff and miscellaneous sources. The
miscellaneous sources of waste water are yard dust control
and runoff from spills and solid waste piles. Concrete-
mobile mixer washout and washoff constitute approximately
75 per cent of the waste water volume. Concrete in the
plastic state is not a source of waste water.
The quantity of concrete-mobile waste water generated at
plant 7759 is 11 liter/cu m (2.2 gal/cu yd); at plant 7760
it is 10 liter/cu m (2 gal/cu yd). Since waste water
volumes are small, treatment practices in the industry .are
not sophisticated. Plant 7759 contains its waste water in a
settling/evaporation area. Plant 7760 collects the waste
water from concrete-mobile mixer washout in a bucket,
carries it to the next job site, and uses the waste water to
87
-------
"prime" the mixer. According to the manufacturer of the
concrete-mobile, this later technique is commonly practiced.
All of the mobile plants contacted discharge waste water to
an evaporation/percolation area.
WASTEWATER TREATMENT SYSTEMS
The waste water from ready-mixed concrete plants contains
suspended solids, high pH, and COD. Tables 9, 10 and 11
detail the types of treatment techniques used throughout
this industry.
Eighty-two per cent of the permanent ready-mixed concrete
plants surveyed use treatment ponds for truck and central
mixer washout water. Fifty-eight per cent of the plants
reported using evaporation or percolation ponds, while 11
per cent use settling ponds, 12 per cent use filter ponds,
and 1 per cent reported using sloped slab basins.
Clarification equipment is used in 12 per cent of the plants
and 6 per cent have no treatment. pH is adjusted in only
1.6 per cent of the plants studied. Sixty-three per cent of
the plants using evaporation or percolation ponds have no
discharge (excluding rainwater runoff). The remainder of
the plants using evaporation or percolation ponds discharge
truck washoff or other miscellaneous water from the plant,
Industry sources have indicated that the use of mechanical
clarification equipment is less widespread than the 12 per
cent found in this study, i.e*, 3 per cent. The prevalence
of sloped•slab basins may be greater than the data reported
indicate since typically a plant with sloped slab basins and
settling ponds would report only the latter.
Those portable ready-mixed concrete plants which- have
treatment use some form of settling ponds or mechanical
clarifiers.
88
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TABLE 9
Summary of Treatment of Central Mixer and Truck
Washout Water in Ready-Mix Concrete Operations
(Information Based on 430 Permanent Ready-Mix Concrete Plants)
Treatment
No,, of Plants*
Ponds
Settling ponds 48
Evaporation/percola- 248
tion ponds
Filter ponds 50
Sloped pond separation 5
Unidentified** 2
Clarification Equipment
Home-made aggregate 8
reclaimer
Screw 9
Drag chain washers 31
Screen 3'
Unidentified " 2
pH Adjustment 7
No treatment 29
No washout at plant site 34
Total
353
53
7
29
34
% of Total
"• 82.1%
11.2%
5-7.7%
11.6%
1.2%
0.5%
12.3%
1.8%
.2.1%
7. 2%
0.7%
0.5.%
1.6%
•6.7%
7.9%
*Some of the plants have more than one kind of treatment.
**Information was not complete enough to identify the exact type
of treatment. .'
89
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TABLE 10
Summary of Treatments of Truck Washoff Water
in Ready-Mixed Concrete Operations (Information
Based on 430 Permanent Ready-Mixed Concrete Plants)
Treatment
No. of Plants
Treated with truck
washout
Ponds
Settling ponds 21
Evaporating/percola- 135
tion ponds
Filter ponds 28
Sloped slab separation 3
ponds
Clarification Equipment
Home-made aggregate 5
reclaimer
Screw 4
Drag chain washers 20
Screen 2
Unidentified 2
pH Adjustment 1
Treated Separately From
Washout Water
Settling 5
Unidentified 2
No Treatment
Becomes yard runoff 155
Doesn't become yard 30
runoff
Unidentified 3
No Washoff at Plant Site 35
Total
221
187
33
1
7
188
35
% of Total
51.4%
43.5%
4.9%
31. a*
6.5%
0.7%
7.7%
1.2%
0.9%
4.6%
0.5%
0.5%
0.2%
1.7%
1.2%
0.5%
43.7%
36.0%
7.0%
0.7%
8.1%
90
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TABLE 11
Waste water and Treatment Technology For
Portable Ready-Mixed Concrete Plants.:
Code Treatment
7362 evap/perc yard none
7595 evap/perc pond 2,650
7601 filter pond 760
7602 evap/perc pond 1,890
7603 evap/perc pond 1,890
7604 evap/perc pond 380
7609 evap/perc pond. 1,890
7627 evap/perc pond 1,890
7632 no treatment 1,890
7633 evap/perc pond 760
7641 no treatment 7,570
7649 filter pond 1,890
7691 evap/perc pond 380
7701 no treatment 760
7702 no treatment 760
7706 evap/perc pond 2,270
7707 evap/perc pond 760
7715 no treatment unknown
7751 evap/perc pond 190
Settling Ponds
Quantity of Waste water (liters/day)
Central Mixer Truck Truck
Washout Washout Wash Off
none
11,350
7,570
3,780
3,780
1,510
15,100
190
9,840
15,100
i,510
13,250
1,890
9,080
11,350
28,390
7,570
2,270
7,570
190*
unknown
hone
unknown
unknown
unknown
'unknown
unknown
.unknown
unknown
190
760
unknown
1,140
1,420
unknown
760
190
unknown
Fifty-two per cent of the plants were found to treat truck
washoff water in the same system used for treating truck
washout water. For thirty-six per cent of the plants truck
washoff water becomes untreated yard runoff. Only 2 per
cent of the plants treat truck washoff water separately from
washout water. The widespread use of
evaporation/percolation ponds is an indication of small
waste water volumes. For the ready-mixed concrete industry
50 per cent of the plants with 75 cu m/day (100 cu yd/day)
concrete production have less than 6,500 liters/day
(1,700 gallons/day) of total waste water. It is likely that
a disproportionate number of the plants with
evaporation/percolation ponds are also plants with small
production.
91
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Most settling systems, including ponds, sloped slab basins
and mechanical clarification units, discharge during periods
of heavy rainfall, even if at no other time. The amount of
discharged water may be minimized by reducing the drainage
area in which wastes are generated. The design of settling
ponds in this subcategory depends on the amount of land
available and the pond clean-out procedure as well as the
amount of waste water to be handled. Many of the ponds are
constructed of concrete with walls at least one foot thick.
Figure 15 gives settling information determined on a sample
of truck washout taken from plant 7363. For this particular
sample a level of 50 mg/liter of suspended solids was
obtained after 4 hours settling time and 19 mg/liter after
20 hours settling time. Washout from concrete trucks and
mixers contains coarse aggregate, sand and cement. When
dumped into a pond the coarse aggregate and sand settle
almost immediately. The cement and a small amount of fines
from the sand and coarse aggregate settle much more slowly
as shown in Figure 15. A residence time of 24 hours in a
undisturbed pond should be adequate for settling pond design
in this subcategory. Settling pond area requirements are of
the order of 18.3 m by 18.3 m (60 ft by 60 ft) for a large
plant and less for smaller plants. Constructed ponds,
usually made of concrete, generally are smaller than this.
Ponds that take advantage of local terrain such as old
gravel or sand pits, quarries, low spots, and bulldozed
earthen pits may be of any size.
Many of the concrete plants are located in neighborhoods
where land availability is limited and the price of
additional land is high. However, ninety-four per cent of
the concrete plants supplying data already have treatment
facilities and space available. Of the remaining !";six per
cent it is likely that many have sufficient land available
for treatment facilities if needed. Therefore, it is
prooable only one or two per cent of the plants will have a
problem with availability of land for treatment facilities
and these problems can probably be overcome with proper
selection of treatment technology.
Most of the solid wastes that require disposal come from:
(1) waste concrete
production.
mix - approximately 1 per cent of
(2) truck washout - approximately 59 kilograms per cubic
meter (100 pounds per cubic yard) at an average of
1.5 washouts per day per truck.
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(3) central mixer washout - approximately 227 kilograms
(500 pounds) per washout, usually once per day,
(4) truck washoff - variable but relatively small
compared to items 1, 2, and 3.
amount
Whenever possible returned concrete is disposed of by using
it to make precast structures for which forms are kept
assembled, or for paving the yard of the concrete plant. If
land is available it may simply be dumped. If clarification
equipment is available, the waste concrete may be processed
to recover the aggregate portion. Truck washout, in the
absence of clarification equipment, will most likely be
settled in the pond and constitutes the major solids
contribution. Truck washoff and central mixer washout may
or may not drain to the pond depending on plant layout.
An evaporation/percolation pond may be natural or
constructed but its primary characteristic is that it
disposes of waste water through the dual mechanism of
evaporating water into the air and allowing water to seep
into the ground. Since most of these ponds are located in
relatively high rainfall areas and the pond surface areas
are usually small most of the water loss is by percolation.
Many, if not most, of these ponds have no discharge to
surface waters.
Often the plant can take advantage of some available config-
uration on its property for waste water treatment or
storage. Low spots, valleys, abandoned quarries or gravel
pits, excavations or other depressions may be used. In some
cases, ponds constructed using these areas have such large
volume that they normally have no discharge. -> -
y,i-
Since the settling ponds used generally need not exceed 18.3
by 18.3 meters (60 by 60 feet), excavation of earthen ponds
is fairly common. As these ponds fill, they may be
abandoned or cleaned out.
Since the settling pond size required is relatively small
and concrete is readily available, many of the settling
ponds are constructed of concrete. The concrete basins or
tanks are more expensive to build than local terrain and
other earthen ponds but are easier to clean and maintain,
and have a better appearance.
94
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In most cases at least two settling ponds are used in
.series. The first pond is used for removing the readily
settleable materials. Most of the sand and gravel, will
settle within the first minute and most of the cement will
usually settle within the next few minutes. The remaining
fines take hours to settle and are sensitive to any
turbulence or disturbance. Therefore, it is common practice
to have at least two ponds in series - the first a roughing
pond to collect most of the suspended solids and the
subsequent pond(s) for attaining low suspended solids levels
and storing water for reuse or discharge. Quite often the
sand and gravel may be removed by sloped slab collection or
a clarification unit prior to the first pond and the bulk of
the cement removed in the first pond. The first pond also
collects the low density floating particles resulting from
air entrainment agents.
Figure 1.6 shows two earthen ponds in series. The first pond
collects most of the suspended solids while the second pond
is primarily for final settling and storage. Water can be
recycled without treatment or discharged after pH
adjustment. Figure 17 shows two concrete basins and a
holding pond in series. The first basin .collects the coarse
aggregate, the second basin is for removing cement and other
fines. The water passes from the settling basin, through
straw bale filters which not only remove some of the
residual suspended solids but also retain the floating
particles caused by air entrainment agents. The holding, or
pumping pond can be used for recycle or pH adjustment prior
to discharge.
Filter ponds are a special kind of settling pond^ In our
study 12 percent of the plants reported using filter ponds
in their treatment system* The relative popularity of this
treatment technology stems largely from its simplicity and
low cost. Figure 18 demonstrates the basic principle of a
filter pond. A portion of the pond wall is constructed of
some porous material such as crushed rock to stone (2,,:to 15
cm diameter) so that drainage occurs in this material. Most
of the settling occurs in the filter pond prior to waste
water discharge through the porous wall. These ponds are
reportedly only about 50 percent as efficient as a : settling
pond due to the short circuiting of water and escape through
the filter without sufficient settling time. In some cases
the filter pond is backed up with a holding pond or -basin,
in other cases it is not and the filtered water is directly
discharged. Aside from its reduced settling efficiency, the
filter pond is much like an earthen settling pond. One
reason for its popularity for treating concrete waste water
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is ability of the filter to retain
material on top of the pond.
Sloped Slab Separation Basins
most of the floating
Since the coarse aggregate and sand settle so rapidly, there
is no need for a settling pond to remove them. If the waste
water is dumped on a slab these components readily separate
from the water. If this slab is gently sloped to provide
drainage of the water, the aggregate will collect on the
sloped surface and can be removed with a front-end loader.
Baffles and other flow diversion installations are often
used to improve the solids removal efficiency. Slope slab
separation basins are generally used in series with settling
basins to remove the concrete fines. Figure 19 shows an
example of a sloped slab separation basin used in series
with three settling basins. The discharge basin shown is
made of reused concrete.
Sloped slab basin size is largely determined by the number
of truck stations desired. Allowing 4.6 m (15 ft) space for
each truck, four truck stations require 18.4 m (60 ft) slab
length. An inclined slope of; 6.1 to 12.2 m (20 to 40 ft) in
width should be ample to collect the coarse aggregate.
Therefore the slab area required may be estimated by
multiplying number of truck stations needed times 56 sq m
(600 sq ft) per truck station.
Approximately 83 per cent of the solids in concrete are made
up of sand and coarse aggregate. Most of this will be
deposited on the sloped slab along with some cement. The
use of readily cleanable sloped slab removes approximately
75 per cent of the solids prior to the settling ponds.
Also, separation of the aggregate from the cement in this
way reduces the amount of drying for the concrete wastes
which would have to be dredged. This reduces the amount of
sludge to be dried by 75 per cent.
Mechanical Clarification
Mechanical clarification devices used in this industry are
of three general types: drag chain washers, screw washers,
and screens.
Drag chain washers consist of one or two chambered wash
tanks with progressive drag chains to remove settled solids.
Figure 20 illustrates a drag chain unit. Truck washout
water is discharged into the wash tank. The fast settling
coarse aggregate and most of the fine aggregate settle to
the bottom of the tank and are conveyed by the drag chain
99
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out of the tank, and dumped in a pile beside the unit. The
slower settling cement fines are removed by a slow moving
drag chain which conveys the fines over the end of the tank.
The clarified waste water is collected in a sump and can be
reused. If truck washout water is the only waste water
handled and it is recycled, the system can probably operate
without discharge. If truck washoff, central mixer washout,
and other waste water is included, some discharge may be
necessary. The discharge from this system requires further
suspended solids removal and pH adjustment. The drag chain
unit is compact, requiring a ground area of only about 6.1 m
x 18.3 m (20 ft x 60 ft). The washout from at least twenty
trucks can be handled in an area this size. Aggregate is
dumped onto a pile convenient for resale or disposal.
Cement sludge is also dumped onto a pile convenient for
handling, but still needs additional drying before final
disposal. The unit is operated by the truck driver.
Automated cycle operation eliminates the need for any other
manpower except for maintenance. Drag chain units are
currently the most widely used of the mechanical separation
devices (31 units out of 53 plants reporting)..
Inclined screws can also be used for removing coarse aggre-
gate and sand from truck washout water. Depending on the
design of the screw, coarse aggregate alone may be removed
or a mixture of coarse aggregate and sand. At least one
commercially available screw washing unit also separates
coarse aggregate and sand into two separate piles by using
an aggregate screw and a sand screw in series. Figure 21
illustrates a screw washer. Truck washout is dumped into
the lower end of the inclined screw and the coarse material
is dumped out at the upper end. Figure 22 illustrates a
double screw washer for separation of coarse aggregate and
sand.
The screw washers differ from most of the treatment systems
discussed so far, in that their primary purpose is recovery
of waste components for reuse in concrete mixes. Single
screws recover coarse aggregate for reuse. Double screw
units recover both coarse aggregate and sand for reuse. The
units are operated by the truck drivers, with no other
operator being required. The single screw units reported
are relatively old installations of a specialized nature.
Essentially they are add-ons to basic sloped slab and
settling pond systems. The double screw units are new and
sold as part of a complete waste water treatment system.
This total system includes not only the double screw washer
but also a fabricated settling tank assembly for fines
removal.
102
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Screens are used to separate coarse aggregate and sand from
cement fines and coarse aggregate from fine aggregate.
Preliminary screening on truck washout will separate the
coarse aggregate from the rest of the waste stream. This
stream can then be passed through a sand screw for sand
recovery. A second alternative is to separate coarse
aggregate and sand, once the mixture has been recovered from
the waste water stream by a drag chain or screw washer unit.
Figures 23 and 24 represent two different utilizations of
screens for separation purposes,.
Once the suspended solids have been removed from the wash
water by pond or tank settling, this water is suitable for
several purposes. Reuse accomplishes several desirable
objectives, including reduction in fresh water costs,
conservation of water, and reduction or elimination of waste
water discharge. Selective recycling of waste water is
widely practiced today in the ready-mixed concrete industry.
The following discussion covers the uses and, problems
encountered. The most common use for recycled water is
truck washout (115 plants of 430 plants). This is logical
for a number of reasons:
(1) Aside from mix water, truck washout consumes the largest
volume of water used.
(2) Most settling systems are 'designed for treating and
recovering truck washout water — the recovered water is
usually stored close to the truck washout systems.
(3) High dissolved solids and:pH for the recycled wash water
are not a problem*, ,
Recycled water is also used for washing out central mixers
in many plants^ but this is not a major water use. Use of
recycled wash water for truck washoff has been reported for
a number of plants (73 plants of 430 plants). Use of
recycled water is restricted for this purpose because the
dissolved solids leave a film on the truck surface and
because truck washoff is often remote from recycled water
availability.
After treatment for suspended solids and recycle of all
possible waste water, it is still necessary in many cases to
discharge a portion of the waste water. This waste water
usually has a pH of 10 to 1.2. - Where pH is adjusted, the
most common practice is to use sulfuric acid to lower pH to
a range of 6 to 9. The amount of concentrated acid required
for adjusting pH to 7 is given in Figure 26. The control of
pH by addition of acids tends to decrease the suspended
solids and increase the dissolved solids in this waste
water.
105
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106
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107
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PRETREATMENT TECHNOLOGY
Concrete products operations are often located in urban or
suburban locations with access to publicly-owned waste water
treatment plants. In areas where publicly-owned facilities
could be used, pretreatment could be utilized to reduce
heavy suspended solids loads, particularly for ready-mixed
concrete waste water. In some instances pH control and some
reduction in oil and grease may be appropriate.
NON-WATER QUALITY ENVIRONMENTAL ASPECTS
For those waste materials considered to be non-hazardous
where land disposal is the choice for disposal, practices
similar to proper sanitary landfill technology may be
followed. The principles set forth in the EPA1s Land
Disposal of Solid Wastes Guidelines (CFR Title 40, Chapter
1; Part 241) may be used as guidance for acceptable land
disposal techniques.
For those waste materials considered to be hazardous,
disposal will require special precautions. In order to
ensure long-term protection of public health and the
environment, special preparation and pretreatment may be
required prior to disposal. If land disposal is to be
practiced, these sites must not allow movement of pollutants
such as fluoride and radium-226 to either ground or surface
water. Sites should be selected that have natural soil and
geological conditions to prevent such contamination or, if
such conditions do not exist, artificial means (e.g.,
linars) must be provided to ensure long-term protection of
the environment from hazardous materials. ,, ; Where
appropriate, the location of solid hazardous materials
disposal sites should be permanently recorded in the
appropriate office of the legal jurisdiction in which the
site is located.
The primary non-water quality environmental impact of wastes
from the manufacture of concrete products is solid waste
disposal. Solid waste comes from waste concrete mix, waste
concrete from truck, bucket and mixer washouts, and dusts
and concrete from truck and yard washoffs. Quantities of
these solids wastes have been given earlier in Section V.
Disposal practices for these
essentially they may be listed as:
solid wastes vary, but
(1) drying and land disposal of all solid wastes
108
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(2) recovery of aggregates for landfill, and drying and land
disposal of cement portion +.
(3) recovery of coarse aggregate'for reuse plus drying, and
land disposal of cement plus sand portions
(4) separation of coarse and fine aggregate for reuse,
drying and land disposal of cement portion
and
(5) separation of coarse and fine aggregate
cement portion in new mixes.
for reuse of
Treatment technology can be varied to suit land
availability. Treatment systems for even the largest
reported ready-mixed plants with the greatest number of
trucks can be placed on less then 930 sq m (10,000 sq ft)
land space if mechanical clarification is used.
Drying, storage and disposal of solid wastes often takes up
more land area than the treatment system. However, the
solid waste disposal technology may be tailored to land
availability. In situations where solid waste storage space
is limited, cement sludges may be sent to off-site landfill
without drying (Plant 7699), and dry wastes such as
aggregate can be reused, sold, or landfilled without
storage.
In many cases ready-mixed concrete plant waste water treat-
ment facilities reflect the neighborhood in which they are
located. Those located in urban or suburban residential
areas are likely to be compact and constructed of painted
concrete with concrete paving and sometimes enclosed in
buildings. Those treatment facilities located in rural or
suburban commercial areas have more space and are more
likely to use earthen ponds and settling basins.
Concrete products other than ready-mixed concrete
very little land for waste water treatment purposes.
require
The waste water treatment technologies used for plants
manufacturing concrete products are not energy-intensive.
Truck washout for ready-mixed concrete is dumped directly
into the treatment facilities. Other waste water usually
flows by gravity either into treatment systems, discharge
ditches or to ground disposal* some pumping is involved in
transferring waste water from one tank to another and in
pumping waste water to and from the treatment system.
109
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In addition to the energy required for waste water
treatment, gasoline and other fuels will be needed to
operate front-end loaders, trucks and other solid waste
handling equipment.
Total energy requirement for the concrete industry waste
water treatment is estimated by EPA to be 1.7 x 10« Kcal/yr
(6.7 x 109 Btu/yr) .
110
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SECTION VII
COST, ENERGY, WASTE REDUCTION BENEFITS AND NON-WATER ASPECTS
OF TREATMENT AND CONTROL TECHNOLOGIES
This section contains cost estimates for treatments to
reduce pollutant levels in. discharged waste water for plants
manufacturing concrete products. It also covers costs for
non-water quality aspects such as solid waste disposal.
Treatment processes to reduce pollutant levels are readily
available for concrete industry waste waters. Suspended
solids may be reduced by settling in ponds, basins, tanks or
sumps. High pH caused by the lime fraction of cement may be
reduced by addition of acid. Oils and greases may be
reduced by gravity separation, skimming, and use of
adsorbents.
In the tables presented in this section. Level A represents
the minimum level of treatment found, while Levels B, C, D,
and others represent improved or alternative treatment
systems.
Cost information contained in this report was assembled
directly from industry, from waste treatment and disposal
contractors, engineering firms, equipment suppliers,
government sources, and published literature. Whenever
possible, costs are taken from existing installations,
engineering estimates for projected facilities as supplied
by contributing companies, or from waste treatment and
disposal contractors* quoted prices. In the absence of such
information, cost estimates have been developed from
plant-supplied costs for similar waste treatment and
disposal for other plants or industries. Modeling of
treatment systems has been used in some cases to provide
coherent cost patterns.
(1) Time Basis for Costs
All cost estimates are based on August 1972 prices and have
been adjusted to this basis as necessary.
(2) Useful Service Life
The useful service life of treatment and disposal equipment
varies depending on the nature of the equipment and process
involved, its use pattern, maintenance care and numerous
other factors. Individual companies may apply service lives
111
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based on their actual experience for internal amortization.
Internal Revenue Service provides guidelines for tax
purposes which are intended to approximate average
experience.
Based on information from industry and condensed IRS
guidelines, the following useful service life values have
been used:
(1) General process equipment 10 years
(2) Ponds, lined and unlined 20 years
(3) Trucks, bulldozers, loaders
and other such material
handling and transporting
equipment 5 years
(3) Capital Costs
Capital costs are defined as all front-end out-of-pocket
expenditures for providing treatment and disposal
facilities. These costs include costs for research and
development necessary to establish the process, land costs
when applicable, equipment, construction and installation,
buildings, services, engineering, special start-up costs,
contractor profits and contingencies.
(4) Annual Capital Costs
Most if not all of the capital costs are accrued during the
year or two prior to actual use of the facility. This
present worth sum can be converted to equivalent uniform
annual disbursements by utilizing the Capital Recovery
Factor Method:
. f, •,
Uniform Annual Disbursement = P i (1+i) nth power
(1 + i) nth power - 1
Where P = present value (Capital expenditure)
i = interest rate, in percent
n = useful life in years
The capital recovery factor equation above may be rewritten
as:
Uniform Annual Disbursement = P(CR-i-n)
Where (CR-i-n) is the Capital Recovery Factor for ±%
interest taken over "n" years of useful life.
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Annual Capital Costs include costs for straight line
depreciation over the n years of useful life as well as the
average annual cost for -interest in 'invested capital. An
interest rate of 10 percent has been used for all cost
calculations.
(5) Land Costs , •
Waste water treatment facilities require removal of land
from other economic use. The amount of land so tied up will
depend on the treatment and disposal method employed and the
amount of wastes involved.. For the concrete products
industry, it is assumed , that, waste , water treatment
facilities and storage or disposal of wastes do not affect
the ultimate market value of the land. Cost estimates
include only interest on land value.
(6) Operating Costs
Annual costs of operating the treatment and disposal
facilities include labor, supervision, materials,
maintenance, taxes, insurance and power and energy. A
factor of 3 per cent of invested capital was taken to cover
interest on working capital, taxes and insurance.
(7) Rationale for Cost Developments
All plant costs are estimated for model plants rather than
for actual plants. ,For the ready-mixed concrete
subcategory, where various treatment technologies are used,
costs are developed for two different size plants for each
technology. For other less complex subcategories, costs are
developed for only one plant size. Cost variances due to
individual circumstances are discussed for the individual
cases.
The effects of treatment technologyff plant location, and
plant size on costs for .treatment and control have been
considered and are detailed in subsequent sections for, each
specific subcategory. For ready-mixed concrete plants,
costs have also been determined for aggregate recovery and
the sensitivity of the treatment and disposal method to
operating labor costs,
C8) Cost Estimating Design Assumptions
(a) All non-contact cooling water is exempted from treatment
(and treatment costs) since no pollutants are
introduced.
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(b) Water treatment, cooling tower and boiler blowdown
discharges are not treated since these are non-process
waters which are not the subject of this document.
(c) All solid waste disposal costs are included as part of
the cost development.
COST ESTIMATES FOR MODEL PLANTS
HIGH-PRESSURE AUTOCLAVE PLANTS
Waste water generated at three plants for which economic
data are available ranges from 18,000 liters/day (5,000 gpd)
to 57,000 liters/day (15,000 gpd). Since suspended solids
are low in the steam condensate, which constitutes most of
the waste water, the only major treatment required is pH
adjustment. Table 12 gives treatment costs. An average
sized plant, 170,000 kkg/year, was selected (plant sizes
range from 63,500 to 250,000 kkg per year).
Cost Variances
Size: Annual production of plants in this subcategory ranges
from 63,500 to 250,000 kkg. Over this range, the total
annual costs are assumed to be proportional to plant waste
water discharge hydraulic load within the level of
uncertainty that exists for the costs. Discharge hydraulic
loads range from 50 to 220 liters per kkg of production.
The typical plant annual costs for Level B are 2£ per kkg.
However, plant-supplied annual costs ranged from 10 to 90
per kkg.
Age: There is no evidence of plant age being
cost variance factor,
Location: Location in geographical areas
evaporation/percolation ponds could be utilized
conserve both capital expenditure and energy.
Cost Basis for Table
Operating year: 250 days
Waste water treated: 38,000 liters/day
a significant
where
would
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TABLE 12
COST ANALYSIS FOR REPRESENTATIVE PLANT
(ALL COSTS ARE CUMULATIVE)
SUBCATEGORY Concrete Brick and Block (High-Pressure Autoclave Curing)
PLANT SIZE 170,000 METRIC. TONS PER YEAR OF Products
' . - .
INVESTED CAPITAL COSTS!
TOTAL
•ANNUAL CAPITAL RECOVERY
OPERATING AND MAINTENANCE
COSTS:
ANNUAL 0 a M (EXCLUDING
.POWER AND ENERGY)
ANNUAL ENERGY AND POWER
TOTAL ANNUAL COSTS
COST/METRIC TON of products '
-WASTJM-OAD PARAMETERS
[kg /metric ton of products )
Suspended Solids
pH
RAW
WASTE
LOAD
<0.035
<12.5
LEVEL
A
(MIN)
0
0
0
0
o
0
<0.035
10-12
B
3,000
350
2,000
0
2,350
0.02
0.007
10--12
C
6,000
700
5,500,
100
6,300
0.04
0.002-
0.005
6-9
D
9,000
1,000
7,000
200
8,200
0.05
0
-_
E
.200,000
32,500
34,000
21 t 000
87,500
0.51
0
__
.
LEVEL DESCRIPTION^
A — No treatment
B — Pond settling of suspended solids
C — B plus pH adjustment with sulfuric acid
D — C plus recycle to aggregate piles and/or convection autoclaves, or total containments
E T- Mechanical evaporation of wastewater
115
_
-------
Capital
Settling pond: $3,000
pH adjustment: $3,000
Pipes & pumps for
recycle: $3,000
Mechanical evaporation system:
$200,000
Operational Costs
Operator Costs
Acid Costs:
Maintenance (Level B,C,D)
Maintenance (Level E)
Taxes & Insurance
Electrical Power
Steam Cost
LOW-PRESSURE STEAM CURING PLANTS
$16,000/yr
$0.055/kg of sulfuric acid
2% of capital investment
10% of capital investment
3% of capital investment
$125/kw-yr
$1/250,000 Kcal
Low-pressure steam plants have at least an order of
magnitude less waste water than that of high-pressure
autoclave plants. Nine reported values range from 0 to
1,900 liters/day (0 to 500 gpd). Estimated treatment costs
are given in Table 13 for a plant producing 60,000 kkg/year.
Cost Variances
Plant size, location and age are not judged to be
significant factors in cost variance. Treatment costs
should be proportional to waste water discharge hydraulic
load, which was found to vary from 9 to 140 liters ..per kkg
of production. . -T
Basis for Costs in Table 13
Operating year: 250 days
Waste water treated: 1,900 liters/day
Capital
Pond Cost: $1,000
pH adjustment: $5,000
Mechanical Evaporation equipment: $50,000
Pumps and pipe for
recycle: $2,500
116
-------
TABLE 13
COST ANALYSIS FOR REPRESENTATIVE PLANT
(ALL COSTS ARE CUMULATIVE)
SUBCATEGORY Concrete Brick and Block (LoW-Pressure Steam Curing)
PLANT SIZE 60,000 METRIC TONS PER YEAR OF Products
INVESTED CAPITAL COSTS!
TOTAL
ANNUAL CAPITAL RECOVERY
OPERATING AND MAINTENANCE
COSTS:
ANNUAL 0 & M (EXCLUDING
POWER 'AND ENERGY)
ANNUAL ENERGY AND POWER
TOTAL ANNUAL COSTS
COST/ METRIC TON products
WASTE LOAD PARAMETERS
(kg /metric ton of oroducts )
Suspended solids
PH
RAW
WASTE
LOAD-
<0.1
<12
LEVEL
A
(MIN)
0
0
0
0
0
0
<0.1
10-12
B
1,000
100
1,000
0
1,200
0.02
0.0002-
0.0005
10-12
c
6,000
700
2,000
100
2,800
0.05
0,0002-
0.0005
6-9
D
2,500
300
3,000
200
3,500
0.06
0
-
E
50,000
8,200
4,000
1,000
13,200
0.22
0
-
LEVEL DESCRIPTION:
A — No treatment
B — Settling ponds for reduction of suspended solids
C — B plus pH adjustment with acid
D — B plus recycle to aggregate pile, or total containment
E — Mechanical evaporation of wastewater
117
-------
Operating Costs
Operating Cost:
Acid Costs:
Maintenance (Level B):
Maintenance (Level C):
Taxes and Insurance:
Electric power:
Steam Cost:
CONCRETE PIPE
$1,000 ,
$0.055/kg of sulfuric
2% of capital investment
10% of capital investment
3% of capital investment
$125/kw-yr
$1/250,000 Kcal
Cost information was available from 15 plants. Five plants
have under 4,000 liters/day (900 gpd) waste water, while 7
others range between 60,000 liters/day (16,000 gpd) and
300,000 liters/day (80,000 gpd). Waste water volumes are
not available for the other three plants. The amounts of
waste water depend on:
- Water use practices in the plant. This includes
amount of water used for floor washdown, central mixer
washout, transport bucket cleaning and various
miscellaneous uses such as hydrostatic testing and form
washoffs.
- The amount of waste water recycled.
Costs have been developed for two cases:
(1) Plants with small volumes of waste water (hydraulic load
about 5 liters per kkg of production).
(2) Plants with relatively large volumes of waste water
(hydraulic load tabout 1,100 liters per kkg of
production) . ,
Since plants with small waste water volumes rarely treat
their effluents, cost estimates for treatment are based on
model facilities. For the plants with relatively large
volumes of waste water, costs are based on supplied data.
The waste water hydraulic loads generated by these plants
ranged from 0.2 to 9,000 liters per kkg of production, with
an average of 174 liters per kkg. The costs were developed
for two representative plants, one below this average, and
the other above this average. The principal treatment cost
scaling factor is the waste water volume. Hence, to apply
the costs contained herein to the entire industry
subcategory, reference must be made to the nonconsumptive
water use distribution shown in Figure 5 in Section V.
118
-------
Plants With Small Waste Water Volumes
The cost estimates of'a modelled treatment facility for a
waste water volume of 4,000 liters/ day are given in Table
"
Cost Variance Factors
Treatment costs ' for waste water from concrete pipe plants
depend heavily on the waste water volume. There appears to
be no correlation with plant location or age.
Cost Basis for Table 14
Operating year: 250 days
Waste water treated: 4,000 liters/day
Capital
3 - concrete settling basins (4 sq m each): $3,000^
1 - oil skimmer: , '. 1,000
--- miscellaneous ditches and piping: 1,000
Operating Costs
Pond cleaning $200
Acid 150
Labor 2,000
Power costs 50
Taxes and insurance 1 50 .
Plants With Larger Waste water Volumes
One concrete pipe plant is able to discharge into a sewer
system without treatment. Six others with relatively large
waste water volumes are currently treating their waste water
prior to discharge. Cost estimates are given in Table '15.
Cost Variance Factors
Cost is principally related to waste water volume, see dis-
tribution data of Section V, Figure 5. '
Cost Basis For Table 15 , :
Level B - Both capital and operating costs are based on
values supplied by plants.
119
-------
TABLE 14
COST ANALYSIS FOR REPRESENTATIVE PLANT
(ALL COSTS ARE CUMULATIVE)
SUBCATEGORY Concrete Pipe i'Q )__
PLANT SIZE 45,000
METRIC TONS PER YEAR OF Products
PLANTS HAVING SMALL WASTEWATER VOLUMES
INVESTED CAPITAL COSTS:
TOTAL
•ANNUAL CAPITAL RECOVERY
OPERATING AND MAINTENANCE
' COSTS:
ANNUAL 0 a M (EXCLUDING
POWER AND ENERGY)
, ANNUAL ENERGY AND POWER
TOTAL ANNUAL COSTS
COST/METRIC TON of Pipe
WASTE LOAD PARAMETERS
(ka/metric Ion of products )
Suspended solids
Oil and grease
PH
RAW
Y/ASTE
LOAD
°-u37o
< 0.001
<12.0
LEVEL .
A
(WIN)
0
0
0
0
0
0
0.01-3.0
<0.001
10-12
B
5,000
600
2/500
50
3,150
0.07
0.0003
0.0001
6-9
c
50,000
8,150
4,000
1,000
13,150
0.29
0
0
-
D
:J.
E
LEVEL DESCRIPTION:'
A — No treatment
U _ Settlingpitsto remove suspended solids, oil and 'grease pit and skimmer, and manual
pH adjustment with acid
C •— Mechanical evaporation of wastewater
120
-------
TABLE '15
COST ANALYSIS FOR REPRESENTATIVE PLANT
(ALL C6STS ARE CUMULATIVE)
SUBCATEGORY Concrete Pipe (2)
PLANT SIZE 90,000
METRIC TONS PER YEAR OF Products
PLANTS HAVING LARGE WASTEWATER VOLUMES
INVESTED CAPITAL COSTS:
TOTAL
• ANNUAL CAPITAL. RECOVERY
OPERATING AND .MAINTENANCE
'COSTS:
ANNUAL 0 a M (EXCLUDING
POWER AND ENERGY)
ANNUAL ENERGY AND POWER
TOTAL ANNUAL COSTS
COST/METRIC TON of pipe
WASTE .LOAD PARAMETERS
kg/metric ton of p|pft )
Suspended solids
Oil and grease
pH
RAW
WASTE
LOAD
0.02-
0.06
0.07
<12.2
LEVEL
A
(WIN)
0
0
0
0
0
0
0-02b-.06
0.07
10-12
B
100,000
13,000
'9,500
500
23,000
0.26
0.013
0.004
6-9
C
125,000
16,250
12,000
6,250
34,500
0.;38
0.007
0.002
6-9
D
500,000
81,400
,50,000
100,000
231 ,400
2. '57'
0
0
0
E
A «— No treatment '
B - Settling ponds to reduce suspended solids, oil and grease pit and skimmer, instrumented
pH control, and water quality monitoring
C — Level B plus partial recycle of wastewafer . '
D ~ Mechanical evaporation of wastewater
12]
-------
Level C - Capital costs are the same as Level B plus
piping and pumps. Annual O & M is the same as Level B
plus $8,250 additional costs for labor and energy.
Level D - Based on estimated costs for mechanical
evaporation of 400,000 liters/day of waste water.
PRECAST AND PRESTRESSED PRODUCTS
The plants making precast and prestressed concrete products
have a wide variation in waste water hydraulic load, 9 to
370 liters per kkg of product. Plant size varies from 1,800
to 227,000 kkgs of annual production. Table 16 summarizes
the cost estimates for a 23,000 kkg/year plant with a . waste
water volume of 19,000 liters per day.
Cost Variances
Treatment costs are principally related to volume of waste
water treated. Generally, the Level B values of Table 16
are conservative. Plants significantly larger than
23,000 kkg/year production will have somewhat lower costs
per kkg than the value shown. Twenty-seven cents per ton is
a valid cost for plants of 23,000 kkg per year and smaller.
Plant age is not a significant factor for cost variance.
Plant location becomes important for onsite disposal of
wastewater through percolation or evaporation.
Cost Basis for Table 16
Production year: 250 days
Waste water treated: nominally 19,000 liters/day
Level B - Values were taken from cost information
supplied by plants.
Level C - Costs for Level C include mechanical clarifi-
cation equipment plus additional settling and pH
adjustment. These costs were supplied by several plants
using this treatment system and have been scaled to this
plant size.
122
-------
TABLE 16
COST ANALYSIS FOR REPRESENTATIVE PLANT
; (ALL COSTS-ARE CUMULATIVE) ; ,
SUBCATEGORY Precast- and Prestressed Products
PLANT SIZE 23,000 METRIC TONS PER YEAR OF Products
...... 1
INVESTED CAPITAL' COSTS:
TOTAL
• ANNUAL CAPITAL RECOVERY-
OPERATING AND MAINTENANCE
'COSTS:
ANNUAL 0 S M (EXCLUDING
POWER AND ENERGY )
. ANNUAL- ENERGY AND POWER
TOTAL ANNUAL COSTS
COST/METRIC TON products
WASTE LOAD PARAMETERS
•7-\3-- . , ,:
(kg/metric ton of products }
Suspended solids
Oil and qrease
PH
RAW
WASTE
LOAD
' 12
<0.1
10-12
LEVEL '•-."' . ,
A:
(MIN)
0
0
b
0
0
0
12
<0.1
10-12
B
11,000
1,300
4,900
50
6,200
0.27
0.013
0.0015
6-9
c
11,600
1,400
14,200
350
15,950
0.69
0.007
0.0015
6-9
D
100,000
16,300
20,000
10,000
46,300
2.01
0
|_^
-
''E. '
'
•<• ..'
LEVEL DESCRIPTION:
A — No treatment
B — Settling ponds for removal of suspended solids plus pH adjustment
C — Mechanical clarification systems plus additional settling tanks, plus pH adjustment
prior to discharge
D — Mechanical evaporation of wastewater
123
-------
PERMANENT READY-MIXED CONCRETE PLANTS
The manufacture of ready-mixed concrete generates both waste
water and solid waste. Since concrete will harden if left
in mixers, trucks, conveying buckets or other containers
even for a few hours, it is necessary to dispose of waste
concrete rapidly and to remove all residual material,
normally through washing. This washwater is then usually
treated to remove the suspended aggregate and cement.
Approximately 94 per cent of all surveyed ready-mixed
concrete plants currently have suspended solids treatment
facilities. These treatment facilities vary greatly as to
their size, complexity, efficiency, and costs. If properly
designed and sized, all of the employed treatment
technologies will reduce suspended solids levels to below
50 mg/liter. An estimated 1 to 2 per cent of the plants are
using acid to reduce pH to 6 to 9.
Types of Systems for Removal of Suspended solids
Although treatments used for suspended solids removal vary
in detail, most of them fall into one of the following:
(1) Earthen ponds - These may be natural low spots, pits,
abandoned quarries or ponds. They may be used
singularly or in series. They are more likely to be
used where land is plentiful.
(2) Concrete tanks or ponds - These systems are generally
used where land is more expensive and less available.
Settled solids can be easily removed from these systems
by crane or clamshell.
(3) Sloped slab system - The sloped slab system is "aw aggre-
gate separation system. The sloped bottom makes it
possible to remove settled solids with a front-end
loader or other equipment.
(1) Mechanical clarification systems - These systems
separate solids from waste water. There are a variety
of drag chain, screw, and screen treatment units in
service. According to industry sources, they represent
about 3 per cent of the treatment facilities used.
(5) Specialized mechanical clarification systems - Several
systems were found that currently recover all solid
wastes and have no discharge of waste water. They
represent less than 0.1 per cent of the total treatment
systems. These specialized systems differ from
-------
mechanical clarification systems primarily
handling and disposal of cement fines.
-"* V '&
Costs for Specific Treatment Systems
in their
A summary of costs for two plant sizes is given in Tables 17
and 18. Levels A through G represent treatment systems
currently used. Level H is the costs for mechanical
evaporation of excess waste water in some treatment systems.
Level I represents a total recycle system currently used by
one company. All waste solids and waste water are recycled
to produce new batches of concrete. This approach shows
promise for the future. There are several features that
restrict its current widespread use. These features include
high initial capital costs, labor costs, and energy costs,
extensive R&D and quality control expenditures, and
regulations on concrete preparation and composition
currently specified by American Society for Testing and
Materials (ASTM) , American Concrete Institute (ACI) , the
state highway departments, state building authorities and
federal agencies.
Treatment systems B, D and F can also achieve no discharge
of process waste water pollutants by various mechanisms.
These mechanisms include reuse of truck washout water,
evaporation/ percolation ponds, reuse of waste water as
concrete mix water, and use of excess waste water for
aggregate moisture control.
To determine costs from one size plant to another, the
following scale factors were used: 1.0 for settling ponds,
0.8 for sloped, slab basins, and 0.6 for evaporation,
mechanical clarification, total recycle and pH adjustment.
Cost Components and Variances ,
The costs may be broken down into contributions from
individual components such as land cost, pH adjustment
costs, solid waste disposal costs, labor costs, arid reuse or
resale values for recovered aggregate. The treatment costs
vary with truck utilization, value of land, solid waste
load, solid waste disposal method, amount of operating
labor, and recycle level for the waste water.
The relative costs of each treatment component and the
variance factors involved are discussed in the following
subsections.
125
-------
TABLE 1 7
COST ANALYSIS FOR REPRESENTATIVE PLANT
(ALL COSTS ARE CUMULATIVE)
SUBCATEGOR Y Permanent Ready-Mixed Concrete Qj
PLANT SIZE 39,300 cubic meters
PER YEAR OF Concrete
INVESTED CAPITAL COSTS'.
TOTAL
•ANNUAL CAPITAL RECOVERY
OPERATING AND MAINTENANCE
COSTS:
ANNUAL 0 a M (EXCLUDING
POWER AND ENERGY)
ANNUAL ENERGY AND POWER
TOTAL ANNUAL COSTS
COST/CUBIC METERS of Concrete
WASTE LOAD PARAMETERS
(kg/cubic meter of concrete)
Suspended solids
pH
RAW
WASTE
LOAD
35
10-12
A
(MINI)
0
0
0 .
0
0
0
<35
10-12
.B
4,200
500
3,400
100
4,000
0.10
0.001
10-12
c
7,600
900
4,100
100
5,100
0.13
0.001
6-9
D
14,300
1,720
3,720
260
5,700
0.145
0.001
10-12
E
17,700
2,100
3,820
360
6,280
0.16
0.001
6-9
F
34,000
5,530
3,350
160
9,140
0.23
0.001
10-12
G
37,400 '
6,080
3,520
360
9,960
0.25
0.001
6-9
-
H
68,000
11,000
10,160
7,280
28,440
0.72
0
N.A.
|.
. 47,500
. 9,420
23,290
6,780
39,490
1.00
0
N.A.
LEVEL DESCRIPTION:
A — No treotment
B — Pond settling of suspended solids, no aggregate recovery - no pH adjustment
C — Same as Level B plus pH adjustment
D — Sloped slab system - recovery of aggregate, partial recycle of wastewater, no
recovery of cement fines and no pH adjustment
E ~ Same as Level D plus pH adjustment
F •— Mechanical clarification system, recovery of aggregate - partial recycle of wastewafer,
no recovery of cement fines, no pH adjustment
G — Same as Level F plus pH adjustment
H — Same as Level F plus mechanical evaporation of excess wastewufer
I — Total recycle of wastewater with recovery and reuse of aggregates and cement
126
-------
.TABLE 18
COST ANALYSIS FOR REPRESENTATIVE PLANT
(ALL COSTS ARE CUMULATIVE)
SUBCATEGORY Permanent Ready-Mixed Concrete (9)
PLANT SIZE 75,000 cubic meters
YEAR OF Concrete
INVESTED CAPITAL COSTS:
TOTAL (1972 Prices)
-ANNUAL CAPITAL RECOVERY
OPERATING AND MAINTENANCE
'COSTS:
ANNUAL 0 G M (EXCLUDING
POWER AND ENERGY)
ANNUAL ENERGY AND POWER
TOTAL ANNUAL COSTS
COST/CUBIC METER of Concrete
WASTE LOAD PARAMETERS
(kg/cubic meter of concrete)
Suspended solids
PH Y"
I-
-
RAW
WASTE
LOAD
35
10-12
A
(WIN)
0
0
0
0
0
0
<35
10-12
B
8,000
950
6,500
Neg.
7,450
0.10
0.001
10-12
C
13,000
1,530
7,500
Neg. .
9,030
0.12
0.001
6-9
D
25,000
2,950
7,050
500
10,500
0.14
0.001
10-12
E
30,000
3,500
. 7,200
700
11, 400
0.15
' 0.001
6-9
F
50,000
8,150
4,950
500
13,600
0.18
0.001
10-12
G
55,000
8,950
5,200
700
14,850
0.20
O'.OOl
6-9
•
H
100,000
16,300
15,000
10,500
41 ,800
0.56
0
N.A.
1
70,000
• 13,900
34,350
10,000
58,250
0.78
b.
N.A.
LEVEL DESCRIPTION: -.>...-
A — No treatment
B '— Pond settling of Suspended Solids, no aggregate recovery
C — Same os Level B plus adjustment of pH
D — Sloped slob system - recovery of aggreage - partial recycle of wostewater - no
recovery of cement fines - no pH adjustment
E — Some as Level D plus pH adjustment
F - Mechanical clarification system - recovery of aggregate fines - no pH adjustment
G— Same as Level F plus pH adjustment
H — Same as Level F plus mechanical evaporation of excess wastewater
I — Total recycle of wasfcwatcr with recovery and reuse of aggregates and cement
127
_
-------
Correlation of Plant Size With Number of Trucks
The cost estimates of waste treatment facilities are based
on a waste quantity per truck basis. Washwater and solid
wastes volumes were found to be more easily and accurately
estimated from the number of operating trucks than from the
production figures. To establish a conversion to production
a correlation was necessary for the average amount of
concrete hauled per day per truck. This is primarily a
function of the average number of trips per day taken by
each truck. Figure 25 gives the distribution, of the trips
per day taken by trucks from 376 permanent ready-mixed
plants for which data are available. Based on this
information, the average number of trips per day per truck
is approximately 2.5. Assuming a 6 cubic meter average
capacity, this is 15 cu m of concrete hauled per day per
truck. On this basis, a 5-truck plant would have an
estimated production of 75 cu m/day. Similarly, a 20-truck
plant would have 300 cu m/day production and a 40-truck
plant, an estimated 600 cu m/day production.
Figure 25 shows the fifty per cent point to be about 2.5
trips per day per truck. Approximately 5 per cent of the
plants on either end of this curve would be expected to vary
from this relationship by over a factor of 2.' The other
ninety per cent of the plants would have variations below
this level with the central 50 per cent of plants varying by
a factor of approximately 1. *J.
Plant Size
Figure 26 summarizes overall waste water treatment annual
operating costs as a function of plant size and treatment
technology employed. The values shown include all pertinent
costs except off-site disposal of solid wastes.
Costs for earthen and concrete pond treatment systems are
represented by a single curve which fits both systems. The
increase in costs for the smaller plants is due to labor
needed for manual acid addition and pH monitoring. The cost
of ponds for settling of suspended solids is not sensitive
to plant size 75 cu m/day plants have almost the same
cost per production unit as 600 cu m/day plants.
Disposal of solids by ponding creates solid waste handling
problems, when the pond has to be dredged. Ponds do not
require large amounts of labor. Small sloped slab systems
require more labor than ponds and therefore have higher
operating costs. However, above a certain size, the sloped
slab systems have lower operating costs than ponds.
128
-------
o
1
09
TRiPS / DAY / TRUCK
2
no
a
3
:o
1
129
-------
UJ
0.55
0.50
0.45
0.40
0.35
0.30
o
CO
g 0.25
•v,
CO
IT .
-J 0.20
O
o
0.15
0.10
0.05
PONDS (EARTHEN OR CONCRETE)
00 7
100 200 300 4OO 500 600
PRODUCTION (CUBIC METERS/DAY)
700
FIGURE 26
ANNUAL OPERATING COSTS FOR WASTEWATER TREATMENT
AT READY-MIXED CONCRETE PLANTS
130
-------
Mechanical clarification systems are more sensitive to plant
size than either ponds or sloped slab systems. This
sensitivity is caused by two basic factors:
(1) Costs for mechanical clarifiers are . directly
proportional to the 0.6 power of plant size. Ponds are
almost directly proportional in cost to plant size.
Sloped slab systems are scaled to the 0.8 power of plant
size.
(2) Labor costs do not vary with size of
clarifier units.
mechanical
Costs in Figure 26 include the following components:
(1) Annualized capital recovery (depreciation plus interest)
plus annual operating expenses,
(2) Interest on land utilized for treatment,
(3) pH control of effluent, ,
(4) Returned concrete is 3% of average annual, production,
and ,
(5) On-site disposal of all solid materials
sold.
Land Costs
not reused or
Land costs used include only interest costs on the land.
Capital cpsts for land for a concrete plant may vary from
$2500/hectare ($1000/acre) to more than $3,700,000/hectare
($1,500,000/acre), one value of $3,460/000/hectare
($1,400,000/acre) for a choice urban location was reported.
Since land is rarely considered depreciable property and the
area occupied by the treatment facilities may be converted
to other use at a later date, only interest costs are
included. in general, interest costs for land are of the
order of $0.02/cubic meter, as shown below.
131
-------
Interest Costs for Land for Treatment Facilities
(based on a 300 cubic meter/day production plant)
Treatmen't
Used
Pond
Concrete
ponds
Sloped slab
system
Treatment Cost At
Area, $250,0007
Hectares Hectare
0.060
0.036
0.070
Mechanical 0.050
clarification unit
15,000
9,000
17,000
12,500
Interest (10%)
Cost $/YR
1,500
900
1,750
1,250
Interest Cost
$/cubic meter
0.02
0.01
0.02
0.02
Off-Site Sludge Disposal Costs
Waste concrete sent to settling ponds poses a sludge
handling and disposal problem of the entire wasteload of
aggregate and cement when the ponds are dredged. Sloped
slab systems and mechanical clarifiers handle smaller
amounts of these solids on a routine basis.
The dredged waste from ponds may be stored on-site if land
is available. However, off-site disposal for these large
amounts of sludge is generally used.
Using an estimate of $2.00/cubic meter for on-site disposal
and SS.OO/cubic meter for off-site disposal, the increased
costs for off-site sludge disposal are shown ~i*h the
following table. er ^
132
-------
Plant
Size
(cu m/day)
75
300
600
75
300
600
#wet basis
Total Waste
Load
(cu m/yr) *
Additional
Off-Site
Disposal Costs
(dollars/yr)
Additional
Off-Site
Disposal Costs
(dollars/cu m)
1 per cent waste concrete returned to ponds
575
2,264
4,528
1,011
4,008
8,016
1,725
6,792
13,504 -
0.092
0.090
0.090
3 per cent waste concrete returned to ponds
3,073
12,024
24,048
0.162
0.160
0. 160
Large quantities of returned concrete may be disposed of in
a more cost effective manner by using aggregate recovery
systems instead of ponds. The costs given above for
disposing of returned concrete at the rate of 3 per cent of
production gives an off-site solid waste disposal cost of
$0.16/cubic meter greater than for on-site disposal.
Effect of Aggregate Recovery on Operating Costs ,
Some sloped slab and most mechanical clarification systems
separate the aggregate from the cement sludge. This
segregation is usually not good enough for complete reuse of
the aggregate in new concrete. The coarse aggregate may, be
reusable /when the coarse and fine aggregate are separated.
Where the coarse and fine aggregate are not separated, as in
all slab systems and many mechanical clarification systems,
the mixture may be sold as fill material.
Table 19 gives the value of recovered aggregate from
mechanical clarification system, assuming $2.OO/cubic meter.
The sludge disposal costs are less than for pond systems. A
comparison (based on a 300 cubic meter/day plant) of the
costs differentials between mechanical clarification systems
and ponds is shown below:
133
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Table 19 Value of Recovered Aggregate and Disposal Cost of
Cement Sludge - Based on a 300 cu m day plant
Type
of
Solid
Waste
Coarse
Amount
Recovered
cu m/yr
1,386
Aggregate
(dry basis)
Fine
992
Aggregate
(dry basis)
Cement
Sludge
Coarse
865
2,455
Aggregate
(dry basis)
Fine
1,757
Aggregate
(dry basis)
Cement
Sludge
1,532
Sale(*)
Value
$/yr.
2,772
1,984
-
„
4,910
3,514
-
Sale(*)
Value
$/cu m
1 percer
0.037
0.026
-
Disposal
Cost
On-Site**
$/yr.
it returned co
-
—
1,730
3 percent returned cc
0.065
0.047
-
-
-
3,064
Disposal
Cost
Off-Site**
$/yr.
ncrete
-
—
4,325
mcrete
-
-
7,660
Disposal
Cost
. On-Site**
$/cu m
-
—
0.023
-
-
:": •_'!
0.041
Disposal
Cost
Off-Site**
$/cu m
-
—
0.058
-
-
0.102
*Value of coarse aggregate, $2.00/cu m; Value of fine aggregate, $2.00/cu m
**$2/cu m for on-site disposal; $3/cu m additional cost for off-site disposal.
134
-------
System
Pond
Sludge
Disposal
Cos,t, $/yr
Off-site
11,342
Reclaimed
Aggregate
Value
$/yr
Cost
Differential
$/yr ($/cu m)
Recover. 4,325
Aggreg.
Pond
20,080
Recover. 7,660
Aggreg.
1 per cent returned waste Concrete
0 -11,342
' • • . i • •
11,773 (0.157)
4,756 +431
3 per cent returned waste concrete
0 -20,080
20,844 (0.278)
8,424 +764
The cost differential for 1 per cent returned concrete
between pond treatment with off-site sludge disposal and the
recovered aggregate systems with off-site cement sludge
disposal for a 300 cu m/day plant is $11,773/yr. For 3 per
cent returned concrete, the cost differential is $20,844/yr.
Specialized mechanical treatment systems also recover cement
fines as well as aggregate. Two such systems are now being
used:
(1) The cement fines are maintained in suspension and
returned to the system. Plants 7729 and 7732 are now
using this technology. ;
(2) The dewatered aggregate containing cement fines is sold
as a road base. Plants 7525, 7526, 7527, 7528, 7529,
7530, and 7531 now use this system.
Labor Costs
Generally most treatment systems do not require a full time
operator or supervisor. Earthen ponds require almost no
attention except when accumulated solids are removed
periodically. Concrete pond and sloped slab systems also
involve low labor costs except for cleaning purposes.
Mechanical clarification units require somewhat more
maintenance and servicing than the other treatment systems
135
-------
but usually need no full time operator. Manual pH
adjustment will increase labor costs, particularly for the
smaller plants. Large plants will most likely install
automated systems and eliminate additional labor. The
effect of labor on the treatment operatihg costs is shown by
the following:
Plant Size
(cu m/day)
75
75
75
300
300
300
600
600
600
% of Man
Assigned
25
50
100
25
50
100
25
50
100
Cost
($/vr)
4,000
8,000
16,000
4,000
8,000
16,000
4,000
8,000
16,000
Cost
($/cu m>
.21
.43
.85
0.05
0.11
0,21
0.03
0.05
0.11
pH Adjustment Costs
Ready-mixed concrete waste water generally has a pH of 10 to
12. This can be reduced to the range of 6 to 9 prior to
discharge through addition of a mineral acid.
Figure 27 shows that approximately 30 liters of acid are
needed to make this reduction in the 37,850 liters
(10,000 gallons) of waste water from a 75 cu m/day plant.
The waste water volume at 50 percentile level is
6,440 liters per day. The cost to treat this amount of
waste water is 10 per cubic meter of concrete produced,
assuming the 1972 price of 5.50/kg for sulfuric acid. T< Small
plants could add acid and check pH manually so that capital
costs would be negligible. Labor costs will increase
rapidly and will have to be balanced against capital
expenditures. Larger plants would install automatic pH
adjustment equipment. Costs would be of the order of
$5,000. For large plants, total acid treatment costs should
be a maximum of $0.02/cu m if no recycle of waste water is
practiced. If part of the waste water is recycled, then pH
control costs should drop to approximately $0.01/cu m of
concrete produced. A $0.10/cu m operating cost for acid
treatment was assumed for plants of 75 cu m/day or less
production.
136
-------
o
to
10.8
FIGURE 27
AMOUNT OF ACID REQUIRED FOR
NEUTRALIZATION TO pH 7 OF CONCRETE WASTWTER
(DEVELOPED FROM FIELD AND LAB TESTS)
12.0
137
-------
Assumptions Used in Calculating Costs for Permanent Ready-
Mixed Concrete Waste water Treatment
The following pages give the basis for cost calculations for
four treatment systems: earthen ponds, concrete ponds,
sloped slab systems and mechanical clarification systems.
Waste water volumes are calculated from cumulative
percentile curves given in Section VII using the 50th
percentile values. Data from over 400 plants, were used in
plotting these curves.
Solid wastes were estimated as follows:
(1) Waste concrete returned from trucks to the treatment
system is assumed to be 1 per cent of annual production.
(2) Solids from truck washout are estimated to be 59.4 kg
per cubic meter of truck volume per washing. Truck
washing averages 1.5 times per day. Average truck size
was taken as 6.1 cubic meters.
(3) Solids from truck washoff are estimated to be 11.4 kg
per day.
(4) Solids from washing one 4 cubic meter central mixer were
estimated as 227 kg/day,
Since washwater volume and solid wastes were found to be
more a function of operating trucks than production
capacity, calculations are based on number of trucks. A
value of 15 cubic meters of concrete production per
operating truck per day has been used throughout these
calculations to estimate plant size.
Cost calculations for treatment options are based on:
(1) Treatment technology used - earthen pond, etc.
(2) 50th percentile water volume
(3) Three plant sizes, 5 trucks (75 cu m/day) , 20 trucks
(300 cu m/day) and 40 trucks (600 cu m/day)
(4) 24-hour settling time required.
(5) Acid requirements for pH adjustment are taken from
Figure 26.
(6) Densities and weights supplied by the NRMCA
below.
are shown
138
-------
Average Density Values
Cqncrete Composition (kgper cu m)
Water , ,
Cement
Sand
Coairse aggregate
Total density
Densities
Coarse aggregate (dry)
Sand (inundated) ,
Sand (6% moisture)
Combined sand and
, aggregate
Cement slurry (after
initial drying)
178
297
758
1,144
2,377
1,733 kg/cu m
1/604 kg/cu m
kg/cu m
2,406 kg/cu m
1,443 kg/cu m
Waste water Volumes - 50 Percentile Level
5 trucks
Truck washout - 5 trucks x 946 'liters/day
Truck washoff - 5 trucks x 246 liters/day
Central mixer washout - 1 x 475 liters/day
i ' - - - . '•
Total Daily Waste water , .
4,730 liters/day
1,230 liters/day
475 liters/day
6,435 liters/day
Similar values for 20 and 40 trucks are t
25,740 liters/day and 51,400 liters/day, respectively.
Solid Wastes . ,
Solid wastes are calculated for two situations:
(1) Total disposal of all solid wastes
(2) Recovery of all aggregate and disposal of cement fines
Solid Waste-Total Disposal
5 trucks (6. 1 cu m capacity)
Truck washout solids - ;
5 trucks x 59.4 kg/cu m/wash x 6.1 cu m/truck x 1.5 washes
per day = 2,725 kg •
139
-------
Truck washoff solids - •
5 x 11.4 = 57 kg
Central mixer washout solids -
3.8 cu m x 59.4 kg/cu m = 227 kkg
1% waste concrete -
2377 kg/m3 x 75m3 x 0.01 = 1781 kg
Total
4,790 kg
Similarly, total solid waste values for 20 and 40 trucks
are 18,478 kg and 36,956 kg.
Solid Wastes - Total Aggregate Recovery - Disposal
of Cement Fines
5 trucks (6.1 cubic meter capacity)
Total solids
Total aggregate recovered
Waste cement
4,790 kg/day (dry basis)
4,143 kg/day (dry basis)
647 kg/day (dry basis)
140
-------
Option A - Earthen Settling Ponds - Direct. Dumping
5 trucks
Basis: (1) Waste water volume
(2) Production rate
(3) Solid wastes
(4) Waste density
6,440 liters/day
75 cu in/day
4,7SO divided by
0.85 (85% solids)
5,635 kg/day
(wet basis)
2,400 kg/cu m
Capital Costs
Pond size:
Pond cost:
Operating Costs
0.03 ha
$190,000/ha
Pond cleaning costs - $1.50/cu m
Maintenance 3) 2% of capital
Taxes and insurance 3)3% of capital
Costs developed similarly for 20 and 40 truck systems.
Option B - Concrete Settling Pond System - Direct Dumping
5 trucks
Basis: same as Option A
Capital Costs
Pond size: 0.0006 ha
Concrete cost: $18/cu m
Operating Costs
Pond cleaning and on-site disposal of solids - $2.00/cu m
Maintenance a 2% of capital investment
Taxes and insurance d 3% of capital investment
Costs developed similarly for 20 and 40 truck systems.
141
_
-------
Option C - Sloped Slab Settling System - Recycle System -
Aggregate Sold at No Profit
5 trucks
Basis:
(1)
(2)
(3)
Waste water volume
Production rate
Solid wastes:
(a) aggregate
(b) waste cement
Aggregate sold as
landfill
(5) Waste density
6,440 liters/day
75 cu m/day
4,143 kg/day (dry basis)
1,294 kg/day
(wet sludge basis)
no profit
1,444 kg/cu m
Capital Costs
Concrete system cost:
Pumps and piping:
Operating Costs
$10,000
$3,000
$2.00/cu m
Pond cleaning and on-site cement disposal:
Labor: $4,000
Maintenance S 5% of capital investment
Taxes and insurance a 3% of capital investment
Power: $ 135/kilowatt - yr
20 trucks
Capital Costs
Concrete system cost: $20,000 i-:
Pumps and piping: 5,000
Operating Costs
Same basis as for 5 truck plant except labor costs taken
as $8,000/yr.
142
-------
40 trucks ,
Capital Costs
Concrete system costs:
Pumps plus piping:
Operating Costs
$30,000
7^500
Same basis as for 5 truck plant except labor costs taken
as $16,000/yr.
Option D - Mechanical Clarification Units - Recycle System
Aggregate sold at no profit.
5 trucks ;
Basis: (1) Waste water volume
(2) Production rate
(3) Solid wastes:
(a) aggregate
(b) waste cement
(c) waste density
Capital Costs
Installed mechanical unit cost:
Operating Costs
6,440 liters/day
75 cu m/day
4,143 kg/day (dry basis)
1,294 kg/day (wet basis)
1,444 kg/cu m
$25,000
Labor: $4,000
Maintenance 5) 5% of capital investment
Power: $135/kilowatt-yr
Cement waste disposal: $2,00/cu m
Taxes and insurance 2> 3% of capital investment
143
-------
20 trucks
Capital Costs
/•
Installed mechanical unit cost: $50,000
Operating Costs
Same basis as for 5 trucks
40 trucks
Capital Costs
Installed mechanical unit cost: $75,000
Operating Costs
Same basis as for 5 trucks.
Option E - Complete Recovery and Reuse of All Waste water
and Solid Wastes
This system is used by only one or two companies.
Costs supplied by one company show:
Capital Investment;
Operating Expenses:
$70,000
$45,700-$83,000
Capital and operating costs are reported to be relatively
independent of plant size; i.e., a 600 cu m/day plant
would have the same costs as a 300 cu m/day plant.
Portable Ready-Mixed Concrete Plants
Portable ready-mixed concrete plants are moved to the
desired location and set up. During their time of operation
at this site, the portable plant will have waste water
volumes similar to a permanent plant. There are several
differences from a permanent plant which are significant to
treatment cost:
(1) Only the simplest of treatment technology will usually
be employed. Earthen settling ponds will predominate.
Concrete settling basins, sloped slab recovery systems
and mechanical clarification units are rarely used.
144
-------
(2) The temporary ponds are smaller than those for permanent
facilities, since storage space for only several months
accumulation of solid wastes load-is required.
(3) Settling ponds are not usually dredged.
Estimated costs of waste water treatment facilities for
portable ready-mixed concrete plants are given in Table 20.
Cost Variance
All capital and operating costs are directly proportional to
plant size for Level B. For Levels C and D, the capital
costs should vary as the 0.6 exponent of plant size. Plant
age has no significance for a portable plant. Plant
location may be significant in that some climates and local
terrains make it possible to use evaporation/percolation
ponds and eliminate much if not all of the waste water
discharge. ,
Mobile Ready-Mixed Concrete Plants •
All of the mobile ready-mixed concrete plants contacted
discharge waste water to an evaporation/percolation area
Therefore, there are no additional treatment costs for this
subcategory.
145
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TABLE 20
COST ANALYSIS FUR REPRESENTATIVE PLANT
(ALL COSTS ARE CUMULATIVE)
SUBCATE60RY Reody-Mixed Concrete (Portable Plants)
PLANT SIZE 75,000,Cupic Meters
PER YEAR OF Concrete
INVESTED CAPITAL COSTS'.
TOTAL
V
ANNUAL CAPITAL RECOVERY
OPERATING AND MAINTENANCE'
COSTS:
ANNUAL 0 a M (EXCLUDING
POWER AND ENERGY)
ANNUAL ENERGY' AND POWER
TOTAL ANNUAL COSTS
COST/CUBIC METER of Concrete
WASTE LOAD PARAMETERS
(kg/cubic meter of concrete)
Suspended solids
pH
RAW
WASTE
LOAD
35
10-12
LEVEL
A
(MIN)
0
0
0
0
0
0
35
10-12
B
5,000
600
1,400
100
2,100
0.03
0.001
6-9
C
50,000
8,150
9,700
500
18,350
0.24
0.001
6-9
D
100,000
16,300
20,000
10,000
46, 300
0.62'
0
-
. E
LEVEL DESCRIPTION:
A— No treatment
B — Pond settling of suspended solids plus pH adjustment
C — Mechanical clarification unit plus pH adjustment
D — Mechanical evaporation of non-recycled wastewater (Level C plus evaporation)
146
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SECTION VIII
ACKNOWLEDGEMENTS
This report was prepared by the Environmental Protection
Agency on the basis of a comprehensive study of this
industry by Versar, Inc. Special thanks are due Mr. Richard
Kinch, Mr. James Berlow, Mr. Ralph Lorenzetti and Mr.
Michael Kosakowski of EPA for their supervision of this
project during the various stages of development. The
efforts of Dr. Robert G. Shaver, Mr. Michael W. Slimak and
Mr. Robert C. Smith of Versar, Inc. are appreciated.
Overall guidance and excellent assistance were provided by
the senior staff of the Effluent Guidelines Division,
particularly Mr. Robert B. Schaffer, Director and
Mr. Walter J. Hunt, Chief, Inorganic Chemicals and Service
Industries Branch.
Appreciation is also extended to the members of the Effluent
Guidelines Support Staff for their aid in assembling,
editing and reproduction of this report. Special
acknowledgement in this respect is given to Ms. Kaye Starr,
Ms. Nancy Zrub'ek, Ms. Carol Swann, Ms. Pearl Smith and
Mrs. Alice Thompson.
Appreciation is extended to the following industry
organizations and private companies for their assistance and
cooperation in the production of this document:
American Concrete Institute
American Concrete Paving Association
American Concrete Pipe Association
American Concrete Pressure Pipe Association
Cellular Concrete Association
Centre Concrete Company
Conrock Corporation
Crider & Shockey, Inc.
Dravo Corporation
Erie-Strayer, Inc.
Gifford-Hill Co., Inc.
H.T. Campbell & Sons Co.
Houston Shell & Concrete
Interpace Corporation
Jadair Corporation
Jetomatic Systems, inc.
Lone Star Industries, Inc.
Maloney Concrete
147
-------
Massey Concrete
Material Service Corporation
Mobile Premix Concrete
National Concrete Burial Vault Association
National Concrete Masonry Association
National Precast Concrete Association
National Ready-Mixed Concrete Association
Prestressed Concrete Institute
Portland Cement Association
Reinforce Concrete Research Council
Rex Nord Division of Rex Industries
Smith, Monroe & Gray Engineers
Super Concrete Corporation
Texas Aggregates & Concrete Association
The Vince Hagan Company
Twin City Concrete
Underwood Builders Supply Company
Virginia Concrete
Appreciation is also extended to the many other companies
who gave us invaluable assistance and cooperation in this
program.
148
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SECTION IX
REFERENCES
1. Akroyd, T.N.W., Concrete Properties £ Manu facture,
Pergamon Press, New York, 1962.
2. Blanks, R.F. , & Kennedy, H.L., "The Technology of Cement
and Concrete", Concrete Materials, Volume I, John Wiley
& Sons, New York, 1955.
3. "Census of Manufactures", 1972, Bureau of the Census,
U.S. Department of Commerce, U.S. Government Printing
Office, Washington, D.C. , MIC 72(p)-32B-2 through MIC
72(P)-32E-6.
4. Ferguson, P.M., Reinforced Concrete FundamentaIs, 2nd
ed. , John Wiley & Sons, New York, 1967.
5. Gaynor, R.D. , "Disposal of Wash Water and Returned
Concrete", NRMCA Publication, June 8, 1971.
6. "Design & Control of Concrete Mixtures", 11th ed.,
Portland Cement Association Bulletin, July, 1968.
7. Godfrey, Robert Sturgis, Editor in Chief, Building
Construction Cost Data 1975, 33rd annual ed. , Robert
Snow Means Company, Inc., Duxbury, Mass.
8. Harger, H.L., "A System for 100% Recycling of Returned
Concrete: Equipment, Procedures & Effects on Product
Quality", NRMCA Publication No. 150, March, 1975.
9. "Industrial Waste Study Report: Flat Glass, Cement,
Lime, Gypsum, & Asbestos Industries", Sverdrup & Parcel
& Associates, Inc., St. Louis, Missouri, July, 1971.
10. Kirk £ Othmer, Encyclopedia of Chemical Technology, 2nd
ed., Volume IV, John Wiley & Sons, New York, 1964.
11. Lauwereins, M.A. , "Water
Modern Concrete, May, 1971.
Pollution-Chicago Style",
12. Mather, B., "New Concern Over Alkali-Aggregate
Reaction", Presentation to the Joint NSGA-NRMCA
Engineering Session, New Orleans, La., 28 January 1975.
149
_
-------
13. Meininger, R.C. , "Disposal of Truck Mixer Wash Water &
Unused Concrete", NRMCA Publication No. 16, December,
1964.
14. Monroe, R.G., "Waste water Treatment Studies in
Aggregate & Concrete Production", EPA-R2-73-003,
February, 1973.
15. Murdock, L.J., and Blackledge, G.F., Concrete .Materials
&. Practice, 4th ed., Edward Arnold Publishers Ltd. ,
London, 1968.
16. Neville, A.M., Properties of Concrete, John Wiley &
Sons, New York, 1973.
17. Orchard, D.F., Concrete Technology, 3rd ed.. Volumes T
and II, John Wiley & Sons, New York, 1973.
18. Perry, R.H., Chilton, C.H., Kirkpatrick, S.D., Chemical
Engineering Handbook, 4th ed., McGraw-Hill, New, York,
1969.
19. Richardson, J.G., Precast Concrete Production, Cement
and Concrete Association, London, 1973.
20. Simons, E.N., Cement *> Concrete Engineering, Frederick
Muller, Ltd., London, 1964.
21. "Symposium Effect of Water Reducing Admixtures & Set
Retarding Admixtures on Properties of Concrete", ASTM
Special Technical Publication 226, 1959.
22. Taylor, W.H., Concrete Technology '& Practice, 3r"dh ed.,
Angus & Robertson Ltd., London, 1969.
23. Troxell, G. E., Davis, H. E. , Kelly, J,W. , Composition &.
Properties of Concrete, 2nd ed., McGraw-Hill, New York,
1968. ' :
24. U.S. Patent No. 3,885,985, "Additive for Improving
Hydraulic Cement Compositions".
25. Waddell, J.J., Practical Quality Control- for Concrete,
McGraw-Hill, New York, 1962.
26. Walker, S., "Ready-Mixed Concrete", NRMCA Publication
No. 120, April, 1966.
27. USGS, Department of the Interior, National Atlas, 1970,
p. 97.
150
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SECTION X
GLOSSARY
1.
2.
3.
4.
5.
7.
8.
9.
10.
•11.
Accelerating Agent: Material added to concrete to
accelerate its setting time and strength development.
Adsorption: The adhersion of a substance to the
surface of a solid or liquid. Adsorption is often used
to extract pollutants by causing them to be attached to
such adsorbents as activated carbon or silica gel.
Hydrophobic, of water- repulsing adsorbents, are used to
extract oil from waterways in oil spills.
Admixture; Material, other than aggregate, cement, or
water added in small quantities to concrete to produce
some desired change in properties.
i -" '•
Aggregate , Coarse; Crushed stone which is retained on a
Number 4 standard sieve.
Aggregate, Fine: sand with a particle size smaller than
a Number 4 standard sieve or approximately 0.6 cm
(1/4 inch) .
Aggregate, Lightweight: Aggregates such as expanded
shale, cinder, clay, slate, pumice, scoria, perlite,
vermiculite, and diatomite.
Aggregate, Heavy we ight : Aggregate such as iron or steel
particles, barite, limonite, magnetite and ilmenite.
Aggregate, Normalweight:
gravel, and crushed stone.
Aggregates such as sand,
Air-entraining Agent: Substance added to concrete
materials before or during mixing to entrain air in the
concrete to improve resistance to freezing and thawing
exposure.
Batching; The weighing and proportioning of twosor more
raw materials which go into the manufacture .of concrete
products.
Baghouse; Chamber in which exit gasses are filtered
through membranes (bags) which remove solids.
151
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12. Block Equivalent:; Standard unit of production of
concrete block and brick, 20 x 20 x 41 cm, (8 x 8 x
16 inches) .
13. Central Mixer: Rotary mixer used to mix concrete with
an average capacity of about 4 cubic meters.
14. Central Mixer Plant: Permanent or portable ready-mixed
concrete plant that prepares concrete in a central mixer
then transfers it to a truck mixer or agitator for
delivery.
15. Concrete, Heavyweight: Concrete made using aggregates
such as barite, limonite, magnetite, ilmenite, and iron
and steel particles. Produced primarily for nuclear
applications.
16. Concrete, Insulating Lightweight; Concrete made using
lightweight aggregates such as pumice, scoria, perlite,
vermiculite, and diatomite.
17. Concrete, Lightweight; Concrete made using lightweight
aggregates.
18. Curing, Atmospheric; Method of curing which uses
ambient heat and humidity,
19. Curing, High Pressure or Autoclave: Method of curing
block .and brick in which loaded curing cars are placed
into a large horizontal, cylindrically shaped autoclave,
where high pressure steam is injected or convected for
approximately 18 hours.
20. Curing, Hot
pressure
Oil Convection; Special type of high
steam curing of block and brick where water is
placed in a trough in an autoclave and hot oil heats the
water to produce steam.
21- Curing, Low Pressure; Method of curing block and brick
in which loaded curing cars are placed in a chamber or
kiln where low pressure steam (less than 9.7 atm) is
injected from perforated pipes for approximately
8-10 hours.
22. Curing, Spray: Method of curing in which
sprayed with a fine mist of water. ;
products are
23. Dry Batch Plant; Permanent or portable ready-mixed
concrete plant that transfers weighed amounts of dry
152
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aggregate and cement with a specific amount of water
into a mixer truck for subsequent mixing.
24. Dispersing Agent; Material added to concrete
separate the individual suspended particles.
to
25. Friable; Term used to describe concrete made with an
insufficient quantity of mix water that crumbles and
breaks apart easily.
26. Form Releasing Agent; oil sprayed onto forms prior to
pouring or casting of the concrete to facilitate the
separation of the concrete and form.
27. Grout; Mixture of cement and water or cement, sand, and
water. .
28• Hy drat ion; Incorporation of molecular water into a
complex molecule with the molecules of another sub-
stance, in this case cement.
29. Hydrostatic Testing; Testing of pipe or other vessel
for strength and leak resistance by pressurization with
a test liquid.
30. Mortar; Mixture of cement,
bonding bricks and masonry.
lime, and sand used for
31. Packerhead; A rapidly revolving and rising steel
element which packs the concrete radially outward
against a stationary form. The force with which the
concrete is packed against the outside form compacts the
concrete sufficiently so that the element can be raised
as more concrete is added.
32. Portland Cement; A hydraulic cement resembling portland
stone when hardened; made of pulverized calcined
argillaceous and calcareous material; proper name for
ordinary cement.
33. Precast Concrete Products: Describes the many types and
varieties of concrete units which are cast in molds
either in a factory or on the site, and are not built
into the structure until they have fully hardened. Most
of the larger precast units are made with steel
reinforcing rods.
34. Pressure Pipe* Reinforcedand prestressed concrete pipe
that uses a permanent steel cylinder, which remains with
the pipe, as a form.
153
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35. Prestressed: Process of casting concrete with tensioned
steel bars or cables embedded in the concrete.
36. Pretension: Prestressed concrete made by placing steel
cablesunder tension in the form before the concrete is
poured. Once the concrete has set, cured, and forms
have been removed, the external tension is released from
the steel cables. The cable retains internal stress due
to the compression of the concrete around it.
37. Prime:
The wetting of the mixing auger in a mobile
plant prior to a mix. This wetting prevents
clogging of the mixing auger by wet sand during the mix.
38. Post-tension: Prestressed concrete made by placing
cables in the form, casting the concrete, allowing it to
set and cure, then placing the cables under tension.
The cables must be protected with a steel qr plastic
tube or mastic coating to prevent bonding with the
concrete prior to tensioning. The cables may or may not
be grouted while under tension and are locked under
tension by appropriate end clamps.
39. Ready-mixed plant, Permanent: Plant with a fixed
location that uses mixer trucks to deliver the concrete.
The concrete may be mixed in central mixers and hauled
in agitator trucks or may be dry batched into mixer
trucks and mixed on the way to the job site.
40. Ready-mixed plant. Portable: Temporary or transient
type of plant used on large highway and airport jobs.
The concrete may be produced by either a central^ mixer
or a dry batch plant. ™~
41. Ready-mixed plant. Mobile: A ready-mixed truck capable
of transporting all raw materials (aggregate, cement,
and water etc.) separately on the truck and pro-
portioning and mixing tnem in the truck mounted mixer at
the job site. (Concrete-mobile)
structural steel
added
42. Reinforced concrete: concrete with
members added to increase strength.
43. Reinforced pipe; Concrete pipe with a steel cage
to provide increased tensile strength.
44. Retarding Agent: Material added to concrete for the
purpose of prolonging the setting time of the concrete.
154
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**5. Shrink-mixed; Concrete mixed partially in a stationary
central mixer and completely mixed in a truck mixer
either on the way or,at the joii. site.
46. Spin Cast Method For Concrete Pipe: A reinforcing cage
(steel cylinder in pressure pipe) is fabricated and
positioned in a form which is then placed horizontally
on a high speed, roller drive mechanism. The form is
rotated at a high rate,, while the concrete is added
evenly by a reciprocating nozzle on the inside of the
form. The spinning action densities the concrete on the
inside of the form and dewaters it. Water flows off the
inside' surface of .the pipe and the concrete surface is
finished by a mechanical roller.
47. Tendons:
Steel cables used E for reinforcement
prestressed concrete products. *
48. Transport Bucket: Bucket used to carry concrete from
the central mixer to the casting area in block, pipe,
precast, and prestressed plants.
49. Vertical Cast Method - Reinforced and Pressure Pipe
Production: Wet concrete mix is produced in a central
mixer and transported to a vertical steel form via
transport buckets. The concrete is poured into the form
containing a reinforcing , cage or cylinder, then
mechanically vibrated for compaction. concrete is
allowed to set and forms removed. This method can
produce any .size of reinforced pipe, but is generally
limited to diameters over 1.5 meters (5 ft).
50. Vertical Packerhead Method - Non-reinforced and
Reinforced Pipe Production; Moist concrete is compacted
and vibrated into a steel form by a packerhead.
Generally used to produce pipe up to 1.5 meters (5 ft)
in diameter.
51. Washoff; Waste water originating from washing off the
exterior of a ready-mixed concrete truck.
52. Washout: Waste water originating from the washing of
the interior of a ready-mixed concrete truck mixer or
central mixer..
53. Water Reducing Agent; Material added to concrete for
the purpose.^ of reducing the quantity of mixing water
required to produce a concrete of a given consistency.
155
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54. Wet-ting Agent; Substance that renders
repellent to liquids.
a surface non-
55. Yard Runoff: Waste water originating from aggregate
pile' runoff, dust control spraying, truck chute runoff
and spillage that follows the contour of the land and
runs off the plant's property or into the treatment
system.
156
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TECHNICAL REPORT DATA
(Please mad Instructions on the reverse before completing)
1. REPORT NO.
2.
"*- f^ Ey. L—/ '' / / / rj / I. S t -
4. TITLE AND SUBTITLE
Guidance Development Document for Effluent Limitations
Guidelines and New Source Performance Standards for the
Concrete Products Point Source Category
3. RECIPIENT'S ACCESSION-NO.
5. REPORT DATE
6. PERFORMING ORGANIZATION CODE
7. AUTHOR(S)
Richard J. Kinch
James R. Perlow
8. PERFORMING ORGANIZATION REPORT NO.
9. PERFORMING ORGANIZATION NAME AND ADDRESS
U. S. Environmental Protection Agency
Effluent Guidelines Division (WH-552)
401 M Street, S.W.
Washington. D. C. 20460
10. PROGRAM ELEMENT NO.
11. CONTRACT/GRANT NO.
12. SPONSORING AGENCY NAME AND ADDRESS
U. S. Environmental Protection Agency
401 M Street, S. W.
Washington, D. C. 20460
13. TYPE, OE REPORT AND PERIOD COVERED
Guidance
14. SPONSORING AGENCY CODE
15. SUPPLEMENTARY NOTES
16. ABSTRACT
This guidance document presents the findings of-a study on the wastewater
e£ the.Concrete ^ducts Industry. Included in the Concrete
1S *? man?acture o£ concrete block and brick; concrete
prestressed concrete; and ready-mixed concrete. Information
a?Pllca5le manufacture processes; the treatment systems in
i°? r?ductl°«/f ^ting from the use of control technologies;
costs is provided.
7.
KEY WORDS AND DOCUMENT ANALYSIS
DESCRIPTORS
Concrete
Wastewater
Pollution
b.lDENTIFIERS/OPEN ENDED TERMS C. COSATI Field/Group
8. DISTRIBUTION STATEMENT
1,000 copies
19. SECURITY CLASS (ThisReport)'
21. NO. OF PAGES
167
20. SECURITY CLASS (Thispage.)
22. PRICE
EPA Form 2220-1 (9-73)
*U.S. GOVERNMENT PRINTING OFFICE: 1978 272-709/6392 1-3
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United States
Environmental Protection
Agency
Official Business
Penalty for Private Use
$300
Fourth-Class Mail
Postage and Fees Paid
EPA
Permit No. G-35
Washington DC 20460
WH-552
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