vvEPA
United States
Environmental Protection
Agency
oncre
ashout
NPDES
Minimum Measure
Construction Site Stormwater Runoff Control
Subcategory
Good Housekeeping/Materials Management
Description of Concrete Washout at
Construction Sites
Concrete and its ingredients
Concrete is a mixture of cement, water, and aggregate material.
Portland cement is made by heating a mixture of limestone and
clay containing oxides of calcium, aluminum, silicon and other
metals in a kiln and then pulverizing the resulting clinker. The
fine aggregate particles are usually sand. Coarse aggregate
is generally gravel or crushed stone. When cement is mixed
with water, a chemical reaction called hydration occurs, which
produces glue that binds the aggregates together to make
concrete.
Concrete washout
After concrete is poured at a construction site, the chutes of
ready mixed concrete trucks and hoppers of concrete pump
trucks must be washed out to remove the remaining concrete
before it hardens. Equipment such as wheelbarrows and hand
tools also need to be washed down. At the end of each work
day, the drums of concrete trucks must be washed out. This is
customarily done at the ready mixed batch plants, which are
usually off-site facilities, however large or rural construction
projects may have on-site batch plants. Cementitious (having
the properties of cement) washwater and solids also come from
using such construction materials as mortar, plaster, stucco,
and grout.
Construction workers should handle wet concrete and
washout water with care because it may cause skin irritation
and eye damage. If the washwater is dumped on the ground
(Fig. 1), it can run off the construction site to adjoining roads
and enter roadside storm drains, which discharge to surface
waters such as rivers, lakes, or estuaries. The red arrow in
Figure 2 points to a ready mixed truck chute that's being
washed out into a roll-off bin, which isn't watertight. Leaking
washwater, shown in the foreground, will likely follow similar
Figure 1. Chute
washwater being dumped
on the ground
Figure 2. Chute
washwater leaking from a
roll-off bin being used as a
washout container
paths to nearby surface waters. Rainfall may cause concrete
washout containers that are uncovered to overflow and also
transport the washwater to surface waters. Rainwater polluted
with concrete washwater can percolate down through the
soil and alter the soil chemistry, inhibit plant growth, and
contaminate the groundwater. Its high pH can increase
the toxicity of other substances in the surface waters and
soils. Figures 1 and 2 illustrate the need for better washout
management practices.
Environmental and Human Health Impacts Best Management Practice Objectives
Concrete washout water (or washwater) is a slurry containing
toxic metals. It's also caustic and corrosive, having a pH
near 12. In comparison, Drano liquid drain cleaner has a pH
of 13.5. Caustic washwater can harm fish gills and eyes and
interfere with reproduction. The safe pH ranges for aquatic life
habitats are 6.5 - 9 for freshwater and 6.5 - 8.5 for saltwater.
The best management practice objectives for concrete washout
are to (a) collect and retain all the concrete washout water and
solids in leak proof containers, so that this caustic material
does not reach the soil surface and then migrate to surface
waters or into the ground water, and (b) recycle 100 percent
of the collected concrete washout water and solids. Another
Office of Water, 4203M
www.epa.gov/npdes/pubs/concretewashout.pdf
www.epa.gov/npdes/stormwater/menuofbmps
EPA833-F-11-006
February 2012
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Stormwater Best Management Practice: Concrete Washout
objective is to support the diversion of recyclable materials from
landfills. Table 1 shows how concrete washout materials can be
recycled and reused.
Table 1 - Recycling concrete washout materials
Uses of Recycled Materials
Reused to washout additional mixer
truck chutes or drums
Reused as a ready mixed concrete
ingredient
Reused as an ingredient of precast
concrete products, e.g., highway
barriers, retaining wall blocks, riprap
Reused as crushed concrete
products, e.g., road base or fill
Reused to pave the yards of ready
mixed concrete plants
Returned back to a surface water,
e.g., river, lake, or estuary
Concrete Washout Materials
Washwater
X
X
X
x°
c
CD re
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CD
CD E
OM=
X"
X
X
CD
"re
O)
CD
^ 0>
.E o>
Ll_ re
X
X
X
CD
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C/D CD
S 0)
0 0)
O re
X
X
X
Hardened
concrete
X
Unused wet
concrete
X
X
a. Fine particles of cementitious material (e.g., Portland cement, slag cement, fly ash,
silica fume)
b. Recyclable, if allowed by the concrete quality specifications
c. Treated to reduce the pH and remove metals, so it can be delivered to a municipal
wastewater treatment plant, where it is treated further and then returned to a natural
surface water
Washwater recycling, treatment, disposal
Washwater from concrete truck
chutes, hand mixers, or other
equipment can be passed through
a system of weirs or filters to remove
solids and then be reused to wash
down more chutes and equipment
at the construction site or as an
ingredient for making additional
concrete. A three chamber washout
filter is shown in Figure 3. The first
stage collects the coarse aggregate.
The middle stage filters out the
small grit and sand. The third stage
has an array of tablets that filter
out fines and reduces the pH. The filtered washwater is then
discharged through a filter sock. An alternative is to pump the
washout water out of the washout container (Fig 4) and treat
the washwater off site to remove metals and reduce its pH,
so it can be delivered to a publicly owned treatment works
(POTW), also known as a municipal wastewater treatment plant,
which provides additional treatment allowing the washwater
to be discharged to a surface water. The POTW should be
Figure 3. Concrete washout
filter
Figure 4. Vacuuming washwater out of a
washout container for treatment and reuse
contacted to inquire
about any pretreatment
requirements, i.e., the
National Pretreatment
Standards for Prohibited
Dischargers (40CFR 403.5)
before discharging the
washwater to the POTW.
The washwater can also
be retained in the washout
container and allowed to
evaporate, leaving only the hardened cementitious solids to be
recycled.
Solids recycling
The course aggregate materials that are washed off concrete
truck chutes into a washout container can be either separated
by a screen and placed in aggregate bins to be reused at
the construction site or returned to the ready mixed plant and
washed into a reclaimer (Fig. 5). When washed out into a
reclaimer, the fine and course aggregates are separated out
and placed in different
piles or bins to be reused
in making fresh concrete.
Reclaimers with settling
tanks separate cement
fines from the washwater,
and these fines can also
be used in new concrete
unless prohibited by the
user's concrete quality
specifications.
Figure 5. Ready mixed truck washing
out into a reclaimer
Hardened concrete recycling
When the washwater in a construction site concrete washout
container has been removed or allowed to evaporate, the
hardened concrete that remains can be crushed (Fig. 6)
and reused as a construction material. It makes an excellent
aggregate for road base and can be used as fill at the
construction site or
delivered to a recycler.
Concrete recyclers can
be found at municipal
solid waste disposal
facilities, private
recycling plants, or large
construction sites.
Figure 6. Crushed concrete stockpile and
crusher
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Stormwater Best Management Practice: Concrete Washout
Wet concrete recycling
Builders often order a little more ready mixed concrete than
they actually need, so it is common for concrete trucks to
have wet concrete remaining in their drum after a delivery. This
unused concrete can be returned to the ready mixed plant and
either (1) used to pour precast concrete products (e.g., highway
barriers, retaining wall blocks, riprap), (2) used to pave the
ready mixed plant's yard, (3) washed into a reclaimer, or
(4) dumped on an impervious surface and allowed to harden,
so it can be crushed and recycled as aggregate. Unused wet
concrete should not be dumped on bare ground to harden at
construction sites because this can contribute to ground water
and surface water contamination.
Washout Containers
Different types of washout containers are available for
collecting, retaining, and recycling the washwater and solids
from washing down mixed truck chutes and pump truck
hoppers at construction sites.
Chute washout box
A chute washout box is mounted on the back of the ready
mixed truck. If the truck has three chutes, the following
procedure is used to perform the washout from the top down:
(1) after the pour is completed, the driver attaches the extension
chute to the washout box, (2) the driver then rotates the main
chute over the extension chute (Fig. 7) and washes down the
hopper first then the main chute, (3) finally the driver washes
down the flop down chute and last the extension chute hanging
on the box. All washwater and solids are captured in the box.
After the wash down,
washwater and solids are
returned to the ready mixed
plant for recycling. A filter
basket near the top of the
washout box separates out
the coarse aggregates so
they can be placed in a
bin for reuse either at the
construction site or back at
the cement plant.
Figure 7. Chute washout box
Chute washout bucket and pump
After delivering ready mixed concrete and scraping the last of
the customer's concrete down the chute, the driver hangs a
washout bucket shown in Figure 8 (see red arrow) on the end of
the truck's chute and secures the hose to insure no leaks. The
Figure 8. Chute washout bucket and
pump
driver then washes down
the chute into the bucket to
remove any cementitious
material before it hardens.
After washing out the chute,
the driver pumps (yellow
arrow points to the pump)
the washwater, sand, and
other fine solids from the
bucket up into the truck's
drum to be returned to the
ready mixed plant, where it can be washed into a reclaimer.
A removable screen at the bottom of the washout bucket
prevents course aggregate from entering the pump. This
course aggregate can also be returned to the plant and added
to the coarse aggregate pile to be reused. All the materials are
recycled.
Hay bale and plastic washout pit
A washout pit made with hay bales and a plastic lining is shown
in Figure 9. Such pits can be dug into the ground or built above
grade. The plastic lining should be free of tears or holes that
would allow the washwater to escape (Fig. 10). After the pit is
used to wash down the chutes of multiple ready mixed trucks
and the washwater has evaporated or has been vacuumed off,
the remaining hardened solids can be broken up and removed
from the pit. This process may damage the hay bales and
plastic lining. If damage occurs, the pit will need to be repaired
and relined with new plastic. When the hardened solids are
removed, they may be bound up with the plastic lining and have
to be sent to a landfill, rather than recycled. Recyclers usually
accept only unmixed material. If the pit is going to be emptied
and repaired more than a few times, the hay bales and plastic
will be generating additional solid waste. Ready mixed concrete
Figure 9. Hay bale and plastic
washout pit
Figure 10. Leaking
washout pit that
has not been well
maintained
3
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Stormwater Best Management Practice: Concrete Washout
trucks can use hay bale washout pits, but concrete pump
trucks have a low hanging hopper in the back that may prevent
their being washed out into bale-lined pits.
Vinyl washout container
Figure 11. Vinyl washout pit with filter bag
The vinyl washout
container (Fig. 11) is
portable, reusable, and
easier to install than a
hay bale washout pit.
The biodegradable filter
bag (Fig. 12) assists in
extracting the concrete solids and prolongs the life of the vinyl
container. When the bag is lifted, the water is filtered out and
the remaining concrete solids and the bag can be disposed of
together in a landfill, or the hardened concrete can be delivered
to a recycler. After the solids have been removed several times
and the container is full of washwater, the washwater can be
allowed to evaporate, so the container can be reused. The
washwater can be removed more quickly by placing another
filter bag in the container
and spreading water gelling
granules evenly across the
water. In about five minutes,
the water in the filter bag will
turn into a gel that can be
removed with the bag. Then
the gel and filter bag can be
disposed to together.
Figure 12. Extracting the concrete
solids or gelled washwater
Metal washout container
The metal roll-off bin (Fig. 13) is designed to securely contain
concrete washwater and solids and is portable and reusable.
It also has a ramp that allows concrete pump trucks to wash
out their hoppers (Fig. 14). Roll-off providers offer recycling
services, such as, picking up the roll-off bins after the
washwater has evaporated and the solids have hardened,
replacing them with
empty washout bins, and
delivering the hardened
concrete to a recycler
(Fig. 15), rather than a
landfill. Some providers will
vacuum off the washwater,
treat it to remove metals and
reduce the pH, deliver it to a
wastewater treatment plant ...
Figure 13. Mixer truck being washed out
for additional treatment and into a roil-off bin
subsequent discharge to a surface water. Everything is recycled
or treated sufficiently to be returned to a natural surface water.
Figure 14. Pump truck using the
ramp to wash out into a roll-off bin
Figure 15.
Delivering
hardened Concrete
to a recycler
Another metal, portable, washout container, which has a
rain cover to prevent overflowing, is shown in Figure 16. It is
accompanied by an onsite washwater treatment unit, which
reduces the pH and uses a forced weir tank system to remove
the coarse aggregate, fine aggregate, and cement fines. The
washwater can
then be reused at
the construction
site to wash
out other mixer
truck chutes
and equipment.
The solids are
allowed to harden
together and can
be taken to a concrete
recycler (Fig. 17) to be
crushed and used as
road base or aggregate
for making precast
products, such as
retaining wall blocks. All
materials are recycled.
Figure 16. Washout container with a rain cover and
onsite washwater treatment
Figure 17. Delivering hardened concrete
to a recycler
Siting Washout Facilities
Concrete washout facilities, such as washout pits and vinyl
or metal washout containers, should be placed in locations
that provide convenient access to concrete trucks, preferably
near the area where concrete is being poured. However they
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Stormwater Best Management Practice: Concrete Washout
should not be placed within 50 feet of storm drains, open
ditches, or waterbodies. Appropriate gravel or rock should
cover approaches to concrete washout facilities when they are
located on undeveloped property. On large sites with extensive
concrete work, washouts should be placed at multiple locations
for ease of use by ready mixed truck drivers. If the washout
facility is not within view from the pour location, signage will be
needed to direct the truck drivers.
Operating and Inspecting Washout
Facilities
Concrete washout facilities should be inspected daily and after
heavy rains to check for leaks, identify any plastic linings and
sidewalls have been damaged by construction activities, and
determine whether they have been filled to over 75 percent
capacity. When the washout container is filled to over
75 percent of its capacity, the washwater should be vacuumed
off or allowed to evaporate to avoid overflows. Then when the
remaining cementitious solids have hardened, they should be
removed and recycled. Damages to the container should be
repaired promptly. Before heavy rains, the washout container's
liquid level should be lowered or the container should be
covered to avoid an overflow during the rain storm.
Educating Concrete Subcontractors
The construction site superintendent should make ready mixed
truck drivers aware of washout facility locations and be watchful
for improper dumping of cementitious material. In addition,
concrete washout requirements should be included in contracts
with concrete delivery companies.
Reference
NRMCA 2009. Environmental Management in the Ready
Mixed Concrete Industry. 2PEMRM. 1st edition. By Gary M.
Mullins. Silver Springs, MD: National Ready Mixed Concrete
Association.
Websites and Videos
Construction Materials Recycling Association
www.concreterecycling.org
National Ready Mixed Concrete Association
www.nrmca.org
National Ready Mixed Concrete Research and Education
Foundation
www. rmc-foundation.org
Additional information and videos on concrete washout
containers and systems can be found by a web search for
"concrete washout."
Photograph Credits
Figures 1, 2. Mark Jenkins, Concrete Washout Systems, Inc.
Figure 3. Mark Shaw, Ultra Tech International, Inc.
Figure 4. Mark Jenkins, Concrete Washout Systems, Inc.
Figure 5. Christopher Crouch, CCI Consulting
Figure 6. William Turley, Construction Materials Recycling Association
Figure 7. Brad Burke, Innovative Concrete Solutions, LLC
Figure 8. Ron Lankester, Enviroguard
Figures 9, 10. Mark Jenkins, Concrete Washout Systems, Inc.
Figures 11, 12. Tom Card, RTC Supply
Figures 13, 14, 15. Mark Jenkins, Concrete Washout Systems, Inc.
Figures 16, 17. RickAbneySr., Waste Crete Systems, LLP
Disclaimer
Please note that EPA has provided external links because they provide additional information that may be useful or interesting. EPA cannot attest to the
accuracy of non-EPA information provided by these third-party websites and does not endorse any non-government organizations or their products or services.
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