WATER POLLUTION CONTROL RESEARCH SERIES 11024 EQE 06/71
Impregnation of Concrete Pipe
ENVIRONMENTAL PROTECTION AGENCY • WATER QUALITY OFFICE
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WATER POLLUTION CONTROL RESEARCH SERIES
The Water Pollution Control Research Reports describe the results and progress
in the control and abatement of pollution of our Nation's waters. They provide
a central source of information on the research, development and demonstration
activities of the Water Quality Office of the Environmental Protection Agency,
through in-house research and grants and contracts with the Federal, State
and local agencies, research institutions, and industrial organizations.
Previously issued reports on the Storm and Combined Sewer Pollution Control
Program:
11023 FDB 09/70
11024 FKJ 10/70
11024 EJC 10/70
11023 12/70
11023 DZF 06/70
11024 EJC 01/71
11020 FAQ 03/71
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11024 DOC 07/71
11024 DOC 08/71
11024 DOC 09/71
11024 DOC 10/71
11040 QCG 06/70
11024 DQU 10/70
Chemical Treatment of Combined Sewer Overflows
In-Sewer Fixed Screening of Combined Sewer Overflows
Selected Urban Storm Water Abstracts, First Quarterly
Issue
Urban Storm Runoff and Combined Sewer Overflow Pollution
Ultrasonic Filtration of Combined Sewer Overflows
Selected Urban Runoff Abstracts, Second Quarterly Issue
Dispatching System for Control of Combined Sewer Losses
Prevention and Correction of Excessive Infiltration and
Inflow into Sewer Systems - A Manual of Practice
Control of Infiltration and Inflow into Sewer Systems
Combined Sewer Temporary Underwater Storage Facility
Storm Water Problems and Control in Sanitary Sewers -
Oakland and Berkeley, California
Evaluation of Storm Standby Tanks - Columbus, Ohio
Selected Urban Storm Water Runoff Abstracts, Third
Storm Water Management Model, Volume 1 - Final Report
Storm Water Management Model, Volume II - Verification
and Testing
Storm Water Management Model, Volume III —
User's Manual
Storm Water Management Model, Volume IV - Program Listing
Environmental Impact of Highway Deicing
Urban Runoff Characteristics
To be continued on inside back cover...
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IMPREGNATION OF CONCRETE PIPE
for the
WATER QUALITY OFFICE
ENVIRONMENTAL PROTECTION AGENCY
by
Southwest Research Institute
8500 Culebra Road
San Antonio, Texas 78228
Program 11024 EQE
Contract #14-12-835
June 1971
For sale by the Superintendent of Documents, U.S. Government Printing Office, Washington, D.C. 20402 - Price 75 cents
Stock Number 5501-0601
J i ','>..,
Chicago,
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EPA Review Notice
This report has been reviewed by the Water
Quality Office, EPA, and approved for pub-
lication. Approval does not signify that the
contents necessarily reflect the views and
policies of the Environmental Protection
Agency, nor does mention of trade names or
commercial products constitute endorsement
or recommendation for use.
11
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ABSTRACT
This program, was undertaken to investigate methods to increase the
corrosion resistance, increase the strength, and reduce the permeabil-
ity of concrete used in sewer line applications by impregnating the
concrete pipe with relatively low cost resins such as asphalt, coal tars,
linseed oil, sulfur, urea-formaldehyde, and others.
Methods to accomplish this end •were achieved and the materials, tech-
niques of application, test results and economics are presented in this
report. A large number of candidate impregnation materials were
obtained and carefully screened both in the laboratory and in limited
field tests. Test specimens were cut from commercial grades of con-
crete pipe and physical property tests were made on the treated specimens
both before and after they were subjected to degrading environments
created to simulate, but at an accelerated rate, the environment that
concrete may be subjected to in sewer applications. Specimens impreg-
nated with sulfur or 5. 0% hydrofluoric acid had scaling rates of 0. 0005
to 0. 00017 respectively as opposed to 0. 005 in. /day for the concrete
control when subjected to a three day exposure in 10% sulfuric acid.
This indicates 10 to 30 times greater corrosion resistance than untreated
concrete pipe. Six other materials, including vinyl-vinylidene chloride,
vinyl acetate-acrylic, nitrile rubber latex, nitrile-phenolic rubber, an
emulsified reclaimed rubber, and a rubber base adhesive, although
failing to impregnate the concrete, formed surface coatings having ex-
ceptional resistance to the 10% sulfuric acid.
Sections of commercial concrete sewer pipe were given applications of
these eight different treatments and placed in severe corrosive sewer
environments in sites provided by the City of Harlingen, Texas, the
City of San Antonio, Texas, and a site on Southwest Research Institute
grounds over the winter of 1970-71. Preliminary results from these
tests indicate that these eight different treatments are functioning
effectively and are thus worthy of further long term evaluation.
This report was submitted in fulfillment of Program No. 11024 EQE,
Contract No. 14-12-835, under the sponsorship of the Water Quality
Office, Environmental Protection Agency.
Key Words: Concrete Pipe, Impregnation, Hydrogen Sulfide Attack,
Acid Attack, Sulfate Attack, Coatings, Chemical Resis-
tance of Concrete.
111
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CONTENTS
Section Page
I Conclusions 1
II Recommendations 3
III Introduction 5
IV Background 7
V Literature Search 13
VI Initial Laboratory Screening of Materials 15
VII Optimization of Materials and Procedures 33
VIII Preliminary Field Tests 41
IX Significance of Laboratory and Field Findings 45
X Economics 49
XI Acknowledgements 55
XII References 57
XIII Appendices 59
v
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LIST OF FIGURES
Page
1. Cross Section of Concrete Sewer Pipe Under Typical 8
Corrosion Conditions.
2. Corrosion of the Floor of a Concrete Lift Station. 10
3. Preferential Acid Attack on Limestone Aggregate by 11
Industrial Wastes.
4. Water Absorption as a Function of Time Under Varying 16
Conditions of Vacuum and Pressure for 18 in. Diameter
Concrete Pipe.
5. Preferential Attack of Limestone Aggregate in Laboratory. 19
6. Scaling of Concrete Pipe as a Function of Sulfuric Acid 20
Concentration.
7. Corrosion Caused by 1, 5, and 10% Sulfuric Acid Solutions 22
After Three-Days' Exposure.
8. Extended Exposure of Concrete to 10% Sulfuric Acid. 23
9. Treatment Plant Corrosion Caused by Citrus and Tomato 27
Acid.
10. Flexural Strength as a Function of Pipe Age for Sulfur Im- 36
pregnated Concrete.
11. Flexural Strength of Impregnated Concrete as a Function 37
of Sulfur Temperature.
12. Staining of Concrete by Sodium Sulfide Solution. 44
13. Surface Attack of Sulfuric Acid. 46
14. Selling Price as a Function of Pipe Diameter for Various 50
Types of Sewer Pipe.
VI
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TABLES
No. Page
1. Properties and Corrosion Resistance of Promising 31
Concrete Treatments
2. Performance of Selected Double-Treated Specimens 35
3. Absorption and Strength of Sulfur Impregnated Concrete 39
Pipe at 30 Psig Pressure
4. Relative Economics of Treating Concrete Pipe 52
VII
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SECTION I
CONCLUSIONS
1. Improvements in the corrosion resistance, impermeability and
strength of concrete pipe can be achieved by impregnation. The
importance of these improvements from an applications stand-
point rank in the order given.
2. Although a number of materials improved the corrosion resist-
ance of cured concrete pipe, (Appendix A) the most promising
impregnation materials found were a 5% solution by weight of
hydrofluoric acid, sulfur and a modified sulfur formulation.
The concrete pipe control specimen when subjected
to sulfuric acid for 3 days suffered a scaling rate
(wall loss) of 0. 005 in. /day. The flexural strength
of the concrete was found to be 1160 psi.
The concrete specimen impregnated with a 5% solution
of hydrofluoric acid when subjected to the same test
as above suffered scaling of 0. 00017 in. /day. The
flexural strength was 1050 psi.
A concrete specimen impregnated with a modified
sulfur formulation when subjected to the same test
as above, suffered scaling of 0.0005 in./day. The
flexural strength was 2800 psi. In addition, the water
absorption of the concrete was reduced from 5% to
0% when impregnated with sulfur.
3. Three days submergence in 10% sulfuric acid is an extremely
severe test for concrete. A solution of 10% sulfuric acid is the
most corrosive concentration as shown below:
Sulfuric Acid Scaling
Concentration
(% by wt. ) (in. /day)
0.1 0.00025
0.5 0.0008
1.0 0.0015
5.0 0.004
10.0 0.0054
30.0 0.0015
50.0 0.0007
98.0 0.0
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4. Although maximum sulfuric acid concentrations of approximately
5% have been determined in certain sewer lines, the maximum
scaling rate uncovered in the literature has been 0. 5 in. /yr or
0. 0014 in. /day. This is the same scaling rate obtained in the
laboratory using a 1% sulfuric acid. Thus, it would appear that
1% sulfuric acid could simulate the most severe environment
expected in the field. This should be examined further.
5. Before reliable predictions can be made on the durability of
impregnated concrete pipe, good correlations must be established
between laboratory experiments and field performance.
6. Materials which failed to impregnate concrete, but which formed
good surface coatings included latexes of vinyl-vinylidene chloride,
vinyl acetate-acrylic, nitrile-phenolic, nitrile rubber, a rubber
base adhesive, and an emulsified reclaimed rubber product. Pre-
dicting durability or service life of concrete treated with these
coatings is extremely difficult. Pinholing, abrasion, or mechanical
damage will expose the concrete, subjecting it to corrosive attack.
The use of these materials should be limited to areas where visual
inspection and manual application can or must be performed.
7. Better coatings were obtained by using wetted rather than dry
concrete specimens. Dry specimens tended to generate gas bubbles
which caused pinholing in the coating. The fact that the walls in
such appurtenances as wet wells and diversion boxes are damp, make
the water base latexes of vinyl-vinylidene chloride, vinyl acetate-
acrylic, nitrile rubber, and emulsified reclaimed rubber particularly
attractive for such applications. Materials' costs per square foot
of treated area for coatings range between 6-8 cents.
8. The cost of impregnating concrete pipe with hydrofluoric acid will
vary between 5 and 10 cents per square foot, while impregnation
with sulfur will vary between 8 and 15 cents per square foot. Typical
costs for epoxy-coal tar or plastic liners vary between 85 cents
and one dollar per square foot. Until service life is established
for impregnated pipe, a cost effectiveness comparison cannot be
made.
9. The possibility that sewer lines can be treated in place, using hydro-
fluoric acid in a manner similar to that used in the oil industry for
acidizing oil and gas wells is of considerable interest and potential.
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SECTION II
RECOMMENDATIONS
1. The use of 5% hydrofluoric acid, sulfur and modified sulfur form-
ulations has proven successful in impregnating concrete pipe to
improve corrosion resistance as measured in the laboratory.
Field testing using these treatments, supported by additional lab-
oratory work should allow for the development of a good correlation
between laboratory and field tests. The fact that 1% sulfuric acid
has been found to impart the same scaling rate as that of the most
severe sewer line cases reported in the literature is encouraging
and should be further pursued so that a valuable aid can be develop-
ed for laboratory evaluation.
2. Pipe sections impregnated with hydrofluoric acid and sulfur along
with a concrete control should be placed in test in domestic sewage
lines and in industrial waste lines which have a recorded history
of severe concrete corrosion. Preferably this should be accom-
plished in several cities to insure measurable differences in a
minimum of time.
3. A representative sewer line should be selected and a portion should
be treated in-place using 5% hydrofluoric acid. The line should be
monitored and a comparison made between the treated and non-
treated sections to determine the success of in-place treatment.
4. A facility such as a wet well, diversion box, treatment tank, or
junction box that is partially corroded should be coated with one
or more of the water base latexes. A four walled structure would
be ideal since vinyl- vinylidene chloride, nitrile rubber, vinyl
acetate-acrylic, and reclaimed rubber could be applied to each
wall and be compared directly with one another in the same instal-
lation under the identical environmental conditions.
5. The fact that Ocrated (a treating process using silicon tetrafluoride
gas) concrete pipe is attacked by dilute sulfuric acid and yet report-
edly performs satisfactorily in sewer service indicates that a re-
evaluation of some of the resins and treatments investigated on this
program may be in order. The effect of any natural bactericidal
effect or that of added bactericides could conceivably control the
bacteria population responsible for the generation of sulfuric acid
and thereby allow some of these materials to provide adequate
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corrosion resistance in a sewer line application, even though
they would not pass the 10% sulfuric acid corrosion test in the
laboratory.
The best treatment methods as determined in the field tests
should be given a complete process design and economic analysis,
so that prospective users would have this material available to
them as an aid in making the decision with regard to installation
of such facilities.
4
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SECTION III
INTRODUCTION
Concrete is a low cost, high strength material that is resistant to water
damage at normal temperatures. Because of this, concrete is used ex-
tensively in water and sewer systems. Corrosion of concrete in sewers
is not a new occurrence, but has been in evidence for years. The sever-
ity of the problem has greatly increased in recent years because of the
rapid expansion of the population, industrial growth, the use of garbage
disposal units, and a reduction in the amount of dilution of the sewage due
to tighter joints and to a reduction in the use of combined sewers. In
sewer systems with a history of corrosion problems a variety of conditions
occur regularly that cause the generation of sulfides which are oxidized to
sulfuric acid and this aggressively attacks the concrete.
Concrete is also attacked by sulfates, particularly those contained in the
surrounding soil and water. The sulfates react with the tricalcium aluminate
and free lime in the cement and cause the concrete to deteriorate. Sulfate
attack can also occur where there is no native sulfate, in that sulfate is
formed when concrete is attacked by sulfuric acid. Thus, attack attribut-
ed to sulfuric acid can actually be a combined attack from both acid and
sulfate. Impregnation of concrete pipe used in water and sewer systems
offers several potential advantages. The interior passages of the concrete
structure would be sealed. The permeability and porosity of the concrete
would be reduced. The physical and mechanical properties of the concrete
would be improved. Realization of these advantages at a moderate cost
would result in a longer service life of installations and improved operat-
ional efficiency.
The problem of corrosive attack of concrete in these applications has
been the subject of extensive past research. Some of the better known
developed control techniques included:
1. The use of forced air ventilation of the vapor spaces in
sewer lines.
2. The running of sewers liquid full.
3. The control of sewer pH.
4. The use of corrosion resistant sewer pipe such as clay
tile, or plastic pipe.
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5. The use of epoxy based coatings.
6. The use of complete or partial plastic liners.
7. The use of sacrificial coatings, (thick wall sections;
concrete which contain high concentrations of limestone
aggregate; etc. )
The objective of the subject program was to investigate a large number of
materials as potential impregnants for concrete sewer pipe to impart
corrosion resistance, reduce permeability, and improve strength. Some
of the materials investigated failed to permeate the concrete specimens,
but rather formed a surface coating.
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SECTION IV
BACKGROUND
The quantity of concrete pipe used attests to the success that has been
achieved with it over a long period of time. Continuous improvements
have been made over the years in its design and manufacture, particular-
ly with respect to the joints and the methods of sealing. ASTM Design-
ations: C 14, the Standard Specification for "Concrete Sewer, Storm Drain,
and Culvert Pipe", and C76, "Reinforced Concrete Culvert, Storm Drain,
and Sewer Pipe" detail tests for design, strength, absorption, and per-
meability. These tests form the basis on which much of this type of pipe
is purchased.
Corrosion of concrete pipe and other concrete structures used in sewers
is not a universal problem, but it is a serious problem in some areas.
It results in leakage, infiltration, and overloading of treatment facilities.
It also results in premature failure of lines necessitating early replace-
ment. Corrosion of concrete in sewer applications has been the subject
of numerous investigations. (1, 2, 3) Conventional sewer corrosion
occurs above the liquid level and it does not occur in lines that are run
liquid full unless some aggressive compound is being discharged to the
sewer, usually from some industrial source.
The consensus of investigators regarding the mechanism of sewer cor-
rosion is that it is directly related to the presence of hydrogen sulfide
in the vapor space of the sewer and to a lesser extent to heavy sulfate
concentrations in the waters carried in the sewers or in the earth sur-
rounding the sewer. The origin of hydrogen sulfide in sewage is from
the action of anaerobic bacteria on organic sulfur compounds, sulfates
and other inorganic sulfur compounds. They use sulfur instead of oxygen
as a hydrogen acceptor. The quantity of hydrogen sulfide produced and
released to the vapor space is considered to be a function of the amounts
of hydrogen sulfide producing elements in the sewage, the time of re-
action, the temperature (minor up to 15 °C, increasing progressively
up to 38°C), the pH (a maximum at a slightly alkaline condition), and
the degree of agitation or turbulence experienced by the sewage. The
hydrogen sulfide entering the vapor space dissolves in the condensed
moisture films on the exposed concrete surfaces and is oxidized to
sulfuric acid by aerobic bacteria. One such bacteria, thiobacillus thio-
oxidans, is capable of producing sulfuric acid in concentrations up to
5%. Figure 1 is a sketch showing the mechanism of typical concrete
sewer pipe corrosion.
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Condensate with large aerobic
bacteria population which oxidizes
hydrogen sulfide to sulfuric acid
which attacks concrete.
Silt
Accumulation
Concrete
Slime accumulation with large
anaerobic bacteria population
which convert sulfur compounds
in sewage to hydrogen sulfide gas
which is released to the vapor space.
Figure 1. Cross Section of Concrete Sewer Pipe Under Typical
Corrosion Conditions.
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Figure 2 is a closeup photograph of the remains of a floor section of a
lift station and is characteristic of the type of deterioration encounter-
ed in concrete sewer appurtenances. Note the exposure of the rein-
forcing steel.
The destructive action of sulfates on concrete is primarily the result
of the reaction between the sulfates and the tricalcium aluminate and
free lime in the cured concrete product. The crystalline calcium
sulfate reaction product is larger in volume than the original constituents
and this causes cracking, swelling, and spalling in the concrete which
becomes progressively weaker and finally disintegrates.
Numerous investigators (3, 4) have shown by extensive studies of this
problem that sulfate attack can be controlled in concrete by keeping the
tricalcium aluminate content of the cement used below 5. 5% or by curing
the pipe with high pressure steam or both. It was also noted by earlier
investigators that the less permeable the pipe, the more sulfate resist-
ance it exhibited. The use of sulfate resistant concrete does not impart
resistance to sulfuric and other acids.
Other mineral and organic acids often tend to react preferentially with
any limestone present in the concrete. An example of this is shown in
Figure 3. This type of failure is more often encountered in industrial
wastes rather than in domestic sewage. The section of pipe shown in
Figure 3 was the top of the line, the bottom half having been completely
corroded away. This is the reverse of what is found in sewers handling
domestic sewage.
When many users of concrete pipe encounter or anticipate problems with
acid or sulfate attack they choose pipe other than that made of concrete.
Often the other types of pipe are more costly than concrete pipe. The
premium price that these other types of pipe command and their wide-
spread use are related to their superior chemical resistance in problem
areas.
The following criteria are thought to be the most significant with respect
to the use of concrete pipe:
1. Concrete pipe is subject to both acid and sulfate attack
and there are locations where it can be subject to both
at the same time. Infiltration into, or seepage from,
concrete pipe can develop as a result of the deterioration
of the pipe.
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10
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Figure 3. Preferential Acid Attack on Limestone Aggregate by Industrial Wastes
11
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2. Impregnation of concrete pipe can improve its resistance
to acid and sulfate attack in that it reduces the permeability
of the concrete and thereby denies the deleterious materials
access to the interior structure of the concrete and any
steel reinforcing. (Corrosion of steel can result in forces
created during the formation of iron oxide sufficient to
spall concrete).
3. A protective process for concrete sewer pipe should not
only impregnate the pipe and reduce its permeability but
it should also protect the interior and exterior surfaces
from attack.
4. Improvements in strength derived from the protection
system are significant and can be used to great advantage,
however, strength improvements are not thought to be of
the same significance as improvements in corrosion
resistance.
5. The cost of the protective systems should be such as to
offer a considerable savings over other present day remedied
actions such as the use of clay tile, plastic liners, and the
various coatings.
12
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SECTION V
LITERATURE SEARCH
This program was initiated with a literature search relating to impreg-
nation and treatment of concrete. In addition to the library facilities
of the Institute, the computer abstracting service of the Highway Re-
search Information Service of the National Academy of Sciences was
employed. Prior to the literature search, the authors were aware of
some very early work (5, 6) relating to the impregnation of concrete and
sandstone with sulfur as well as some recent -work on impregnation of
concrete with polymer materials (7, 8, 9) being conducted at Brook-
haven National Laboratory by the Bureau of Reclamation, Atomic Energy
Commission and Office of Saline Water. Limited investigations of impreg-
nating concrete sewer pipe with sulfur (10) demonstrated the technical and
economic feasibility for improving strength and reducing permeability.
One other known protective treatment for concrete sewer pipe was the
Dutch Ocrate process (11) wherein silicon tetrafluoride gas was impreg-
nated under pressure into concrete pipe to improve its corrosion resist-
ance.
The literature search failed to uncover any additional treatments or
processes for impregnating concrete as relates to controlling corrosion
resistance. Several good references were uncovered, however, on
coatings or treatments for waterproofing or protecting concrete in general.
(12,-14) These documents served as valuable guidelines insofar as materials
which showed any promise as simple waterproofing agents were generally
considered as potential impregnants.
13
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SECTION VI
INITIAL LABORATORY SCREENING OF MATERIALS
With the valuable literature references, the laboratory phase of the
program was initiated.
Impregnation Techniques
In addition to samples obtained from the local concrete pipe manu-
facturers, samples were also requested from various plants throughout
the United States. However, most of these contacts referred us to the
local manufacturers and as a result, all of the data generated in this
program were obtained from pipe that was manufactured from plants in
San Antonio, and Harlingen, Texas. The fact that concrete pipe is manu-
factured according to rigid ASTM standards should insure that the concrete
pipe is a fairly uniform product. This was confirmed by representatives
of the American Concrete Pipe Association and from our limited labora-
tory tests.
The impregnation procedure used throughout this program was as follows:
Concrete specimens predried at 250°F for 12 hours were
completely submerged in the impregnating solution. The
vessel containing the specimens and solution was then
placed inside a larger pressure vessel. Depending upon
the particular solution, a vacuum of between 26 and 28
inches of mercury was then applied, followed immediately
by a positive air pressure with the specimens still submerged
in the impregnating liquid.
In initial experiments, specimens from 4, 6, 12, and 27 in. diameter
pipe were first dried and then submerged in water and subjected to 28
in. of mercury vacuum. The weight gain for all of the specimens sub-
jected to vacuum for 10 minutes varied between 5. 5 and 6. 5%. When
subjected to vacuum for 15 minutes followed by 30 psig for 10 minutes,
the weight gain varied between 6 and 7%. No major absorption differ-
ences were found among the various diameter pipe. Eighteen in. diameter
pipe was selected for test work because of its relatively thick wall.
Sections of 18 in. diameter pipe were submerged and subjected to pressures
varying from 10 to 50 psig for timed intervals. The results of these tests
are shown in Figure 4. It was found that the bulk of the absorption takes
place in the first 10 minutes of submersion and above 10 psi the absorption
15
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is relatively independent of pressure. Next, specimens were impreg-
nated under vacuum only and then vacuum followed by pressure. Specimens
were submerged under vacuum only for 10 minutes, under vacuum for 15
minutes followed by 30 psig for 15 minutes (total immersion time of 30
minutes), under vacuum for 20 minutes followed by 100 psig for 20 min-
utes, and under vacuum for 1 hour followed by 30 psig for 1 hour. These
data are also shown in Figure 4. The standard procedure adopted for
preparing test specimens was to subject the specimens to a 28 in. mercury
vacuum for 30 minutes followed by 30 psig pressure for 30 minutes for
a total immersion time of one hour, with some allowance being made for
some of the more viscous impregnants.
Specimens were submerged in various impregnating solutions in separate
containers. Several of these containers were then placed in a large
pressure vessel and in this manner, a number of materials could be run
at one time.
Mechanical Properties
A common problem in any type of screening program conducted in the
laboratory is the selection of appropriate tests that relate to field per-
formance. For strength determinations flexural strength was selected
since specimens for this test could easily be prepared by cutting the
cured concrete pipe with a diamond bladed saw. Tensile strength may
have been a better test, however, preparing suitable specimens from
cured concrete pipe was not practical. The standard D-load test where-
in concrete pipe is placed horizontally and then subjected to a compressive
load along its horizontal axis is used extensively in industry. If ring
sections had been used instead of flexural specimens, it would have re-
quired large volumes of impregnating materials, large impregnating
vessels, and the specimens would have been less convenient to handle.
In addition, the resulting data from a D-load test is not easily related to
a fundamental stress property which is dependent on specimen dimensions.
This was important since the specimen dimensions changed after exposure
to the corrosive media.
The flexure specimens were prepared from non-reinforced 6 in. concrete
pipe and were approximately 0. 5 in. x 1 in. x 5 in. Each specimen was
carefully measured with a vernier caliper and broken in flexure. The
average flexural strength or modulus of rupture for the untreated pipe
was approximately 1160 psi. Specimens with a number of larger pieces
of aggregate in the broken cross section tended to be lower than this
17
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(690 psi) while specimens without large aggregate in the broken cross
section tended to be higher (1360 psi). Asa result, differences in
flexural strength were not viewed as significant unless they were orders
of magnitude different.
Corrosion Tests
Selection of the corrosive media was based on the fact that sulfuric
acid is the most prevalent type of corrosive attack encountered. Pre-
liminary laboratory tests showed that attack by dilute sulfuric acid
was immediate, being measurable after several days, whereas sulfate
salts took considerably longer. Also, from laboratory experiments it
was observed that dilute sulfuric acid attacked the mortar preferentially
to the limestone aggregate such that ultimate attack was very similar to
prolonged sulfate attack. The normal attack of other acids, including
concentrated sulfuric acid, is preferential attack on the limestone
aggregate which leaves depressions in specimens as indicated in Figure
5 and almost identical to that shown in Figure 3.
Scaling rate as used throughout this report to determine corrosion rate,
is a measure of the erosion of the concrete pipe wall reported as in. /day.
Laboratory experiments were conducted wherein different acid con-
centrations were evaluated for a 3-day exposure period. Figure 6 plots
the scaling rate versus sulfuric acid concentrations and shows a maximum
rate of approximately 10% concentration of sulfuric acid. Although the
98% sulfuric acid attacked the limestone aggregate, it did not attack the
mortar. The 0.5, 1, 10, 30, and 50% solutions preferentially attacked
the mortar, whereas the 0.1% sulfuric acid attacked both the limestone
aggregate and mortar at about the same rate.
Asa final consideration, ASTM "Standard Methods of Testing Clay Pipe"
(C 301-68) requires a 48 hour exposure of the clay pipe to a IN solution
of hydrochloric, nitric, sulfuric, or acetic acid. For sulfuric acid this
is equivalent to a 5% weight solution. The maximum concentration of
acid measured in working sewer lines has been approximately 5%.
For the laboratory tests, the most severe acid attack -was desirable so
that corrosion would occur in a minimum period of time. Thus 10%
sulfuric acid was selected as the preliminary screening corrosive media
because it was more severe than the 5% reported in sewers, the scaling
rate was easily measurable after 3 days, and there was never any
indication that the 10% sulfuric acid was attacking or charring any of the
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20
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treatments. More concentrated solutions of sulfuric acid have been
known to char hydrocarbon materials. Typical 3-day attack of 1, 5,
and 10% sulfuric acid on concrete is shown in Figure 7.
Figure 8 shows the typical performance of the concrete pipe used
throughout this study for an extended period of time in 10% sulfuric
acid. Most of the large aggregate protruding is limestone, whereas
the mortar is principally silica sand and cement. As already explained,
this phenomenon has been recognized and is the principal reason why
some pipe manufacturers are considering switching to high limestone
aggregate concrete in sewer pipe production,
Types of Protective Systems
Generally speaking, there are three principal ways of protecting cured
concrete pipe from corrosive attack. One way that has been of principal
interest in this program has been the impregnation or saturation of the
voids within the concrete pipe with an inert or noncorrosive material.
Preferably this material is a good film-former as well as a good wetting
agent for the concrete constituents. While simply blocking the pores or
void spaces within the concrete should slow down and limit attack to the
surface only, unless the material readily wets the concrete particles and
forms an impermeable barrier, corrosion will occur.
A second means of protecting the concrete is to initiate a chemical
change in the concrete itself, whereby the soluble and/or more reactive
constituents are insolubilized or changed to a less reactive species.
Because of the complex nature of concrete itself, as well as the complex-
ities that can occur with the resultant chemical reactions, this particular
means of protecting concrete is usually better evaluated by performance
studies. This area includes steam curing of concrete, the silicate and
fluosilicate treatments, fluoride treatments, carbonating, etc. This
approach is potentially as attractive as impregnation, particularly if
more than a surface treatment can be obtained. Unfortunately, most of
these treatments afford only surface protection, or form gels which
provide some protection under very mild acid conditions, but not against
typical sewer acid concentrations. These treatments have been used
principally as surface hardening, or water proofing applications in the
past.
The third means of protecting concrete from attack is by the use of'
coatings. This area has received by far the most attention in the past.
While there are commercial coatings available which are currently used
in sewer applications, the most successful are usually relatively thick
21
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coatings, applied after the pipe is cured, or liners of polyvinyl chloride
which are made part of the pipe or fixture during casting. The principal
drawback to the most successful of these liners is generally cost. They
normally cost between $0. 80 to $1. 00 per square foot of coating and
increase the cost of concrete pipe to the point where clay pipe or other
more expensive pipe is competitive. The problems associated with most
coatings relate to pinholes, bonding, or blistering or peeling of the
coating from the interior surface.
Of these three ways of protecting cured concrete pipe, it must be
emphasized that principal consideration was given to impregnation, even
though the latter two ways are a degree of impregnation. For a material
to chemically react with the concrete in depth, it must be able to pene-
trate, otherwise only a surface change will occur. A coating can be
thought of as an inefficient impregnating technique. Predicting before-
hand, however, which materials would or would not impregnate was not
possible. Even with the materials that did not penetrate, but simply
coated, attempts were made to modify the material with surfactants or
diluents in order to allow for better penetration.
Evaluation of Materials
Thus materials investigated in this study were first screened for their
ability to impregnate concrete. The standard test method consisted of
submerging predried concrete specimens in the impregnating material
and then applying 28 in. of vacuum for 30 minutes followed by 30 psi
pressure for 30 minutes, removing the specimens and recording the
weight increase. The specimens were allowed to air dry for three days
at room temperature. Certain specimens, depending on the treatment
they received, were oven dried. One specimen was then tested in flexure,
while the duplicate was submerged in 10% sulfuric acid for three days.
The weight loss and scaling were determined and then the specimen -was
also tested in flexure.
From the weight increase as well as inspection of the failed flexural
specimens, it was easily determined which materials failed to penetrate,
but nevertheless did offer a protective surface film. These particular
materials were then further investigated as coatings. With many of
these materials, particularly the latex emulsions, various techniques
and approaches were investigated in attempts to improve the impregnation.
Use of surfactants and diluents, as well as variation of the impregnating
conditions, usually failed to improve impregnation as such, although
bonding to the concrete was, in most cases, improved.
24
-------
Materials which reacted with the concrete were also observed after
the impregnation procedure. Usually these materials underwent a
surface reaction which was destroyed in the 10% sulfuric acid. The
more promising materials, however, penetrated in depth and caused a
chemical reaction throughout the concrete.
By comparing the weight loss and scaling rate of the treated specimens
against that of the concrete control, several promising materials were
singled out and further evaluations were conducted.
A complete list of materials evaluated and their performance is included
as Appendix A. A brief description of the performance of the various
types of treatments will be discussed, with further elaboration on some
of the more promising materials.
During the course of this program approximately 100 different chemicals
or materials were evaluated. The general classes of materials can be
broken down into water soluble salts or acids, water base latexes, solvent
base latexes, liquid resins, and hot melts. One principal problem en-
countered with all of the materials which coated the surface of the specimen
was drainage of the material from sharp edges. This left a relatively
thin coating in these areas which the acid rapidly penetrated. A brief
review of each class of materials follows.
Water Soluble Salts and Acids
This class of materials included silicates, fluosilicates, fluorides,
phosphates, and oxalates. The silicates and fluosilicates required a
series of treatments, wherein dilute solutions were followed by more
concentrated solutions. These materials did not give adequate protection
for the intended application. This is not surprising since others have
found that these treatments are usually poor waterproofing agents as
well. (15)
Several experiments using varying concentrations of hydrofluosilicic
acid were conducted since it was expected that a treatment similar to
that of the Ocrate process would be obtained. The resistance to sulfuric
acid was poor, whereas Derated concrete is reported to give good corrosion
resistance in sewer applications. In checking the literature, (16) it was
found that sulfuric acid does attack (Derated concrete, although its success
in sewer applications is related to a reported bacterial effect which
inhibits the formation of sulfuric acid on the concrete walls. (16, 17)
25
-------
The only materials from this group which appeared encouraging were
a commercial product by the name of SP-4 (Patented Product of Road-
ways International, Baton Rouge, Louisiana) and a dilute solution of
hydrofluoric acid. According to the label, SP-4 also included hydro-
fluoric acid. The fact that the hydrofluoric acid does impart corrosion
resistance is unexpected since it is usually recognized as a corrosive
material to concrete. Specimen numbers 1 and 3 in Appendix A give
the specific data on these treatments. The treated specimens suffered
a weight loss of from 2. 3 to 2. 7 grams as compared to 9. 2 for the con-
crete control. In addition, a scaling rate of 0 to 0. 00017 was obtained
as compared to 0. 0054 in. /day for the control.
Water Base Latexes
This class of materials included copolymers of vinyl chloride and
vinylidene chloride, acrylics and vinyl acetate; polyvinyl acetate and
copolymers of vinyl acetate and acrylics; copolymers of acrylonitrite
and butadiene-styrene; natural rubber emulsions; and reclaimed rubber
emulsions. None of these materials impregnated the concrete, but
rather gelled or formed a coating on the concrete surface. Gelling was
more pronounced on dry concrete specimens. The use of water wetted
specimens did not improve penetration. By far the most promising
materials of this group were the vinyl chloride-vinylidene chloride
copolymers, a vinyl acetate-acrylic copolymer, a nitrile rubber, and
a reclaimed rubber emulsion. Even these materials, however, if not
applied in sufficient thickness, allowed acid to pass by way of pinholes.
If properly applied, these coatings completely protected the concrete
from acid attack. The principal applications envisioned for this class
of materials are the protection of manholes, junction boxes, wet wells,
treatment tanks, and other concrete structures which lend themselves
to easy visual inspection, wherein failed sections can easily be detected
and repaired. A typical potential application is shown in Figure 9. The
bulk of this damage occurred when the pH of the sewage dropped to 2
during one canning season for citrus and tomatoes in Harlingen, Texas.
The fact that these are water emulsions makes them attractive from an
application point of view because of essentially no toxic odors or fumes,
good adherence to damp concrete walls, as well as easy clean-up of
26
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equipment with water. Although slightly more expensive, the re-
claimed rubber product is particularly attractive since it is a re-
claimed product of a pollution problem itself -- old tires.
Solvent Base Latexes
The third class of materials included latexes of nitrile-phenolic
copolymers, chloronated polyethylene, vinyl chloride- vinylidene chloride
copolymers, a rubber base adhesive, and reclaimed rubber. Impregnation
was achieved if sufficiently dilute solutions were used. Because of the
relatively large amount of solvent present, however, a good film coating
was not obtained on the specimen surface and as a consequence, good
corrosion resistance was not achieved. Repeated impregnations would
probably offer a solution although this approach was not considered
practical. As a result this class was also considered for multiple coatings.
As with the water base latexes, the film thickness had to be sufficient to
eliminate pinholes. These materials appeared to have excellent resistance
to the dilute sulfuric acid. Because of solvent vapors and fumes, as well
as the increased cost, they are not as attractive for inplace treatments
as the water base latexes. Nevertheless, this class of materials should
find limited application in sewer systems.
Liquid Resins
The fourth class of materials included a number of materials in both
water and solvent systems, as well as undiluted resin systems. Urea-
formaldehyde, urea-formaldehyde-alkyds, melamine-alkyds, phenolics,
furans, and epoxies are but several of the materials investigated.
Linseed oil, perhaps one of the oldest concrete treatments, impregnated
the concrete in depth, but unfortunately failed to impart any acid resist-
ance. The phenolic and furan resins were somewhat better than the urea-
formaldehyde, but even so were only marginally better than the concrete
control. The urea-formaldehyde-alkyd resin investigated was considerably
better than the straight urea-formaldehydes, but the melamine-alkyd was
superior to either of these materials. The principal problem encountered
with the melamine-alkyd, however, was the drainage from sharp edges.
This same problem was encountered with the epoxies. With few excep-
tions, the viscosity of the epoxies was too great to allow penetration.
The practical problem of pot life makes most epoxies unattractive as
impregnants. From the large number of epoxies investigated as coatings,
only one (#125) exhibited outstanding acid resistance, and even here, the
edges suffered damage. While the epoxy coatings themselves had good
28
-------
resistance to the sulfuric acid, pinholes in the coating allowed the acid
to pass. Once behind the coating, the acid attacked the concrete to the
point that after three days' exposure, the epoxy coating usually re-
mained intact but simply separated from the specimen. Thicker coat-
ings or fillers in the epoxy gave mixed results.
The principal difficulty encountered with the resins in this class
appears related to the film-forming abilities of the resins. With few
exceptions, acid attack on the treated specimens appeared uniform across
the surface of the specimen indicating acid penetration through the coat-
ing. Of this entire group, certain selected epoxies, the melamine-alkyd,
and urea-formaldehyde-alkyd, appeared the most promising, although
performance was not as good as for materials from the other classes.
Hot Melts
The last class of materials considered was that of the hot melts, in-
cluding sulfur, asphalts, coal tars, polyethylene waxes, paraffin, and
a gilsonite-asphalt mix. Although not hot melts as such, cut-back
asphalt and coal tar pipe dips are also included here, since they were
applied heated as well as at room temperature. Impregnation with the
hot melts was much better than that of any of the other groups, generally
speaking. Inspection of the broken specimens usually revealed complete
penetration. The interesting point, however, is the fact that even though
impregnation was achieved, with few exceptions, the corrosive attack was
about the same or worse than that of the concrete control. Surprisingly,
for the degree of penetration obtained by the asphalts, coal tars, and
paraffin, the corrosion resistance was poor. The corrosion resistance
imparted by impregnation with sulfur was considerably better than that
of the other hot melts. Elemental sulfur and certain selected modified
sulfur treatments also imparted outstanding strength improvements.
The asphalts and coal tars performed better as coatings than as impreg-
nants, provided adequate thicknesses were employed to reduce pinholes.
Dicussion
In all fairness to the materials investigated and to the manufacturers
who supplied them, it must be remembered that the nature of this program
was essentially one of screening a large number of materials to select
those materials showing the greatest promise, before proceeding to
optimize materials and procedures. The fact that most of the materials
investigated failed is not as much an indictment of those materials as it
29
-------
is a demonstration of the severity of attack of 10% sulfuric acid. In all
probability, continued investigations with each of the different materials
might lead to better selection, modifications, and ultimately an accept-
able material. To do this, however, would have required time and
expenditures beyond those available.
To recapitulate, from these initial investigations the most promising
materials uncovered included HF, SP-4, vinyl-vinylidene chloride co-
polymer, vinyl acetate-acrylic copolymer, nitrile rubber latex, an
emulsified reclaimed rubber, nitrile-phenolic rubber, a rubber base
adhesive, a melamine-alkyd resin, one epoxy, and sulfur. The specific
test results are summarized for these materials in Table 1 and compared
against that of a concrete control.
30
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TABLE 1
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31
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SECTION VII
OPTIMIZATION OF MATERIALS AND PROCEDURES
Although discussed separately, the optimization of materials and
procedures was actually integrated into the program. As the perform-
ance of the materials was being evaluated, manufacturers would supply
additional materials, modifications would be made, or impregnating or
coating techniques would be varied in attempts to improve performance.
These materials or modifications of materials have been included in the
respective sections of Appendix A.
With the water soluble salts and acids, optimization included varying
concentrations, or combinations of materials. With the water base
latexes, several anionic surfactants were investigated, along with the
use of wet and dry specimens. Although the use of the surfactants did
not necessarily improve the corrosion resistance, the surfactants did
improve the bonding of some latexes to the concrete. Dry concrete
specimens generally caused the gellation of a thicker latex film than did
the wet specimens. When applying the latexes as a coating over the dry
specimens, there appeared to be more pinholing on the initial coat due
to the escape of the air, whereas with the wetted specimens, this
problem was not as pronounced. This is of definite benefit when consider-
ing the coating of installations in-place since the walls in these instal-
lations are usually damp or wet from condensate or capillary water.
One technique that proved useful in the coating applications -was the use
of multiple coatings for both the water base and solvent base latexes.
This included the use of a primer coat followed by one or more layers
of the latex coat. In most cases a primer coat of nitrile-phenolic latex
improved adhesion of the finish coat. With the multiple coatings, two
layers were better than one, and three appeared to be the optimum. While
the corrosive attack with single coatings was not always measurable, pin-
holes did appear, whereas additional coatings eliminated them completely.
One other technique that improved the performance of some coatings was
the use of filler material, particularly plate-shaped particles such as
talc.
In addition to the techniques already mentioned, when using the hot melts,
particularly asphalt and coal tar, heated and room temperature specimens
were employed. The heated specimens allowed for more drainage and
thus thinner coatings, particularly at the sharp edges. As a result the
33
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room temperature specimens had thicker coatings and better corrosion
resistance.
A double treatment employing two promising systems was also investi-
gated. Hence, specimens treated with HF were also impregnated with
sulfur and coal tar. Other specimens were impregnated with sulfur
for the strength improvement and then coated with latex. The double
treatment, although more costly than a single treatment, was definitely
better and should be considered where extremely severe conditions
might be expected. Table 2 lists the most promising double treatments
investigated.
Of the materials investigated on this program, sulfur was the most
promising material that imparted considerable strength improvement to
the concrete. Since both sulfur and the concrete pipe must be heated in
order to obtain impregnation, experiments were conducted wherein the
optimum times, temperatures and conditions were determined for optimum
strength.
The first consideration when heating concrete to elevated temperatures
is the age of the concrete itself. Even though concrete pipe has cured
sufficiently in one day to be handled and moved, the strength continues
to grow with time. Usually the nominal strength is obtained within several
days as shown in Figure 10. It is interesting to note that even though the
strength of the pipe has plateaued at about five days, considerably better
strengths were obtained by impregnating with sulfur only after 20 days.
The specimens used for the 180 day test are from a different batch of
pipe, however, from the data, this appears to be of little significance.
The second consideration was that of the temperature at which impregna-
tion would be carried out. Previous investigations using elemental sulfur
(18, 19) have shown that the time - temperature history of the sulfur is
very important in obtaining optimum mechanical properties. For example,
in one study it was found that the maximum tensile strength was obtained
from specimens prepared at approximately 150 °C. This phenomenon has
been related to the allotropic modifications of sulfur under these temper-
ature conditions. To determine the effects of temperature on the impreg-
nated concrete, the temperature of the sulfur was varied between 130 °C
(slightly above the melting point of sulfur) and 160°C (the temperature at
which sulfur becomes very viscous. ) This data is presented in Figure 11.
The maximum strength is obtained at approximately 150 °C.
The final consideration of impregnating with sulfur is the process conditions
necessary for impregnation. The use of vacuum or partial vacuum
34
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TABLE 2
PERFORMANCE OF SELECTED DOUBLE-TREATED SPECIMENS
After Exposure tolO%H2so4
Specimen
68 HF Impregnated
followed by Coal Tar
Impregnation
69 HF Impregnated
followed by Sulfur
Impregnation
131 Sulfur Impregnated
coated with Vinyl-
Vinylidene Chloride
132 Sulfur Impregnated
coated with Nitrile-
Phenolic Latex
133 Sulfur Impregnated
coated with Rubber
Adhesive
134 Sulfur Impregnated
coated with Reclaimed
Rubber Emulsion
135 Coal Tar over Primer
Coat
Wt. Loss
(g)
+ 1.9 *
+ 2.6
+2.5
Scaling
(in. /day)
0
Flexural Strength
(psi)
2300
2080
* Plus Sign Indicates Wt. Gain
** Dash Line Indicates No Data Taken
35
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necessarily limits a process to a batch type operation. Pressure, how-
ever, can be related to a liquid pressure head, and if one envisions a
deep vat filled with impregnating liquid, the pipe can be submerged to
an appropriate depth for a specific period of time and be automatically
placed and removed, as with a conveyor belt. To determine the effect
of pressure only, specimens were submerged under liquid sulfur and
then an air pressure of 30 psig was applied for time periods ranging
from 5 to 30 minutes. The quantity of sulfur impregnated into the
concrete as well as the flexural strength was then determined and is
reported in Table 3. From the data, although there was a continual
increase in sulfur absorbed by the concrete, the strength is fairly
constant, indicating that 5 to 10 minutes under this pressure is sufficient.
For operation at a lower pressure head, a longer impregnation would no
doubt be required.
38
-------
TABLE 3
ABSORPTION AND STRENGTH OF SULFUR IMPREGNATED
CONCRETE PIPE AT 30 psig PRESSURE
Time , Absorption Flexural Strength
(min. ) (%) (psi)
5 7.4 2120
10 7.4 1730
15 7.7 2080
20 8.0 2020
25 8.4 1810
30 8.9 2530
39
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SECTION VIII
PRELIMINARY FIELD TESTS
Once several promising materials had been developed, it was decided
that limited experiments would be conducted in active sewer lines. While
acid attack was readily simulated in the laboratory on an accelerated rate,
correlation with that experienced in a sewer line is difficult. For example,
films and coatings can be totally impermeable to liquids, but not to gases.
Thus it was possible that even though the coatings investigated showed
excellent resistance to sulfuric acid, when subjected to a sewer environ-
ment the hydrogen sulfide, water vapor, and air, could penetrate these
coatings and cause corrosion behind the coating. Another unknown was
the effect that bacteria would have on the treatments, particularly sulfur
and the latex coatings.
Eight specimens were prepared and placed in an influent diversion box at
Harlingen, Texas on November 6, 1970. The gases in this diversion box
are extremely corrosive and this particular box had just been rebuilt
because of failure by concrete corrosion. The eight specimens placed in
Harlingen were prepared from six inch inside diameter concrete pipe
and were each approximately six inches in length. The weights were re-
corded before being suspended in the diversion box. A brief description
of each specimen follows:
A. Control
B. Coated with a water emulsified reclaimed rubber
C, Coated with nitrile-phenolic rubber diluted 30% with toluene
D. Coated with a synthetic rubber adhesive in a solvent system
E. Coated with a vinyl acetate-acrylic copolymer in a water
emulsion.
F. Coated with a vinyl chloride-vinylidene chloride copolymer
in a water emulsion
G. Impregnated with elemental sulfur
H. Chemically treated with a 5% hydrofluoric acid solution
41
-------
On February 15, 1971 one additional specimen was placed in Harlingen.
This specimen was impregnated with sulfur containing 0. 5% by weight
sodium pentachlorophenate, an effective bactericide for sulfur. (20)
On December 8, nine specimens were placed in a siphon station in the
southeast part of San Antonio which has had a long history of hydrogen
sulfide corrosion. The concrete interior of this station is badly corroded
from the corrosive gases. The specimens -were placed on a walkway
above the liquid level but condensate collects readily on the walls, the
walkway, and the specimens. The nine specimens placed in San Antonio
were prepared from 6-in. inside diameter concrete pipe and were each
approximately 6 in. in length, and with the exception of the ninth specimen,
were identical to those prepared for the Harlingen site.
A. Control
B. Coated with a water emulsified reclaimed rubber
C. Coated with nitrile-phenolic rubber diluted 30% with toluene
D. Coated with a synthetic rubber adhesive in a solvent system
E. Coated with a vinyl acetate-acrylic copolymer in a water
emulsion
F. Coated with a vinyl chloride-vinylidene chloride copolymer
in a water emulsion.
G. Impregnated with elemental sulfur
H. Chemically treated with a 5% hydrofluoric acid solution
I. Coated with a reclaimed rubber-solvent system
Also, on December 8, 1970, three specimens were submerged in one of
the active septic tanks on the Institute grounds. These specimens were
prepared from 6-in. inside diameter concrete pipe and were approximately
3 in. in length. The first specimen was a control, the second specimen
was impregnated with elemental sulfur, while the third specimen was
impregnated with elemental sulfur containing 0. 5% by weight of the bac-
tericide sodium pentachlorophenate. The purpose of these tests was' to
determine the relative attack of the bacteria on concrete impregnated
with sulfur and the effect of bactericide in a sulfur system. It would appear
42
-------
that a bactericide is a simple solution to the bacterial attack on sulfur
experienced in the past. (20-22)
Within one week, the concrete control in the septic tank began to
discolor, indicating a chemical reaction occurring between constituents
in the concrete and the sewage. A check of the specimens in the siphon
station in San Antonio indicated this same reaction with the concrete
control was occurring in the air space, although not as severe. Subsequent
inspection revealed identical staining of the control specimen in Harlingen.
Hydrogen sulfide or soluble sulfide salts were suspected and subsequent
laboratory experiments confirmed this. Concrete specimens were sub-
jected to a 10% solution of sodium sulfide as well as to a hydrogen sulfide
gas atmosphere. The discoloration or staining was observed in each
instance and is attributed to a reaction between the sulfide and iron present
in the cement. When submerged in a 10% sodium sulfide solution for 3
days, discoloration occurred throughout the specimen. When suspended
in a hydrogen sulfide gas atmosphere for one week, staining had penetrated
to an average depth of 0.12 in. , but in some areas as much as 0. 25 in.
To test the theory that an impregnant, by blocking the voids, should
eliminate penetration of liquid or gas, one specimen impregnated with
sulfur was submerged one week in a 10% solution of sodium sulfide. Cut-
ting the specimen revealed that only the surface of the specimen was dis-
colored, and penetration of the liquid had not taken place. Likewise a
specimen impregnated with sulfur suspended in a hydrogen sulfide gas
atmosphere showed only slight discoloration on the surface but no penetra-
tion. Figure 12 is a photograph showing the staining and protection afford-
ed by impregnation, when subjected to a 10% sodium sulfide solution. The
specimen on the left is a concrete control, while the center specimen,
which is the concrete control submerged in sulfide solution, shows the
discoloration throughout the cross-sectional area. The specimen on the
right shows a surface staining but the cross-sectional area is unstained,
indicating that the sulfur blocked the pores and eliminated penetration.
Although the specimens were exposed in the field tests for approximately
four months, they were winter months when acid generation is at a min-
imum. The concrete control specimen in Harlingen is beginning to show
signs of corrosion. The entire specimen is covered with a white, frangible
efflorescent coating typical of sulfate formation. The control in the siphon
station in San Antonio is showing slight efflorescence and one specimen
coated with the vinyl-vinylidene chloride emulsion has several pinholes.
All other specimens in San Antonio and Harlingen are showing no signs of
corrosion.
43
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SECTION IX
SIGNIFICANCE OF LABORATORY AND FIELD FINDINGS
As described in detail earlier, 10% sulfuric acid causes the most severe
attack on concrete. Typical maximum concentrations of approximately
5% as found in sewers are also severe. As severe as this attack is,
however, it is tempered by the fact that although maximum concentra-
tions of 5% have been measured in sewers, during the cooler months this
concentration drops considerably so that the most severe attack reported
(3) in sewers is approximately 1/2 in. /yr. (0. 0014 in. /day) wall loss,
very nearly the same as that of limited laboratory tests of a 1% solution
of sulfuric acid with scaling rates of approximately 0. 0015 in. /day. If
further correlation studies can indeed verify that a 1% sulfuric acid
solution can simulate the most severe attack encountered in sewer lines,
then a very valuable laboratory tool will have been established for deter-
mining and predicting sewer pipe life.
The second interesting point as relates to sulfuric acid attack in labor-
atory tests is the fact that for all concentrations the attack is limited to
the surface. Attempts using vacuum and pressure failed to cause any
sulfuric acid to penetrate the concrete any deeper than 1/8 in. from the
surface. This is attributed to the fact that the sulfate and sulfo-aluminate
products have larger crystal volumes than the reactants and as such tend
to seal or block the passages. As this protective coating falls away, the
attack progresses into the specimen. Figure 13 shows the surface attack
typical of sulfuric acid action in the laboratory test. Limited specimens
taken from sewers indicate this type of attack is also typical of the attack
found in some concrete sanitary sewers.
Hydrogen sulfide or sulfide solutions readily penetrate concrete. To
what extent this plays in the corrosion process has not been determined.
References to this occurance have not been uncovered in the literature.
The fact that sulfuric acid seals the surface, may eliminate or minimize
attack in this manner. The fact that impregnated specimens were not
penetrated by the sulfides is most encouraging.
Another point of major significance relates to the performance of the most
promising systems developed. The scaling rate as determined for the
various systems is a valuable aid since it not only gives an indication of
the relative performance of the different systems, it also allows for a
prediction of the life of the treated pipe of known wall thickness. While
the hazards of predicting pipe life based only on the laboratory findings
45
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are fully realized, it is recognized that the acid test conditions of the
laboratory are much more severe than those encountered in the field.
It must be emphasized that considerably more field data have to be
obtained for good correlations, however, some conservative estimates
can still be made. As already pointed out, the most severe corrosion
measured in a sewer line has been as much as 1/2 in. /yr, or approx-
imately 0. 0014 in. /day. Thus a pipe having a wall thickness of 1 inch
would be consumed in 2 years. This rate of attack is obtained in the
laboratory with a 1% solution of sulfuric acid. When using 10% solutions
of sulfuric acid, the scaling rate for the concrete control averages
0. 0054 in. /day or approximately 3. 8 times greater than the most severe
cases found in sewer lines.
Although most of the better treatments did not have a measurable scaling
rate, as indicated in Tables 1 and 2, continued exposure should produce
a measurable rate after an extended time. For the coating alone, once
the coating has failed, corrosion of the underlying concrete should pro-
ceed at the same rate as unprotected concrete, hence the useful life of
the coating systems is difficult to assess. For the materials with measur-
able scaling rates, however, estimates of useful life can be made.
From Table 1, specimen No. 17, which was impregnated with modified
sulfur, had a laboratory scaling rate of 0. 0005 in. /day. The concrete
control has a laboratory scaling rate of 0. 0054 in. /day. Thus, the sulfur
impregnated pipe is approximately 10 times better than concrete according
to the laboratory tests. Thus, as a conservative estimate, impregnated
pipe with a wall thickness of 1 inch would be consumed in 20 years rather
than 2 years. If the fact is considered that the laboratory tests are 3. 8
times more severe than that of actually measured sewer values, then it
would take 76 years to consume the pipe.
As another example, from Table 1, specimen No. 1, which was impreg-
nated with hydrofluoric acid, has a measurable laboratory scaling rate
of 0. 00017 in. /day or approximately 30 times better than the laboratory
scaling rate of concrete. Thus a pipe of 1 inch wall thickness would be
consumed in 60 years as a conservative estimate, or 228 years using
the factor of 3.8.
Pipe with wall thicknesses greater than one inch would take proportionately
longer to be consumed. The fact that many of the better systems had
scaling rates of 0 after 3 days in 10% sulfuric acid indicates that their
ultimate scaling rate might be better than those used in the two examples
above.
47
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The final point of significance from this program's findings is the
possibility of in-service treating of lines using the hydrofluoric acid
treatment. Essentially this would entail a low pressure acidizing
process very similar to oil and gas well acidizing which is carried out
routinely in the petroleum industry.
48
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SECTION X
ECONOMICS
It is estimated that nearly 90 million linear feet of concrete pipe are
manufactured annually. Its low cost, ease by which it can be manu-
factured and its attractive physical properties all play a role in its
popularity. Whenever pipe other than concrete is used in sewer app-
lications, the additional cost is usually justified because of the improved
corrosion resistance of the other type pipe, although weight consider-
ations can sometimes be important. Figure 14 is a graph showing San
Antonio selling prices for the various types of sewer pipes available.
While selling prices may vary somewhat from locality to locality, these
figures are representative of the relationships between the different
types of sewer pipe. All of the prices reflected in Figure 14 were
obtained from local manufacturers or suppliers, except for the vinyl
chloride lined/epoxy-coal tar lined pipe. This curve area was calculated
by adding to the cost of reinforced concrete pipe $0. 60 to $0. 75 for
materials cost and $0.15 to $0. 25 for labor per square foot of treated
concrete pipe. The material and labor costs were obtained from lining
and pipe manufacturers and reflect typical additional costs. Thus, in
order for impregnated concrete pipe to be accepted, it must have a cost
effectiveness better than the other types of pipe.
In discussing the economics of potential treatment systems the predicted
treatment costs are general figures since further processing studies are
needed to generate firmer economic figures. Nevertheless, these estimates
give a good indication of the relative economics.
To impregnate or treat sewer pipe, two extreme cases have been select-
ed and the economics calculated. The first case envisions a rather simple
automated process, requiring a minimum of hand labor. In this process
the impregnation vat would operate at atmospheric pressure on a contin-
uous automated basis. For the hot melts, this vat would in many ways
resemble a typical sulfur melter or Frasch sulfur mine relay station.
The rectangular pit or tank of steel or concrete would be lined with steam
heating coils of Schedule 80 black steel pipe. Material make-up to the pit
would be supplied from either a molten storage tank or by melting material
on site. One simple design for a sulfur melter consists of laying steam
piping on a concrete apron sloped into the pit. Sulfur or the other materials
would be stockpiled on the apron. When additional material is required,
steam is circulated through the pipes and the melted material drains into
the pit. Temperature of the molten material would be automatically
49
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controlled by regulating the steam pressure. Conveyors could be used
for moving the pipe into and out of the pit. For impregnation materials
not requiring heat, the steam lines would be eliminated. This type
of operation should represent a very low impregnation cost.
The second process assumes almost exclusive hand labor such as
required in autoclaving the pipe on a batch basis. Typical labor costs
are generally a maximum of $0. 25/ft^ of treated surface. This cost
was used in calculating the costs under the hand labor columns in
Table 4. The cost of impregnating concrete pipe with sulfur is report-
ed for both types of processes. The automated column assumes that the
pipe could be handled and treated for essentially the same costs that
the Frasch sulfur producers can mine the sulfur by heating with super-
heated water a massive limestone formation several thousand feet
below ground surface, melt the sulfur, pump it to the surface, store
it, and finally sell it at a profit for $0. 01/lb. This cost should reflect
the projected minimum cost. The maximum projected cost is represent-
ed by having to use hand labor methods of a batch process.
The hydrofluoric acid treatment was viewed essentially as a materials
handling process since heat is not required. The typical selling price
for crushed aggregate is approximately $2. 00/yd3. This includes mining
or blasting, crushing, washing, and screening to specifications. As
seen in Table 4, the hydrofluoric acid impregnation costs are slightly
less but of the same magnitude as those for sulfur impregnation.
The coating costs as represented by the latexes assume hand labor with
spray equipment similar to that currently used in lining concrete pipe,
and were computed for actual film thicknesses used in the laboratory for
adequate acid protection. As can be seen, the labor accounts for the
major portion of the cost. These types of coatings, however, should find
acceptance more readily in treating in-place structures such as treat-
ment tanks, junction boxes, wet wells, etc. More detailed calculations
are reported in Appendix B.
From an economic point of view, impregnation or treatment of concrete
pipe with either sulfur or hydrofluoric acid appears very attractive -with
substantial savings over other types of pipe as well as lined concrete pipe.
From the laboratory studies and preliminary field studies, the projected
service life of these two treatments is certainly encouraging. Because
of these facts, the next major step in this program should be one of
extended field tests, paralleled by continued laboratory study to further
develop a correlation between the laboratory and field data, so that
51
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optimum treatment systems can be developed with predictable service
lives. Once an optimum system is determined, a specific process
design can be undertaken and the economics can be established on a
very accurate basis.
53
-------
SECTION XI
ACKNOWLEDGEMENTS
Test sites provided by the City of Harlingen, Texas and the City of
San Antonio, Texas are gratefully acknowledged. Special appreciation
is due Messrs. L. N. Rice, City Engineer, Harlingen, Texas, H. C.
Norris, Sewer Engineer, City of San Antonio, Donald Carrell, Mission
Concrete Pipe Company, San Antonio, Texas, and Harry T. Peck,
Gifford-Hill Pipe Company, Dallas, Texas for their interest and tech-
nical contributions. Finally, grateful acknowledgment is made to the
many manufacturers and suppliers who provided sample quantities of
their materials for inclusion in this program.
Key Personnel
Allen C. Ludwig, Project Manager and Principal Investigator
Southwest Research Institute
8500 Culebra Road
San Antonio, Texas 78228
Tel: 512 684-2000
John M. Dale, Manager, Systems Development Section
Southwest Research Institute
8500 Culebra Road
San Antonio, Texas 78228
Tel: 512 684-2000
Frank Condon, EPA Headquarters, Project Manager
Combined Sewer Pollution Control Branch
Environmental Protection Agency
Washington, D. C. 20242
Tel: 703 557-7390
George J. Putnicki, Project Officer
Environmental Protection Agency
1402 Elm Street
Dallas, Texas 75202
Tel: 212 749-2161
Robert L. Hiller
Environmental Protection Agency
1402 Elm Street
Dallas, Texas 75202
Tel: 212 749-3842
55
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SECTION XII
REFERENCES
1. Munger, C.G. , "Sewer Corrosion and Protective Coatings",
Civil Engineering. May I960, pp. 57-59.
2. South African Council of Scientific and Industrial Research,
"Corrosion of Concrete Sewers", Series DR 12, 1958.
3. Lea, F. M. and Desch, C.H. , "The Chemistry of Cement and
Concrete", revised ed. Edward Arnold Lts. , London, 1956.
4. Hansen, W. C. , "Attack on Portland Cement Concrete by Alkali
Soils and Waters - A Critical Review", Highway Research Record
No. 113, Highway Research Board, 1966.
5. Kobbe, W. H. , "New Uses for Sulfur in Industry", Ind. and Eng.
Chem. , Vol. 16, No. 10, October 1924, p. 1026.
6. Kessler, D. W. , "Sulphur Impregnated Sandstone", Stone, Vol.
XLV, No. 6, June 1924, p. 347.
7. Steinberg, M. , et. al. , "Concrete-Polymer Materials, First
Topical Report", BNL SO134(T-509), December 1968.
8. Steinberg, M. , et. al. , "Concrete-Polymer Materials, Second
Topical Report", BNL 50218(T-560), December 1969.
9. Kukacka, L. E. , Steinberg, M. , and Manowitz, B. , "Preliminary
Cost Estimate for the Radiation-Induced Plastic Impregnation of
Concrete", BNL-11263, April 1967.
10. Ludwig, A. C. , "Utilization of Sulphur and Sulphur Ores as
Construction Materials in Guatemala", United Nations Report
No. TAO/GUA/4, July 19 69.
11. Ocrate Journal, N. 5, January 1965.
12. ACI Committee 515, "Guide for the Protection of Concrete Against
Chemical Attack by Means of Coatings and Other Corrosion-
Resistant Materials", Proc. J. A. C. I. , Vol. 63, No. 12, December
1966.
57
-------
13. Jumper, C.H. , "Tests of Integral and Surface Waterproofings
for Concrete", Bur. Standards J. Research, Vol. 7, 1931,
pp. 1147-77.
14. Kessler, D. W. , "Experiments on Exterior Waterproofing Materials
for Masonry", J. Res. Nat'l. Bureau Standards, Vol. 14, 1935
pp. 317-43.
15. Meyer, A. H. , and Ledbetter, W. B. , "Sulfuric Acid Attack on
Concrete Sewer Pipe", J. of Sanitary Engr. Div. , ASCE, October
1970, pp. 1167-82.
16. Schremmer, H. , "Attacking of Concrete by Hydrogen Sulphide",
Ocrate Journal, No. 5, January 1965.
17. Caudy, A. F. , Jr. , "Studies on the Resistance to Corrosion of
Ocrated Concrete", Project Report, A. F. Gaudy, Jr. and Associates,
Stillwater, Oklahoma.
18. Dale, J. M. , and Ludwig, A. C. , "Mechanical Properties of Sulfur
Allotropes", Materials Research and Standards, Vol. 5, No. 8,
August 1965, pp. 411-417.
19. Ludwig, A. C. , and Dale, J. M. , "Determination of the Mechanism
Whereby Sjj. Affects the Mechanical Properties of Sulphur", Final
Report, Southwest Research Institute, San Antonio, Texas.
20. Frederick, L. R. , and Starkey, R. L. , "Bacterial Oxidation of
Sulfur in Pipe Sealing Mixtures", J. Amer. Water Wks. Assoc. ,
Vol. 40, No. 7, July 1948, pp. 729-36.
21. Duecker, W. W. , et. al. , "Studies of Properties of Sulfur Jointing
Compounds", J. Amer. Water Wks. Assoc. , Vol. 40, No. 7,
July 1948, pp. 715-28.
22. Bates, P. H. , "The Use of Sulfur in Rendering Cement Drain Tile
Resistant to the Attack of Alkali", Ind. and Eng. Chem. , Vol. 18,
No. 3, March 1926, pp. 309-10.
58
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SECTION XIII
APPENDICES
Page
A. Part A - Water Soluble Salts and Acids 61
Part B - Water Base Latexes 62
Part C - Solvent Base Latexes 65
Part D - Resins 66
Part E - Hot Melts 69
B. Detailed Materials Cost and Impregnation 73
or Coating Costs
59
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APPENDIX A
Properties and Corrosion Resistance of
Impregnated Concrete
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Detailed Materials' Cost and Impregnation or
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5
Accession Number
r\ Subject Field & Group
08G
SELECTED WATER RESOURCES ABSTRACTS
INPUT TRANSACTION FORM
Organization
Snntriwe>st Rf>sparrK Institute
San Antonio, Texas
Title
IMPREGNATION OF CONCRETE PIPE,
10
Authors)
Ludwig, Allen C.
Dale, John M.
16
Project Designation
Contract #14-12-835
Program 11024 EQE
21 Note
22
Citation
23
Descriptors (Starred First)
,*
Concrete, Concrete pipes, Corrosion, Corrosion control,
Protective coatings, Sewers, Sulfur,* Hydrogen sulfide,
Resins
25
Identifiers (Starred First)
Impregnation, Hydrofluoric acid, Acid resistance, Bacterial
action, Sulfate resistance
27
Abstract
Methods to increase the corrosion resistance, increase the strength,
and reduce the permeability of concrete used in sewer line applications by im-
pregnating the concrete pipe with relatively low cost resins such as asphalt,
coal tars, linseed oil, sulfur, urea-formaldehyde, and others •were investigated.
The materials, techniques of application, test results and economics
are presented. A large number of candidate impregnation materials were ob-
tained and screened both in the laboratory and in limited field tests. Dilute
hydrofluoric acid, sulfur and modified sulfur were found to impart the best
corrosion resistance by impregnation. Other materials including vinyl-
vinylidene chloride, vinyl acetate-acrylic, nitrile rubber latex, nitrile phenolic
rubber, an emulsified reclaimed rubber and a rubber base adhesive, although
failing to impregnate the concrete, formed surface coatings having exceptional
corrosion resistance.
This report was submitted in fulfillment of Program No. 11024 EQE,
Contract No. 14-12-835 under the sponsorship of the Water Quality Office,
Environmental Protection Agency. (Ludwig-Southwest Research Institute)
Abstractor
A. C. Ludwig
Institution
Southwest Research Institute
WR:I02 (REV JULY 1969)
WRSIC
SEND TO:
WATER RESOURCES SCIENTIFIC INFORMATION CENTER
U.S DEPARTMENT OF THE INTERIOR
WASHINGTON. D C 20240
* GPo: 1989-359-339
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Continued from inside front cover....
11022
11023
11020
11023
08/67
09/67
12/67
05/68
11031 08/68
11030 DNS 01/69
11020 DIM 06/69
11020 DES 06/69
11020 06/69
11020 EXV 07/69
11020 DIG 08/69
11023 DPI 08/69
11020 DGZ 10/69
11020 EKO 10/69
11020 10/69
11024 FKN 11/69
11020 DWF 12/69
11000 01/70
11020 FKI 01/70
11024 DOK 02/70
11023 FDD 03/70
11024 DMS 05/70
11023 EVO 06/70
11024 06/70
11034 FKL 07/70
11022 DMU 07/70
11024 EJC 07/70
11020 08/70
11022 DMU 08/70
11023 08/70
11023 FIX 08/70
11024 EXF 08/70
Phase I - Feasibility of a Periodic Flushing System for
Combined Sewer Cleaning
Demonstrate Feasibility of the Use of Ultrasonic Filtration
in Treating the Overflows from Combined and/or Storm Sewers
Problems of Combined Sewer Facilities and Overflows, 1967
(WP-20-11)
Feasibility of a Stabilization-Retention Basin in Lake Erie
at Cleveland, Ohio
The Beneficial Use of Storm Water
Water Pollution Aspects of Urban Runoff, (WP-20-15)
Improved Sealants for Infiltration Control, (WP-20-18)
Selected Urban Storm Water Runoff Abstracts, (WP-20-21)
Sewer Infiltration Reduction by Zone Pumping, (DAST-9)
Strainer/Filter Treatment of Combined Sewer Overflows,
(WP-20-16)
Polymers for Sewer Flow Control, (WP-20-22)
Rapid-Flow Filter for Sewer Overflows
Design of a Combined Sewer Fluidic Regulator, (DAST-13)
Combined Sewer Separation Using Pressure Sewers, (ORD-4)
Crazed Resin Filtration of Combined Sewer Overflows, (DAST-4)
Stream Pollution and Abatement from Combined Sewer Overflows -
Bucyrus, Ohio, (DAST-32)
Control of Pollution by Underwater Storage
Storm and Combined Sewer Demonstration Projects -
January 1970
Dissolved Air Flotation Treatment of Combined Sewer
Overflows, (WP-20-17)
Proposed Combined Sewer Control by Electrode Potential
Rotary Vibratory Fine Screening of Combined Sewer Overflows,
(DAST-5)
Engineering Investigation of Sewer Overflow Problem -
Roanoke, Virginia
Microstraining and Disinfection of Combined Sewer Overflows
Combined Sewer Overflow Abatement Technology
Storm Water Pollution from Urban Land Activity
Combined Sewer Regulator Overflow Facilities
Selected Urban Storm Water Abstracts, July 1968 -
June 1970
Combined Sewer Overflow Seminar Papers
Combined Sewer Regulation and Management - A Manual of
Practice
Retention Basin Control of Combined Sewer Overflows
Conceptual Engineering Report - Kingman Lake Project
Combined Sewer Overflow Abatement Alternatives -
Washington, D.C.
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