United States
Environmental Protection
Agency
Atmospheric Sciences Research —*f.
Laboratory
Research Triangle Park NC 27711
Research and Development
EPA/600/S3-85/011 Apr. 1985
f/EPA Project Summary
Effects of Acid Deposition on the
Properties of Portland Cement
Concrete State-of-Knowledge
R. P. Webster and L. E. Kukacka
Presented are the results of a program
conducted to determine the state-of-
the-art knowledge pertaining to the
effects of acid deposition on the proper-
ties of Portland cement concrete struc-
tures. Information was collected from a
computerized literature survey, inter-
views, and replies to mail and telephone
inquiries addressed to cement and
concrete researchers and to govern-
mental agencies and private firms active
in the maintenance and restoration of
concrete structures. In general, the
study revealed very little qualitative or
quantitative information on the effects
of acid deposition on portland cement
concrete structures. The rate of deteri-
oration of reinforced portland cement
concrete structures in polluted areas,
however, appears to be increasing, and
available information makes it readily
apparent that acids and acid waters
significantly affect the durability of
concrete, and that SO2, NOX, and HCI
accelerate the corrosion of reinforcing
steel.
This Project Summary was developed
by EPA's Atmospheric Sciences Re-
search Laboratory, Research Triangle
Park, NC, to announce key findings of
the research project that is fully docu-
mented in a separate report of the same
title (see Project Report ordering infor-
mation at back).
Introduction
As part of the National Acid Precipi-
tation Assessment Program (NAPAP)
Task Force project G3-1.05, sponsored by
the U.S. Environmental Protection
Agency/ Atmospheric Sciences Research
Laboratory (EPA/ASRL), Brookhaven
National Laboratory (BNL) conducted a
program entitled "Effects of Acid Deposi-
tion on the Properties of Reinforced
Portland Cement Concrete Structures."
The objectives of the program were (a) to
determine the state-of-the-art knowledge
pertaining to the effects of acid deposition
on the properties of portland cement
concrete (PCC), and (b) if the results
indicated a need for quantitative data, to
develop recommendations for an experi-
mental test program to be submitted for
Task Group G approval and implementa-
tion.
Information for the state-of-the-art
review was obtained from a computerized
literature survey, interviews, and replies
to mail and telephone inquiries addressed
to cement and concrete researchers and
to governmental agencies and private
firms active in the maintenance and
restoration of concrete structures.
Results of Survey
In general, the computerized literature
survey indicated that an abundance of
literature on acid precipitation is avail-
able, but most of it deals with the
chemistry of acid precipitation and its
effects on the natural environment. Liter-
ature dealing with the effects of acid
deposition on buildings and building
materials does exist; however, very little
of it pertains to cement or concrete. The
information that was found regarding the
effects of acid deposition on buildings and
building materials indicates that the
increasing acidity of precipitation en-
hances normal weathering and corrosion
processes. In addition, private communi-
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cations indicated that a rapidly increasing
number of reinforced concrete structures
in cities are showing deterioration which
the respondents attributed to S02, NO,,
andHCI.
Because the literature on the effects of
acid deposition on PCC is limited, the
large amount of literature dealing with
the corrosive effects of acids, acid waters,
and sulfates on concrete was reviewed in
an attempt to estimate the effects of acid
deposition on PCC. This review indicated
that acid solutions generally attack con-
crete in a combination of four ways: (a) by
dissolving both hydrated and unhydrated
cement compounds present in the cement
paste; (b) by dissolving calcareous aggre-
gates present m the composite; (c) through
physical stresses induced by sulfate and
nitrate salts crystallized within the pore
structure; and (d) by salt-induced corro-
sion of the reinforced steel.
The first two forms of attack involve the
same mechanism: the leaching away of
water-soluble salts formed by reaction of
the acid with the calcium compounds
present in the cement paste and aggre-
gate. This is one of the major mechanisms
of the deterioration of many ancient
statues, monuments, and buildings made
with calcareous building stone in and
near industrialized areas of Europe.
The latter two forms of attack involve
the development of stresses within the
pores of the cement paste or aggregate
which eventually cause the concrete to
crack or spall. These stresses result from
the crystallization of salts that have
accumulated beneath the surface of the
concrete or from salt-induced corrosion
of the reinforcing steel.
In addition to the forms of deterioration
identified above, the cracking and spading
of concrete due to acid-induced corrosion
can also lead to and accelerate other
forms of deterioration, most notably
freeze-thaw deterioration.
The literature review concentrated on
the effects of three specific pollutants,
carbon dioxide, sulfur dioxide, and nitro-
gen oxides.
Carbon dioxide was found to affect
concrete in two ways, through carbona-
tion of the concrete surface and carbonic
acid attack. The carbonation of the con-
crete surface results in a decrease of the
pH value of the cement paste, which
eventually leads to the corrosion of the
reinforcing steel near the surface. Car-
bonic acid attack primarily results in the
leaching of calcium hydroxide from the
surface and interior of the concrete.
Sulfur dioxide, when dry, has little or no
effect on dry concrete. It does, however,
combine with water and oxygen to form
sulf urous and sulf uric acid, both of which
will attack concrete. Sulfuric acid attacks
concrete (a) by converting calcium car-
bonate to gypsum, which is subsequently
leached away; and (b) by reacting with
calcium compounds to form salts which
crystallize; the crystallization produces
enormous stresses within the pores of
the cement paste, which eventually lead
to spelling and cracking. The latter form of
attack is commonly known as sulfate
attack.
Very little information was available
regarding the effects of nitrogen oxides
on concrete. They do, however, react with
water or, as ammonia, with oxygen to
form nitrous and nitric acid. Nitric acid is
not as strong as sulfuric acid; however, it
is destructive enough to bring about
extensive deterioration, even in highly
diluted solutions, primarily through the
transformation of calcium hydroxide into
highly soluble calcium nitrate.
None of the individuals and organiza-
tions responding to the mail and telephone
inquiries was aware of any documented
information dealing specifically with the
effects of acid deposition on PCC struc-
tures, or of any research that had been or
was being done in this area. Comments
on the need for such research were
varied: some respondents thought it was
needed because the large volume of
concrete structures in the United States
could present a potentially large problem;
others thought the need for such research
was open to question because they
considered other mechanisms of deteri-
oration to be more important.
Conclusions
The study revealed very little qualitative
or quantitative information on the effects
of acid deposition on PCC structures. The
rate of deterioration of reinforced PCC
structures in polluted areas, however,
appears to be increasing, and available
information makes it readily apparent
that acids and acid waters significantly
affect the durability of concrete, and that
S02, NOX, and HCI accelerate the corro-
sion of reinforcing steel.
On the basis of this evidence, it is
recommended that an experimental test
program, consisting of both laboratory
and field tests, be developed and imple-
mented to quantitatively measure the
effects of acid deposition on PCC struc-
tures. It is, however, recommended that a
preliminary series of accelerated labora-
tory tests be carried out before a full-scale
field evaluation program is instituted. The
objectives of the laboratory test progra
should be to identify the magnitude of tf
problem and to attempt to differentia
between the effects of wet deposition, d
deposition, and normal weathering.
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R. P. Webster and L. E. Kukackaare with Brookhaven National Laboratory, Upton,
NY 11973.
John W. Spence is the EPA Project Officer (see below).
The complete report, entitled "Effects of Acid Deposition on the Properties of
Portland Cement Concrete. State-of-Knowledge," {Order No. PB 85-171
452/AS; Cost: $8.50, subject to change) will be available only from:
National Technical Information Service
5285 Port Royal Road
Springfield, VA 22161
Telephone: 703-487-4650
The EPA Project Officer can be contacted at:
Atmospheric Sciences Research Laboratory
U.S. Environmental Protection Agency
Research Triangle Park, NC 27711
US GOVERNMENT PRINTING OFFICE 1985-559-016/27029
United States
Environmental Protection
Agency
Center for Environmental Research
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