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
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