response of concrete to sulfuric acid attack

7/29/2019 Response of Concrete to Sulfuric Acid Attack

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I MATERIALS JOURNAL TECHNICAL PAPER

of Concrete to Sulfuric Acid Attack

K. Attiogbe and Sami H. Rizkallaoj our different concrete mixes to sulfuric acid attackin an accelerated laboratory test program. Small test

cut from standard concrete cylinders and a 1 percent sulpH oj J were used in the test program.

in weight and thickness of the test specimens were used as0/ the degree of deterioration, while increase inof the test specimens was used as a chemical indicator

of deterioration .study shows that all three indicators of deterioration are effec

oj concrete response to the acid attack. However, thesuggests that the increase in thickness (expansion) of small

may be a moreof larger specimens when

of different sulfuric acid concentrations onof the concrete microstructure show that

from the acid-exposed surface andes inward. The degree of concrete deterioration is increased

of exposure to sulfuric acid. The rate ofof sulfuric acid

be described by a variation in sulfur concentration with theof acid penetration.

is susceptible to attack by sulfuric acid proor sulfur dioxide present in

of industrial cities. This attack is due toof portland cement concrete, which

as well. Sulfuric acid issulfate attack, in addition to the dissolution

as a result of the sulfuric acid-cement pasteof concrete

of the chemicalof deterioration.previous studies, weight loss, reduction in com

ofof concrete

to sulfuric acid attack. 2.' These studindicate that damage starts at the surface of the

ofof penetration of acid is not

I November-December 1988

clearly defined. This information is necessary to accurately estimate the minimum thickness of the concretecover in reinforced concrete structures or to adequatelydesign for sacrificial layers in concrete structures exposed to sulfuric acid solutions .As expected, the previous studies have generallyshown that weight loss of the test specimens increaseswith a decreasing pH level of the acid solutions . However, in a recent study,' a solution with a pH of 3 produced a greater weight loss than one with a pH of 2.This apparent anomaly needs to be resolved for an adequate comparison of the resistance of different concrete mixes to acid attack.The present study is aimed at evaluating the responseof different concrete mixes to sulfuric acid attack, using both physical and chemical indicators of the degreeof deterioration . An accelerated laboratory test program was conducted. The program involved alternateacid immersion and drying of test specimens, as well ascontinuous acid immersion of other test specimens.Changes in weight and thickness of the test specimenswere used to evaluate the physical degree of deterioration of the concrete, while the increase in sulfur content of the test specimens, as measured with a scanningelectron microscope (SEM) equipped with an energydispersive x-ray analyzer, was used to evaluate thechemical change in the concrete. Photomicrographs ofthe test specimens were used to study the extent of theacid attack.

RESEARCH SIGNIFICANCEThis research sheds new light on the mechanism ofsulfuric acid attack on concrete . The experimentaltechniques used in the study provide information on theextent of damage that occurs in concrete as a result ofacid attack. Photomicrographs show the nature of the

Received Oct. 14 , 1987, and reviewed under Institute publication policies.Copyright 198B, American Concrete Institute. All rights reserved, includingthe making of copies unless permission is obtained from the copyright propri etors. Pertinent discussion will bc published in the Septemb er-October 1989 AC IMaterials Journal if received by June I, 1989.481


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ACI member Emmanuel K. Attiogbe is a research associate at the University0/ Manitoba, Canada. He received the BSc degree from the University of Science and Technology in Ghana and his MS and PhD degrees in civil engineer-ing from the University 0/ Kansas. His research interests include durability andmicromechanics of concrete.A CI member Sami H. Rizkalla is an associate professor and the head of theStructures Division of the Civil En gineering Department at the University ofManitoba, Canada. He received the BSc degree/rom Alexandria University inEgypt and MS and PhD degre es from Nor th Carolina State University. He is amember of ASCE, PCI, and CSCE. He is also a member of the ExecutiveCommittee of the Structures Division Of the Canadian Society of Civil Engi-neers. His research activilies are in the areas of reinforced and prestressed con-crete structures .

Table 1 - Characteristics and composition ofthe concrete mixesMix numher

Concrete components M1 M2 M3 M4Coarse aggregate, lh / yd l 1600 1600 1600 1600Fine aggregate, lb/yd! 1400 1400 1400 1400Wa ter , tb / yd l 310 310 310 310Type 10 cement, lh/yd! 540 540 540 -(ASTM Type I)Type 50 cement, lh / yd ! - - - 540(ASTM Type V)Waterreducing agent, oz - 22 - -Superplasticizer, oz 65 65 65 65Air-entraining agent, oz - - 7 -Slump, in. 7.0 8.0 7.0 6.5Air content, percent - - 6.0 -Average 28 day compressive 5640 4670 5220 6230strength, psiNote: 1 Ib/yd! _ 0.593 kg / m!; I oz = 29.6 mI; I pSI - 6.895 kPa; I m. -25.4 mm.

acid damage to the cement paste matrix of concrete.The study shows that the increase in thickness (expansion) and the increase in sulfur content of concretespecimens are good indicators of the degree of deterioration. The effect of wet-dry cycles of concrete exposure to sulfuric acid was investigated.

EXPERIMENTAL PROGRAMMaterials and test proceduresThe experimental progra m utilized four different

concrete mixes. Three of the mixes were made withCSA Type 10 (ASTM Type J) portland cement, whileone mix was made with CSA Type 50 (ASTM Type V)portland cement. A water-reducing agent was used inone mix and an air-entraining agent was used in another mix. A superplasticizer was used in all mixes toincrease slump. Siliceous fine aggregate and a blend ofcalcareous and siliceous coarse aggregate were used.The characteristics and composition of the differentconcrete mixes are shown in Table 1.Standard 152 x 305 mm (6 x 12 in.) concrete cylinders were made from each concrete mix. The cylinderswere moist-cured for 28 days. At the end of the curingperiod, two cylinders were used to determine the compressive strength of each concrete mix. To inducestresses similar to those that exist in concrete under service load conditions, a third concrete cylinder for eachmix was loaded to 40 percent of the compressive482

strength. From this cylinder, small test specimens werecut and used in the acid attack test program.Test specimens-The test specimens for each concrete mix were obtained as follows. A disk approxi mately 6 mm (\I.i in.) thick was cut near the midheightof each cylinder. Each disk was then cut into small 12mm (y, in .) wide specimens . The final prismatic testspecimens, approximately 100 mm (4 in .) long x 12 mm(V, in .) wide and 6 mm (\I.i in .) thick, were used toevaluate the sulfuric acid resistance of the concretemixes. A total of six test specimens were used for eachconcrete mix: two for periodic physical measurements,two for continuous immersion in the acid solution, andthe remaining two for microscopic examination. Thetest specimens were oven-dried to a constant weight for24 hr at about 100 C, and their weights and thicknesseswere measured prior to the start of the acid attack testprogram . The weight was measured using a balancewith a 0 .01 g sensitivity; the thickness was measuredwith a pair of calipers . The average thickness for threelocations along the length was recorded for each specimen. These locations were marked with waterproof inkfor subsequent thickness measurements following periodic immersion of the specimens in the acid solutions .The marks were retouched after taking measurements.

Additional test specimens for Mix MI were coveredwith two coatings and used in the acid attack test program . These coatings were applied to the test specimens with a brush and allowed to air dry for 2 days before being immersed in the acid. The first coating, amethyl methacrylate sealant, provided a visible layerabout I mm (0.04 in) thick on the surface of the testspecimens, while the second coating, an acrylic sealer,penetrated without any visible layer on the surface ofthe test specimens.

Sulfuric acid solutions-The test specimens were immersed in jars filled with 'equal quantities of I percentsulfuric acid solutions (pH = I). This concentration ofsulfuric acid is representative of that found in sewersthat are in the process of deterioration.'7The pH levelsof the acid solutions were monitored at an average interval of 2 days with a portable pH meter. All solutionswere replaced with fresh I percent solutions if the pHof any solution exceeded a value of 1.1. All solutionswere also replaced prior to reimmersion of the testspecimens after taking measurements. The periodic useof fresh acid solutions along with the use of small testspecimens provided an accelerated evaluation of theacid resistance of the concrete mixes . The test programwas concluded after about 10 weeks when some of thetest specimens completely disintegrated in the acid solutions.Test measurements- Measurements of the test specimens were performed after selected periods of immersion in the acid. The test specimens for weight andthickness measurements, as well as those for SEM examination, were removed from the acid, immersed infresh water several times , and oven-dried to a constantweight for 24 hr. Upon removal from the oven, the twotest specimens of each mix that had been marked forACI Materials Journal I November-December 1988


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1 - SEM specimen as mounted on stud

Scanning electron microscope (SEM) examinationof each concrete mix, small

(\4 in.) thick12 mm (\I, in.) long x 6 mm (\4 in.) high, were pre

of the test specimens that had beenas mounted on a stud, is shown in Fig. I. To ob

of theof aluminum about 0.02 p.m thick. No conductiveenergy-disper.

Photomicrographs were taken of both unattacked-attacked specimens. Quantitative elementalof the specimens was performed at a magnifi

of 500X, using computer software available on.sulfur contentof primary interest in this analysis. The elemental

at three locations along theof each specimen. At each location, the analysisperformed on the cement paste matrix within an

(0.01 in.'), and three adof the specimen were

EXPERIMENTAL RESULTS AND DISCUSSIONPercentage change in thickness of the test specimens

immersion time in the acid solutions are shown

is an average of two speciof the same mix. The data for the individualthan 5 percent from the averageThe increases in thickness indicate that the

or swelling as aof the sulfuric acid attack.

Materials Journal I November-December 1988

15b. Mix M I : No Woter - Reducing Admixtureg 0 Mix M2 : Includes a Woter - ReducingAdmixtureoQ . 10":!:!J 5

.50g-ou 0 10 20 30 40 50 60

Immersion Time, days 70 80

Fig. 2 - Expansion oj specimens jo r concrete mixeswith and without a water-reducing admixture15 l:l. Mix M : No Air Entrainmentg * Mix M3 : Air Entrained'in

". 10o!l

.ECI)'"u 10 20 30 40 50 60 70

Immersion Time J days80

Fig. 3 - Expansion oj specimens ja r concrete mixeswith and without air entrainmentof!. 15

"2:g8. 10o!l

.ECI)'""u

to. Mix M I : Type 10 (ASTM Type I ) Cement+ Mix M4 : Type 50 (ASTM Type,,) Gement

20 30 40 50 60Immersion Time J days

70 80

Fig. 4 - Expansion oj specimens jo r concrete mixesmade with Types 10 and 50 (ASTM Types I and V)portland cementsFig. 2 shows percentage change in thickness versusimmersion time for the concrete mixes without and witha water-reducing admixture, Mixes M 1 and M2, respectively. The test specimens for Mix M2 expand more

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15o

.S;;g-o.t::U a

Uncoated Specimenx Cooted Specimen - No Visible Protective Surface Loyer Coated Specimen - With Protective Surface Loyer

10 20 30 40 50 60 70 80Immersion Time days

Fig. 5 - Expansion of uncoated and coated specimensthan the specimens for Mix Ml. This larger expansionof Mix M2 is probably due to its lower compressivestrength compared to Mix MI (Table I). Th e lowercompressive strength is thought to be due to an excessive amount of air entrainment caused by the additionof the water-reducing admixture.In Fig. 3, concrete mixes with and without air entrainment are compared. The air-entrained concrete hasa slightly smaller expansion. Air entrainment improvesthe chemical resistance of concrete insofar as it helps toproduce a more uniform, well-compacted, and, hence,denser concrete.sFig. 4 shows that beyond about 20 days' immersionin the sulfuric acid solution, the test specimens for theconcrete made with sulfate-resistant Type 50 (ASTMType V) cement expand more than those for the concrete made with Type 10 (ASTM Type I) cement. Thus,in the long run, sulfate-resistant cement does not appear to provide concrete a better resistance to sulfuricacid attack than that provided by normal portland cement. This observation is consistent with the findingsof previous studies'' and is explained by the fact thatsulfate attack is only one aspect of sulfuric acid attackon concrete.

As shown in Fig. 5 for test specimens of Mix Ml,coated specimens expand less than uncoated specimens.Also, the coated specimens with a protective surfacelayer expand less than those without a visible protectivesurface layer. These results support the well-known factthat measures aimed at making concrete more impermeable to ingestion of chemical solutions are th emost efficient in providing resistance to chemical attack.

The preceding discussions show that expansion of thesmall test specimens used in this study provides a consistent measure of the deterioration of concrete due tosulfuric acid exposure.Wet-dry cycles versus continuous immersion- Fig. 6compares the expansion of test specimens that were alternately immersed in the acid solutions and dried tothat of specimens that were continuously immersed until the end of the test program. Specimens that underwent alternate immersion and drying showed a greater484

;fl 15co.11 I,co&. 10".,.,0>co 1'" 5.S;; t:; Wet - dry Cycles of Acid Exposure0>'" o Continuous Acid Immersiono0.t:: au a 2 3 4

Mix NumberFig. 6 - Expansion of specimens that were subjected towet-dry cycles of acid exposure compared to expansionof specimens that were continuously immersed in theacid solutionsexpansion than those that were continuously immersed.This suggests that wet-dry cycles of exposure to sulfuric acid solutions increase the degree of concrete deterioration. The increased permeability of concrete dueto drying cracks would lead to a greater volume of material being attacked by th e sulfuric acid.Weight loss of test specimens

Percentage changes in weight of the test specimensare shown in Fig. 7 through 10. Fig. 7 shows thatweight loss is greater for the test specimens of Mix M2,which contained a water-reducing admixture, than forthe specimens of Mix Ml. Weight loss of the test specimens for the air-entrained concrete, Mix M3, is smallerthan that of the specimens fo r the non-air-entrainedconcrete, Mix M2 (Fig. 8). As shown in Fig. 9, theweight loss is slightly greater for the test specimens ofMix M4 with Type 50 (ASTM Type V) cement than forthe specimens of Mix MI with Type 10 (ASTM Type I)cenient . The effect of using surface coats is shown inFig . 10 by the smaller weight loss of the coated specimens in comparison to the uncoated specimens. Theweight loss is smaller for coated specimens with a protective surface layer than fo r those without a visibleprotective surface layer. These results (Fig. 7 through10) are consistent with those discussed in the previoussection based on the expansion of the test specimens.

It should be noted that th e test specimens initiallygain weight followed by weight loss. The weight gaincannot be attributed to saturation of the specimenssince the specimens were oven-dried prior to weighing.The reaction between sulfuric acid and the cement constituent of concrete results in the conversion of calciumhydroxide to calcium sulfate (gypsum) which, in turn,may be converted to calcium sulfoaluminate (ettringite). Each of these reactions involves an increase involume of the reacting solids by a factor of about twO.1OThe formation of calcium sulfate leads to softening(decrease in density) of the concrete. Since weight depends on both volume and density, the initial weightACI Materials Journal I November-December 1988


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5

Immersion Time I days- 5-10

-I S

-2 06. Mix M I : No 'Noter -Reducing Admixtureo Mix M2 : Includes 0 Woter - Reducing Admixture

. 7 - Weight loss oj specimens ja r concrete mixes

5

-5

-10

10 20 50Immersion Time ,doys

-15 l:l. Mix M : No Air Entrainment* Mix M3 : Air Entrained,-2 0

80

8 - Weight loss oj specimens ja r concrete mixesair entrainmentof the test specimens is probably due to the rela

density.Both the increase in volume and the decrease in denof the concrete due to the sulfuric acid-cement

of the acid solution. This implies

lution due to a significant increase in theof the concrete in comparison to the reductionThis phenomenon explains the results of

of concrete cylinders exposed to sulfuric/nitric acidpH of 2 was smaller than the weight loss

identical specimens exposed to the acid solutionspH of 3. In the same study, the weight loss of theas expected.It seems, therefore, that weight loss may not be a

of difex-

of concrete specimens may be a more consisof the specimens since

In this regard, the use of test specimens withas those used

t Materials Journal I NovemberDecember 1988

5

:s. -5.5: -10g-oo -15

-2 0

60 70

t:. Mix M : Type 10 (ASTM Type I ) Cement+ Mix M4 : Type 50 (ASTM Type 1 [)CementFig. 9 - Weight loss oj specimens jar concrete mixesmade with Types 10 and 50 (ASTM Types 1 and V)portland cements

-s='".; t.5.,i?0.s=U

5

0

-5

-10

-15

-2 0

Immersion Time , days

l:::.. Uncoated Specimenx Cooted Specimen - No Visible Protective Surface Layer Coaled Specimen - With Protective Surface Layer

Fig. 10 - Weight loss oj uncoated and coated specimens

in this study) may be preferred since the acid attack isa surface phenomenon, as indicated by previouss t u d i e s 2 ~ and supported by results discussed in a subsequent section of this paper. Further investigation isneeded to evaluate specimen expansion and weight lossas measures of concrete deterioration due to acids withdifferent strengths and for specimens with differentsurface area-to-volume ratios. In such an investigation,more than two test specimens would need to be used forthe expansion and weight loss measurements to clearlyestablish the statistical reliability of the tests.ScannIng electron microscope (SEM) analyses

Micrographs - Photomicrographs of unattackedand acid-attacked specimens are presented in Fig. IIand Fig. 12 through 15, respectively. Fig. 12 through 14are micrographs of specimens that were not coatedprior to immersion in the acid solutions, while Fig. 15is a micrograph of a coated specimen. The changes inmicrostructure, as discussed later, are typical for all theconcrete mixes studied . However, as discussed in earlier sections, the extent of deterioration as a function ofacid immersion time varies among the concrete mixesdue to differences in mix composition, such as the typeof cement and the admixtures used.

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Fig. 11 - Microstructure of an unattacked specimen

Fig. 12 - Microstructure of an acid-attacked specimenimmersed for 32 days: region near acid-exposed surfaceof the specimen

Fig. 13 - Microstructure of an acid-attacked specimenimmersed for 32 days: middle region of the specimenA typical micrograph of the cement paste matrix ona fractured surface of matured concrete is shown inFig. II. The predominant structure appears to be amodified Type II I calcium silicate hydrate (CSH) , one

of the prime hydration products of portland cement."!' A calcium hydroxide crystal is seen in thelower right corner of the micrograph. Fig. 12 is a micrograph of a specimen that had been immersed in theacid for 32 days. A comparison of Fig. 12 to Fig. 11486

Fig. 14 - Microstructure o f an acid-attacked specimenimmersed for 71 days

Fig. 15 - Microstructure o f a coated, acid-attackedspecimen immersed fo r 49 days; the coating is the darkvertical band on the leftshows that the acid reacts with the cement paste matrixreducing the matrix to a more porous material consisting of smaller particles.Fig. 12 shows a region near the acid-exposed surfaceof the specimen, while Fig. 13 shows a region fartherfrom the acid-exposed surface of the same specimen.These micrographs show that the deterioration issmaller in the region farther from the acid-exposed surface of the specimen than in the region near the acidexposed surface. This result supports previous studiesand clearly indicates that the acid attack is a surfacephenomenon: the deterioration starts at the surface ofthe concrete and progresses inward.A typical micrograph of a specimen that had beenimmersed in the acid for 71 days is presented in Fig. 14.This micrograph is representative of the total surface ofthe specimen at this stage of the acid attack. Thespherical fibrous structures that are visible in severallocations on this micrograph are Type I CSH. Thesestructures are usually not visible on the fractured surfaces of matured cement paste and concrete. The fracture path usually passes through Type III CSH (see Fig.11 and References 13 through 15). Comparing Fig. 14to Fig. 11 and 12, it appears that after 71 days immersion, the acid has dissolved the Type III CSH to a largeextent exposing the Type I structures .ACI Materials Journal I NovemberDecember 1988


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Mg - MagnesiumAt - AluminumSi - Silicon -

Ca S - SulphurK - PotassiumCo - Calcium -Fe - Iron

-Si -

Al --

S A. 16 - Elemental energy-dispersive spectrum for anspecimen

A micrograph of a specimen that was coated before49 days is presented in

15 . The protective surface layer of the coating isof the

of this micrograph to Fig.shows that the extent of deterioration is less in the

- Typical energy-dispersive specobtained from the quantitative elemental analysis

16 and 17 for unattacked and acid

.25 mm (0.01 in.) wide, along the thickness ofs. Since sulfur compounds are formed as af the reaction between sulfuric acid and cement, sulfur components of the spectra are of primaryThe figures show that the sulfur content of-attacked specimen is higher than that of the

concentrations obtained from the elementalas those in Fig. 16 and 17, are shown in

18 versus specimen immersion time in the acid soof acid penetration. Each data point is an averof the sulfur concentrations for three locationsf the SEM specimen. Fig. 18 showsthe sulfur concentration increases with immersioning larger in the region near thesurface during the initial period of im

than in the regions farther from the acid-ex. As the sulfur concentration in the rean opti

m value, the concentration in the adjacent regionfrom the acid-exposed surface increases less

Materials Journal I November-December 1988

Mg - MagnesiumAI - Aluminuml- Si - Silicon -S - Sulphur

Ca- K - PotassiumCo - Calcium -Fe - Iron- S -

- -Si-

- ifi CaMg '-I ~ ~ -Fig. 17 - Elemental energy-dispersive spectrum for anacid-attacked specimen

40 -- 0.00- 0.25 mm from Acid - Exposed Surface----0.25-0.5Omm from Acid-Exposed Surface;,l!0 35 - " - 0.50-0.75 mm from Acid -Exposed Su1 e"i 30c0 25


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4035r -__________-,

_ 30 -. 25eC 20 -8 15S 10 -

--- Uncoated Specimen....- Coated Specimen

15.. ....................._.M. __Jl 5 ............- - ........... "" "__ ~ ~ _ ' " _ _ _ __ _ _ _ _ _ _ _ _ _ _ _

0.00 0.25 0.50 0.75Distance from Acid - Exposed Surface,mm

Fig. 19 - Sulfur content of uncoated and coated specimens versus distance from acid-exposed surfaceto sulfuric acid, the rate of deterioration along thedepth of penetration of acid should be known. Theminimum cover thickness was estimated in Reference 5by assuming the degree of deterioration to be linearlyrelated to the depth of penetration of acid, with fullsulfuric acid-cement reaction at the exposed surface andzero reaction at the maximum depth of acid penetration. This relationship could be more accurately represented by the variation in sulfur concentration with thedepth of penetration of acid. Further investigation isrequired to explore this issue.

CONCLUSIONSThe following conclusions are drawn from the testresults and analysis presented in this paper.I . The increase in sulfur content of test specimens, asmeasured with an SEM equipped with an energy-dis

persive x-ray analyzer, is a good indicator of the extentof damage in concrete due to exposure to sulfuric acid.2. Photomicrographs, as well as the variation in sulfur concentration with distance from the acid-exposedsurface of test specimens, clearly show that deterioration of concrete due to sulfuric acid attack starts at thesurface and progresses inwards.3. The increase in thickness (expansion) of smallspecimens (with large surface area-to-volume ratios)may be a more consistent measure than the weight lossof larger specimens when comparing the effects of different sulfuric acid concentrations on concrete.4. Wet-dry cycles of exposure to sulfuric acid increase the degree of concrete deterioration.

5. The relationship between degree of concrete deterioration and depth of penetration of sulfuric acid

488

could be represented by the variation in sulfur concentration with the depth of acid penetration.

ACKNOWLEDGMENTSThis research was performed at the Structural Engineering and

Materials Laboratory of the University of Manitoba. Electron microscope analysis was carried out on the JEOL JXA-840 Scanning Electron Microscope of the Department of Mechanical Engineering, University of Manitoba. The authors are grateful for the technical andfinancial assistance provided by Barkman Concrete Ltd., Steinbach,Manitoba.

REFERENCES1. Mindess, Sydney, and Young, J. Francis, Concre te, Prentice

Hall, Englewood Cliffs, 1981, pp. 548-555.2. Meyer, Alvin H. , and Ledbetter, William B., "Sulfuric Acid

Attack on Concrete Sewer Pipe," Proceedings, ASCE, V. 96, SA5,Oct. 1970. pp. 1167-1182.3. Hughes, B. P. , and Guest, J. E., "Limestone and Siliceous Ag

gregate Concretes Subjected to Sulphuric Acid Attack," Magazine ofConcrete Research (London), V. 30, No. 102, Mar. 1978, pp. 11-18.

4. Fattuhi, N. I., and Hughes, B. P. , "Effect of Acid Attack onConcrete with Different Admixtures or Protective Coatings," Ce-ment and Concrete Research, V. 13, No.5, Sept. 1983, pp. 655-665.

5. Raju, P. S. N., and Dayaratnam, P. , "Durability of ConcreteExposed to Dilute Sulfuric Acid," Building and Environment, V. 19,No.2, 1984, pp. 75-79.

6. Kong, Hendrick, L., and Orbison, James G., "Concrete Deterioration Due to Acid Precipitation," ACI Materials Journal, V. 84,No.2, Mar.-Apr. 1987, pp. 110-116.

7. Sand, W., and Bock, E. , "Concrete Corrosion in the HamburgSewer System," Science and Technology Letters, V. 5,1984, pp. 517-528 .

8. Wilder, Car l R., and Spears, Ralph E., "Concrete for SanitaryEngineering Structures," Concrete International: Design & Con-struction, V. 3, No.4, Apr. 1981, pp. 29-34.

9. Wenger, E. C., "Concrete for Sewage Work," ACI JOURNAL,Proceedings V. 54, No.9, Mar. 1958. pp. 733-738.

10. Soroka, Itzhak, Portland Cem'ent Paste and Concrete, Macmillan Press, London, 1979, pp. 151-152.

11. Berger, R. L.; Young, J. F.; and Lawrence, F. V., Discussionof "Morphology and Surface Properties of Hydrated Tricalcium Silicate Paste" by M. Collepardi and B. Marchess. Cement and Con-crete Research, V. 2, No.5, Sept. 1972, pp. 633-636.

12. Diamond, Sidney, "Cement Paste Microstructure-An Overview at Several Levels," Proceedings, Conference on Hydraulic Cement Pastes; Their Structure and Properties (Sheffield, Apr. 1976),Cement and Concrete Association, Wexham Springs, 1976, pp. 2-30 .

13. Lawrence, F. V., Jr., and Young, J. F., "Studies on the Hydration of Tricalcium Silicate Pastes: Scanning Electron MicroscopicExamination of Microstructural Features," Cement and ConcreteResearch, V. 3, No.2, Mar. 1973, pp. 149-161.

14. Attiogbe, Emmanuel K. , and Darwin, David, "Submicrocracking in Cement Paste and Mortar in Compression," 8M ReportNo. 16, University of Kansas Center for Research, Lawrence, Nov.1985,439 pp.15. Attiogbe, Emmanuel K., and Darwin, David, "Submicro-cracking in Cement Paste and Mortar," ACI Materials Journal, V.84, No.6. Nov.-Dec. 1987, pp. 491-500.

ACI Materials Journal I NovemberDecember 1988

response of concrete to sulfuric acid attack

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