BEHA VIOR OF CONCRETE PAVING BLOCKS UNDER EXTERNALSULFATEATTACK

N. Ghafoori 1 and R.P. Mathis2

1. ABSTRACT

The rapid growth of concrete block pavements in the United States within the last two decades has raised the need for developing a comprehensive evaluation program for this type of pavement that is suited to different local conditions and applications. This need was shared by both block manufacturers and various private agencies who have been trying to compete with the more conventional pavements, mainly the flexible asphaltic pavements. This paper presents experimental results pertaining to the sulfate resistance of various concrete paving blocks using a standard test method, ASTM ClO12. The effects of matrix proportions and bulk properties on length expansion are discussed. Test results conclude that the sulfate resistance of concrete block pavers is directly related to the aggregate-cement ratio of the matrix. Similar relationships exist between expansion and the pavers' bulk properties.

2. INTRODUCTION

Concrete paving blocks were first manufactured in the United States in 1976 (Smith, 1987). Since then, production has increased from 1.3 million m2 (14 million ft2) in 1980 to a total area of about 14 million m2 (150 million ft2). Today, concrete block pavements are found in roads, pons, railroad crossings, industrial plants, driveways, footpaths, sidewalks, shopping maUs, parking areas, cycle tracks, bus stops, sloped paving, and

Keywords: Concrete Block Pavers; Sulfate Durability; Aggregate-Cement Ratio; Bulk Properties; and Durability

1 Assistant Professor, Department of Civil Engineering and Mechanics, Southem Illinois University, Carbondale !L. 62901

2Graduate Research Assistant, Civil Engineering and Mechanics, Southem Illinois University

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embankment walls. Undoubtedly, bloek paving, in eertain areas of applieation, is the paving of ehoiee due to its superior engineering properties, eost effectiveness, aesthetie appeal, ease of eonstruetion, and in-serviee applieations.

An important aspeet to the steady growth of the paving bloek market is the need for the produetion of quality pavers. This is partieularly true as the industry moves into ports and industrial paving applieations. While literature abunds dealing with the bulk eharaeteristies and physieal durability of eonerete bloek pavements, to date, little or no information relevant to the long-term performance in sulfate-rieh environments has been reported.

The aim of this paper is to examine the sulfate resistanee of eonerete bloek pavers. Laboratory results obtained with ASTM standard methods are reported and diseussed for the speeimens of various mixture proportions. Relationships between sulfate durability, matrix proportions, and bulk properties are also presented.

3. MATERlALS

The matrix eonstituents of the eonerete bloek pavers included portland eement type I, washed siliea sand, and erushed limestone eoarse aggregate. The portland eement eonformed to the requirements of ASTM C150 "Standard Speeifieation for Portland Cement", whereas the eoarse and fine aggregates satisfied ASTM C33 "Standard Speeifieation for Conerete Aggregate." Information on the ehemieal eomposition and physieal properties of the eementitious binder is given in Tables 1 and 2, respeetively. As indieated, the tri-ealcium aluminate (C3A) of the portland eement, a gauge of eement resistanee to externaI sulfate attaek, was measured at 6%. Table 3 shows the physieal eharaeteristies of both aggregates. The weight ratio of eoarse to fine aggregate of all test pavers was kept eonstant at 1 :2. No ehemieal admixtures were used for this researeh programo

The 60 mm reetangular pavers (nominally 100 mm wide by 200 mm long) were manufaetured at Baleon Inc., in Crofton, Maryland. After fabrieation, the eonerete bloeks were air-eured for a period of one day, and then staeked and plaeed outdoors prior to shipment. A detailed deseription of the three matrix proportions utilized for this investigation, denoted as groups A, B, and C, are given in Table 4.

4. SPECIMEN PREPARATION AND TESTING

This experimental program eonsisted of the determination of bulk properties and sulfate resistivity of eonerete bloek pavers. Unit weight, absorption and eompressive strength were determined aeeording to ASTM C140-90 "Standard Method of Sampling and Testing Conerete Masonry Unit." Tensile Splitting was aeeomplished using the apparatus of the International Standard ISO 4108-1980 "Determination of Tensile Splitting Strength of the Test Speeimens." Tensile strength ealeulation followed ASTM C1006 "Standard Test Method for Splitting Tensile Strength of Masonry Units."

ASTM ClOl2-89 "Standard Test Method for Length Change of Hydraulie-Cement Mortars Exposed to a Sulfate Solution" was utilized to measure the length expansion of eonerete bloek pavers. It should be noted that the length of the pavers (200 mm or 7 7/8 in.) differed from that of the mortar bars (286 mm or 11 1/4 in.). Measurement of the expansion resulting from sulfate attaek required designing a speeial length eomparator to aeeommodate the size of the eonerete pavers. This deviee was manufaetured in

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accordance with ASTM C490-89 "Standard Practice for Use of Apparatus for the Determination of Length Change of Hardened Cement Paste, Mortar and Concrete."

Test specimens were chosen from a preselected location of the individual pallet. Their "as-received" unit weight and absorption values were determined prior to sulfate exposure. For the expansion measurements, the block samples had to be fitted with stainless steel gage studs at each end. This was accomplished by first drilling two holes (approximately 11.11 mm deep) along the centerline of the length. A steel stud was then placed in each hole and permanently affixed by means of a chemical resistant epoxy. The epoxy was allowed to dry in a room temperature of approximately 73 ± 3 degrees F (22.8 ± 1.67 degrees C) for a period of rwo weeks prior to irnrnersion in the sulfate solution.

Each test specimen was placed in an individual container over a seating, allowing complete exposure of the bottom surlace. A 5% sodium sulfate solution (sulfate content of approximately 34000 ppm) was poured into each container to a depth of 0.5 inches above the paver's top surlace. This concentration is classified as "very severe attack" by ACI Building Code 318-89. The containers were then sealed and stored at a room temperature. Twenty-four hours later the test specimens were measured for their initial reading. Future readings were taken weekly for about four months, followed, thereafter, by bi-weekly measurements up to nine months.

5. EXPERIMENTAL RESULTS

The results for the bulk characteristics of the tested concrete pavers are reported in Table 5. The mean (MN), standard deviation (SD), and coefficient of variation (CV) are shown for the three matrix proportions listed in Table 4. The statistical indicators for unit weight and absorption were obtained from 3, 4, and 4 test samples for the mixes containing cement content of 223, 356, and 594 kg!m3, respectively. In addition, for each mix proportion, four separate specimens were tested for compressive and split-tensile strengths. As can be observed, the bulk properties of the test pavers improved when the cement content of the matrix increased (decrease of aggregate-cement ratio). The values for unit weight increased 7.9% and 3.8% as the cement content increased from 223 kg/m3

to 356 kg/m3 and 356 kg/m3 to 594 kg!m3, respectively. On the other hand, the absorptive capacity of the block pavers decreased with an increase in cement content, a drop of 43% as the aggregate-cement ratio decreased from 8: 1 to 3: 1. A change in matrix proportion also affected the strength characteristics of concrete pavers. When the cement content changed from 223 kg/m3 to 594 kg!m3, compressive and split-tensile strengths increased by nearly 82% and 110%, respectively. The improvement in the above­mentioned bulk properties is attributed to the higher cement content of the matrix, a lower aggregate-cement ratio. Consequently, the additional paste tends to fill the voids berween the coarse particles, resulting in a better interlocking behavior and an improved bond strength. Moreover, the effective water-cement ratio decreases when the cement content is increased, further improving the bulk properties of concrete block pavers.

Results of length expansion associated with irnrnersion age in sulfate solution are given in Figures 1 through 4. The first three figures present individual and mean data for the mixes having cement contents of 223, 356, and 594 kg!m3, respectively. As shown, the expansion of the test samples progressed over time. Block samples containing 223 kg/m3

portland cement showed an average expansion of 0.038% at 3 months. This value increased to 0.079% at the age of 6 months. At the end of 9-month immersion, the total expansion reached a value of 0.11 %. For the pavers having cement content of 356 kg!m3, the average expansion at 3, 6, and 9 months were 0.039%, 0.056%, and 0.065 %,

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respectively. The mixes of group C (594 kg/m3 cement content) displayed expansion results of 0.024%, 0.033%, and 0.035% for the same immersion periods. A major distinction was found between the rates at which expansion occurred for each of the three mixes. For the test specimens containing cement content of 223 kg!m3, the expansion rates (given as a percentage per month) remained fairly constant throughout the entire immersion period. Rates of 0.013%, 0.014%, and 0.010% were measured for the immersion ages of O to 3 months, 3 to 6 months, and 6 to 9 months, respectively. The percentages for groups B and C dropped significantly over the same time period; 0.013%, 0.006%, and 0.003% for the pavers containing 356 kg!m3 ponland cement, and 0.008%, 0.003%, and 0.0007% for the samples having 594 kg/m3 portland cement in their matrices. In addition, for the test specimens containing cement contem of 223 kg!m3, the sulfate expansion increased 107% from the age of 3 to 6 months, and 39% from 6 to 9 months. The percentages for groups B and C were significantly lower; 44% and 16% for the pavers containing 356 kg!m3 ponland cement, and 38% and 6% for those samples with 594 kg!m3 ponland cement.

Figure 4 shows a comparison of the mean expansions at various immersion ages for the three mixture proportions. Initially, there was little difference in the performance of the mixes containing 223 kg!m3 and 356 kg!m3 portland cement, with nearly identical expansions at the age of 3 months. When a cement content of 594 kg!m3 was used, the expansion value reduced by nearly 37% as compared to that of the other two mixes. After 6 months of immersion, groups B and C displayed 29% and 58% improvements in expansion, respectively, as compared to that of group A. These percentages increased to 41 % and 68% by the time test samples had been exposed to the sulfate solution for a period of nine months. This trend suggests that the increase of cement content results in a decrease of expansion property. A matrix of low cement content (high aggregate-cement ratio) demands a higher mixing water and subsequent water-cement ratio (as is the case with group A). Additional water produces voids that are larger in number and size, hence, adversely affecting the permeability of concrete. Consequently, there is an accelerated reaction between sulfate ions and cement paste, resulting in an increased expansion. In addition, as concrete cracks, its permeability increases, allowing further penetration of sulfate solution and subsequent deterioration of the hardened product. The test specimens with a higher cement content contained a smaller void system (as evidem by the absorption results) and, therefore, more effectively restricted the passage of aggressive water into the pavers' pore system. This resulted in a decrease of the expansion rate and less overall expansion, as was well documented by the test results shown.

The effects of matrix constituents and bulk properties on length expansion are presented in Figures 5 through 8. Only data for 3, 6, and 9 months of sulfate exposure are plotted. Figure 5 shows the relationship between expansion and the cement content of the matrix. As can be seen (and which was previously discussed), the measured expansion decreased with an increase in cement contento Moreover, the relationship between the dependent and independent variables (expansion and cement content, respectively) appears to be in linear formo In a similar fashion the expansion due to sulfate exposure is linearly related to the unit weight of the test pavers (Figure 6). As expected, the increase in unit weight, which is generally associated with an increase in cement content, results in a decrease in length expansion. For the absorption, the reverse is observed, higher absorption rate is linked to higher expansion (Figure 7). Again, a fairly linear relationship; however, not quite as strong as those previously discussed; was obtained. Most likely the explanation lies in the fact that the exact absorption values are difficult to measure and often test samples carry a higher standard deviation than that of other bulk characteristics. Finally, Figure 8 displays expansion versus the mean compressive strength of the three different

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matrix proportions. The plot shows that as compressive strength is increased, the expansion decreases in a linear manner.

6. CONCLUSIONS

Analysis of the data presented in this paper has lead to the following conclusions concerning the sulfate resistance of concrete block pavers:

1. In general, the test samples performed well in severe sulfate-rich environments, considering the type of cement (portland cement, Type I with C3A = 6%) and the aggregate-cement ratios used in this investigation. This performance can be partially attributed to the low C3A content of the portland cement. However, a greater emphasis should be placed on the low water-cement ratio and porosity of the concrete pavers and their profound effects on low permeability and, consequently, sulfate resistance.

2. At the end of 6 months, rnixes having cement contents of 223, 356, and 594 kg!m3

had expansion values of 0.079%, 0.056%, and 0.33%, respectively. Performance limits for mortars exposed to a sulfate solution have been suggested by Patzias (Patzias, 1992). At the age of 6 months, samples with expansions of less than 0.10% are considered to be of "Moderate Sulfate Resistance", whereas those of less than 0.05 % are "High Sulfate Resistant." When the proposed lirnits are used, the specimens of groups A and B can be rated as "moderately sulfate resistant," whereas, the mix containirig 594 kg/m3 portland cement is classified as a "high sulfate resistant" concrete.

3. The expansion due to sulfate attack can be adequately predicted by the cement content of the matrix and the bulk properties of the concrete block pavers . Linear relationships exist between expansion and the cement content, unit weight, absorption rate, and compressive strength of the test specimens.

7. ACKNOWLEDGMENTS

The authors are thankful to the Concrete Paver Institute, a division of the National Concrete Masonry Association (NCMA), for partial sponsorship of the research project. The contribution of Balcon Inc. , in fabricating the experimental paving units, is greatly appreciated.

8. CONVERSION FACfORS

1 mrn = 0.03937 in. 1 kN/m2 = 0.145 psi I kg!m3 = 1.684 Ib/yd3

9. REFERENCES

1 m3 = 35.32 ft3

1 kg = 0.2248 Ibm 1 kg!m3 = 16.02 Ib/ft3

1. ACI Committee 318. Building Code Requirements for Reinforced Concrete 318-89. American Concrete Institute, Detroit, 1989, pp. 35.

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2. American Society for Testing and Materials, "Standard Method of Sampling and Testing Concrete Masonry Units," (ASTM CI40-90), 1990 Annual Book of ASTM Standards, Voi. 4.05, ASTM, Philadelphia, pp. 87-90.

3. American Society for Testing and Materiais, "Standard Practice for Use of Apparatus for the Determination of Length Change of Hardened Cement Paste, Mortar, and Concrete," (ASTM C490-89), 1990 Annual Book of ASTM Standards, Voi. 4.02, ASTM, Philadelphia, pp. 271-274.

4. American Society for Testing and Materiais, "Standard Specification for Solid Interlocking Concrete Paving Units," (ASTM C936-88), 1989 Annual Book of ASTM Standards, Voi. 4.02, ASTM, Philadelphia, pp. 583-587.

5. American Society for Testing and Materials, "Standard Test Method for Length Change of Hydraulic-Cement Mortars Exposed to a Sulfate Solution," (ASTM ClOI2-89), 1990 Annual Book of ASTM Standards, Voi. 4.02, ASTM, Philadelphia, pp. 475-479.

6. American Society for Testing and Materials, "Standard Test Method for Splitting Tensile Strength of Concrete Masonry Unit," (ASTM ClO06), 1990 Annual Book of ASTM Standards, Vol. 4.05, ASTM, Philadelphia, pp. 629-631.

7. Mehta, P. Kumar, "Concrete - Structure, Properties, and Materiais," Prentice-Hall, Inc., Englewood Cliffs, New Jersey, 1986, pp. 137-145.

8. Morrish, c., "Interlocking Paving - A State of the Art Review," Proceedings, Symposium of Precast Paving Block, Johannesburg, South Africa, 1979.

9. National Concrete Masonry Association, "Concrete Block Pavements Design and Construction," Herndon, VA., 1979.

10. Neville, A. M. , "Properties of Concrete," 2nd edition, John Wiley and Sons, New Y ork, 1980, pp. 671 .

11. Patzias, T., "The Sulfate Resistance of Blended Cements," Proceedings, CANMET/ACI International Workshop on Advances in Concrete Technology, Athens, Greece, May 1992, pp. 227-245.

12. Shackel, B., and Candy, C. C. E., "Factors Influencing the Choice of Concrete Blocks as a Pavement Surface," Third International Conference on Concrete Block Paving, Pavitalia, Rome, Italy, 1988, pp. 78-83.

13. Smith, D.R., "Mechanized Installation of Concrete Block Pavement," Concrete International, July 1987, pp. 37-40.

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Table 1 - Chemical Compositions of Portland Cement

Type I Portland Cement Test Standard Chemical Compositions Results Requirements

(ASTM C150)

Silicon Dioxide (Si02) 21 % N.A. Aluminum Oxide (A120 3) 4.2 % N. A. Ferric Oxide (Fe20 3) 3.4 % N. A. Carbon Oxide (CaO) 62.5 % N. A. Magnesium Oxide (MgO) 4.2 % Maximum 6.0 % Sulfur Trioxide (S03) 2.3 % 3.0% Loss on Ignition 1.3 % Maximum 3.5 % Tricalcium Silicate (C3S) 54 % N. A. Tricalcium Aluminate (C3A) 6.0 % N. A. Insoluble Residue 0.40 % Maximum 0.75 % Total Alkalies 0.53 % Maximum 0.60 %

Table 2 - Physical Properties of Portland Cement

Type I Portland Cement Test Standard Requiremems Physical Tests Results (ASTM C150)

Compressive Strength: 1 day 1822 psi N. A. 3 days 3216 psi Minimum 1800 psi 7 days 4196 psi Minimum 2800 psi

Surface Area (Fineness): Blaine 4086 m2fKg Minimum 2800 m2fKg

#325 Mesh (45 11m) 87.2 % 85 % to 95 % (ASTM C430)

Setting Time: Vicat Initial 135 mino Minimum 45 mino Vicat Final 247 mino Maximum 375 mino

Autoclave Expansion 0.41 % Maximum 0.80 % Air Contem of Mortar 7.50 % Maximum 12.0 %

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Table 3 - Physical Characteristics of Coarse and Fine Aggregates

Rodded Grain Size Distribution, Percent Passing Specific Unit

Sieve Size (mm) Gravity Weight 9.53 4.75 2.36 1.18 0.60 0.30 0.15 SSD (kg/m"3)

Coarse Aggregate 100 I 63.17 I 13.35 I 1.72 I 0.72 I 0.48 I 0.28 2.70 1585.4 Fine Aggregate 100 I 99.08 I 83.65 I 70.61 I 52.91 I 19.40 I 6.40 2.60 ----

Table 4 - Mixture Proportion Details

Specimen Cement Content Aggregate/Cement* Water/Cement* Code (kg/m"3)

A 223 8:1 0.29

B 356 5:1 0.22

C 594 3:1 0.21

*By Weight

Table 5 - Bulk Properties of Concrete Block Pavers

UnitWeight Absorption Compressive Strength Split-Tensile Strength

Spec MN SD CV MN SD CV MN SD CV MN SD CV Code

(k~mA3) (k~mA3) (%) (%) (%) (%) (MPa) (MPa) (%) (MPa) (MPa) (%)

A 2084.0 4.31 0.21 6.56 0.21 3.18 43.46 2.710 6.23 3.634 0.135 3.72

B 2248.7 19.22 0.86 4.18 0.18 4.37 61.23 4.406 7.20 5.667 0.375 6.61

C 2333.8 t7.64 0.76 3.75 0.04 1.06 79.10 9.087 11.5 7.639 0.570 7.46

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IV

<.D

~ c o

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~ c .2

~ '"

0.14

0. 12

0 .1

0.08

0.06

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lest sample I tes! sample 2

50 100 150 200 250 300 lllunersion Age (Days)

Fig. 1 - SuJratc E"pansion for lhe Samplcs Containing 223 kglm"3 Ponland Cemenl

0.14 lcst sample I

0. 12-1 I lesl samplc 2 tesl sample 3

o lesl sample 4

0.1-1 I ---- mean

0.08

0.06

0.04

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50 100 150 200 250 300 Immcrsion Age (Days)

Fig. 3 - Sul fale E-.: p.1nsion for lhe Samples Containing 594 kglm"3 POr1land Cem ent

~ g ." ~ '"

t c o

l '"

0.14 lesl Mmple 1

0.12 -I I leSl sample 2 Icst sample 3 lest sample 4

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50 100 150 200 250 300 lmmersion Age (Days)

Fig . 2 - Sulfale Exp.:tnsion for the Sarnples Containing 356 kg/m"3 Portland Cemenl

0.14"]'];:, ===========::::;--------, 0.12

0.1

0.08

0.06

U.()4

0.02

~ AIC = H: I (223 kglm") cemenl conten!) ~ AIC = 5:1 (356 kgJm "3 cemenl conlenl) --o-- NC::: 3:1 Ci94 "gim") ceme"! COnle!!!)

o, , I O 50 100 150 200 250 300

lnunersioo Age (Day') Fig. 4 - Mean Sul fale Expansion for Various Aggregale ·Cement Ratios

N N o

~14

~12

~I

~~ ~ o

I~ ~

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~m

~

2

---. .. 3 months - mean 3 monlhs - indiv.

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_____ 9 months - mean

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o I, I '

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0.12

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10 (223) 12 14 16 (356) 18 20 22 24 (594) 26 Ccment Content (% by weight, kglm"3)

Fig, 5 - Sulfale Expansion versus Cernenl Content for Different Days of Immersion

--.. . - 3 months - mcan

E .6 3 monlhs - indiv. - ..... 6 months - mean

o 6 months - indiv. ____ 9 months - mean

o 9 months - indiv.

~. &\

·r

o ,.

~ .. -.....

o I ' 3.5 4 4 .. \ 5.5 6.5

Absorption (%)

Fig.7 - Sulfate Expansion versus Absorption for Differcnt Days of lmmersion

0.14

0.1 2

0.1

~ 0.08 c o

'1 0.06 ~

().~

0.02

o I 2000 2050

~

--.. - 3 rnonlhs - mean 3 months - indiv .

- e- 6 months - rncan o 6 months - indiv.

_____ 9 monlhs - mean

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2100 2150 2200 2250 2300 2350 2400 Uni! weight (kg/mA3)

Fig. 6 - Sulfate Expansion versus Unit Weight for Different Days af lnullcrsion

0.14] .I

0.12

0.1

~ 0.08 c .~

~ 0.06 ~

O.~ ;:-----_ . .. _-. . -._-- ... -.

0.02

O 35 45 55 65 75 85

Compressive Strenglh (MPa) Fig.8 - Sulrate Expansion versus Compressive Strength for Differcnt Days of lmmersinn