Wang et al, submitted to NRMCA Concrete Technology Forum: Focus on Pervious Concrete, May 24-25, 2006, Nashville, TN

Development of Mix Proportion for Functional and Durable Pervious Concrete Wang, K.1, Schaefer, V. R.2, Kevern, J. T.3, and Suleiman, M.T.4

Abstract Portland cement pervious concrete (PCPC) mixes made with various types and amounts of aggregates, cementitious materials, fibers, and chemical admixtures were evaluated. Porosity, water permeability, strength, and freezing-thawing durability of the concrete were tested. The results indicated that the PCPC made with single-sized coarse aggregates generally had high permeability but not adequate strength. Addition of a small amount of fine sand (approximate 7% by weight of total aggregate) to the mixes significantly improved the concrete strength and freezing-thawing resistance while maintaining adequate water permeability. Addition of a small amount of fiber to the mixes increased the concrete strength, freezing-thawing resistance as well as void content. Based on these results, performance-based criteria are discussed for proportioning functional and durable PCPC mixes. Introduction Portland cement pervious concrete (PCPC) is increasingly used in the United States because of its various environmental benefits such as controlling storm water runoff, restoring groundwater supplies, and reducing water and soil pollution (Youngs 2005 and Kajio et al. 1998). Due to the permeability requirement, PCPC is typically designed with high void content (15-25%). Singlesized aggregate is commonly used to achieve such void content (Tennis et al. 2004). Because of the high void content, PCPC generally has low strength (800-3000 psi), which not only limits its application in cold weather regions but also is responsible for various distresses in and failures of the related structures. Lately, PCPC has been considered for some pavements in cold weather regions (such as Iowa and Minnesota). However, limited research has been conducted to characterize PCPC mix proportions and to investigate its serviceability under cold weather conditions. The present study was conducted to fill this gap and to spur PCPC applications. In this paper, PCPC mixes were designed with various types and amounts of aggregates, cementitious materials, fibers, and chemical admixtures. Porosity, water permeability, strength, and freezing-thawing (F-T) durability of the concrete samples were tested. The effects of these materials and mixture proportions on the PCPC performance/ properties were explored. The following sections describe the detailed experiments, test results, and major findings. 1

Assistant Professor, Civil, Construction, and Environmental Engineering, Iowa State University, Ames, IA,[email protected] 2 Professor, Civil, Construction, and Environmental Engineering, Iowa State University, Ames, IA, [email protected] 3 Research Assistant, Civil, Construction, and Environmental Engineering, Iowa State University, Ames, IA, [email protected] 4 Research Assistant Professor, Civil, Construction, and Environmental Engineering, Iowa State University, Ames, IA, [email protected]

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Wang et al, submitted to NRMCA Concrete Technology Forum: Focus on Pervious Concrete, May 24-25, 2006, Nashville, TN

Experimental Work Materials. Type I/II cement was used in all mixes, and the cement had a fineness of 384 m2/kg and a specific gravity of 3.15. A single-sized limestone (3/8”LS, which passed the ½” (12.5 mm) sieve but retained on the 3/8” (9 mm) sieve), and two single-sized river gravels (3/8”RG, which passed ½” (12.5 mm) sieve but retained on 3/8” (9 mm) sieve, and #4RG, which passed 3/8” (9 mm) sieve but retained on No.4 (4.75 mm) sieve) were used as coarse aggregate. The properties of the coarse aggregate are summarized in Table 1, where unit weight and voids tests were performed based on ASTM C29, and the specific gravity and absorption tests were performed based on ASTM C127. Table 1: Properties of coarse aggregates Aggregate

3/8”RG

#4RG

3/8”LS

3/8”LS*

Unit weight (lb/ft3)

102.6

99.6

86.5

88.8

Voids (%)

37.3

38.5

43.5

44.2

Abrasion mass loss (%)

14.4

14.4

46.1

32.9

Specific gravity

2.62

2.62

2.45

2.55

Absorption

1.1

1.1

3.2

3.2

Note: 3/8”LS* was from the same source but received at a different time and used for Mix 3A only

To improve concrete strength, a small amount of river sand was incorporated in the PCPC mixes. The sand had a fineness modulus of 2.9, specific gravity of 2.62, and absorption of 1.1%. To improve the cement-aggregate bond and the F-T durability, a styrene butadiene rubber (SBR) latex was used. The SBR latex is approved by the Federal Highway Administration for latex modified concrete use in bridge deck overlays (Ramakrishnan 1992). The SBR used had a solid content of 48% and pH of 10. Various amount of polypropylene fiber is also used in selected PCPC mixes. Air entraining agent (AEA) and high-range water reducer (HRWR) were used in the mixes that did not contain latex. The specific gravity and pH were 1.01 and 10 for the AEA (Everair plus) and 1.07 and 7.8 for the HRWR (Glenium 3400 NV), respectively. Mix Proportions. The mix design was divided into two parts. Part I was designed to investigate the effects of aggregate size and type on the void ratio and strength of pervious concrete, and Part II was to investigate the effects of sand, latex, fiber and admixtures (AEA and HRWR) on PCPC properties. All concrete mix proportions used are summarized in Table 2. The slump of the mixtures was between 0 in. to ½ in. (0 cm and 1.27 cm ).

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Wang et al, submitted to NRMCA Concrete Technology Forum: Focus on Pervious Concrete, May 24-25, 2006, Nashville, TN

Part II

Part I

Table 2: Mix proportions Mix

C. Agg.

Cement (lb/yd3)

1 2 3 1A 1B 2A 2B 2C 2D 2E

3/8”RG #4RG 3/8”LS 3/8”RG 3/8”RG #4RG #4RG #4RG #4RG #4RG

600 600 600 571 520 571 520 520 542 485

2F 2G 2H 3A 3B

#4RG #4RG #4RG 3/8”LS* 3/8”LS

600 600 571 571 571

Latex Solid (lb/yd3) ----52 -52 52 29 86 -52

C. Agg. (lb/yd3)

Sand (lb/yd3)

Water (lb/yd3)

Fiber (lb/yd3)

w/c

168 168 168

162 162 154 114 154 116 114 114 114

AEA/HRA (oz/100 lb PC) 2.15/4.25 2.15/4.25 2.15/4.25 2.15/4.25 -------

2700 2700 2700 2500 2500 2500 2500 2500 2500 2500

----

162

-----------

0.27 0.27 0.27 0.27 0.22 0.27 0.27 0.22 0.22 0.22

2700 2700 2500 2500 2500

168 168 168

162 162 154 154 126

2.15/4.25 2.15/4.25 2.15/4.25 2.15/4.25 --

0.5 1.5 1.5 ---

0.27 0.27 0.27 0.27 0.22

168 168 168 --

Specimen Preparation. To improve the bond between cement paste and aggregate, the following mixing procedure was used: 1. A small amount of cement (15%) for PCPC applications. In other words, although the permeability of Mix 2A decreased from 354 in./hour to 141.7 in/hour (from 0.25 cm/sec to 0.1 cm/sec) when compared with Mix 2, this permeability value is still higher than the maximum requirement to drain the maximum 25 year-24 hour storm across the United States (i.e., 12 inch (30.5 cm) (USDA 1986). Effect of Latex on PCPC Properties. To improve the PCPC properties, approximate 10% latex solid (by weight of cement) was used into selected mixes. Due to the consideration of the material cost, the latex was used to replace the same amount of cement. As a result, the cement content of the PCPC mixes reduced from 571 lb/yd3 to 520 lb/yd3. Water-to-cement ratio (w/c) also reduced from 0.27 to 0.22 for the latex modified PCPC to reach given slump. Table 5 presents the properties of the PCPC mixes made with the sand and latex. Probably due to the less cement used, the PCPC mixes with latex (Table 5) had lower compressive strength than the mixes without latex (Table 4). However, even though less cement was used, the PCPC mixes with latex still had higher splitting tensile strength than the mixes without latex. This indicates that the addition of latex in PCPC might improve the concrete cracking resistance. Table 5: Properties of PCPC mixes with sand and latex (w/c=0.22, cement content 308.2 kg/m3) Compressive Strength (psi) Unit Void Splitting Water Mix C. Agg. Weight Content Strength Permeability 7-day 21-day 28-day (lb/yd3) (%) (psi) (in./hour) 127.3 1B 3/8”RG 20.2 2641 -2924 -340 2C

#4RG

126.8

19.0

2969

3313

3349

453

255

3B

3/8”LS

117.4

25.7

2483

--

--

--

666

Table 6 presents the effect of amount of latex on PCPC properties, where latex was again used for cement replacement, rather than addition. As observed in the table, the void content of the PCPC decreased with the increased amount of latex replaced for cement. The optimal amount of latex appeared to be 10% based on the consideration of the concrete strength and permeability.

Mix

Table 6: Properties of PCPC mixes with different amount of latex (w/c=0.22) Cement Unit Void Compressive Splitting Water Latex Content Weight Content Strength Strength Permeability Solid (lb/yd3) (lb/ft3) (%) (psi) (psi) (in./hour) (lb/yd3)

2D

29

542

120.3

26.0

1307

--

--

2C

52

520

126.8

19.0

2969

453

255

2E

86

485

132.2

14.1

2735

--

57

Effect of Fiber on PCPC Properties. Table 7 presents the effect of fiber addition on PCPC properties, where Mixes 2F and 2G had no sand and Mix 2H had 7% sand for coarse aggregate replacement. Generally, addition of the fiber in PCPC slightly increased the void content and significantly increased the permeability of the concrete. More importantly, it

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Wang et al, submitted to NRMCA Concrete Technology Forum: Focus on Pervious Concrete, May 24-25, 2006, Nashville, TN

improved the splitting tensile strength of concrete, which in turn enhanced the concrete F-T durability. Table 7: Properties of PCPC mixes with fiber (w/c=0.27, cement content 308.2 kg/m3) Splitting Water Compressive Strength (psi) Fiber Unit Void 3 Mix Strength Permeability (lb/yd ) Weight Content 7-day 21-day 28-day (psi) (in./hour) (lb/yd3) (%) 2F .05 120.4 18.9 2587 2941 3106 348 383 2G

1.5

119.4

22.1

2601

2765

3106

358

964

2H

1.5

122.5

19.0

2988

3220

3849

353

425

F-T Durability Test Results. As mentioned before, only selected concrete mixes that had adequate void ratio and 7-day compressive strength were tested for F-T durability using ASTM C666 ⎯ procedure A. Due to its high permeability, field PCPC is rarely in a saturated condition. The investigators have noted that ASTM C666 method may not appropriately simulate the field PCPC condition. However, it is believed that this simple, rapid test method simulates the extreme case that PCPC might experience, and the method is suitable for a comparison study of the PCPC F-T durability. Mix 1A 2 2A 2C 2F 2G 2H 3 3A 3B

Table 8: Summary of F-T test results Descriptions F-T cycles to failure 3/8” RG-7% sand 136 #4 RG 153 #4 RG-7% sand >300, 2.1%weight loss at 300 cycles #4 RG-7% sand-10% latex replacement 216 #4 RG -0.30 kg/m3 fiber 201 #4 RG -0.89 kg/m3 fiber 181 #4 RG-7% sand-0.89 kg/m3 fiber Test is in progress; less weight loss than sample Mix 2A 3/8” LS 196 3/8” LS-7% sand 110 3/8” LS-7% sand-10% latex 110

Table 8 summarizes the F-T test results of the PCPC mixes presented in the paper. Among these mixes, Mix 2H (with #4RG, 7% sand, and 1.5 lb/yd3 fiber) is currently showing the highest F-T resistance, which had 0.4% weight loss after subjected to about 180 F-T cycles. Mix 2A (with #4 RG, 7% sand) is the second to the highest, which had 0.8% weight loss at 180 F-T cycles and 2.3% weight loss at 300 F-T cycles. Mix 2C (with #4RG, 7% sand, and 10% latex replacement) comes to the third, which reached 15% weight loss at 216 F-T cycles. These results imply that when properly designed and constructed, PCPC can have an excellent serviceability under cold weather conditions. Discussion

Figures 2-7 illustrate the relationships Relationships among the PCPC Properties. among the PCPC properties tested. Most of the relationships are similar to those of conventional concrete. 7

Wang et al, submitted to NRMCA Concrete Technology Forum: Focus on Pervious Concrete, May 24-25, 2006, Nashville, TN

22

140

3

Unit Weight (kN/m ) = 24.19 - 0.2177 * Void Ratio

Unit Weight (kN/m3)

R2 = 0.92

130

20 125 19

120

18

115

Unit Weight (pcf)

135

21

110

17

105 16 10

15

20

25

30

35

Void Ratio (%)

Figure 2: Relationship between unit weight and void content

3000

y = 13.257e0.1579x R2 = 0.6522

Water Permeability (in./hr)

2500

2000

1500

1000

500

0 10

15

20

25

30

35

Void Content (%)

Figure 3: Relationship between permeability and void content 4,000 No. 4 sieve

3/8 inch sieve

7-day Compressive Strength (psi)

3,500

1/2 inch sieve 3,000 2,500 2,000 1,500 1,000 500 0 0.1

0.2

0.3

0.4

0.5

0.6

Aggregate Size (in.)

Figure 4: Relationship between coarse aggregate size and PCPC 7-day Strength (River Gravel)

8

3500

24 22

3000

20 18

2500

16

4.75 mm (No. 4), RG 9.5 mm (3/8 in.), RG 4.75 mm (No. 4) PG

14 12

2000

Best FIt

10

15

20

25

4000

Strength (MPa) = 49.95 - 1.181 * Void ratio 2

R = 0.97

24

3500 3000

20

2500 16 2000 9.5 mm (3/8 in.)

12

Best Fit

1500

8

1500

10

28

20

30

22

24

26

28

30

32

34

36

Void ratio (%)

Void Ratio (%)

(a) river gravel and pea gravel

(b) crushed limestone

Figure 5: Relationship between void content and 7-day compressive strength

28-day Splitting Strength, psi

500 450

R2 = 0.68

400 350 300 250 200 150 100 1000

2000

3000

4000

28-day Com pre s s ive Stre ngth, ps i

Figure 6: Relationship between compressive and splitting strength

350 # of F-T Cycles to Failure

350 300 250 200 150 100 50 0 1000

2000

3000

4000

300 250 200 150 100 50 0 100

200

300

400

28-day Splitting Stre ngth, ps i

28-day Com pre s s ive Stre ngth, ps i

(a) F-T durability vs. compressive strength

(b) F-T durability vs. splitting strength

Figure 7: Relationship between strength and F-T durability

9

500

7-day compressive strength (psi)

26

7-day compressive strength (MPa)

4000

Strength (MPa) = 33.45 - 0.725 * void ratio 2 R = 0.73

7-day compressive strength (psi)

28

# of F-T Cycles to Failure

7-day compressive strength (MPa)

Wang et al, submitted to NRMCA Concrete Technology Forum: Focus on Pervious Concrete, May 24-25, 2006, Nashville, TN

Wang et al, submitted to NRMCA Concrete Technology Forum: Focus on Pervious Concrete, May 24-25, 2006, Nashville, TN

Figure 2 shows that unit weight of the PCPC studied decreased linearly with void content. Figure 3 illustrates that the permeability of the concrete increased exponentially with the concrete void content. As a result, the unit weight test can serve as a simple, quick quality control test in field to ensure proper void content or permeability of the concrete. Figures 4 and 5 demonstrate the relationships between aggregate size, void content, and 7-day compressive strength of PCPC. There is a trend (Figure 4) that 7-day compressive strength of PCPC decreases with increased coarse aggregate particle size, which is similar to what is observed in conventional concrete and largely due to the weak interfacial transition zone between the cement paste the large size aggregate. Because of the reduced effect cross section area, the 7-day compressive strength of PCPC also decreases with the void content of the concrete (Figure 5). Figure 6 illustrates an acceptable linear relationship (R2=0.74) between the 28-day compressive and splitting tensile strength of the PCPC tested. If all the test data are considered, there is no clear relationship between the concrete strength and F-T durability (Figure 7). However, if one data point is taken away (Mix 3, in hollow), Figure 7b demonstrates a good relationship between the PCPC splitting/tensile strength and F-T durability. Therefore, the splitting tensile strength test results can serve as preliminary evaluations for the F-T resistance of PCPC. PCPC Mix Design Criteria and Considerations. The mix design criteria and procedure for PCPC are under development. In the consideration of PCPC function (permeable) and application (carrying traffic loads and exposed to a mild or cold weather condition), permeability, strength, and F-T durability of PCPC should be considered simultaneously in the concrete mix design. Table 9 summarizes the related PCPC properties from literature. Table 9: PCPC properties from literature Void Ratio

Unit Weight lb/ft3

Permeability in/hour

28-day Compressive Strength

Flexural Strength

(%)

(kg/m3)

(cm/sec )

psi (MPa)

psi (MPa)

15 to 25

100 - 125 (1602 -2002)

288 -756 (0.203-0.533)

15 to 35

NA

NA

United States 800 -3000 (5.5 -20.7) NA

150- 550 (1.03 -3.79) 363- 566 (2.50 -3.90)

Reference

Tennis et al. 2004 Olek and Weiss 2003

International 19

NA 118- 130

NA

20 to 30

(1890-2082)

NA

NA

NA

11 to 15

NA

NA 36-252 (0.025-0.178)

18 to 31

NA

NA

3771 (26.0) 2553 -4650 (17.6-32.1)

638 (4.4) 561 – 825 (3.87- 5.69 )

Beeldens et al. 2003

2756 (19.0)

NA 606- 1085 (4.18 -7.48 )

Tamai and Yoshida 2003

NA

Park and Tia 2004

NA 1595-3626 (11.0 -25.0)

NA = not available

10

Beeldens 2001

Kajio et al. 1998

Wang et al, submitted to NRMCA Concrete Technology Forum: Focus on Pervious Concrete, May 24-25, 2006, Nashville, TN

Based on the results from available literature and the present study, the performance-based mix design criteria for PCPC in a cold weather climate are proposed as follows: (1) water permeability: ≥ 140 in./hour (0.1 cm/sec ) (2) compressive strength at 28 days: ≥ 3000 psi (20 MPa ) (3) F-T durability (based on ASTM C666-Procedure A): ≤5% after 300 F-T cycles. These preliminary mix design criteria should be verified in field, and other important durability issues, such as clogging and wearing resistance, may be considered in the mix design in future. In order to meet the above permeability criterion, larger than 140 in/hour (0.1 cm/sec ), selecting coarse aggregate with proper void content is very important. Based on the present study, the void content of raw coarse aggregate should be higher than 35%. In the present study, a raw coarse aggregate, #4RG, had void content of 38.5%. The void content of the PCPC made with this aggregate was 25.3%, decreased approximate 10% when compared with raw aggregate. After replacing 7% of the coarse aggregate with sand (for strength and durability improvement), the corresponding PCPC had another deduction in the void content by 10%. As a result, the PCPC mix (Mix 2A: #4 RG with 7% sand) had void content of 18.5% and permeability of 140 in./hour (0.1 cm/sec ). This sequential deduction of void content may provide engineers with an insight to aid selection of raw aggregate materials in PCPC mix design. There are many factors affecting concrete strength, such as concrete materials, w/c, mixing and consolidation methods, some of which (such as consolidation) are discussed by authors in a separate paper. To meet the PCPC strength criterion above, using small amount of sand (7% weight of total aggregate in the present study) is recommended for the concrete permeability and cost considerations. The recommend w/c is 0.27 or lower; however, it can be further reduced if workability of the concrete is improved. The cement content should be just enough to coat the aggregate particles with a thin layer. In the present study, cement content of 570 lb/cy (338 kg/m3 ) was used for most mixes. The calculated average paste thickness around aggregate particles in these PCPC mixes is approximate 0.008” (200 micrometer). Excessive cement may seal the voids between aggregate particles and significant reduces permeability of the concrete. However, cement content may vary when different aggregate is used. For conventional concrete, F-T resistance of concrete largely depends on aggregate quality, concrete air void system (especially the void spacing factor) and strength (especially the strength of the interfacial transition zone between aggregate and cement paste). It is well accepted that concrete with void spacing factor of 0.008” (200 micrometer) generally has good F-T resistance. In PCPC, void system may be less important due to the open structure of the material. As mentioned above, the calculated average paste thickness around aggregate particles in the most PCPC mixes studied is approximate 0.008” (200 micrometer), which indicates that requirement for AEA might be arbitrary. However, it was observed under microscope that the paste thickness in some regions of the PCPC was often larger than the average value. Therefore, AEA is still recommended for the PCPC application under a cold weather condition until further research is conducted. Figure 7 has shown that PCPC F-T durability increases with concrete strength, especially the splitting tensile strength. Addition of micro-fiber or latex generally increases concrete tensile strength, and it therefore is recommended for the PCPC in the cold weather climate region. (Note that some latex modified PCPC in the present study did not perform well during the F-T tests, 11

Wang et al, submitted to NRMCA Concrete Technology Forum: Focus on Pervious Concrete, May 24-25, 2006, Nashville, TN

which is probably because the latex was used for cement replacement, rather than addition.) Based on the present study, the recommend 28-day splitting tensile strength value for the PCPC in the cold weather climate region is 360 psi (2.5 MPa) and higher. Concluding Remarks

In the present paper, effects of concrete materials (coarse aggregate, sand, cementitious materials, fibers, and latex) and mix proportions on PCPC functional properties (permeability and strength), quality control properties (void content and unit weight), and F-T durability are evaluated. The relationships between these properties are explored. The PCPC mix design criteria and considerations are discussed. The study concludes that when properly designed and constructed, PCPC can have an excellent serviceability under cold weather conditions. Proper strength and F-T durability of PCPC can be achieved by use small amount of sand and microfibers in the concrete. References Beeldens, A,. Van Gemert, D., and Caestecker, C. (2003). Porous Concrete: Laboratory Versus Field Experience. Proceedings 9th International Symposium on Concrete Roads, Istanbul, Turkey. Kajio, S., Tanaka, S., Tomita, R., Noda, E., and Hashimoto, S. (1998). Properties of Porous Concrete with High Strength, Proceedings 8th International Symposium on Concrete Roads, Lisbon, pp 171177. National Ready Mixed Concrete Association (NRMCA). (2004). Freeze-Thaw Resistance of Pervious Concrete. Olek, J., and Weiss, W. J., (2003). Development of Quiet and Durable Porous Portland Cement Concrete Paving Materials. Final Report SQDH 2003-5 Center for Advanced Cement Based Materials, Purdue. Park, S., and M. Tia. (2004). An experimental study on the water-purification properties of porous concrete. Cement and Concrete Research 34,177-184 Ramakrishnan, V. (1992) “Latex-Modified Concrete and Mortars,” NCHRP Synthesis 179, Transportation Research Board, National Research Council, Washington, D.C. Tamai, M., and Yoshida, M. (2003). “Durability of Porous Concrete.” Paper presented at the Sixth International Conference on Durability of Concrete, American Concrete Institute. Tennis, P.D., Leming, M.L., and Akers, D.J. (2004). Pervious Concrete Pavements, Special Publication by the Portland Cement Association and the National Ready Mixed Concrete Association.

United States Department of Agriculture (USDA). (1986). Technical Release 55: Urban Hydrology for Small Watersheds. Youngs, Andy. (2005). Pervious Concrete It’s for Real. Presentation at Pervious Concrete and Parking Area Design Workshop, Omaha.

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