A RATIONAL AND SUSTAINABLE APPROACH TO PAVEMENT CONCRETE MIXTURE DESIGN Md Sarwar Siddiqui 1 and David W. Fowler 2. The University of Texas at Austin

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1 A RATIONAL AND SUSTAINABLE APPROACH TO PAVEMENT CONCRETE MIXTURE DESIGN Md Sarwar Siddiqui 1 and David W. Fowler 2 1 Graduate research assistant 2 Professor The University of Texas at Austin Md Sarwar Siddiqui PhD Candidate The University of Texas at Austin Construction Materials Research Group 11 Burnet Rd, Bldg 18B Austin, TX Phone: (785) mssiddiqui@utexas.edu David W. Fowler Professor The University of Texas at Austin Civil, Architectural and Environmental Engineering Department International Center for Aggregates Resources 31 E. Dean Keeton St. Stop C1747 Austin, TX Phone: (512) dwf@mail.utexas.edu 214 International Concrete Sustainability Conference 1 National Ready ed Concrete Association

2 ABSTRACT There is an increasing need to use manufactured sands in pavement concrete in areas where sources of natural sand are not available or are being depleted. Manufactured sands usually do not meet the ASTM C33 grading requirements and have high micro fine contents, poor shape, and poor texture. The primary problems of using manufactured sands in concrete are (1) that there is no recognized mixture design method available for manufactured sand and (2) carbonate sands produce concrete that has poor long-term skid resistance and required blending to provide adequate surface friction. Concrete with manufactured sand, designed by ACI 211, often results in unacceptable workability and experiences segregation, excessive bleeding, and edge slump. A logical method of concrete mixture design has been developed based on the previous work done by the International Center for Aggregates Research (ICAR). This method was based on the densest combined grading of fine and coarse aggregate. Major advantages of the proposed mixture design are: (1) aggregates from any sources irrespective of grading, shape, and texture can be used, (2) allows aggregate blending, which is important from the coefficient of thermal expansion and skid resistance point of view, and (3) permits the adjustment of the paste volume, thus has the potential to reduce the cement content in the concrete mixture. Laboratory results have shown that the proposed mixture design can save up to 15 lb/yd 3 of cement compared to mixtures designed by ACI 211 without compromising strength or durability. Therefore, this proposed mixture design has the potential to produce less expensive and sustainable concrete without sacrificing performance. 214 International Concrete Sustainability Conference 2 National Ready ed Concrete Association

3 INTRODUCTION Concrete is the single most widely used construction material in the world. Cement, aggregate, and water are the key ingredients of concrete. Cement is the most expensive component in concrete as well as the component with highest carbon footprint. Cement industry is responsible for about 5% of the global anthropogenic CO 2 emission (Worrell et al. 21). As a result, the concrete industry has been pushing to reduce cement content to produce more economical and sustainable concrete. This goal was partially achieved by replacing cement with other supplementary cementation materials. One of the other alternatives, and probably the most logical way to achieve economical and sustainable concrete, is to reduce the cement content by increasing aggregate volume. However, due to increased use of construction materials good quality aggregate sources are also being depleted. Consequently, the concrete industry is forced to use other aggregate sources such as manufactured sand. Every year a huge quantity of manufactured sand is produced as a byproduct of the crushed aggregate industry in the U.S. Use of manufactured sand can also reduce the overall coefficient of thermal expansion (CTE) of concrete, because typically manufactured sands have lower CTE than siliceous river sands. High CTE of concrete is responsible for some early age cracking in concrete structures, also one of the major factors of pavement distresses including faulting, punchouts, and delamination (Darwin et al. 21; Mallela et al. 25). Very recently the Texas Department of Transportation (TxDOT) assigned an upper limit of 5.5x1-6 strain/ o F on the CTE of continuously reinforced concrete pavement (CRCP) coarse aggregates to reduce pavement distresses. In addition to the use manufactured sand, another alternate ways of optimizing concrete CTE are to blend low CTE aggregates with high CTE aggregates (Siddiqui and Fowler 213, 214) and to reduce cement content. But, currently available mixture design methods do not have rational way of selecting cement content, not suitable for manufactured sand that typically has poor grading, shape, texture, and high micro fines content (aggregates passing #2 sieve), and do not provide guideline for three or more aggregate blends. LIMITATION OF ACI 211 Concrete mixture design is the method of choosing different ingredients of concrete such as cement, aggregates, water, chemical admixtures, and mineral admixtures. The objective of a successful mixture design is to achieve desired fresh and hardened concrete properties in the most economical and sustainable manner. The concrete industry has been trying to use manufactured sand for years for two reasons, to promote use of an aggregate industry byproduct to make more sustainable concrete and to use manufactured sands as viable alternate sources of fine aggregate in regions where natural sources of fine aggregate are not available. Often manufactured sands have poor grading, shape, texture, and high micro fines content. Manufactured sands typically do not meet ASTM C33 (213) requirement and are too fine or too coarse. Hence, concrete proportioned with conventional mixture design such as, ACI 211 (29) with manufactured sand showed poor workability, excessive bleeding, edge slump, and edge shear, since additional adjustments were not made for poor shape and texture (Saunders 1995; Siddiqui et al. 214). ACI 211was not designed for manufactured sand and only suitable for well graded aggregates as specified by ASTM C33. Studies have shown that shape, texture, and the combined aggregate grading (fine and coarse aggregate) are the major factors that affect the workability of concrete (Quiroga and Fowler 24; Koehler and Fowler 27; Rached et al. 29). ACI 211 does not consider all these factors while determining cement content and mixing water requirement. This method only suggests adjusting the mixing water requirement based on 214 International Concrete Sustainability Conference 3 National Ready ed Concrete Association

4 the shape of coarse aggregates (rounded vs angular). ACI 211 uses the fineness modulus (FM) of fine aggregate (FA) to determine the coarse aggregate fraction. It is not clear how fine aggregate FM can be rationally used to determine the coarse aggregate fraction. Moreover, completely different aggregate gradings can produce the same FM (Hudson 23). The FM is an unreliable method of representing aggregate grading. This may not be significant for ASTM C33 aggregates, but for manufactured sand with high fine content, this difference can be significant. ACI 211 uses the dry roded unit weight (DRUW) of coarse aggregate in concrete mixtures, which accounts for the effect of size, shape, and texture. However, it does not consider the effect of size, shape, and texture of fine aggregate. Quiroga and Fowler (24) showed that shape and texture of fine aggregates have more significant effect on the workability of fresh concrete than coarse aggregate. Combined grading of coarse and fine aggregates obtained from ACI 211 can be gap graded (Shilstone 199). Gap graded aggregates need a higher volume of cement paste than well graded aggregate to achieve the same workability (Andersen and Johansen 1993; Glavind et al. 1993; Goltermann and Johansen 1997; Johansson 1979). ACI 211 allows only one fine and one course aggregate in concrete, but, does not provide any guideline for three or more aggregates, which has become important for CTE optimization. There are other mixture design methods available namely, band gradation, Shilston s optimized concrete mixture design, Europack, theory of particle mixture, and the compressible packing model method. All of these methods have the objective of increasing the packing density of the concrete by optimizing aggregate grading. Higher packing density reduces the void content and also the cement and water demand. However, these methods do not consider the combined aggregate grading, provide a method for calculating the cement content, or are too complex. Koehler and Fowler (27) proposed a mixture design for self-consolidating concrete known as the ICAR mixture design. This paper uses the same philosophy of proportioning but is modified for designing slip-form pavement concrete. MIXTURE DESIGN PHILOSOPHY Increasing the packing density of aggregate to reduce cement paste volume has been a common philosophy for most of the mixture design methods. Increased packing density reduces the void content and also decreases the cement paste requirement. The usual approach has been to improve the grading of coarse aggregate to improve the packing density. The void content does not depend on the grading of coarse aggregate only; it depends on the combine grading of coarse and fine aggregate. Hence, this proposed method took a more rational approach to improve the combined grading of coarse and fine aggregates to achieve highest packing density. Combined grading is adjusted by varying the volume fraction of each aggregate that allows multiple aggregate blending. Selection of paste volume is arbitrary for most of the mixture designs. Theoretically, cement paste volume should be equal to the volume of voids to achieve desired strength, but additional paste is usually required to achieve workability. This method determines the required cement paste volume from the void content of combine aggregate. This is the minimum theoretical paste requirement for concrete. The paste volume is later adjusted from trial batches to achieve desired strength and workability. 214 International Concrete Sustainability Conference 4 National Ready ed Concrete Association

5 PROPOSED MIXTURE DESIGN STEPS Based on the above mixture design philosophy the proposed mixture design method can be stated as follows: 1. Evaluate aggregate properties such as, aggregate grading, specific gravity, and moisture content. 2. Determine optimum aggregate combination to achieve maximum packing density. The power.45 curve is recommended, but any other aggregate packing model can be used. 3. Determine the void content for combine aggregate obtained in step 2 from the DRUW test (ASTM C29 / C29M ). This void content is equivalent to the theoretical paste volume of the trial mixture. % _ 1 / % Here, p i is the volume of aggregate fraction i divided by the total aggregate volume, and (SG OD ) i is the oven-dry specific gravity of aggregate fraction i. 4. Select property of cement paste, i.e., water-to-cement ratio (w/c), chemical admixtures, mineral admixtures, and percent air content. 5. Perform trial batches and adjust the cement paste volume to achieve the desired fresh and hardened concrete properties. Figure 1 represents different steps of the proposed mixture design. This is a concrete mixture consist of two course and two fine aggregates. 214 International Concrete Sustainability Conference 5 National Ready ed Concrete Association

6 Fine aggregate % Passing % Passing 6 5 RS2 4 MS3 3 ASTM C33 Limit Size (in.) 5 CA3 4 CA4 Coarse aggregate Size (in.) (a) Determine aggregate properties. Fine and coarse aggregate grading are presented here. 214 International Concrete Sustainability Conference 6 National Ready ed Concrete Association

7 % Passing Sieve Sizes ^.45 (in.) (b) Selection of aggregate proportion to achieve highest packing density. In this mixture design 18, 5, 2, and 12% of CA4, CA5, RS2 and MS3 was used, respectively. (c) Coarse and fine aggregates before blending (at the left) and after blending (at the right) to determine DRUW. Theoretical cement paste volume was equal to the void content calculated form DRUW. 214 International Concrete Sustainability Conference 7 National Ready ed Concrete Association

8 28-day strength Slump day compressive strength (psi.) Slump (in.) Offset from theoretical paste volume (%) (d) Perform trial batches to determine the optimum paste volume based on strength and workability requirement. FIGURE 1 Proposed mixture design steps for a blend of two coarse and two fine aggregates. MATERIALS Six different sand and five different coarse aggregates were used in this study. Two of the sands were natural river sand (RS) and the rest were manufactured sand (MS). Bothe river sands (RS1 and RS2) and one manufactured sand (MS4) met the ASTM C33 requirements. Other manufactured sands (MS1, MS2, and MS3) did not meet the ASTM C33 graduation requirement; MS1 and MS3 also had high micro fine contents, about 8 and 22%, respectively. Three coarse aggregates (CA1, CA2, and CA5) met ASTM grade 57 (TxDOT grade 4) and CA4 met ASTM grade 467 (TxDOT grade 2) grading requirements. Coarse aggregate CA3 met TxDOT grade 3 but did not meet the ASTM C33 grading requirement. Additional information on the aggregate properties can be found elsewhere (Siddiqui et al. 214). An ASTM C15 (212) Type I/II and an ASTM C494 (213) Type A water reducing admixture (WRA) was used for all concrete mixtures. The recommended dose of WRA was 3 to 1 fl oz/1 lbs (195 to 652 ml/1 kg) of cement. A.45 water-to-cement ratio (w/c) was used for all laboratory concrete mixtures. 214 International Concrete Sustainability Conference 8 National Ready ed Concrete Association

9 MIXTURE PROPORTIONING AND TEST METHODS Eleven different aggregate blends were used for concrete mixtures. Table 1 shows aggregate blends and percent volume of each aggregate to achieve highest packing density, as density, as well as optimum paste volume obtained from combined DRUW. es 1 to 1 1 consisted of one coarse and one fine aggregate and ture 11 was a blend of two coarse and two fine aggregates. Concrete was mixed according to ASTM C192 (212). Two to four concrete mixtures were used for each aggregate blend by varying the cement paste volume to determine the effect of paste volume on workability and strength. The WRA dosages were selected by trial and error and adjusted to obtain slumps greater than 1-in. To achieve a better distribution, WRA was premixed with mixing water. Concrete workability was determined by the slump test according to ASTM C143 (212). Concrete cylinders were made to determine the 28-day compressive strength and modulus of elasticity (E) according to ASTM C39 (212) and C469(21), respectively. The cylinder size for concrete tures 1 to 8 was 4-in.x8-in. and for tures 9 to 11 was 6-in.x12-in. TABLE 1 Concrete tures Showing Aggregate Fractions and Optimized Paste Volume ID Coarse Aggregate Fine Aggregate Optimum Paste Volume 1 6% CA1 4% RS % CA1 4% MS % CA1 45% MS % CA1 38% MS % CA1 42% MS % CA 2 35% RS % CA 2 36% MS % CA 2 42% MS % CA3 4% RS % CA3 38% MS % CA4 + 5% CA5 2% RS2 + 12% MS RESULTS AND DISCUSSIONS Physical Properties of Concrete mixtures With the Theoretical Paste Content tures 1 to 11 presented in this section are those made with minimum theoretical paste volume obtained from combined DRUW. Figure 2 shows the slump and WRA dose used for mixtures with optimized paste volume. Typical slump requirement for slip-form pavement concrete is 1 to 3 in. with 1 to 1.5 in. considered to be desirable. Eight concrete mixtures had slump values 1-in. or higher. Higher slump mixtures can be easily adjusted to achieve desirable workability by reducing w/c, paste volume, and WRA. tures 2, 4, and 8 had slumps lower than 1-in. It is possible to improve the workability of tures 2 and 8 by increasing the dose of WRA. Even though the maximum WRA dose was used for ture 4, only ¼-in. slump was achieved. ture 4 contained MS3, which had high micro fines content. Higher micro fines 214 International Concrete Sustainability Conference 9 National Ready ed Concrete Association

10 content significantly increased the water demand, which explains the reason of poor workability of ture 4. Figure 3 shows the 28-day compressive strength and modulus of elasticity for tures 1 to 11. The 28- day compressive strengths of all the mixtures were more than 6 psi, which typically satisfies the 28-day compressive strength requirement of pavement concrete for most state agencies. The 28-day modulus of elasticity varies from 3.5 to 5 million psi. tures 3 and 8 had the lowest moduli of elasticity and contained sand CM2. From visual inspection CM2 had the worst shape and texture. Poor particle shape and texture of fine aggregate may generate weaker interfacial transition zones and can be the reason for low modulus of elasticity. Slump WRA dose/max dose Slump (in.) WRA dose normalized to max. dose ture ID FIGURE 2 Slump and WRA dose of concrete mixtures with optimized paste volume. 214 International Concrete Sustainability Conference 1 National Ready ed Concrete Association

11 28-day Str. E Strength (psi.) Millions E (psi.) ture ID FIGURE 3 28-day compressive strength and E of concrete mixtures with optimized paste volume. Solid horizontal line is the TxDOT 28-day strength requirement of 44 psi. Effect of Paste Volume on the Physical Properties of Concrete Volume of cement paste controls the fresh and hardened properties of concrete. Paste volumes of the concrete mixtures were varied to determine the effect on the measured properties of concrete. Reduction in cement paste while keeping other parameters unchanged typically reduce the workability. Figure 4 illustrates the effect of paste volume on the workability of concrete. Even though higher WRA dosages were used with reduced paste volume, workability decreased as the paste volume decreases. 214 International Concrete Sustainability Conference 11 National Ready ed Concrete Association

12 Slump (in.) Offset from theoretical paste volume (%) FIGURE 4 Effect of paste volume on the workability of concrete mixtures. Figures 5 and 6 show the effect of paste volume on the 28-day compressive strength and modulus of elasticity, respectively. All the concrete mixtures tested had a compressive strength higher than the TxDOT 28-day compressive strength requirement of 44 psi. tures 3, 5, and 8 showed reductions in 28-day concrete strength with reduced paste volume beyond the minimum theoretical paste volume, probably due to the lack of cement paste necessary to cover all the aggregate particles. tures 3 and 8 contain fine aggregate MS2. MS2 had poor grading and shape, which increased the paste demand and contributed to the strength reduction. ture 6 and 7 showed reductions in strength with increased paste volume. The reason for this behavior cannot be readily explained. The variation of modulus of elasticity due to the variation of paste volume is not significant and might fall within the variation of the test. 214 International Concrete Sustainability Conference 12 National Ready ed Concrete Association

13 Compressive strength (psi.) Offset from theoretical paste volume (%) FIGURE 5 Effect of paste volume on the 28-day strength of concrete. E (psi.) Millions Offset from theoretical paste volume FIGURE 6 Effect of paste volume on the modulus of concrete. 214 International Concrete Sustainability Conference 13 National Ready ed Concrete Association

14 Comparison of ACI 211 and Proposed ture Design Trial concrete mixtures were proportioned according to ACI 211 to compare with the proposed mixture design. ture 1, 2, 5, 6, and 7 were chosen, because aggregate used in this mixtures meet ASTM C33 requirement, except MS1 which did not quite meet the ASTM C33 grading requirement. For ACI 211 concrete proportions, 6 and 5 psi 28-day compressive strengths were considered. Although, 6 psi is a better match for the 28-day compressive strength of the concrete mixtures with theoretical paste volume, 5 psi was considered due to the over design nature of ACI 211. Figure 7 shows the cement requirement for concrete mixtures proportioned by the proposed method and by ACI 211 method. The proposed mixture design required up to 15 and 8 lb/yd 3 less cement compared to the 6 and 5 psi ACI method. Reduction of cement not only saves money, but also reduces the carbon footprint of concrete, making it a more sustainable construction material. 7 6 Cement Content (lb/yd 3 ) ACI-5 ACI-6 psi psi ture ID Figure 7 Comparison of Proposed and ACI 211 ture Design Method CONCLUSIONS Producing more economical and sustainable concrete has been a target of the construction industry because of its wide use as a construction material. Currently available mixture design methods are unable to address important issues in a rational way, i.e.to determine cement paste volume, use aggregate sources irrespective of grading, shape, and texture, and to use multiple 214 International Concrete Sustainability Conference 14 National Ready ed Concrete Association

15 aggregate blends. This study presents a mixture design method that provides the solution to these shortcomings of ACI 211. Important findings of this study are as follows: This mixture design method can use aggregates from any source irrespective of grading, shape, and texture and provides a rational way to determine the required cement paste volume. Using this method three or more aggregates can be used in a concrete mixture. This method has the potential to reduce cement without sacrificing the performance of concrete and can use locally available aggregate sources which were not considered before. This is a simple and easy method that does not require complex calculation. Though this study is focused on pavement concrete, this mixture design generally can be used for any type of concrete. Further study is needed to check the suitability of this mixture design method for all types of concrete. ACKNOWLEGEMENT The authors acknowledge the help and support of the Construction Materials Research Group at the University of Texas at Austin and in particular the assistance from David Whitney, Michael Rung, and Marc Rached. REFERENCES ACI (29). Standard Practice for Selecting Proportions for Normal, Heavyweight, and Mass Concrete. ACI manual of concrete practice, Part 1, American Concrete Institute, Detroit, Mich, 38 pp. Andersen, P. J., and Johansen, V. (1993). Particle packing and concrete properties. Volume 43 of RH & H bulletin. ASTM C143 / C143M (212). Standard Test Method for Slump of Hydraulic-Cement Concrete. ASTM International, 1 Barr Harbor Drive, PO Box C7, West Conshohocken, PA , United States, 8. ASTM C15 / C15M (212). Standard Specification for Portland Cement. ASTM International, 1 Barr Harbor Drive, PO Box C7, West Conshohocken, PA , United States, 9. ASTM C192 / C192M - 12a. (212). Standard Practice for Making and Curing Concrete Test Specimens in the Laboratory. ASTM International, 1 Barr Harbor Drive, PO Box C7, West Conshohocken, PA , United States, 8. ASTM C29 / C29M - 9. (29). Standard Test Method for Bulk Density ( Unit Weight ) and Voids in Aggregate. ASTM International, 1 Barr Harbor Drive, PO Box C7, West Conshohocken, PA , United States, 5. ASTM C33 / C33M (213). Standard Specification for Concrete Aggregates. ASTM International, 1 Barr Harbor Drive, PO Box C7, West Conshohocken, PA , United States, International Concrete Sustainability Conference 15 National Ready ed Concrete Association

16 ASTM C39 / C39M - 12a. (212). Standard Test Method for Compressive Strength of Cylindrical Concrete Specimens. ASTM International, 1 Barr Harbor Drive, PO Box C7, West Conshohocken, PA , United States, 7. ASTM C469 / C469M - 1. (21). Standard Test Method for Static Modulus of Elasticity and Poisson s Ratio of Concrete in Compression. ASTM International, 1 Barr Harbor Drive, PO Box C7, West Conshohocken, PA , United States, 5. ASTM C494/C494M. (213). Standard Specification for Chemical Admixtures for Concrete. ASTM International, 1 Barr Harbor Drive, PO Box C7, West Conshohocken, PA , United States, 1. Darwin, D., Browning, J., Lindquist, W., McLeod, H., Yuan, J., Toledo, M., and Reynolds, D. (21). Low-Cracking, High-Performance Concrete Bridge Decks. Transportation Research Record: Journal of the Transportation Research Board, 222(-1), Glavind, M., Olsen, G. S., and Munch-Petersen, C. (1993). Packing Calculations and Concrete Design. Nordic Concrete Research, 13(2), Goltermann, P., and Johansen, V. (1997). Packing of Aggregates: an Alternative Tool to Determine the Optimal Aggregate. ACI Materials Journal, 94(5), Hudson, B. (23). Blending Sands for Concrete. Field Evaluation, Austin, TX. Johansson, L. (1979). The Effect of Aggregate Grading and Proportions on the Workability for Concrete Made with Entirely Crushed Aggregate. Studies on Concrete Technology, Swedish Cement and Concrete Research Institute, Koehler, E. P., and Fowler, D. W. (27). Aggregates in Self-Consolidating Concrete. Research Report, International Center for Aggregates Research, The University of Texas at Austin, Austin, TX, 353. Mallela, J., Abbas, A., Harman, T., Rao, C., Liu, R., and Darter, M. (25). Measurement and Significance of the Coefficient of Thermal Expansion of Concrete in Rigid Pavement Design. Transportation Research Record: Journal of the Transportation Research Board, 1919(-1), Quiroga, P. N., and Fowler, D. W. (24). The Effects of Aggregates Characteristics on the Performance of Portland Cement Concrete. Research Report, International Center for Aggregates Research, The University of Texas at Austin, Austin, TX, 382. Rached, M., De Moya, M., and Fowler, D. W. (29). Utilizing Aggregates Characteristics to Minimize Cement Content in Portland Cement Concrete. Research Report, International Center for Aggregates Research, The University of Texas at Austin, Austin, TX, 117. Saunders, C. H. (1995). Manufactured Sand Usage in North Carolina. Austin, TX. Shilstone Sr, J. M. (199). Concrete ture Optimization. Concrete International, 12(6), Siddiqui, M. S., and Fowler, D. W. (213). Optimizing the COTE of Concrete by Blending High and Low COTE Aggregates to Meet TxDOT Limit. Sustainable pavements and materials, 2nd T&DI Green Street, Highways and Development 213, Austin, TX, Siddiqui, M. S., and Fowler, D. W. (214). Effect of Internal Water Pressure on the Measured Coefficient of Thermal Expansion of Concrete. Journal of Materials in Civil Engineering (ASCE), 14, in press. Siddiqui, M. S., Rached, M., and Fowler, D. W. (214). A Rational ture Design for Pavement Concrete. Transportation Research Record: Journal of the Transportation Research Board, 13, in press. 214 International Concrete Sustainability Conference 16 National Ready ed Concrete Association

17 Worrell, E., Price, L., Martin, N., Hendriks, C., and Meida, L. O. (21). Carbon Dioxide Emissions from the Global Cement Industry1. Annual Review of Energy and the Environment, 26(1), International Concrete Sustainability Conference 17 National Ready ed Concrete Association