Aggregate Effects on Pervious Portland Cement Concrete Static Modulus of Elasticity L. K. Crouch, P.E. 1 ; Jordan Pitt 2 ; and Ryan Hewitt 3 Abstract: The effects of aggregate gradation, amount, and size on pervious portland cement concrete PCC static modulus of elasticity were compared using four different mixtures. A standard mix and three variable mixes using a uniform gradation, increased aggregate amount, and increased aggregate size were used. The effective air void content was determined for each mixture. The compressive strengths and static elastic moduli were determined and compared at equal void contents. For a uniform gradation, the compressive strengths and static elastic moduli appeared to be higher within an optimal range of voids; however, there was no statistically significant difference between the results from the different gradations. An increased aggregate amount resulted in a statistically significant decrease in both compressive strength and static elastic moduli due to the subsequent decrease in paste amount. While the compressive strengths were higher for mixtures containing smaller aggregate sizes, there was no significant difference between the static elastic moduli when different aggregate sizes were used. Further research is needed to understand the effects of aggregate size on the static modulus of elasticity of pervious PCC. DOI: 10.1061/ASCE0899-1561200719:7561 CE Database subject headings: Concrete; Portland cements; Aggregates; Elasticity; Compressive strength; Compaction. Introduction and Literature Review Pervious concrete is a mixture of portland cement, water, coarse aggregate, and, in some cases, chemical admixtures and/or supplementary cementing materials. Excluding fine aggregate from the mixture lowers the workability of the fresh pervious portland cement concrete PCC. Therefore, a compactive effort must be applied in order to obtain desired properties, which in- clude strength and permeability. The lack of fines also creates an open void structure, allowing water to percolate from the surface down through the interconnected voids. The effective air voids are those which are accessible from the surface ASTM 2005b. The effective air void content plays a major role in the hardened properties of pervious PCC. Current research has shown that the effective void content affects the compressive strength and water permeability of the hardened concrete—at higher effective void contents, water permeability is increased, but the compressive strength is decreased Meininger 1988; Ghafoori and Dutta 1995. Thus, it is essential to optimize the effective void content in order to achieve both strength and permeability. Effective void contents in pervious PCC typically range from 15 to 35%. The desired void content may be achieved either by modifying the level of compactive effort or by adjusting the aggregate proportions and properties. When the level of compactive effort is minimal, the effective void content is typically increased. As the void content increases, there is a concomitant reduction in the compressive strength when using limestone aggregates Kevern et al. 2005; Meininger 1988. As no standard specifications have been determined for achieving compactive effort in the field, it is difficult to ensure that pervious PCC will obtain the desired amount of effective air voids, which directly affects strength and permeability. Therefore, experience has proven that it is more beneficial to modify the aggregate proportions and properties, such as gradation, size, and amount, rather than change the level of compactive effort, to reach desired void contents. Pervious PCC research at Tennessee Technological University, Cookeville, Tenn., has shown that the effective void content, com- pressive strength, and permeability are largely dependent upon the aggregate. The compressive strength is dependent on the size of the aggregate, whereas the effective void content is dependent upon gradation ACI 2004; Ghafoori and Dutta 1995. As the aggregate size decreases, the number of particles per unit of vol- ume increases. As the amount of particles increases, the binding area increases, resulting in improved strengths Yang and Jiang 2003. It has also been observed that pervious PCC fails at the binder layer between the aggregates, and the cement paste area should be increased in order to improve strength properties Yang and Jiang 2003. Modulus of elasticity and compressive strength are important properties used for the design of pervious PCC pavements Pasko 1998. Although the effect of aggregates on compressive strength has been studied, there has been no pub- lished research that reveals the effect of aggregates on the static modulus of elasticity of pervious PCC. Understanding the behav- ior of the elastic modulus in relation to aggregate proportions and 1 Professor, Dept. of Civil Engineering, Tennessee Technological Univ., Box 5015, Cookeville, TN 38505. 2 Field Engineer, Stanley D. Lindsey & Associates, Ltd., 1801 W. End, Suite 400, Nashville, TN 37203. 3 Graduate Research Assistant, Tennessee Technological Univ., Box 5015, Cookeville, TN 38505. Note. Associate Editor: Baoshan Huang. Discussion open until December 1, 2007. Separate discussions must be submitted for individual papers. To extend the closing date by one month, a written request must be filed with the ASCE Managing Editor. The manuscript for this paper was submitted for review and possible publication on January 11, 2006; approved on December 28, 2006. This paper is part of the Journal of Materials in Civil Engineering, Vol. 19, No. 7, July 1, 2007. ©ASCE, ISSN 0899-1561/2007/7-561–568/$25.00. JOURNAL OF MATERIALS IN CIVIL ENGINEERING © ASCE / JULY 2007 / 561