EVALUATION OF THE EFFECT OF COARSE AGGREGATE TYPE ON CRCP THICKNESS

Abstract

The significant effect of the coarse-aggregate type on the performance of concrete pavements has not been fully accounted for in the design­ construction process. Among the principal properties of concrete that vary with coarse­ aggregate type are the modulus of elasticity, the coefficient of contraction and expansion, and the tensile strength. These properties, in turn, influence concrete pavement performance. However, the selection of coarse aggregate type is often left to the contractor without evaluating the consequences of using an aggregate whose properties were not considered in the design stage. In order to illustrate the variation of CRCP performance with the two coarse-aggregate types most often used in Texas, i.e., crushed limestone and siliceous river gravel, typical values of the physical properties of concrete produced with these two aggregates were selected from laboratory results. Three different approaches were used to estimate thickness equivalencies between a limestone and a siliceous river gravel CRCP. In the first approach, the AASHTO equation for design of rigid pavements permitted the development of equivalent thicknesses for· CRC pavements. The second and third approaches rely on a design equation and a distress-prediction model, respectively, derived from CRCP condition survey data collected in the state of Texas. The theoretical analyses described in this report and laboratory results both agree with the observed performance of CRC pavements built with these two coarse aggregate types, which is that for similar conditions, generally less distress has been observed in limestone CRC pavements, Findings developed herein could be used to determine approximate equivalent thicknesses for the two aggregate types considered in the study if there is no need for a detailed analysis. Additionally, by using the recommended thickness equivalencies, the designer has enough information to estimate costs of construction of a CRCP section when he is permitted to employ either limestone or siliceous river gravel coarse aggregate.