Waste generation in household, industry, and highway reconstruction has spurred recycling nationwide. One of the venues for use of recycled materials is in road construction. Th is study evaluated the suitability of 17 mixtures of four recycled materials with aggregates as a replacement of 100% virgin aggregates in base and subbase layers of roads. Recycled materials tested were recycled asphalt pavement (RAP), recycled concrete material (RCM), fly ash (FA), and foundry sand (FS). Properties characterized were water retention, hydraulic conductivity, resilient modulus (M R), shear strength, and leaching characteristics. In this paper, we discuss the hydraulic and mechanical characteristics of these mixtures. The shapes of the water retention curves of recycled mixtures were nearly similar whereas the saturated hydraulic conductivities of these mixtures were higher than that of 100% aggregates. Th is suggested that the drainage characteristics of these particular recycled materials mixtures with aggregates will be similar or better than that of 100% aggregates. Generally, addition of RAP, RCM, and FA+RAP to aggregates increased M R values but addition of FS (fine material) to aggregate decreased the MR values. Th ese results suggest that the stiff ness of these particular RAP, RCM, and FA mixtures of aggregates will be similar or better than that of 100% aggregates. Addition of RAP, RCM, and FA+RAP to aggregates generally increased the cohesion values whereas friction angles mostly varied within a narrow range (38-49°). Addition of FS to aggregates, however, did not improve the shear strength of the mixtures. Based on these results, we concluded that FA, RAP, and RCM mixtures will be good substitutes for virgin aggregates in base and subbase layers of roads.
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