The reuse of recycled crushed concrete aggregate (RCCA) and reclaimed asphalt pavement (RAP) can provide a sustainable solution for the disposal of C&D waste materials instead of sending them to landfills. More importantly, it will conserve energy and reduce environmental concerns. Several states in the USA have been using RCCA and RAP as base materials for years, focusing on the quality of the recycled materials. The structure of Recycled Aggregate (RA) is more complex than that of Natural Aggregate (NA). RAs have old mortar adhered on them that forms a porous surface at the interfacial transition Zone (ITZ) and prevents new cement mix from bonding strongly with the aggregates. The objective of this study was to correlate microstructural properties such as microporosity, inter and intra aggregate pores with the unconfined compressive strength (UCS) of RAP and RCCA molds, mixed at different proportions. In this paper, the quantity of micropores and their effect on the strength of mixed materials is used as the basis of microstructural analysis of recycled concrete and reclaimed asphalt. Microstructural properties obtained from analyzing scanning electron microscope (SEM) images were correlated with unconfined compressive strength. Intra-aggregate and interaggregate pores were studied for different ratios of cement treated mixture of RAP and RCCA. The results show that addition of RAP considerably increases the number of pores in the mixture, which eventually causes reduction in unconfined compressive strength. In addition, significant morphological and textural changes of recycled aggregates were observed by SEM image analysis.

The use of recycled flex-base materials such as recycled crushed concrete aggregate (RCCA) and reclaimed asphalt pavement (RAP) are increasing considerably nowadays in pavement base layer applications. Increased use of these materials address the issues of depletion of natural resources and provide solution to the adverse effect on environment. The recycled materials utilized in this study was collected from the Texas Department of Transportation (TxDOT) approved sources. The properties of recycled base materials depend solely on the sources and their environmental aspects of using as base material needs to be analyzed. A comprehensive laboratory evaluation of geo-environmental properties of RCCA and RAP in untreated or cement treated condition were conducted in this study. The amount of RAP and RCCA varied from 0%-100% in the combination at 50% interval with cement content varying from 0% to 6% at 2% interval. The specimens were prepared at optimum moisture content and maximum dry density obtained from the test results. The geo-environmental tests included permeability and leaching tests. Leaching tests included pH, total and volatile dissolved solids, total and volatile suspended solids, turbidity and chemical oxygen demand (COD). Tests results were compared with the requirements of different environmental protection agencies. The comparison of tests results indicated that the recycled base materials were environmentally sound alternative to regular virgin aggregates and can be used in pavement base or sub-base layer.