Recycled Concrete Aggregates in Roadways: A Laboratory Examination of Self-Cementing Characteristics

This paper examines the self-cementing phenomenon of the road construction material known as recycled concrete aggregate (RCA). Two RCA types were selected as study materials: (1) high-grade RCA (HRCA), a quality RCA manufactured from relatively high-strength concrete structures; and (2) road base RCA (RBRCA), a high-grade RCA blend combined with brick and general clean rubble (road base material). Laboratory tests were performed to obtain the unconfined compressive strength, indirect tension dynamic modulus, and resilient modulus of the test samples to examine their hardening characteristics when subjected to varying curing periods. These tests were performed in conjunction with microstructure analyses from X-ray diffractometry (XRD) and scanning electron microscope (SEM) techniques. The HRCA samples, which were prepared and subjected to varying curing conditions, transformed from an initially unbound material into a bound (fully stabilized) material. The results of XRD and SEM analyses clearly demonstrate that secondary hydration occurred. The RBRCA samples were able to maintain their unbound granular properties, with nonsignificant self-cementing, thus supporting the hypothesis that the mixing of nonactive materials such as bricks and clean rubble into RCA will lessen the tendency of RCA toward self-cementing