Durability of a pavement foundation made from recycled aggregate concrete subjected to cyclic wet-dry exposure and fatigue loading

Long term durability of recycled materials continues to be a major concern for their wide-scale use in civil engineering construction. The purpose of this study is to provide an insight into the damaging effects of combined wet-dry cycles, and repeated mechanical loading in a roller-compacted concrete pavement base course, made from recycled crushed aggregate (80 % by weight) and cement. This laboratory-based investigation was divided into three phases, each consisting of specimens subjected to prior wet-dry cycles (WD specimens), and control specimens which were not exposed to wet-dry cycles (NWD specimens). Phase I experiments involved monotonic loading tests, under compression and flexure, to evaluate the strength properties. Phase II involved testing cylindrical specimens in cyclic compressive (fatigue) loading at three different stress ratios. After each regime of cyclic loading, residual compressive strengths were determined. In addition, the load-deformation hysteresis loops, and the accumulated plastic deformation, were continuously monitored through all loading cycles. Phase III included an evaluation of flexural fatigue behavior and fatigue endurance limit of beam specimens. It was found that the specimens subjected to wet-dry cycles suffered significantly higher damage characterized by permanent deformation, residual compressive and flexural strengths, and fatigue resistance, compared to specimens not exposed to wet-dry cycles. These findings should be important design considerations when recycled products are incorporated in the pavement structure as promising alternative materials for achieving sustainable growth, environmental benefits, and possible economic savings.