Extended water/cement ratio law for cement mortar containing recycled asphalt pavement

Abstract

In this research study, the strength development of cement mortar (CM) containing recycled asphalt pavement (RAP) as fine aggregate replacement for natural sand was investigated by means of strength, X-ray diffraction and scanning electron microscopy tests. The effect of the RAP replacement ratio, water to cement ratio (w/C) and curing time on strength development was evaluated. RAP had noticeably higher water absorption at saturated surface dry (SSD) state and slower rate of absorption than sand. The additional water to be compensated for the SSD state remained as the free water in the mix after hardening. RAP replacement at an optimum ratio of 25% increased the production of cementitious products and compressive strength for low w/C of <0.5, which was insufficient for cement hydration. While RAP replacement caused larger porosity and the production of lower cementitious products and compressive strength for high w/C of >0.5. Based on the critical analysis of the test results, the combined water (w*) parameter was defined as the sum of reacted water (w) and after-hardening unabsorbed water (wu). This parameter was used to generate the extended water to cement ratio law for prediction of strength development in RAP-CM. The outcome of this research will facilitate the mix design of RAP-CM at various RAP replacement ratios, w/C ratios and curing times.