Physicochemical Properties Evaluation of Asphalt-Coated Aggregates and Its Influence on Cement Hydration

The detrimental effect of asphalt-coated (reclaimed asphalt pavement or RAP) aggregates on the mechanical strength of portland cement concrete is well documented; however, the aggregates influence on the cement hydration process and subsequent effect on the concrete’s performance is not well established. This study investigates the effect of asphalt-coated RAP aggregates on the cement hydration process and its effect on mechanical strength. Asphalt-coated RAP aggregates were characterized by their physical, chemical, and mineralogical properties. The aging index and asphalt content were also investigated. A total of 13 mixes were formulated at different RAP replacement levels (volume replacement of coarser fraction) of 0%, 20%, 40%, 60%, and 80%. Based on test results, the addition of RAP reduced compressive strength and flexural strength by 8.16%–43.22% and 0.19%–24.95%. Fourier transform infrared (FTIR) analysis indicated an increase in the peaks associated with the clinker phase while peaks associated with the ─ OH stretch of calcium hydroxide disappeared in the RAP-concrete samples. In addition, the reduction in the nonevaporable water content in the RAP-concrete was observed. Thermogravimetric analysis (TGA) also revealed a reduction in the consumption of calcium hydroxide, indicating its impact on cement hydration. This study demonstrates that the mechanical strength of asphalt-coated RAP-concrete is closely linked to changes in cement hydration.