Bonding in cementitious materials with asphalt-coated particles: Part II - Cement-asphalt chemical interactions

Reclaimed asphalt pavement (RAP), when used as an aggregate in concrete, will reduce bulk concrete strength and modulus. While Part I of this study investigated the properties of the interfacial transition zone (ITZ), Part II focuses on the nature of the cement-asphalt bond. Several chemical oxidative treatments of the asphalt were found to improve the interfacial cement-asphalt bond energy without affecting the ITZ porosity and size. Based on surface free energy measurements, the failure mode was estimated to occur preferentially as asphalt cohesion rather than cement-asphalt adhesion or ITZ cohesion. Based on the findings from Parts I and II, RAP aggregates reduce concrete strength and modulus because of: (1) the higher porosity in the ITZ, which produces a lower bulk modulus and allows for easier crack initiation, and (2) the preferential asphalt cohesion failure, which occurs rather than adhesive failure of the cement-asphalt interface or cohesive failure of the ITZ.