Chemical and Microstructural Changes in Reclaimed Asphalt Pavement Aggregates by Pyrolysis

The utilization of reclaimed asphalt pavement (RAP) aggregates as an alternative for rigid pavements is limited. The main objective of this study is to explore and improve the utilization of RAP aggregates as an alternative material for rigid pavement. Specifically, this study focuses on addressing a significant challenge associated with RAP aggregates, which is their poor bond with cementitious binders. The poor bonding results in low compressive and tensile strengths of concrete or mortar. The poor bonding is mainly due to the presence of a thin oily layer of asphalt residue. A proposed method was carried out to reduce the negative impact on the bond between the aggregate and mortar by exposing the RAP aggregates to the pyrolysis process. The research focused on the analyses of the physical and chemical behavior of the aggregates, using the SEM, EDX, and FTIR approaches, as well as reviewing the mortar in both compressive and flexural tensile strength. The pyrolysis affected the physical and mechanical properties positively and the chemical composition of the RAP showed significant changes. The chemical constituents of asphalt attached to RAP aggregates are hydrocarbons. The thin layer of RAP asphalt is the cause of weak bonding, but this layer was altered by the pyrolysis procedure. As a result, water absorption decreased, which had a positive impact on the hydraulic synergy of cement. It is shown that the pyrolyzing RAP improves the compressive strength and flexural tensile strength through modification of the asphalt residue covering the aggregates.