Evaluation of healing characteristics of reclaimed asphalt pavement (RAP) mixtures using monotonic loading

Healing characteristics of bituminous mixtures containing reclaimed asphalt pavement (RAP) material are expected to be different from the virgin mixtures as the chemical properties of unaged and aged binders are different. The macro crack healing characteristics significantly influence the overall fatigue life of RAP mixes, making it crucial to understand these properties. Hence, the present study aims to examine the macro-crack healing characteristics of RAP mixtures. Blends of RAP and virgin binder (VG30) were prepared corresponding to varying proportions of RAP material (0, 15, 25, 35, and 45%) in the mixture. FTIR (Fourier transform infrared) spectroscopy and contact angle measurements were carried out on the short-term aged binder blends to estimate the chemical indices (ICO - carbonyl, ICH - aliphatic, and ICC – aromatic indices) and surface free energy, respectively. The Marshall specimens were subjected to complete fracture by conducting monotonic indirect tensile loading tests and were healed under specific conditions. The healing potential of the mixes was evaluated in terms of the recovery of indirect tensile strength (ITS) value. While the healing ability of the mixtures reduced significantly with an increase in the RAP content, an opposite trend was observed with the increase in the binder content. Chemical indices which indicate the aging characteristics of binder and surface free energy that indicates the wetting ability of binder correlated well with the healing index (HI_s). Relationship between the viscosity, softening point, time lag parameters and the healing index indicated the significance of the visco-elastic characteristics of the binder, which govern its flow behaviour during the healing of macro-cracked asphalt mixtures.