Effect of initial damage on healing characteristics of bituminous mixtures containing reclaimed asphalt material (RAP)

Abstract

Fatigue damage healing of bituminous mixtures containing reclaimed asphalt pavement material (RAP) is of research interest since the healing ability of RAP mixtures is expected to be different from that of virgin mixtures which is due to the differences between the chemical properties of un-aged and aged binders. Very limited research work has been reported in the literature about the healing ability of RAP mixtures. Hence, the present study focuses on investigating the fatigue damage healing characteristics of RAP mixtures. For this purpose, blends of RAP and virgin binders (VG30) were prepared corresponding to varying proportions (0, 15, 25, 35 and 45%) of RAP material in the mix. RAP asphalt mix specimens were subjected to indirect tensile fatigue testing and were damaged to different levels of damage (25%, 50% and 75% of the total fatigue life). Different sets of specimens were healed by conditioning them at temperatures of 40 °C and 60 °C for a duration of four hours and were tested again for their fatigue lives. The healing potential of the mixes was evaluated in terms of fatigue life healing index (HIL) and modulus healing index (HIM). Results from the study indicated that the fatigue life of the mix increased with increase in the proportion of RAP in the mix. The two healing indices estimated from fatigue life and modulus value reduced with increase in the initial damage. The degree of healing was also found to depend significantly on the RAP content in the mix. However, there is no significant difference between the healing abilities of the mixes healed at 40 °C and 60 °C. Methyl and methylene hydrogen to carbon (MMHC) ratio and CH2/CH3 ratio were used to explain the healing characteristics of the mixes and were found to be correlated well with the fatigue life healing ability.