Comparative Evaluation of Surface Science Approach with Indirect Tensile Strength and Binder Bond Strength Tests to Determine Aggregate-Bitumen Bond

Abstract The present study investigated the efficacy of moisture sensitivity parameters obtained from the surface free energy (SFE) approach, namely the energy ratio (ER) and physiochemical parameters, by comparing the tensile strength ratio (TSR) and bond strength ratio (BSR) parameters, obtained from indirect tensile strength and binder bond strength tests, respectively. The bond strength against the moisture damage of basalt aggregates collected from two different sources with three different binder types, namely, unmodified (VG30), crumb rubber–modified (CRMB60), and polymer-modified (PMB40) binders, was evaluated. Results showed that both the ER parameter, which evaluates stripping potential of bitumen, and physiochemical parameters, which relate the compatibility of water with aggregate and bitumen, evaluated different rankings of an aggregate-bitumen system against moisture damage. However, the comparative study showed that physiochemical parameters evaluated similar rankings of aggregate and bitumen as obtained using TSR and BSR parameters in determining the aggregate-bitumen bond. Thus, it indicates that stripping of a binder may not always be the primary reason for moisture damage in bituminous mixes. It was observed that B2-CRMB60 with the highest ER of 0.71 was the least favorable combination in terms of resistance to moisture damage because of its lowest value of standard TSR and BSR parameters (i.e., 0.72 and 0.74, respectively) compared with five other combinations of aggregate-bitumen systems. Therefore, it is advised to carefully select the bond strength parameters to identify compatible aggregate-bitumen combinations while using the SFE approach. Further, it was found that the SFE approach is capable of addressing the complex moisture damage mechanisms in bituminous mixes; hence, it can be used for forensic investigations related to moisture damage in the field.