An investigation on the relationship between FTIR indices and surface free energy of RAP binders

The performance of RAP bituminous mixes depends on the properties of the binder in the RAP material. Surface free energy of a binder, which is a fundamental property of materials, can be used to explain moisture damage, rutting, fracture and healing potential of bituminous mixes. Similarly, different chemical properties of binders can be used to estimate their mechanical properties. The relationship between the surface free energy of the binders and their chemical composition (in terms of functional groups) has been investigated in this study. For this purpose, blends of a virgin binder (VG30 grade) and the RAP binder extracted from a RAP material were prepared. Surface free energy of the binder blends was measured using sessile drop technique. The chemical composition of the blends was obtained using Fourier transform infrared spectroscopy (FTIR) analysis. Different ageing and healing indices were calculated from FIR analysis. Different ageing indices are found to have good correlation with surface free energy and its components. No significant relationship could be observed between healing indices and surface free energy of the binder blends. The correlations presented in the study between different indices estimated from FTIR analysis and the surface free energy components obtained by sessile drop method will be useful in furthering the understanding of the characteristics of binders, especially RAP binders.