Evolution of Characteristics of Warm-Mix Rubber-Modified Asphalt during Water Damage under Different Immersion Times

Abstract

Fourier-transform infrared spectroscopy (FTIR), atomic force microscopy (AFM), and contact angle measurements were conducted in the present research to analyze the characteristics of warm-mix rubber-modified asphalt during water damage under different immersion times. The evolution of characteristics of asphalt binders was investigated based on their chemical compositions, functional group indexes, nanomechanical characteristics, and surface free energies. It was found that water molecules changed the proportion of each component of asphalt binders. With the increase of immersion time, the functional group index representing the damage degree increased and more water molecules interacted with polar components of asphalt binders, resulting in more molecular fracturing and recombination. Water molecules penetrated asphalt binders, and the interfacial tension and the hydrostatic pressure in the presence of water caused the redistribution and aggregation of molecules in asphalt binders, forming a new morphology and structure. The increase of the immersion time aggravated the reduction of the adhesion force and the increase of the Derjaguin-Muller–Toropov (DMT) modulus of asphalt binders. In addition, with the increase of the immersion time, the surface free energy (and its dispersion component) of asphalt binders decreased gradually and, in turn, the van der Waals force between asphalt molecules also decreased. The addition of warm-mix additives (EM and SDYK) changed the morphology of the rubber-modified asphalt (60MCR) and increased the adhesion force, DMT modulus, and surface free energy of asphalt binders. Simultaneously, the antiwater damage ability of asphalt binders was also improved. After different immersion periods, it was found that for the rubber-modified asphalt with SDYK additive (0.6S-60MCR), the increment degrees of the DMT modulus and the functional group index as well as the reduction degrees of the adhesion force and the surface free energy of asphalt binders were lower than those of the rubber-modified asphalt (60MCR) and the rubber-modified asphalt with EM additive (1E-60MCR), indicating its superior resistance to water damage.