Analysis of moisture susceptibility of foamed warm mix asphalt based on cohesion, adhesion, bond strength, and morphology

Abstract

Although foamed warm mix asphalt (FWMA) offers several benefits, concerns exist regarding the potential moisture damage that can be produced within it. Boiling water tests, the surface free energy (SFE), the binder bond strength (BBS), and atomic force microscopy (AFM) morphologies are all used to analyse the moisture damage of asphalt. These methods were evaluated and compared in this study. The results indicate that some residual moisture remains trapped in asphalt after foaming and that the foaming states for base asphalt and SBS modified asphalt attain stability after 6 min and 15 min, respectively. Boiling water tests are unsuitable for evaluating the adhesion of FWMA. SFE and BBS tests demonstrated that the residual foaming water undermines the bond strength of FWMA by reducing the cohesion energy. The Scanning Electron Microscope (SEM) and AFM methods were used to identify differences between morphologies by investigating the various foaming water contents. The results of SFE, BBS, and AFM morphologies were observed to be in agreement. Although cohesive failure modes were observed in the BBS experiment, foaming water aggravates the adhesion failure and causes moisture damage owing to the participation of external water. Furthermore, the results indicate that less water damage resistance is associated with substantial amounts of foaming water. These findings provide a clearer understanding of the moisture susceptibility of FWMA.