Effect of Foaming Water on Rheological and Microscopic Properties of Foamed Warm-Mix Asphalt Binders

Abstract

Foamed warm-mix asphalt (WMA) produced by water injection has been gradually accepted and used. However, several key concerns should be answered such as whether the water exists in asphalt after foaming and how it will influence the asphalt properties. In this study, foamed warm-mix asphalt binders were prepared with two binders and various water dosages. Strain sweep and frequency sweep tests were conducted to determine the rheological properties. Fourier-transform infrared spectroscopy (FTIR) and differential scanning calorimetry (DSC) methods were carried out to investigate the microscopic characteristics. The results show that the foamed binders have rheological behaviors similar to those of unfoamed binders, and the linear viscoelastic characteristics have almost no change after foaming. Foamed binders seem to have less gel structure than unfoamed binders. FTIR and DSC analyses prove that asphalt foaming is a physical process with no new functional groups or compositions produced, and some water is still trapped in the asphalt after foaming. The retained moisture seems to make the thermodynamic properties of asphalt more stable.