Estimating Moisture Sensitivity of Warm Mix Asphalt Modified with Zycosoil as an Antistrip Agent Using Surface Free Energy Method

With increasing interest in the use of warm mix asphalt (WMA) in the paving industry, more studies in this field for improvement of WMA properties seem to be necessary. In past decade, several studies focusing on use of Sasobit and asphamin as warm additives in asphalt mixtures have been conducted; however, the effects of these additives on moisture susceptibility of asphalt mixture are still not fully understood. In this study, the moisture susceptibility of WMA evaluated with and without a new nanotechnology material as antistrip additive (namely Zycosoil) by determining the micromechanisms that affect the adhesion bond between the aggregate and asphalt binder and the cohesion strength of the asphalt binder using the surface free energy (SFE) concept and laboratory testing analysis. Indeed, the primary goal of this research was to decrease the moisture damage in WMA. Two types of aggregates, limestone and granite, and two types of WMA additives, namely Sasobit and aspha-min, in addition to as Zycosoil as an antistrip additive were evaluated in this study. Moisture sensitivity index, which is the percentage of the aggregate surface exposed to water (P) as calculated by using the measured SFE and dynamic modulus results, was considered an index for the moisture susceptibility of mixtures. The findings suggest that WMA additives cause an increase in the acid component and a reduction in the SFE base components of asphalt binder. This causes decreased adhesion between acidic aggregate that is more moisture damange and asphalt binder. Moreover, Zycosoil additives cause an increase in the adhesion SFE between asphalt binder, modified with WMA additives and aggregates in the presence of water. A dynamic modulus test of Zycosoil performance yielded similar results, suggesting that using this material causes the ratio of the dynamic modulus values for wet/dry condition to increase significantly in samples made with WMA additives. For these reasons, the percentage of aggregate surface area wetted by water, index P, decreased when Zycosoil was used in all samples. DOI: 10.1061/(ASCE)MT.1943-5533.0000455. (C) 2012 American Society of Civil Engineers.