Moisture Susceptibility Evaluation of Nanosize Hydrated Lime-Modified Asphalt–Aggregate Systems Based on Surface Free Energy Concept

Abstract

Moisture susceptibility can cause cohesive and adhesive failures in the asphalt–aggregate system, resulting in serious pavement distresses. The role of regular hydrated lime (RHL) as an antistripping agent in asphalt pavements has been widely addressed with traditional moisture susceptibility evaluation methods. However, the use of nanosize hydrated lime (NHL) in asphalt industries has not yet been initiated. The first objective of this study was to assess the RHL- and NHL-modified asphalt binders on the basis of the surface free energy (SFE) concept by using the Wilhelmy plate method. Advera, a warm-mix asphalt (WMA) foaming additive, was added to the hydrated lime-(RHL and NHL) modified asphalt binders to address the effect of foaming on cohesive bond strength. The NHL material was added with particle sizes of 50 and 100 nanometers. The second objective was to address the adhesive bond strength between the aforementioned asphalt binders and different aggregates. Different acidic and basic aggregates with known SFE components were used along with measured SFE components of the asphalt binders to determine quantitatively the free energy of adhesion in the system. Overall results reveal that SFE components of asphalt binders are dependent on the particle size of hydrated lime. In general, the cohesive bond of the NHL-modified asphalt binder was higher than that of the RHL-modified binder. As hydrated lime particle size decreases, dry and wet adhesive bonds increase. Moisture susceptibility of Advera-foamed mixes seems to depend on aggregate type. The NHL-modified mixes are expected to perform better than RHL-modified mixes in dry and wet conditions.