Measurements of Surface Energy and Its Relationship to Moisture Damage

Moisture damage in asphalt mixes can be defined as loss of strength and durability due to the presence of moisture at the binder-aggregate interface (adhesive failure) or within the binder (cohesive failure). This research focuses on the evaluation of the susceptibility of aggregates and asphalts to moisture damage through understanding the micro-mechanisms that influence adhesive bond between aggregates and asphalt and the cohesive strength and durability of the binder. Moisture damage susceptibility is assessed using surface energy measurements and Dynamic Mechanical Analysis (DMA). Surface energy is defined as the energy needed to create a new unit surface area of material in vacuum condition. Surface energy measurements are used to compute the adhesive bond strength between the aggregates and asphalt and cohesive bond strength in the binder. DMA testing evaluates the rate of damage accumulation in asphalt binders and mastics. The DMA apparatus applies a cyclic, torsional strain-controlled loading to cylindrical asphalt mastics until failure. DMA results are analyzed using continuum damage mechanics that focus on separating the energy expended in damaging the material from that associated with viscoelastic deformation. This report represents a new approach developed to analyze DMA results and calculate the rate of damage. The developed approach is used to evaluate six asphalt mixtures that have performed either well or poorly in the field. The resistance of the field mixes to moisture damage is shown to be related to the calculations of bind energies and the accumulated damage in DMA.