Determining Normal and Shear Pull-off Strength of Asphalt Mastic Films due to Diffusion of Water Vapor

摘要

In this study, normal and shear pull-off strength of asphalt mastic films are measured at threeRelative Humidity (RH) conditions. Mastic films of size 5 mm~2 with thickness ranges from 0.193mm to 0.210 mm were prepared in between two aggregate slices. Laboratory RH conditioningwas applied by aqueous solution of Potassium Acetate (25% RH), Potassium Carbonate (49%RH), and Sodium Chloride (71% RH) in enclosed desiccators. After humidity conditioning, oneaggregate slice was attached to the base of a testing frame, and pull-off force was applied on theother aggregate slice. Load-displacement curves indicate that mastic films show ductile behaviorat high RH% conditioning and brittle behavior at low RH% conditioning while normal pull-offstrength is measured. Mastic films behave more ductile by showing a definite yield point,ultimate strength, and failure strength with high elongation at 71% RH. However, at 49% RH,mastic films tear down abruptly like elastic-perfectly plastic material. At 25% RH, mastic filmstear down suddenly like a brittle material. Average yield and ultimate strength for 71% RH is thelowest compared to those at 49% and 25% RH. The ductile nature of mastic films at high RH%influences the shear pull-off strength by showing higher shear pull-off strength. Average shearstrength of mastic films increases with an increase in relative humidity. As humidity increases,viscosity decreases and elasticity increases due to diffusion and absorption of vapors in themastic. Reduction in viscosity causes insufficient bonding between aggregates and masticmaterials, and accelerates damage.