Behavior of asphalt mastic films under laboratory controlled humidity conditions

•Normal strength and direct shear strength of asphalt mastic films were measured after vapor conditioning.•Normal strength of mastic films decrease with increase in vapor absorption.•Direct shear strength of mastic films increase with increase in vapor absorption.•Mastic films consist of binder and fines lose viscosity after vapor absorption.

Normal and shear pull-off strength of asphalt mastic films are measured at three relative humidity (RH%) conditions. Mastic films of size 5 mm2 with thickness ranges from 0.193 to 0.210 mm were prepared in between two aggregate slices. Laboratory RH conditioning was applied by aqueous solution of potassium acetate (25% RH), potassium carbonate (49% RH), and sodium chloride (71% RH) in enclosed desiccators. After humidity conditioning, one aggregate slice was attached to the base of a testing frame, and pull-off force was applied on the other aggregate slice. Load–displacement curves indicate that mastic films show ductile behavior at 71% RH conditioning and brittle behavior at 49% and 25% RH conditioning while normal pull-off strength is measured. Average yield and ultimate strength for 71% RH is the lowest 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 shear strength of mastic films increases with an increase in relative humidity.