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.