Effect of Test Temperature and Displacement Rate on Semicircular Bend Test

Asphalt concrete behavior under load is heavily influenced by displacement rate and temperature. It was the objective of this study to quantify the effect of these two parameters on asphalt mix performance under a semicircular bend (SCB) test. The ultimate goal of this study was to find the most suitable combination of displacement rate and temperature for the SCB test to be conducted in the northeast region of the United States. In addition, the effects of air void, binder content, and binder stiffness in the SCB test were investigated. SCB tests were performed at a temperature range from 10°C to 30°C, and displacement rates ranging from 1 to $50\mathrm{mm}/\min$. Material variables included air voids (4% versus 7%), binder contents (design versus design + 0.5%), and binder stiffness (three different grades). Characterization parameters from the test included fracture energy (FE), flexibility index (FI), peak load (PL), stiffness index (SI), and prepeak fracture energy (PPFE). The data were analyzed statistically to evaluate the sensitivity of characterization parameters to material variables under different displacement rates and test temperatures. The results indicated that FE, PL, and SI all increase with the increase of displacement rate and decrease with the increase of test temperature, while FI exhibited an opposite trend. The previously used PPFE demonstrated poor sensitivity to material variables regardless of displacement rate and test temperature. FE, FI, and SI show higher sensitivity to material changes compared with PPFE. Among all response parameters, PL proved the most sensitive to material variables irrespective of test conditions. The effective temperature concept was used to determine a suitable fatigue test temperature for the northeast region. The level of sensitivity was not affected as a result of changing the test temperature from 25°C to the effective temperature. Based on the test results, a displacement rate between 5 and $20\mathrm{mm}/\min$ is recommended for use with the SCB test.