Lab and Field Validation of a Simplified Low-Temperature SCB Test for Airfield Asphalt Mixtures

Low-temperature cracking is a prevalent distress in airfield asphalt concrete (AC) pavements, yet the Federal Aviation Administration’s current mix design method does not specify a test to assess the low-temperature cracking potential of AC. To bridge this gap, current efforts to adopt a balanced mix design (BMD) framework are examining low-temperature tests for routine specification. This study assessed the simplified low-temperature semicircular bend (SLT-SCB) test for airfield BMD applications by quantifying its sensitivity to key material and production variables. This study incorporated seven airfield mixtures and four binder cross-combinations for evaluating their effects on the newly proposed low-temperature cracking index (LCI). The effect of air-void levels and aging was studied for lab-mix lab-compacted (LMLC) specimens. Cross-combination lab-mix lab-compacted specimens were used to isolate the impact of asphalt grade and content at various temperatures. The results were used to validate the use of prepeak fracture energy and stiffness as key metrics to characterize low-temperature cracking potential. LCI was found to be sensitive to aging conditions and binder grade, while the air voids and binder content effect was discernible but secondary. Comparison of the LMLC and plant-mix lab-compacted specimens showed generally similar LCI values for AC mixes. Additionally, disc-shaped compact tension tests were performed on these mixtures to compare with the SLT-SCB results. Overall, the SLT-SCB procedure demonstrated both practicality and sensitivity for use within a BMD protocol, leveraging fundamental material properties to assess low-temperature cracking potential and rapid testing time as compared to LT-SCB.