Development of a simplified low-temperature SCB test protocol to characterise cracking potential of airfield mixtures

Low-temperature cracking is a critical distress in airfield pavements, yet the Federal Aviation Administration (FAA) Advisory Circular AC 150/5370-10H does not include a performance test to evaluate the cracking potential of asphalt concrete (AC) mixtures. With increasing interest in balanced mix design (BMD), practical, fundamental, and rigorous tests are needed to assess the cracking potential of AC mixtures. This study presents a simplified low-temperature semi-circular bend (SLT-SCB) test protocol developed under monotonic load-line displacement mode. The protocol standardises specimen volumetrics, testing temperature, and loading configurations. An optimised loading rate of 0.15 mm/min was selected based on experimental calibration and supported by numerical analysis. AC mixtures and field cores from nine airfields and FAA test sections were evaluated. A low-temperature cracking index (LCI) derived from stiffness and pre-peak fracture energy was developed, which distinguished mixtures with varying cracking potential and captured ageing effects, with a coefficient of variation below 20%. The index differentiated cracked mixtures from non-cracked mixes from field cores and FAA test sections that underwent accelerated loading. The test offers a practical means for agencies to incorporate low-temperature cracking into airfield BMD specifications, while being approximately six times faster than the traditional low-temperature semi-circular bend test, requiring no external instrumentation.