Sensitivity analysis and validation of the Simple Punching Shear Test (SPST) for screening HMA mixes

This study assessed the sensitivity of the Simple Punching Shear Test (SPST) to different hot-mix asphalt (HMA) mix-design variables, as part of the TxDOT efforts to improve the screening of HMA prone to rutting, permanent deformation, and shear failure under heavy traffic loading, high temperature environments, and severe shear stress conditions. The SPST, which is simply a monotonic penetration of a 1.5-inch diameter solid steel block into a typical Hamburg Wheel Track Test (HWTT) HMA specimen, was further compared to Hamburg Wheel Track Test (HWTT) in order to validate its usefulness. Both the SPST and HWTT tests were comparatively conducted at the traditional 50 °C and elevated temperature of 60 °C. Three SPST-HMA parameters namely, shear strength, shear strain, and shear modulus, were identified to validate the SPST and only the shear strength exhibited a good correlation with HWTT rutting. Additionally, both the HWTT and SPST tests showed that the HMA shear strength and shear failure are sensitive to changes in asphalt-binder content/type, mix types, and test temperature. Most of the HWTT rutting tests failed prematurely when the temperature was elevated to 60 °C, whereas for the SPST, only the magnitude of the HMA shear strength reduced. This suggests that the SPST could be a good supplementary test to identify and screen HMA prone to rutting and shear failure, particularly in high-temperature regions under high shear stress conditions. In addition, the findings indicate that balancing and optimizing the HMA design variables with consideration of field temperature conditions is imperative to ensure adequate HMA shear strength and satisfactory rutting performance.