Another look at the semi-circular bend test for the performance ranking of hot mix asphalt

Semi-circular bend (SCB) testing has been widely used to evaluate the cracking resistance of asphalt mixtures. However, it remains unresolved which of the various SCB protocols can provide the most sensitive and precise ranking of different asphalt mixtures. This study aims to improve the current SCB protocol, emphasizing mixture preparation, testing condition and evaluation indices. The effect of aging methods in terms of reversible aging and irreversible aging and loading rates on the intermediate and low temperature cracking resistance of asphalt mixtures was analyzed. Subsequently, the response of different cracking evaluation indices was analyzed. Finally, the repeatability of different cracking evaluation indices was discussed. The results show that higher loading rates are slightly more sensitive to mix composition, possibly due to the toughening effect of polymer modifiers. However, whether higher or lower rates are more accurate remains to be investigated with ongoing field studies. Cracking initiation and resistance indices (CII and CRI) were superior from a repeatability and dynamic range perspective in comparison to flexibility and balanced cracking indices (FI and BCI). Thermoreversible aging over three days of cold conditioning at − 20 °C was found to significantly affect binder properties in selected samples. However, none of the SCB parameters after testing appropriately cold conditioned samples at room temperature reflected this deterioration. Hence, it remains to be investigated whether mixture testing at ambient temperatures properly ranks superior quality Alberta, Canada and Venezuelan sourced materials that are low in wax.