Assessing correlations between two linear amplitude sweep (LAS) standards for evaluating the fatigue properties of aged bitumen

Abstract

Linear amplitude sweep (LAS) is an accelerated and well-established testing method to evaluate bitumen fatigue. However, there are different versions of LAS procedures employed. Significant differences in loading modes, damage failure criteria and calculations exist between existing standards, leading to the inconsistency in the performance characterisation of bitumen. This study investigated the fatigue performance of six different bitumen at various ageing levels using two versions of the LAS standards (TP101-14 and T391-20). The stress–strain curves, damage characteristic curves, prediction of fatigue life and cracking length were analysed and compared. It was seen that conclusions drawn from the old version of LAS standard (TP101-14) were unclear as no distinct trends related to change in fatigue life could be observed for binders with progressively increased ageing levels, regardless of the strain levels used for analysis. The new version of LAS (T391-20), however, showed acceptable consistency. The trends indicate that at low strain levels, the fatigue life increases with ageing levels, while opposite trend was observed at higher strain levels. Moreover, the cracking length as defined in the T391-20 standard increases with progressively increased ageing. The new version of LAS standard (T391-20) is recommended for characterising the fatigue performance of aged bitumen.