Evaluation of the sensitivity of asphalt concrete modulus to binder oxidation with a multiple length scale study

It is well known that the properties of asphalt concrete mixture are affected by the oxidation of asphalt cement. However, the precise relationship between these two length scales remains largely uncharacterized. In the present study, a multiple length scale evaluation approach is applied to study and quantify the sensitivity of the mechanical properties of asphalt concrete mixture to asphalt cement oxidation. The study involves temperature and frequency sweep experiments on unaged and aged asphalt cement (to establish baseline properties), asphalt mastic (to consider physico-chemical aspects), and Fine Aggregate Matrix (FAM - to consider air voids and aggregate interaction effects). The multiscale approach separates effects of aggregate-binder physico-chemical interactions from those caused by air voids and physical aggregate interactions. Also, all asphalt cements were pre-aged to specific aging levels before preparing respective aged mastics or FAM samples. The methodology adopted for assessment of sensitivity was based on the theory of crossover modulus and second order rate kinetics of asphalt binder oxidation. The results from the analysis indicate that the mechanical properties of mastics are more sensitive to binder oxidation than FAM. Also, mechanical properties of mastics and FAM materials prepared with softer binders are more sensitive to oxidation than those with higher modulus asphalt cements. Finally, it is found that if a laboratory aging procedure is found to match the rheological properties of in-service level of asphalt oxidation at a given level of accuracy, then the expected accuracy in matching the resulting modulus of an asphalt mixture tested after being subjected to that laboratory process will be 1.5-3.6 times higher.