Effect of mineral filler on changes in molecular size distribution of asphalts during oxidative ageing

Asphalt binder is always present in contact with fine and coarse mineral particles in the pavement and roofing shingles. Therefore, the mechanisms of oxidative ageing of binders are expected to be influenced not only by the characteristics of the binder but also by the properties of the mineral surface due to the molecular interaction between these two components. The purpose of this study is to develop a fundamental understanding of the mechanisms of interaction between binder and filler and the resulting changes in the molecular size distribution (MSD) after oxidative ageing. In this study, a method to characterise the behaviour of mastics (binder mixed with mineral dust) with ageing was developed by using the Pressure Ageing Vessel. The changes due to this ageing is measured by monitoring the mastics |G*| ageing index (ratio of complex modulus before and after ageing). The results clearly indicate that fillers can significantly change the effect of oxidative ageing of binders. Gel Permeation Chromatography testing results supported mentioned findings regarding |G*| changes, as the presence of mineral filler appears to decelerate the rate of production of larger molecular size oxidation products in the binder phase of mastics. Implication of the findings is that change in MSD of asphalts during ageing – a controlling factor in mechanical and thermo-volumetric behaviour – can be engineered by proper selection of fillers in the mastic phase. It is thus concluded that by selecting a proper type and concentration of filler, ageing of pavement, or roofing shingles and, consequently, durability and performance, can be controlled.