Investigation of the influence of Off-Spec coal combustion waste on asphalt binder rheological performance and aging sensitivity

Abstract

Previous studies show promising effects of some standard fly ash classes on asphalt. However, there is limited research into off-spec fly ash. Multiple studies published presented fly ash as unique compared to traditional mineral fillers. In this paper, several coal combustion wastes (CCW) are examined in terms of their physio-chemical interaction with asphalt binders. Eight types of CCW are blended with two types of asphalt binders: unmodified and polymer modified (PMA). The physical properties and chemical composition of the CCW are characterized. Testing is focused on identifying changes in binder performance after blending with the CCW to understand the role of the CCW. The experimental program is focused on damage healing, rheological performance, and Low-temperature cracking potential. All the blends are conditioned using the pressure aging vessel. Oxidative aging is quantified through measurement of both carbonyl (ICO) and sulfoxide (ISO) indices by Fourier-Transform Infrared Spectroscopy (FTIR). Results show that some of the CCWs are associated with improved rheological performance, damage healing, and cracking resistance. The improvement is attributed to the level of interaction between the binder and the CCW and the physical and chemical characteristics of the CCW. Testing results demonstrate that synergy between the CCW particles and polymer modifiers needs further investigation. Statistical regression analysis is used to quantify the level of significance of influencing factors on the blend performance. The analysis revealed that the level of interaction between the CCW and the binder is measurable by the phase angle of the blend. The CCW’s silicon (Si), Sulfur (S) content, along with particle size distribution and specific gravity, are the significant chemical and physical properties influencing the blend performance. These findings propose a fruitful upcycling opportunity for some CCW as an enhancer of asphalt performance.