Publication: The microscale effect of fillers from industrial by-products on the rheological, physicochemical and bonding behaviours of asphalt mastics
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Date
2022-01-01
Authors
Mukhtar, Najib
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Abstract
The interaction between asphalt binder, aggregates, and mineral fillers would essentially affect the behaviour and performance of asphaltic concrete paving materials as a whole. One of the interactions is the asphalt-filler interphase within the asphalt mixture component is known as asphalt mastic. Whereby it undoubtedly affects the asphalt binder properties as a result of filler incorporation. This study aims at establishing a fundamental understanding of the asphalt-filler interactions at the asphalt mastics microscale level. Additionally, studies on the utilization of fillers in asphalt mixtures over the years have been motivated by the intensity of energy required during filler’s production and the quest for the use of sustainable alternative materials as the mineral filler. This is owing to the fact that the most conventionally used fillers in asphalt mixture production, i.e., hydrated lime and ordinary Portland cement (OPC), are less environmentally friendly and less cost-effective in terms of their production. Thus, feasible fillers from industrial by-products or waste, which also possess similar if not better properties, are being sought after as potential alternatives to paving industry. This motivated the utilization of lime kiln dust (LKD) and crushed dolomitic rocks or dolomite powder (DP) in this study as viable replacements to conventionally used ordinary Portland cement in asphalt mixture production. Whereby, in depth assessments of the asphalt mastics were performed in this research. The overall experimental results indicated that incorporation of fillers in asphalt binders improves its properties in terms of rheology, physicochemical behaviour, and 26 adhesive bonding. Novel approaches to assessing particle surface electrostatic potential due to pH change caused by protonation and deprotonation of asphalt mastic, as well as microscale procedures to account for chemical and mineralogical change, morphological change, wettability, and adhesive properties, were used. The incorporation of mineral fillers in the asphalt binder led to a significant improvement in the binder’s physical properties, rheology, and morphology. The chemical and mineralogical composition of the fillers played a major role in improving the binder’s stiffness and rheology. The change by calcium-based LKD and OPC fillers on binder surface morphology was evidently dependent on filler reactivity. Likewise, the surface morphological analysis indicated that the particle shape of fillers affected the stiffness and workability of mastics. Meanwhile, fillers with angular particle shapes were more prone to interlocking with less bitumen between their interstices, while round fillers were more workable and required less energy to move. It also revealed that the ionic strength and adhesion of all mastics are pH dependent, with the LKD and OPC performing better than the DP mastic. Analytical measurements based on surface free energy results showcased the overall improvement in binder wettability, spreadability, work of dry adhesion and work of debonding due to filler incorporation to be dependent on aggregate and mastic types. The pull-off tensile strength and stripping results also exhibited aggregates of limestone interfaces to possess better moisture damage resistance by which mastics of the OPC and LKD outperformed the DP mastic. Overall, the findings showcased the LKD as being more viable to replace the OPC, more than the DP in nearly all the conducted tests.