Micro-scale investigation of oxygen diffusion on bitumen surfaces
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This study investigates the evolution of microstructures due to oxygen diffusion on bitumen surface and its effect on bulk properties utilizing Atomic Force Microscopy (AFM) and Differential Scanning Calorimetry (DSC). The bitumen specimens were conditioned in four different modes: both light and air, only air but no light, only light but no air and neither light nor air, for 15 and 30 days. From the AFM investigation after 15 and 30 days of conditioning period, it was found that the percentages of microstructure on the surface reduced with ageing. The DSC heating scan showed that the amount of wax remains constant even after the systematic conditioning. Interestingly, during the cooling cycle, crystallization of wax molecules started earlier for the oxidized specimens than the non-oxidized one. The analysis of the obtained results indicated that the oxidation created a thin film upon the exposed surface, which acts as a barrier and creates difficulty for the wax induced microstructures to float up at the surface. From the DSC analysis, it can be concluded that the oxidation product induced impurities in the bitumen matrix, which acts as a promoter in the crystallization process. 2014 Taylor & Francis Group, London.