Abstract
Asphalt concrete consists of coarse aggregate, fine aggregates, fillers and binder. Fines passing a #200 sieve are called fillers, and most often contain mica. Previous studies show that the presence of mica reduces the strength of asphalt concrete. This study evaluates the mineral and chemical composition of asphalt mastic containing mica. Five different concentrations of mica were added to the fines and then X-ray diffraction (XRD) was used to identify the mineralogy of the mica and the presence of mica. An XRD pattern can differentiate mica from fillers and determine the presence of mica in fines. Then mastic containing different percentages of mica was aged and examined with a scanning electron microscope and a bending beam rheometer to determine the chemical composition and low-temperature stiffness. Scanning electron microscopy showed that, with the addition of mica, the microstructure of mastic changed and the number of uncoated flakes increased. However, the number of uncoated flakes decreased with aging. Also for high concentrations of mica, the presence of oxygen and sulfur decreased with aging. Bending beam rheometer test results showed that the addition of mica decreased the mastic stiffness. However, the rate of stiffness increase due to aging decreases with the addition of mica. This could suggest that mica reduces the rate of aging.
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