Application of coal waste powder as filler in hot mix asphalt

The main objective of this research was to investigate the effect of coal waste powder as filler material in hot mix asphalt. After sampling the coal waste material from a coal washing plant, it was processed to achieve natural coal waste filler. Furthermore, after incinerating the natural coal waste powder at 750 °C, the coal waste ash was produced. The results of an X-ray diffraction test revealed pozzolanic compounds which encouraged the application of these materials as active filler in hot mix asphalt. The main laboratory program consisted of Marshall stability, indirect tensile strength and resilient modulus tests conducted in dry and saturated conditions. Based on the obtained results in comparison to the reference mix (i.e. a mix containing limestone powder) the coal waste and its ash resulted in higher stability and resilient modulus. Furthermore, the combination of coal waste and limestone powders in equal proportion resulted in a desirable mix with high water resistance. Moreover, the water sensitivity of mixes was also improved by coal waste powder and especially its ash. Considering the stress–strain curve obtained from indirect tensile strength the toughness index parameter was determined which is an indicator of energy absorbency or material flexibility. Results indicated that the hot mix asphalt containing coal waste powder exhibited more flexible behavior than the reference mix.