Effect of Using a Combination of 50% Coal Dust 50 % Course Sand as Filler in Bituminous Mix Design

Bituminous concrete, also referred to as asphaltic concrete, represents one of the most sophisticated and high-cost types of flexible pavement layers utilized in surface courses. Given its elevated cost and performance demands, bituminous mixtures must be meticulously designed to satisfy standards for structural integrity and durability. The mixture typically includes well-graded coarse aggregates, fine aggregates, and mineral filler, all bound together with bitumen. The mineral filler component, which passes through a 0.075 mm sieve, significantly influences the mechanical performance of the mix. An increase in filler content generally enhances Marshall Stability. According to the Asphalt Institute, 4 to 8% filler is recommended in asphalt concrete [1]. Traditional fillers like cement, limestone, and granite powder are not economically feasible or widely available in Bangladesh. In this context, a 50:50 combination of coal dust and coarse sand is considered a viable alternative, as both are inexpensive and readily accessible. This study evaluates the effect of this blended filler on the behavior of bituminous mixtures. It compares the performance of mixes containing a coal dust–coarse sand blend with that of mixes using conventional filler types such as fine sand with stone dust in Bangladesh. The evaluation was conducted using the Marshall mix design approach. The Marshall stability values for mixtures containing fine sand with stone dust and the coal dust–coarse sand blend were measured at 2.15 kN, and 1.79 kN respectively, all of which surpass the minimum threshold of stipulated by Marshall Design criteria. These results indicate that a 50% coal dust and 50% coarse sand combination can serve as an effective and economical filler in asphaltic concrete.