Estimation of Appropriate Filler Quantity in Asphalt Mix from Microscopic Studies

Abstract

The type and quantity of filler influences the property of the asphalt mix. The filler quantity, similar to fine and coarser aggregates, is typically specified in proportions of weight. If the specific gravity of the filler is significantly different than the rest of the aggregates (for example, alternative fillers derived from industrial and domestic wastes), weight proportioning may lead to undesirably low or high quantity of filler in the mix. To investigate this issue further, in the present work filler concentration (in terms of percentage area occupancy) is studied at the microscopic level with the help of a scanning electron microscope. Three different types of fillers are chosen and are separately added to asphalt mix in varying proportions. The indirect tensile strength values and the corresponding filler concentration levels of these samples are noted. From limited data gathered in the present study, it appears that the average filler concentration values corresponding to the maximum indirect tensile strength levels for the mixes are statistically same. That means, even though optimum filler quantities (by weight) are different for these three mixes, the filler concentration values are almost the same. Subsequently, design chart is suggested to estimate the optimum quantity (by weight) of filler for asphalt mix for any given type of filler.