Coal Ash Utilization in Asphalt Concrete Mixtures

Abstract

Dwindling supplies and rising costs of natural resources used in road construction as well as concerns over shrinking landfill spaces prompt researchers to investigate the use of waste products, such as coal ash, as substitute materials in highway construction. This research examines the effect of coal ash (i.e., fly and bottom ash) when used as partial replacement of fine aggregate in asphalt concrete mixtures. Specimens were made using three aggregate sources, two ash sources, three ash percentages (0, 6, and 8%), and hydrated lime. Selected physical properties (e.g., tensile strength) were measured and statistically analyzed. Results indicated that partial substitution of fine aggregates by coal ash had a moderate detrimental effect on short-term tensile strengths. However, a number of coal ash/lime mixtures met the minimum tensile strength requirements set by the South Carolina Department of Transportation. A limited field study was also conducted to study the environmental effects of coal ash mixtures as detected by heavy-metal concentrations in nearby soils. Results showed that 3 months after placement metal concentrations in soils were not substantially altered.