Use of Ash in Hot Dense Mixtures Alternative to Reduce Environmental Liabilities

Bituminous ash produced by the oil industry is used in landfill in large quantities. Recycling ashes coming from the oil industry can have significant benefits for the environment and is an attractive option for highway construction because it saves material acquisition and disposal costs. An experimental study was undertaken to investigate the use of these ashes as a replacement for mineral filler in hot-mix asphalt concrete. Physical tests were performed on the bituminous ash to determine its gradation, specific gravity, and chemical composition. Two cases were considered for determining the ash proportion. To evaluate the effect of a reduction in asphalt binder, ash with a maximum particle size of 0.074 mm [i.e., passing the Number (No.) 200 sieve] was used as a replacement for the asphalt cement content at percentages of 0 (i.e., control mix), 5, 10, and 15 by total asphalt weight. Also, ash was used as a replacement of the fine aggregate at percentages of 0, 30, 50, and 70 by total aggregate weight. In both cases, the ash came from thermal desorption in the hydrocarbon processes. Mix design was accomplished according to the Marshall mix design method (ASTM D1559). The results of these studies showed that use of ash passing the No. 4 sieve improved asphalt concrete character-istics while it reduced the use of aggregates when the asphalt proportion was 4.5%. Likewise, use of 0.8% fine ash (i.e., finer than the No. 200 sieve) to reduce the asphalt content in the hot dense mixture also improved the performance of asphalt concrete.