Experimental evaluation of hot mix asphalt using coal bottom ash as partial filler replacement

The purpose of this study is to evaluate the performance of hot mix asphalt (HMA) prepared with coal bottom ash (CBA) as an alternative mineral filler. In this study, the effect of CBA on rutting, stiffness and fatigue resistance was experimentally evaluated. Combinations of conventional filler (stone dust) with different percentages of CBA (at 1.5%, 3%, and 4.5% by volume) were adopted. The HMA samples were prepared and tested using the Marshall mix design method. Following the Asphalt Institute MS-2 and the Pakistani National Highway Authority (NHA) General Specifications, sixty samples of HMA were compacted; stability tests at varying bitumen contents (3.5%, 4.0%, 4.5%, 5.0%, and 5.5%) were used to determine the optimum bitumen content (OBC) in the mixture for each percentage of CBA in the filler. For 0%, 1.5%, 3%, and 4.5% CBA, the optimum bitumen contents of 4.27%, 4.47%, 4.53%, and 5.0% were obtained, respectively. They were used throughout the study. Three samples with the optimum binder content were made for each of the four analysed CBA proportions. The wheel tracker test was run on 12 OBC samples, and the dynamic modulus test was run on 12 OBC samples. The Marshall stability and flow test results showed that the samples prepared with 3% CBA as filler and an OBC of 4.53% satisfied the NHA requirements for flexible pavement. It was noted that CBA greatly improves the rutting resistance and stiffness of asphalt mixtures. It also improved the fatigue life. Therefore, adding up to 3% CBA by volume to stone dust used as filler in asphalt concrete can minimize the need for stone dust and provide a suitable method of CBA disposal.