Durability and leachability of concrete containing coal bottom ash and fly ash

Concrete is one of the main construction materials, though its application in construction has negative environmental impact such as carbon dioxide (CO2) emission and depletion of natural resources. In order to reduce the use of river sand as natural fine aggregate, the utilization of waste materials such as coal bottom ash (CBA), recycle concrete aggregate and recycle glass is quite effective. Moreover, in terms of reducing the amount of CO2 emission from cement industry, the utilization of supplementary cementitious materials (SCMs) such as coal fly ash (CFA), silica fume, blast-furnace slag and biomass ash is quite common and beneficial. In this study, the effect of using CBA as sand replacement and CFA as partial replacement of cement on various mix designs, was examined. The performance was investigated based on physical and mechanical properties, durability and leaching performance. The resistance to sulfuric acid and sulfate solutions and elevated temperature was also investigated. Two different leaching methods to obtain leaching performance of coal ash concrete performed were batch and tank leaching tests. Results revealed that concrete workability reduced with increasing percentage of CBA content replacing sand. At the early age of 28 days, no significant effect was observed in compressive, flexural and tensile strengths of all concrete samples. After curing ages of 91 and 180 days, compressive strength of both the experimental and control concrete samples increased significantly but remained almost similar. However, flexural and splitting tensile strengths of the experimental mix containing 75% CBA and 20% CFA exceeded more than the control sample. Moreover, drying-shrinkage of experimental concrete mixtures containing 50%, 75% and 100% CBA and 20% CFA was lower than the control mix. In general, the study revealed that coal ash concrete exhibited good influence in terms of resistance to chemical attacks than the control specimen. On the other hand, coal ash concrete mixtures showed higher loss in weight when exposed to higher temperature. Finally, from the results of leaching tests, it is observed that there is no leaching of any heavy metals. It is concluded that the experimental concrete mixes can be used which will minimize the use of natural resources, reducing energy and environmental problems to a great extent