In Malaysia, seven coal-fired power plants under Tenaga Nasional Malaysia continuously produce around 790 tons of solid residue namely coal bottom ash (CBA) per day. The aim of this research was to optimize concrete mix design containing CBA as cement replacement via statistical modelling, response surface methodology (RSM). The fineness, water cement ratio and percentage inclusion of ground coal bottom ash (GCBA) were analyzed followed by RSM resulted on compressive strength at 28 days. Coal bottom ash was ground to three different sizes; 45 lm, 75 lm and 100 lm, water cement ratio was set to three different value; 0.40, 0.45 and 0.50 and percentage of GCBA inclusion was set up to three different percentages; 5, 10 and 15. Results indicate that GCBA increase compressive strength at 28 days regardless of different values of each variables. It is found that with the increasing percentage of inclusion of GCBA with lower water cement ratio will lower the compressive strength due to its characteristic of water absorbance. In conclusion, with adequate water cement ratio, and optimum percentage of GCBA, complete hydration process will be achieved, and the development of compressive strength is significantly increase. © The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd. 2021.