This study aims to enhance the practical applications of coal ash and silica fume as a very early strength cementitious composite material. Both coal ash and silica fume are an industrial by-product from power plants and making silicon metal or alloy. This study considered high SiO2 coal ash and silica fume simultaneously. Various replacement ratios of coal ash and silica fume were evaluated to come across an optimized mix proportions. Compressive strength was a key monitoring factor in determining the mix proportions and durability characteristics was investigated through the permeability. Both coal ash and silica fume are not quality controlled during their productions and in the consideration of their primary applications in the field, their potential contamination was evaluated by investigating the leachate. The compressive strength development satisfied the required specifications. Potential hazardous contamination was evaluated to be very low. Permeability was high but by adding silica fume it can be greatly reduced. Therefore, coal ash from an electric power plant can be successfully applied to the very early age cementitious composite by replacing the cement. However, the replacement ratio is recommended not to exceed 15% and simultaneous addition of silica fume is necessary.

Keywords: Coal ash, silica fume, recycling, very early strength, permeability, contamination