Coal is the single largest fuel source for the generation of electricity worldwide and consists of 38% yearly electricity generation. In Mauritius, thermal power generation accounts for about 96 % of the total energy produced.This project aims to investigate the feasibility of the use of coal bottom ash as replacement for all in aggregates in concrete in Mauritius, as a means to reduce the exploitation of natural resources and to contribute to a sound management of coal ash on the island. In this research, the all in aggregates in both grade 40 and grade 15 concrete mixes were replaced by coal bottom ash in varying proportions by weight. The effect of bottom ash on the 7 and 28 days compressive strengths were then determined. In addition, leaching characteristics of heavy metals from the bottom-ash concrete at 90 days were determined as per BS EN12457-1:2002 and results compared with limits specified in
BS6920:2000-Materials in Contact with Drinking Water and in Mauritian Drinking Water Standards. Five grade 40 concrete mixes were designed comprising 15%, 26% and 54% respectively replacement by weight of all in aggregates by coal bottom ash. The 7 and 28 days compressive strength of cubes as well as the leaching characteristics of heavy metals from the bottom-ash concrete were determined. Results show that the compressive strength of concrete decreases drastically as bottom ash content increases and thus use of bottom ash in structural concrete is not technically and economically feasible. Subsequently, two grade 15 concrete mixes were designed comprising 31% and 100% respectively replacement by weight of all in aggregates by coal bottom ash. 7 and 28 cube test results showed that compressive strengths of both mixes are comparable to those of control mix. In addition, leachability tests showed concentrations of heavy metals at 31% replacement were within limits. However, limits for barium and lead at 100% replacement were slightly higher than the threshold limits. This research concludes that the use bottom ash as all in replacement/aggregate replacement in structural concrete is not technically feasible and is uneconomical. However, bottom ash in low strength concrete applications e.g. blinding, mass concrete and concrete infills is
technically feasible and economical. In this respect, the replacement of all in aggregates by bottom ash up to 31% can be implemented safely. Since there is a potential risk of the low strength concrete getting into contact with drinking water because of percolation, the replacement of all in aggregates by bottom ash up to 100% must be done with caution. This impact will have to be assessed in situ because of varying levels of dilution likely to occur in nature.