Influence of furnace bottom ash on properties of concrete

Abstract

Furnace bottom ash (FBA) is a by-product from thermal power plants. Unlike its companion, pulverised fuel ash (PFA), FBA has coarse particle size, higher water absorption and usually no pozzolanic effect. Therefore, it is dumped in landfill sites. Past recycle attempts of FBA have been mainly focused on using it in blocks, highway embankments, subgrades, sub-bases and structural fills. However, this may still be a source of environmental contamination by way of leached trace elements. A previous investigation carried out by the authors has indicated that FBA would be a potential fine aggregate in concrete. The effects of FBA on workability, compressive strength, permeability, depth of carbonation and chloride transport of concrete were further investigated and the results are reported in this paper. The natural sand was replaced with FBA by 0, 30, 50, 70 and 100% by mass, at fixed free water–cement ratios of 0·45 and 0·55 and a cement content of 382 kg/m3. The results indicated that the workability of the concrete increased with an increase in replacement level of natural sand with the FBA. Most of the FBA concrete was lower in compressive strength than the control that was manufactured with the natural sand up to an age of 28 days for both the water–cement ratios, but most of the FBA concretes were comparable with that of the control concrete at 365 days. The air permeability, water absorption and the carbonation rate at the age of 365 days were higher than those of the control concrete. However, the chloride transport coefficient decreased with the increase of the replacement level of natural sand with FBA up to 50% and it increased beyond this replacement level for both the water–cement ratios. Further investigation is required to assess whether properties of concrete could be improved by taking account of the decrease in water demand of the FBA concrete while determining the water–cement ratio of the mix.