CARBONATION OF CONCRETE

Abstract

This research project studies the effects of water to cementitious material ratio, precuring condition, pre-curing duration and partial replacement of ordinary portland cement (OPC) with a mineral admixture on carbonation of concrete under an accelerated condition. The mineral admixtures used are silica fume, fly ash (pulverized fuel ash) and ground granulated blast furnace slag with different finenesses ranging from 3,000 cm2/gm to 8,000 cm2/gm. It is observed that a lower water to cementitious material ratio can lead to a significant increase in the resistance of concrete against carbonation. The resistance of concrete with or without a mineral admixture can also be improved by extending the duration of water curing. However, the higher the replacement percentage of OPC with a mineral admixture, the faster is the carbonation rate of concrete. The relationship between OPC content of concrete containing a mineral admixture and its carbonation coefficient is found to be a straight line with a good correlation coefficient. It is also observed that the fineness of mineral admixtures affects carbonation. It is also found that concrete pre-cured under an ambient relative humidity of 80 % has a lower carbonation rate than identical concrete pre-cured under an ambient relative humidity of 65%.