Effect of ultra-ne SiO2 and metakaolin on high strength concrete in aggressive environment

Abstract. The behavior of SiO2 and metakaolin in an aggressive environment, when used separately as a supplementary cementitious material, was studied for three dierent replacement levels: 5%, 10%, and 15%. SiO2 and metakaolin were used in two states, namely unground and ground (ultra-ne). Ultra-ne state was achieved by subjecting the mineral admixtures to grinding in a planetary ball mill for an optimum period of one hour. The microstructure of the unground and ground mineral admixtures was studied using Scanning Electron Microscope and X-Ray Diraction. The compressive strength of these systems in normal and aggressive environments was tested after initial curing in water for a month, and another subsequent curing in acid or base environment for a period of three months to arrive at the rate of deterioration. The rate of corrosion in rebars was also determined using Half-cell potential method. The results obtained from the tests were compared with control concrete. Based on the results, it was understood that concrete with 10% ground SiO2 and 5% ground metakaolin provided better resistance to deterioration and corrosion. It also exhibited improved microstructure as well as ller action. Comparing the results of the two admixtures, performance of concrete with ground metakaolin was found to be better than that of ground SiO2.