Determination of Sulfate Resistance of Concretes Containing Silica Fume and Fly Ash

Abstract

One of the durability problems relating to reinforced concrete buildings is sulfate attack. Sulfate causes certain deteriorations like cracking, expansion and spalling through particular reactions inside concrete. As a result, degradation is observed in concrete strength. In this study, the effect of silica fume and fly ash on sulfate resistance of concrete was investigated. For this purpose, in the produced concrete, silica fume at the ratios by weight of 5%, 10% and 15% and fly ash at the ratios by weight of 10%, 20% and 30% were replaced with cement. Compressive strength, flexural strength and unit weight tests were conducted on the prepared specimens from the produced concrete after 28-, 90- and 180-day curing times. Furthermore, the prepared specimens from the produced concrete were exposed to sulfate effect after 28-day curing time in 100 g/l water containing sulfate (Na2SO4) for 90 days and 180 days to conduct sulfate tests according to ASTM C 1012. Control specimens were compared with the specimens under sulfate attack. The best sulfate resistance performance for both compressive and flexural strengths was taken from the concretes containing 10% fly ash and 5% silica fume. Internal structure was examined through SEM images, EDS and XRD measurements in the control group and those containing mineral at a ratio of 10%. In all groups, cement type (CEM I), total binder amount (400 kg/m3), sulfate amount (100 g/l), aggregate type and its gradation were kept constant.