Strength Deterioration of Plain and Metakaolin Concretes in Aggressive Sulfate Environments

This study investigates the effectiveness of metakaolin (MK) on the improvement of durability of concretes to sulfate attack. Experimental parameters of the study were MK replacement levels, water to cementitious materials ratio, initial curing procedure in terms of air curing and water curing, and type of the sulfate exposure regimes such as continuous and drying-immersion cyclic exposures. The degree of sulfate attack was evaluated by the reduction in compressive strength (CS) of concrete. The tests were conducted at specified periods up to 365 days. At the end of initial curing, concrete specimens were divided into three groups such that the first group was transferred into tap water to be used as control in the assessment of CS reduction while the other groups were immersed in 10% Na2SO4 solution for the period of 365 days under continuous or cyclic exposures. The results indicated that inclusion of MK as modifying agent increased the resistance of concrete against sulfate attack depending mainly on the MK replacement level, w/cm ratio, and initial curing procedure adopted.