Effectiveness of metakaolin on the strength and durability properties of air-cured and water-cured concretes

This study investigates experimentally the effectiveness of metakaolin (MK) inimproving the strength and particularly durability properties of the air-cured andwater-cured concretes. Three MK replacement levels were considered in the study:0%, 10%, and 20% by weight of cement. The other experimental parametersinvestigated in the study were: water-to-cementitious material ratio (w/cm), age,curing procedures, and chloride and sulfate exposure periods. The performancecharacteristics of the plain and MK modified concretes were evaluated by measuringthe compressive strength, water sorptivity, water absorption, resistance to chlorideion penetration, drying shrinkage, weight loss due to the corresponding drying, andsulfate resistance. The porosity and pore size distribution of the mortar phase of theconcrete were also examined by using mercury intrusion porosimetry. Themeasurements were conducted at different ages up to 180 days according to thespecified test methods. Test results revealed that replacement level of MK and curingprocedure adopted had significant effects on the durability characteristics; inparticular the most prominent effects were observed on the water-cured MK blendedcement concrete, which performed well when the amount of MK used in the mixtureincreased up to 20%.Keywords: Metakaolin, Chloride penetration, Curing condition, Drying shrinkage,Durability, Sorptivity, Pore structure, Sulfate attack