Influence of metakaolin on fresh properties, mechanical properties and corrosion resistance of concrete and its sustainability issues: A review

As an available and high-quality supplementary cementing materials (SCMs), Consumption of Metakaolin (MK) was proposed by many research to replace Portland cement to improve concrete quality and reduce the negative effects of cement industry on the environment. With that being said, it is necessary to summarize the recent finding and gaps on the effect of replacing Portland-cement by MK in different replacement levels on various fresh and hardened properties of concrete. This review paper presents an overview of recent investigations on MK effect on fresh properties, mechanical strength, and corrosion resistance of concrete and mortars. Besides, the synergic effect of MK and other SCMs, its optimum replacement level for different purposes, and application of in different types of concretes are discussed as well. The literature indicates that using MK, up to a certain replacement level, improves the pore structure of concrete; consequently, increases its durability against chloride-induced corrosion. Because of the high aluminum (Al) composition of MK, using MK increases chloride binding as well. In the case of carbonation, using MK was reported to increase the carbonation depth mostly under high CO2 concentrations. Nevertheless, under the conventional concentration of CO2, MK containing specimens show acceptable performance against carbonation, especially combined to the limestone. From another perspective, MK can play a major role to reduce the direct and indirect CO2 emission of cement industry, and using it seems an inevitable step toward more sustainable cement industry and concrete construction.