High strength concrete and the impact of metakaolin on its mechanical, durability and microstructural characteristics – A review

High strength concrete (HSC), which is generally categorised by a low water-to-binder ratio and high cement content, has found widespread usage in infrastructure projects such as high rise buildings, precast constructions and long-span bridges. The study covers the fundamental characteristics of high strength concrete with a brief historical context. The present review study examines the importance of the role of metakaolin (MK) as a supplementary cementitious material in enhancing the performance of high strength concrete mix. The study critically evaluates the role of metakaolin on mechanical properties such as compressive strength, flexural strength, splitting tensile strength, modulus of elasticity, creep and toughness of high strength concrete. In terms of durability, the study also covers the effects of metakaolin on permeability and the damage caused by external chemical attacks (chlorides, sulfates, acids, carbonation) as well as internal attacks (alkali–silica reaction). The study also discusses the positive impact of metakaolin on the performance of high strength concrete under freeze–thaw cycles, and its contribution to increased electrical resistivity. The negative impact of MK on carbonation resistance, as well as its complex and dosage and temperature-dependent effect on the high-temperature performance of high strength concrete, is also examined in the study. A conceptual framework was established, which linked the results of the microstructural studies such as SEM-EDS, XRD, TGA and MIP to the macro properties. The study further explores predictive modeling for metakaolin based high strength concrete mixes, incorporating both regression and machine learning approaches to enhance the understanding of relationships among various mix design parameters. The synergistic effects of metakaolin with other supplementary materials such as silica fume, fly ash and glass powder were also evaluated to further maximize its potential in high strength concrete. The implications of the study's findings were discussed in relation to field conditions and the existing research gaps and future challenges were also identified. • Discussion on chronological development, current challenges and future research directions of the HSC has been presented. • Effect of metakaolin on various properties of HSC has been discussed. • Synergistic effect of the metakaolin with other materials in high strength concrete has been covered. • Comparative graph depicting various properties of HSC mixes with varying metakaolin quantity has been presented. • Mathematical and machine learning techniques for predicting various parameters of high strength concrete have been presented.