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Towards understanding the influence of metakaolin in the prevention of alkali-silica reaction

The role of supplementary cementitious materials (SCM) in the prevention and mitigation of the Alkali-Silica Reaction (ASR) in concrete materials and structures is becoming increasingly significant and relevant in the civil engineering. The use of SCMs in South Africa is limited to Ground Granulated Blast-Furnace Slag (GGBS) and Fly Ash (FA) as they are readily available. With recent advancements in concrete technologies, it has been found that calcined clays such as Metakaolin (MK) have been useful in concrete to improve the chemical, mechanical, and physical properties of concrete material. Deposits of MK have been found in some regions of South Africa and are now available for consumption with various applications but have not yet been widely accepted as conventional SCM within the concrete ready-mix industry. This article aims to summarise state-of-the-art and existing knowledge gaps in the application of SCMs in concrete material and identify the feasibility and benefits of extending the use of SCMs with MK in a comparative study with FA Class F and SF. The performance of MK with respect to the key variables such as exposure conditions, reaction mechanisms and pore solution composition in the prevention of ASR in concrete material relative to the mentioned SCMs is discussed.