Chloride and Carbonation Resistance of Calcined Clay and Metakaolin Concretes: Systematic Review, Meta-Analysis and Indian Service-Life Implications

Abstract

Limestone calcined clay cements are now standardized in India, but durability design under IS 456 remains prescriptive, and quantitative evidence on chloride transport and carbonation is fragmented. This study combined a PRISMA 2020 systematic review of open-access literature (1800 records, 2010–2026) with a random-effects meta-analysis of log response ratios between calcined clay or metakaolin mixes and same-study Portland cement controls, and with a meta-regression on clay kaolinite content. Twenty-five studies were synthesized. Calcined clay and metakaolin binders reduced the chloride migration coefficient (response ratio 0.40, 95% CI 0.29–0.55; 12 studies), the charge passed (0.36, 0.23–0.56; 12 studies) and the apparent diffusion coefficient (0.28, 0.13–0.61; 5 studies), but approximately doubled the accelerated carbonation depth (2.09, 1.43–3.07; 5 studies; exploratory). Heterogeneity was very high, prediction intervals included unity, and calcined clay and metakaolin did not differ. Each 10-percentage-point increase in kaolinite content multiplied the chloride response ratio by 0.70 (0.59–0.84). In an illustrative mean-value calculation with the fib Bulletin 34 chloride model and identical ageing assumptions, the pooled migration ratio reduced the cover needed against chloride-induced depassivation by more than one third. Kaolinite-rich calcined clay binders therefore offer a consistent chloride advantage, whereas carbonation requires explicit cover or curing provisions. Performance-based Indian specifications should require mix-specific migration and carbonation testing.