Comparison of commercially-available metakaolins and slags in binary and ternary concrete mixtures

The use of metakaolin (MK) as a supplementary cementitious material (SCM) hasbeen documented in the literature for over 20 years. However, few studies have compared the performance of multiple commercially-available MKs as both binary and ternaryreplacements of cement. A total of 18 cement-pozzolan combinations were evaluated; nine binary MK combinations, three binary combinations incorporating other pozzolans, and six ternary combinations of MKs and slags. The mixture parameters were: cement content of 711 pcy, a coarse aggregate content of 1,660 pcy, and a w/cm ratio of 0.43. Tests measured compressive strength, flexural strength, split-cylinder tensile strength, dynamic modulus of elasticity, drying shrinkage, coefficient of thermal expansion, resistance to chloride-ion penetration, and resistance to sulfate attack and alkali-silica reaction (ASR). Two of three MKs consistently contributed to increased mechanical strengths, higher indicators of durability, reduced drying shrinkage, and higher CTE values. Recommendations for use are discussed.