Calcined Marine Clay as Cement Replacement to Make Low-Carbon Mortar

Studies have revealed that kaolinite-containing marine clay (MC) exhibits pozzolanic reactivity after thermal activation, making it a sound supplementary cementitious material for concrete production. In this study, calcined MC with two different finenesses was used to substitute cement in the mortar at 0, 10, 20, and 30% replacement ratios. The pozzolanic activity of calcined MC was confirmed by the reduced portlandite content in hydration products (by quantitative X-ray diffraction [QXRD]) and the formation of the calcium-silicate-hydrate (C-S-H) and calcium-aluminum-silicatehydrate (C-A-S-H) gels (by scanning electron microscopy/energy-dispersive X-ray spectroscopy [SEM-EDS]). The microstructural, mechanical, and transport properties of mortar were investigated. The pore volume increased with the incorporation of calcined MC, while obvious pore refinement was noted. Due to the cement dilution effect and higher pore volume in the mortar, the strength and modulus of elasticity generally decreased with higher MC content. Chloride transport in the mortar was greatly inhibited due to the reduced pore sizes and higher chloride-binding capacity of calcined MC. With the addition of 10% fine calcined MC, the low-carbon mortar exhibits an earlier and increased heat release, similar strength, 8% lower water absorption, 14% lower water sorptivity, 44% lower chloride migration coefficient, and 12% loss in modulus of elasticity.