Influence of nano metakaolin on thermo-physical, mechanical and microstructural properties of high-volume ferrochrome slag mortar

This study investigates the effect of nano metakaolin (NMK) on the thermo-physical, mechanical and microstructural properties of hardened cement mortar containing high amount of ferrochrome (FeCr) slag. Sand was replaced with FeCr-slag aggregate at the ratio of 50 mass, %. Cement was partially replaced with different amounts of NMK at the ratios of 2, 4, 6, 8, 10, 12 and 14 mass, %. Compressive strength, flexural strength, drying shrinkage, capillary water absorption and thermal conductivity of the hardened nano-modified mortars were determined in accordance with ASTM standards at 28 days of water curing. The microstructure characteristics of the hardened samples were investigated by scanning electron microscope (SEM) equipped with energy dispersive analytical X-ray unit (EDAX). The results showed considerable improvements in the mechanical and thermal performance of cement mortar, due to the incorporation of FeCr-slag; in addition, the replacement of cement by NMK was found to be effective in providing an additional enhancement in the mechanical strength and thermal conductivity. Furthermore, NMK containing mortar has considerably reduced drying shrinkage and capillary water absorption. The reduction in drying shrinkage for the mortar containing 50 mass, % FeCr-slag and modified with 10 mass, % NMK reached 87% relative to the reference mortar. The microstructure of the hardened mortar containing NMK appeared quite dense and compact with finer pore structure.