Ferrochrome ash – Its usage potential in alkali activated slag mortars

Abstract

This study is an attempt to develop a sustainable construction material, i.e., alkali activated slag (AAS) in combination with ferrochrome ash (FCA) as a replacement to ordinary Portland cement (OPC). The effect of the various levels of FCA (0, 25, and 50%) replacing ground granulated blast furnace slag (GGBS) in AAS mortars with 4% of Na<inf>2</inf>O dosage is studied. Further, five levels of the modulus of silica (Ms = 0.75, 1.00, 1.25, 1.5, and 1.75) are chosen to achieve targeted compressive strength at 28 days under ambient temperature curing conditions. The compressive strength decreases with the increase in level of the FCA replacement. The targeted design compressive strength is achieved with 25% FCA replacement to GGBS in the AAS mortar system with Ms = 1.25. In addition, microstructure and mineralogical studies are undertaken to ascertain the formation of different hydration products with the aid of the scanning electron microscope (SEM) and the X-ray diffractometer (XRD). Gismondine and calcium aluminate silicate hydrate (C-A-S-H) are the major hydration products in the AAS mortar mixes. Sodium aluminate silicate hydrate phases (N-A-S-H) are also observed prominently as the FCA replacement level increases in the AAS mortar mixes. The Fourier-transform infrared spectroscopy (FTIR) confirms the presence of the Si–O-(Si or Al) functional group. The addition of FCA in the AAS system is of vital significance in the reduction of the embodied carbon dioxide (ECO<inf>2eq</inf>), embodied energy (EE<inf>eq</inf>) and cost. © 2020 Elsevier Ltd