Performance Evaluation of Ferrochrome ASH Based Alkali Activated Slag Mortars

Abstract

The use of ground granulated blast furnace slag (GGBS), fly ash (FA), silica fume (SF), etc. are gaining importance as cementitious materials for researchers, as these reduce carbon footprint, indirectly providing a viable solution to the threat of global warming and waste disposal problems. In particular, industrial byproducts are very promising in their use, due to their mechanical strength and long-term durability performance under aggressive conditions. Hitherto, one of the industrial byproducts not largely researched is ferrochrome ash (FCA). FCA is obtained from the gas cleaning plant of ferrochrome industries during the production of chromium. One of the possible ways of utilizing FCA is as a binder in the alkali activated slag (AAS) binder system. The addition of FCA in the AAS system addresses one of the important issue of the landfill problem and associated cost reduction. The main aim of the present study is to synthesize an AAS system using FCA as a binder material. Three important factors, including alkaline dosage (Na2O = 4-6% of the binder), modulus of silica (Ms = 0.75-1.75), and FCA replacement in the AAS binder system (0-50%) were considered for the experimental design. The microstructure and mineralogical studies were performed using scanning electron microscopy - energy dispersive spectroscopy (SEM-EDAX) image analysis and X-ray diffraction (XRD), respectively. Functional group identification was carried out using the Fourier Transform Infrared (FTIR) spectroscopy. Durability studies like, volume of permeable voids (VPV), sulphate attack, acid attack, elevated temperature studies, and ecological studies were also carried out. Optimization of FCA based AAS mortars were done based on grey relational analysis (GRA), technique for order preference by similarity to ideal solution (TOPSIS), and desirability function approach (DFA). As the replacement of FCA increases in the AAS mortars, N-A-S-H is observed to be predominant with the co-existence of C-S-H, C-A-S-H, and gismondine. The reduction of C-S-H, C-A-S-H, and gismondine is the main reason for the reduction in compressive strength in FCA based AAS mortars compared with 100% GGBS based AAS mortars. As the amount of Na2O dosage increases, compressive strength of FCA based AAS mortar mixture also increases. VPV of FCA based mortar mixture decreases with increase in Na2O dosage. Sulphate and acid resistance of FCA based AAS mortar mixture increases with increase in Na2O dosage. VPV also increases with increase in FCA content. Sulphate and acid resistance decreases with increase in FCA content in AAS mortar mixtures. Elevated temperature resistance of AAS mortar mixture increases with increase in both FCA content and Na2O dosage. ECO2eq and EEeq increases with increase in Na2O dosage. However, ECO2eq and EEeq decreases with increase in FCA content. Ranking obtained from DFA method is found to be best alternative for optimal mixture identification in terms of VPV, sulphate resistance, and acid resistance of FCA based AAS mortar mixtures. TOPSIS method ranking order can be used for obtaining optimal mixture identification of these mortar mixtures in terms of elevated temperature resistance, ECO2eq and EEeq.