Effect of Ferrochrome Slag Substitution on High Temperature Resistance and Setting Time of Alkali-Activated Slag Mortars

The novelty of this study is to investigate the effect of ferrochrome slag (FS) replacement on the high temperature resistance of alkali-activated granulated blast furnace slag (AAS). The alkali-activated mortar samples were prepared by granulated blast furnace slag (GBFS) and FS at rates of 100/0, 80/20, 70/30, and 60/40 wt.%. A mixture of Na2SiO3 and NaOH was used as the activator. Alkali dosage was determined as 6 wt.% for all mixtures. The ratio of total SiO2 to total Na2O of the activator mixture was 1.5. Prepared samples were exposed to temperatures of 200, 400, 600, 800, and 1000 °C. The effect of high temperature on the compressive strength and ultrasonic pulse velocity was investigated. The changes in the microstructure after high temperature exposure were investigated using Fourier transform infrared spectroscopy. The impact of the substitution level of FS on the setting time of AAS was also investigated. The results revealed that the FS substitution increased the high temperature performance of the AAS. At 23 °C, the compressive strength of the sample containing 100% GBFS was 5.4% higher than the sample containing 20% FS substitution. However, after temperatures above 200 °C, the 20% FS substituted sample showed higher compressive strength. Another contribution of the use of FS was the prolongation of the setting time, which is one of the obstacles to the practical use of AAS. The final setting time was prolonged from 119 to 164 min with the lowest substitution rate of 20% FS. It was concluded that FS could partially replace GBFS in AAS production by increasing the high temperature resistance as well as prolonging the setting time.