Mechanical properties and setting time of geopolymer paste and mortar produced from ferrochrome slag

Many researches have been done to investigate using raw materials in the production of geopolymer cements. The aim of this paper is the effect of dosage of alkali and silica modulus when using sodium metasilicate solution at different curing conditions on the geopolymerisation of ferrochrome slag (FS). As alkali activation for geopolymerization, NaOH and Na₂SiO₃ solution were used. Geopolymer cement was produced using FS and 3 different silica modulus (0.50, 0.60, and 0.70) and 4 different Na₂O concentrations (4, 7, 10, and 12%). The setting time, heat of hydration and compressive strength of geopolymer paste samples and compressive strength of geopolymer mortar samples were obtained. The setting time varies between 120 and 870 min, it shows variability depending on content of Na₂O. As a result of the highest 28 day strength of the geopolymer paste sample was obtained at Na₂O concentration of 7% and at silica modulu of 0.70. Geopolymer mortars were prepared for the determination of compressive strength by adding FS:sand:alkali activator ratio 1:2:0.30, 0.35 and 0.40. The specimens were cured at 60°C, 80°C kept in 20 hours and the other mortars were stored under laboratory conditions. Compressive strength of the material decreases, when w/b ratio increases. The highest 28 day strength of the geopolymer mortar was obtained at 0.30 w/b ratio and at curing temperature laboratory conditions. The hydration heat of geopolymer paste samples was found to be less than normal Portland cements. Microstructural changes in the specimens were studied with SEM and XRD.