Impact of Ca, Al, and Mg on reaction kinetics, pore structure, and performance of Fe-rich alkali-activated slag

Alkali-activated materials can be formed by alkali-activation of Fe-rich non-ferrous metallurgical slags (AA-NFMS). To study NFMS in AA-NFMS systematically, five NFMS were synthesized, with different CaO (6-16 wt%), Al2O3 (7-11 wt%), and MgO (0-4 wt%) contents, while keeping the same FeOx/SiO2 molar ratio. The effect of slag chemistry and the alkali ions (Na+/K+ = 0, 0.5, and 1) in alkali-activating solution on the reaction kinetics, compressive strength (3, 7, and 28 days), and pore structure of AA-NFMS was investigated. The reactivity up to 3 days was evaluated via isothermal calorimetry, and the pore structure was analyzed via mercury intrusion porosimetry. Higher Al/Si in the slag showed higher reactivity, higher compressive strength, and lower total porosity of the AA-NFMS. Higher Ca/Si yielded lower cumulative heat after 3 days and decreased early compressive strength but higher strength after 28 days of curing. Ca replacement by Mg led to faster reaction kinetics but inferior mechanical properties and increased porosity. Increased K+ concentration in the activator resulted in higher reactivity and compressive strength despite the higher total porosity. Empirical model fitting using JMP software revealed that K+/(N++ K+) in the activator, Ca/Si, and (Ca+Mg)/Si in NFMS are significant factors that affect the strength of AA-NFMS.