Characteristics of slag cement with complex activator with gypsum-bearing waste

In recent decades, alkaline activation materials, in particular slag cements, have attracted increasing attention among scientists and the industrial sector. Their performance characteristics largely depend on the type of alkali activator. The most effective in this case are considered to be hydroxides or salts of alkali and alkaline earth metals, which are not natural resources and can only be synthesized using energy-intensive technologies, which makes them a source of environmental pollution due to carbon dioxide emissions. As part of the research work, the effect of various combinations of Ca2+ and Na+ (Ca2+/Na+ ratio) components (Ca(OH)2, Na2CO3 and CaSO4∙2H2O), including gypsum-containing waste in the composition of a complex alkali activator on the strength characteristics of a slag-alkaline binder was studied. It was found that with a constant Ca(OH)2 content, an increase in the curing time promotes a shift in the optimal concentrations of Na+ and Ca2+ containing components in the binder matrix towards higher values. With a constant concentration of citrogypsum (CaSO4∙2H2O) in the binder system, the optimal dosage of the Ca2+ containing component (Ca(OH)2) does not change, and the content of the Na+ containing component (Na2CO3) shifts towards lower values with an increase in the curing time of the binder. It was found that an increase in the Na+/Ca2+ ratio due to an increase in the concentration of Na+ cations (Na2CO3) with a constant content of Ca2+ cations (Ca(OH)2 + CaSO4∙2H2O) promotes a decrease in the compressive strength of the binder. At the same time, a decrease in the Na+/Ca2+ ratio due to an increase in the concentration of Ca2+ cations (Ca(OH)2 + CaSO4∙2H2O) also leads to a decrease in strength characteristics.