Effect of Water-Reducing Admixtures on the Workability of Carbonate-Containing Magnesium Silicate Hydrate Binders

Abstract

Carbonate-containing magnesium silicate hydrate cement binders are a low-carbon, sustainable alternative to portland cement, but current workability issues hinder practical applications such as construction. In this study, three water-reducing admixtures, sodium hexametaphosphate, triethanolamine, and polycarboxylate ether, are investigated to determine which is the most effective at improving the workability of carbonate-containing magnesium silicate hydrate systems while maintaining compressive strength. Mini-slump measurements were performed to determine the effect of the admixtures on workability, while their effect on mechanical properties was analyzed using compressive strength testing and ultrasound measurements. X-ray diffraction was used to assess how the admixtures affect the phase assemblage of the binders, and zeta potential measurements were performed to analyze the aqueous surface chemistry of the starting materials. After testing, sodium hexametaphosphate is determined to be the most effective at improving workability while also improving compressive strength. At higher SHMP dosages, the potential formation of an amorphous Mg-phosphate phase that may contribute to early compressive strength in place of the expected carbonate-containing binder phases is hypothesized. Polycarboxylate ether is determined to greatly improve workability but decrease strength, and triethanolamine is observed to have minimal effects on the binder.