Investigation of the relationship among the hydration, microstructure and compressive strength of alkali-activated phosphorus slag

Abstract

In this study, the relationship among the hydration, microstructure and compressive strength of alkali-activated phosphorus slag (AAPS) was systematically investigated to provide a foundation for its design and application. The alkali dose and silicate modulus had both positive and negative effects on PS hydration due to the change in the pH, the concentrations of Si-containing ions and the hydrate coating on the PS surface, and the overall effect depended on their relative magnitudes. The hydration of waterglass-activated phosphorus slag (WAPS) experienced a transformation of NASH first into CNASH (low Ca) and then into CNASH (high Ca) due to the stronger polarization ability of Ca2+ over Na+, and the gel transformation was accompanied by dealumination. The more early hydrates there were, the higher the early densification and early compressive strength of AAPS. The later densification and later compressive strength were influenced by a combination of the hydrate content, early hydration rate and gel type. CNASH (high Na) was incompatible with CNASH (low Na), which degraded the later densification. When the contents of later hydrates were comparable, the slower early hydration and lower CNASH (high Na) contributed to the greater later densification and compressive strength.