Strength Characteristics and Microstructure Analysis of Alkali-Activated Slag-Fly Ash Cementitious Material

Modifying the admixture of alkali-activated cementitious materials using components such as fly ash and fine sand may reduce CO2 emissions and conserve natural resources and energy. This study adopted strength testing, scanning electron microscopy, and mercury intrusion porosimetry to investigate the influence of different admixtures on the compressive strength and flexural strength of alkali slag cementing materials and the microstructure characteristics of hardened slurry under the action of load. The flexural strength of alkali slag cement slurry and mortar was reduced by replacing slag powder with fly ash. Content of fine sand less than 20% had little effect on the strength of alkali slag cement mortar; however, when the content of fine sand exceeded 30%, the strength decreased significantly. The hydration degree at 3 d was large, and the density of slurry increased with the extension of age. Increased fly ash or fine sand content decreased the density of the slurry, and increased fly ash resulted in a large number of unhydrated fly ash particles in the cementitious materials. Addition of fine sand resulted in a large number of microcracks in the slurry, which gradually decreased with the extension of hydration age.

Automated summary

Modifying alkali-activated cementitious materials using fly ash and fine sand as components can reduce CO2 emissions and save natural resources and energy. The use of fly ash instead of slag powder lowers the flexural strength of alkali slag cement, while the strength of alkali slag cement mortar is less affected by the content of fine sand, except when it exceeds 30%. The hydration degree increases with time, and the density of the slurry decreases with increased fly ash or fine sand content.