Pilot Study on Solid Activators for Strength and Microstructural Enhancement in One-Part Alkali-Activated Binders

One-part alkali-activated binders offer a safer and more efficient alternative to conventional systems by replacing liquid activators with solid counterparts. In this pilot study, one-part alkali-activated fly ash and slag binders were prepared using single and composite solid activators, specifically sodium silicate and sodium hydroxide. The effects of these activators on flowability, compressive strength, hardened density, porosity, and microstructure were examined. Combining composite activators improved both early and final compressive strength but reduced flowability. A strong correlation was observed between density, porosity, and compressive strength, where higher density and lower porosity in composite activator mixes contributed to enhanced strength development. The mix containing 60% fly ash and 40% slag, activated by sodium silicate and sodium hydroxide, achieved the highest compressive strength of 52.81 MPa at 28 days, with a high density (2.12 g/cm³) and low porosity (1.15%), confirming improved microstructural densification. SEM images revealed a more compact gel structure in composite activator mixes, while XRD analysis confirmed increased calcite formation, indicating a higher degree of reaction. This enhanced reaction contributed to a denser microstructure, reduced porosity, and improved compressive strength.