Fly Ash–Based Aqueous Nanosilica Enhanced Activator for Efficient Production of Room Temperature–Cured Concrete with Two-Part Alkali-Activated Binders

Abstract

Room temperature–cured alkali-activated binders of enhanced strength are produced without external silica addition. The extraction of nanosilica and its use in producing alkali-activated binders made of fly ash and slag are explored. Low-energy extraction of an aqueous nanosilica activating solution is developed in a zero-waste utilization process. Alkali-activated slag–fly ash (AASF) binders are activated with alkaline fly ash–based aqueous nanosilica (FABANS) solutions. FABANS is highly amorphous nanosilica extracted from fly ash through dissolution in an alkaline solution that also activates the slag. The reaction kinetics, compressive strength, and reaction products are evaluated in an AASF made with alkaline FABANS. There is a significant strength improvement from the enhanced formation of calcium aluminosilicate hydrate (C─ A─ S─ H) gel and densification of the microstructure in AASF made with FABANS. The Na in the activated AASF binder is recovered by water leaching. The setting and strength gain in the AASF are due to slag hydration. Using FABANS efficiently mobilizes the reactive silica from fly ash to enhance reaction product formation in AASF. FABANS is suitable for enhancing the strength of concrete produced with AASF binders achieved at room temperature.