Influence of NaOH Activator Concentration on Efflorescence and Compressive Strength of Sustainable Mortar with Alkali-activated Slag and Fly ash Binders
Description
The rapid expansion of the global infrastructure has intensified the demand for ordinary Portland cement (OPC) and other high-performance binders. Ground granulated blast slag (GGBS) and fly ash have been widely used as more sustainable partial or full replacements for OPC. This study investigates the effect of sodium hydroxide (NaOH) activator concentration on the 28-day compressive strength of mortar using combinations of GGBS and fly ash as binders, activated using Na2SiO3 and NaOH. The concentration of NaOH was varied from 6 to 12 mol/L to assess the effect of solution alkalinity on the compressive strength and efflorescence. Mortar cured under water produced a higher compressive strength when the GGBS content exceeded 50% of the total binder content, compared to ambient curing. When the GGBS content was 50% or less of the total binder, the strength of the mortar cured in water was comparable to or lower than that cured under ambient conditions. An optimum NaOH concentration of 10 mol/L produced the highest 28-day compressive strength in mortars with 75% or 100% GGBS binder. Substantial efflorescence and strength degradation were observed in ambient-cured mortar samples with a 100% slag binder activated using a 6 mol/L NaOH solution