Influence of NaOH Activator Concentration on Efflorescence and Compressive Strength of Sustainable Mortar with Alkali-activated Slag and Fly ash Binders

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

全球基础设施的快速扩张，显著加剧了对普通硅酸盐水泥（ordinary Portland cement, OPC）及其他高性能胶凝材料的需求。粒化高炉矿渣粉（Ground granulated blast slag, GGBS）与粉煤灰已被广泛用作更具可持续性的OPC部分或完全替代胶凝材料。本研究以GGBS与粉煤灰复合体系作为胶凝材料，采用硅酸钠（Na₂SiO₃）与氢氧化钠（sodium hydroxide, NaOH）复合激发，探究了NaOH激发剂浓度对砂浆28天抗压强度的影响。实验中将NaOH浓度设置为6~12 mol/L，以评估溶液碱度对砂浆抗压强度与泛碱现象的影响。当GGBS占总胶凝材料比例超过50%时，水中养护的砂浆抗压强度高于常温养护试样；当GGBS占比不超过50%时，水中养护砂浆的抗压强度与常温养护试样相当甚至更低。当GGBS掺量为75%或100%时，10 mol/L的NaOH浓度为最优激发参数，此时砂浆28天抗压强度达到峰值。采用6 mol/L NaOH溶液激发的100%矿渣胶凝体系常温养护试样，出现了严重的泛碱现象与强度劣化。