EFFECT OF SUPERPLASTICIZER DOSAGE ON WORKABILITY AND 28-DAY STRENGTH OF GGBFS-FA GEOPOLYMER MORTAR IN VIETNAM

Using by-products such as ground granulated blast furnace slag (GGBFS) in binder can be a sustainable alternative to ordinary Portland cement, exhibiting rapid setting and workability loss, which can affect practical applications for this material in mortar and concrete.This research evaluates the effects of chemical admixture, which is a water-reducing and superplasticizer agent made from naphthalene formaldehyde sulfonate, at different dosages on the fresh and hardened properties of geopolymer mortar using GGBFS as a mineral admixture and fly ash (FA) as a filler.The results indicate that workability loss becomes evident when chemical admixture is used at 1.0% and 1.5% of binder weight.Despite the initial decrease in workability over time, the mix proportion using 1.0% and 1.5% chemical admixture demonstrates improved compressive strength at 28 days compared with the mix proportion using 0.5% chemical admixture, which can be up to 26.5% with a p-value is 1.8%.The optimal performance was observed at the mix proportion using 1.5% water reducing and superplasticizer, which balanced workability retention and mechanical strength development.The research promotes the use of eco-friendly GGBFS-FA-based geopolymers with assured performance toward the sustainable development of the construction sector in Vietnam.