Effects of alkaline concentration on workability and strength properties of ambient cured green geopolymer concrete

Geopolymer concrete, made with by-products from industrial waste, is a promising construction material that reduces carbon dioxide emissions and eliminates the need for natural resources used in traditional Portland cement. Despite numerous studies conducted over the years to investigate different characteristics of geopolymer concrete, there remains a lack of understanding on how various factors affect its properties. In this investigation, we explore the setting time, workability and compressive strength of ambient-cured geopolymer concrete, using GGBS and class F fly ash as geopolymer binder. We consider the quantity of sodium hydroxide (SH), fly ash to GGBS ratio and binder content to alkaline solution ratio (AS/B) as influencing factors. Based on experiments with 45 mixes of geopolymer concrete, we found that increasing SH concentration and GGBS content, as well as reducing AS/B ratio, decreased workability by about 60% and shortened setting time by 63–71%. However, a reduction in AS/B ratio and increased replacement of GGBS led to improved compressive strength. Compared to mixes with various SH concentrations, a slight decrease in strength was observed at higher SH concentrations (10 M and 12 M). These findings will be useful to produce geopolymer concrete components with greater strength.