Impact of low NaOH molarities on mechanical and durability properties of ambient and oven-cured fly ash geopolymer concrete

Ambient cured fly ash based geopolymer concrete (GPC) is a promising environmentally friendly alternative to Ordinary Portland Cement Concrete (OPCC). However, adoption of geopolymer concrete has been hampered by the challenges associated with the use of highly concentrated activators and the need for heat curing to achieve sufficient fresh and hardened properties, as well as the limited research on its durability. This paper aims to address these issues by focusing on producing high strength geopolymer concrete using low molarity activators and ambient curing conditions. The effect of curing temperatures and Sodium Hydroxide (NaOH) activator concentrations ranging from 2, 4, 6, and 8 M were evaluated in terms of strength and durability performance. Durability studies examined carbonation, chloride penetration, and abrasion resistance. Porosity and permeability of the concrete mixtures were also investigated through an examination of water absorption and sorptivity performance. Further, SEM analysis clarified the microstructural changes which occurred as a result of differing curing temperatures and NaOH molarities. Lastly, a cost comparison was conducted which compared the costs of all the developed geopolymer mixtures with respect to a reference OPCC mix and significant cost were observed for the GPC mixes compared to OPCC of equivalent strength.