Effect of initial water content and curing moisture conditions on the development of fly ash-based geopolymers in heat and ambient temperature

•Alkali activated fly ash geopolymers are synthesized at room temperature.•Curing moisture conditions after hardening are controlled in various methods.•Low initial water content plus low moisture condition during curing are beneficial.•Samples got similar strength levels to the heated ones in a relatively short time.

It has been claimed that water has no role to play in the formation of hardened geopolymer paste apart from providing the workability and necessary reaction medium. It has further been generally accepted that heat treatment is necessary for producing fly ash geopolymer concrete. This is considered a drawback affecting its manufacture and feasibility. The research presented in this paper was conducted in the aim of improving the ambient-cured (20 °C) geopolymer. This has been achieved by controlling the moisture condition of the specimens after hardening. This paper also examines whether there are mechanical effects as a result of variation in the initial water content. It further explores whether a combination of such variation together with controlling the curing regime may lead to desired improvement in the mechanical properties. The role of water was studied by monitoring the microstructural and mineralogical developments and relating them to the gain in strength. It has been found that reducing water content in the initial state and controlling the moisture condition during a curing period after hardening are beneficial and lead to extra strength gain in the ambient-cured fly ash-based geopolymer. This helps the ambient-cured geopolymer achieve strength levels comparable to those of heat treatment within a relatively short curing period.