Performance of geopolymer paste under the different NaOH solution concentrations

With the characteristics of low carbon, environmental protection, energy saving, and emission reduction, geopolymer pastes can effectively alleviate environmental and economic problems caused by the construction materials industry. The mechanical properties of geopolymer pastes are greatly affected by the composition of alkaline activators, while the existing research on their influence rules is not uniform. This study investigated the effects of alkaline activators composed of varying concentrations of NaOH solution under standard curing conditions on the mechanical properties and material characteristics of fly ash and slag-based geopolymer pastes. The results of the study indicated that under standard curing conditions, the mechanical properties of geopolymer pastes increased with the increase of NaOH solution concentration in alkaline activators. Under the influence of alkaline activators with 16 M NaOH solution, the flexural strength and compressive strength of geopolymer pastes reached the highest values at 28 d, up to 5.43 MPa and 39.13 MPa, respectively. Increasing the NaOH solution concentration in alkaline activators can promote the production of gel products such as N-A-S-H, forming a dense microstructure with a lower porosity, leading to higher mechanical properties.