Performance of geopolymer paste under different concentrations of sodium hydroxide solution

Compared with traditional cement pastes, geopolymer pastes can effectively alleviate environmental and economic problems caused by the construction industry as they are characterised as low carbon dioxide materials, with energy reduced energy consumption and emissions. However, the mechanical properties of geopolymer pastes are greatly affected by the composition of the alkaline activators used in their preparation, and existing research results on this influence is not consistent. In this study, the effects of alkaline activators composed of varying concentrations of sodium hydroxide (NaOH) solution under standard curing conditions on the mechanical properties and material characteristics of geopolymer pastes made with fly ash and slag were investigated. Under standard curing conditions, the mechanical properties of the geopolymer pastes increased with an increase of sodium hydroxide solution (SHS) concentration in the alkaline activator. The use of alkaline activator with 16 M SHS led to the greatest flexural and compressive strengths of the geopolymer pastes at 28 days, reaching values of 5.43 MPa and 39.13 MPa, respectively. Increasing the SHS concentration in the alkaline activator promoted the production of gel products such as N-A-S-H, which formed a dense microstructure and led to higher mechanical properties.