Sea sand seawater geopolymer concrete

Geopolymers are cementitious materials known for their environmental benefits and comparable characteristics to conventional Portland cement. This paper investigates the mechanical properties of eight geopolymer mixes with varying mix designs. The objectives of this study are to investigate the effect of how unwashed sea sand and seawater influence the mechanical properties of the geopolymer mixes, as well as the impact of different binders, activators and curing conditions. Fly ash, slag and metakaolin are investigated as binders, while pentahydrate sodium metasilicate (Na₂SiO₃·5H₂O), anhydrous sodium metasilicate (Na₂SiO₃) and sodium hydroxide solution are employed as alkaline activators. The geopolymer specimens were cured at room temperature for 24h, contrasting curing conditions between an atmospheric environment and submerged in seawater. The materials properties were characterized via compressive strength, density, cone penetration, sorptivity and nuclear magnetic resonance relaxation measurements. Compressive strength was measured after 3-, 28- and 56-days. The ultimate compressive strength of 54.28 MPa was obtained by incorporating fly ash, slag and normal silica sand, and sodium hydroxide solution submerged in seawater. Our results showed that the fly ash based geopolymer mixes activated by sodium hydroxide may be optimized to achieve high compressive strength. The use of unwashed sea sand affected geopolymer workability but had little influence on compressive strength.