Seawater used to Metakaolinite-based geopolymer preparation

Abstract

The use of seawater (SW) to prepare geopolymers has attracted increasing attention, for its potential to save fresh water and reduce carbon dioxide emission. However, the ions in SW influence the geopolymers. This study investigated the effects of SW concentration on the microstructure and mechanical properties of metakaolinite (MK)-based geopolymers with different Si/Al molar ratios (1.3, 1.6, and 2.0). The compositions and structures of the obtained geopolymers were characterized via several techniques, including X-ray diffraction, Fourier-transform infrared spectroscopy, scanning electron microscopy, and mercury intrusion porosimetry.With an increasing Si/Al molar ratio, the high soluble silica content promoted geopolymer formation, further increasing the microstructure density and compressive strength of the geopolymer. The reaction between MK and alkaline solution with an Si/Al ratio of 1.3 resulted in the formation of a zeolite A-containing geopolymer, which exhibited a 28-day compressive strength of only 12.7 MPa. SW addition did not significantly influence the geopolymer microstructure and mechanical properties, but zeolite formation was inhibited with increasing SW concentration.In contrast, geopolymers with Si/Al ratios of 1.6 and 2.0 exhibited a dense microstructure, with 28-day compressive strengths of 35.0 and 57.5 MPa, respectively. The SW-mixed geopolymers exhibited a lower compressive strength than the pure water-mixed geopolymers. With increasing SW concentration (artificial SW), the geopolymer compressive strengths gradually decreased, but to a limited extent. The ions in SW altered the geopolymer composition, resulting in the formation of some salts. The formation of these salts negatively influenced the microstructure and pore size distribution of the geopolymer, thereby reducing its compressive strength. In addition, Cl- was distributed in the geopolymer matrix, but SO42- underwent precipitation at a high concentration of artificial SW.Overall, the results showed that the ions in SW reduced the compressive strength slightly by changing the microstructure and composition of the MK-based geopolymer. These findings suggest that SW-mixed MK-based geopolymers can be suitably used as building materials in the marine environment.