Anti-dispersion, rheological, and mechanical properties of GBFS/FA geopolymer for underwater engineering applications

Abstract

Cementitious materials used in underwater engineering primarily face challenges such as water infiltration, chloride ion penetration, and sulfate attack. Therefore, the use of fast curing, strong corrosion resistance, and high-performance geopolymers is critical in underwater engineering. In this study, NaOH was selected as the activator, with granulated blast furnace slag (GBFS) and fly ash (FA) serving as precursors. The effects of hydroxypropyl methylcellulose (HPMC) content, alkali content, and the GBFS/FA ratio on the anti-dispersion, rheological, and mechanical properties of the geopolymers were systematically investigated. The results indicated that when the Na₂O content was below 5 wt%, increasing the HPMC enhanced the anti-dispersion properties of the geopolymer paste. However, in a highly alkaline environment (Na2O≥7 wt%), HPMC did not enhance the anti-dispersion properties of the paste. Infrared spectrum analysis suggested that the degradation of HPMC chemical bonds was responsible for the loss of underwater anti-dispersion properties in the geopolymer paste. The workability of the paste was negatively impacted by the thickening effect of HPMC. As the HPMC content increased, both the yield stress and plastic viscosity of the paste rose. FA enhanced the paste's workability, increasing its flowability by 13.36 %. At a constant alkali content, the rheological behavior of the paste was significantly affected by the HPMC content and the GBFS/FA ratio. The Bingham and modified Bingham (MB) models were employed to fit the rheological curve of the geopolymer paste, yielding satisfactory results. While GBFS contributed to the improvement of early strength, FA had a contrary effect. HPMC could delay the hydration process, increase the porosity of geopolymers, and reduce the strength of the samples. Underwater pouring further exacerbated the porosity, negatively affecting the geopolymer's strength. This study offers valuable insights for the application of geopolymers in underwater engineering.