Nano-silica-modified alkali activated multi-solid waste-based concrete: Hydration characteristics and seawater corrosion mechanism

This study addresses the issue of seawater corrosion faced by solid waste-based concrete in marine environments by introducing nano-silica (NS) to optimize the alkaline-activated gelling material system. It investigates the impact of activator types and gelling material proportions on the hydration characteristics of neat paste and the seawater resistance of concrete. The results indicate that when the ratio of fly ash to steel slag is 1:1 and dual activation with NaOH and Na₂SiO₃ is employed, the 28-day compressive strength reaches 28.41 MPa, which is 2.41 MPa higher than that of the group with only NaOH. After adding 2% NS, the 28-day strengths of the B1N2 and B2N2 groups increase to 29.67 MPa and 29.41 MPa, respectively. In the seawater corrosion test, the strength of the B1 group without NS decreased by 28.6% after soaking in high-concentration seawater for 90 days, while the strength of B2N2 only decreased by 2.1%, with a corrosion resistance coefficient of 97%. Moreover, the chloride ion concentration at the surface layer (5 mm) was only 10% at 90 days. NS significantly inhibits the intrusion of Cl⁻ and SO₄²⁻ by filling pores and promoting the densification of C-A-S-H gel. Additionally, ICP-MS results show that after soaking B2N2 in seawater for 90 days, the concentrations of Al and Fe in the seawater were 2.6 µg/L and 1.2µg/L, respectively, indicating that this multi-solid waste-based concrete has an extremely low risk of metal leaching in marine environments. This study holds significant value for the development of high-performance, environmentally friendly marine engineering concrete.