Improved mechanical response of Nano-SiO2 powder cemented soil under the coupling effect of dry and wet cycles and seawater corrosion

The average salinity of seawater is 3.5%, with a significant presence of corrosive ions, primarily Cl- and SO42-. In contrast to cement engineering in terrestrial natural environments, cement-reinforced structures exposed to corrosive marine environments not only endure ion erosion but also undergo periodic desiccation due to tidal variations in seawater. The coupling of these effects results in a reduction in the mechanical properties of cemented soil, inevitably leading to the degradation of cemented foundations, posing a serious threat to their safety and normal functionality. Investigating the improvement of the mechanical properties of cemented soil in corrosive coastal environments is a crucial engineering challenge in current coastal construction projects. To address this engineering challenge, this study proposes the use of Nano-SiO2 to enhance the mechanical characteristics of cemented soil, aiming to improve the strength and durability of cement-reinforced structures. Simulating the main corrosive ions in seawater by using different concentrations of SO42- ions, the study subjected cemented soil samples to dry-wet cycles to simulate the desiccation caused by tidal changes in seawater. Unconfined compressive strength tests were conducted on cemented soil and nano-cemented soil samples under coupled conditions, revealing that the incorporation of Nano-SiO2 increased the strength of cemented soil and slowed down the corrosion rate. With an ion concentration of 12.3 g/L, after 60 dry and wet cycles, the compressive strength of nano-cemented soil increased by 90% compared to conventional cemented soil, with a mass loss only half that of conventional cemented soil. XRD, SEM, and NMR tests on various cemented soil samples indicated that the addition of Nano-SiO2 filled small pores, suppressed pore development, and interacted with cement hydration products, forming a gel-like structure that improved the compactness of cemented soil. This, in turn, mitigated ion corrosion and the degradation of cemented soil under dry-wet cycles.