Abstract: Nanomaterial modification can significantly enhance the mechanical properties and durability of engineering materials. However, its impact on the basic properties of geopolymer cutoff wall materials and their durability under freeze-thaw cycles remains unclear. In this study, fly ash-based geopolymer was modified with nano-silica (NS) and graphene oxide (GO). The slump, heat of hydration, hydraulic conductivity, and compressive strength of the materials were systematically tested to assess the effects of nanomaterial type and content on the basic properties of cutoff wall materials. Furthermore, freeze-thaw cycling test was conducted to evaluate the durability of geopolymer. Fourier-transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), and mercury intrusion porosimetry (MIP) were used to explore the modification mechanisms. Results showed that the addition of nanomaterials resulted in an increase in hydraulic conductivity compared to unmodified samples. As NS content increased, the nanomaterial filled the pores, reducing hydraulic conductivity. GO addition, on the other hand, accelerated geopolymerization, further lowering the permeability. NS improved freeze-thaw resistance by refining the pore structure through micro-aggregate effect and inducing secondary hydration products that filled cracks, thus slowing down material degradation during freeze-thaw cycles. However, GO addition caused exfoliation of nanosheets and associated geopolymer gels during freeze-thaw cycles, resulting in localized structural damage and reducing freeze-thaw durability and impermeability.

Key words: cutoff wall, geopolymer, nanomaterial, hydraulic conductivity, freeze-thaw cycles