Long-term compressive strength and hydraulic property of nanosilica-improved sand in different soaking environments

Abstract

Traditional grouting materials (such as cements, sodium silicates and organic polymers etc.) have some limitations in improving soil, the rheological property of cement-based slurries is inferior to chemical grouting materials, sodium silicates have non-negligible shrinkage, organic polymers are often toxic. As a new kind of grouting materials, nanosilica has nano-scale particles, low initial viscosity, good penetration, and environment friendly characteristics. Literature showed that nanosilica could effectively increase the compressive strength and reduce the pore volume of sand. But the long-term mechanical and hydraulic properties of nanosilica-improved sand (NIS) in different soaking environments were rarely studied. In this study, different soaking environments (dry air, pure water, seawater, and acidic water) were adopted to simulate various practical engineering environments, with a soaking time of up to 365 days. The long-term compressive strength, hydraulic property, and microscopic structure were monitored. The results showed that the performance of NIS in pure water was better than in other environments. The compressive strength of NIS in pure water reached 283 KPa, and the erosion resistance time of NIS in pure water reached 350 hours. The maximum compressive strengths of NIS in acid water, seawater and air were 270 KPa, 253 KPa and 250 KPa, respectively. The maximum erosion resistance times of NIS in acid water, seawater and air were 263 hours, 205 hours and 261 hours, respectively. According to the microscopic results, the improved sand transformed from loose particles to agglomerates, and finally, to cemented aggregates. The NIS showed obvious roughening and shrinkage in dry air, while remained relatively complete in other three saturated environments. The results may provide reference for practical application of nanosilica-improved sand. • Nanosilica can improve the mechanical and hydraulic properties of sand. • The long-term performance of NIS can be basically maintained at a stable level. • The performance via environments is ranked as follows: Water, Sea, Acidic, Air. • The early strength of NIS increased with the concentration of catalyst. • NIS transformed from loose particles to agglomerates, and to cemented aggregates.