Experimental comparative study on the performance of nano-SiO₂ and microsilica in stabilization of clay

Abstract.

Nano- SiO₂ and microsilica are two types of additives with the same elemental structure but different particle sizes that are introduced by the researchers for ground improvement. The major difference in the two additive materials is the difference in the specific surface area, which its effect has been evaluated in this study. For this purpose through experimental tests, the effects of each of two additives on the change in geotechnical parameters of clay are compared. The additive percentages of each of the two additives are limited to 6% and the samples have been tested after a 28-day curing time. Variations in the consistency limits, compaction conditions of the samples, as well as undrained shear strength of soil have been measured for each mixture. The results of the unconfined compression test demonstrated that the nano- SiO₂ had a more prominent effect in doses lower than 2% on the unconfined compressive strength and modulus of elasticity of the soil. By increasing the amount of nanomaterial, the strength of the samples is closer to that obtained for stabilized specimens with microsilica. In samples containing nanosilica, the increase in strength in percentages of less than 1% of the nano-material had a higher rate, while microsilica followed a relatively stable trend. By adding additives, the maximum dry density dropped up to 5% and shown a higher optimum moisture content. The plasticity changes were somewhat different for both additives. By adding more than 2% of nano- SiO₂ , an increase in the liquid limit and the plasticity index of soil were observed, while microsilica slightly reduced these parameters. The X-Ray Diffraction (XRD) showed that no significant chemical reaction was occurred in the soil by additives. Moreover, the examination of Field Emission Scanning Electron Microscopy (FESEM) demonstrated that both materials played a significant role in reducing porosity and creating particle integrity. However, the pattern of filling the pores and enclosing particles by the two materials were different. This difference was particularly influential in terms of water absorption by the sample.