Improvement of Thermal and Hydraulic Properties of Soil Using Nano Silica Aerogel to Reduce Frost Effects on Pavement

Soil frost in cold regions is the most important factor in the deterioration and reduction of pavement efficiency of roads and other soil-based structures. The present work aims at introducing a novel method to reduce the adverse effects of frost in the soil. In the proposed method, a moisture-compatible thermal insulation was prepared to prevent the penetration of cold air in the subgrade. Silica aerogel nanomaterial with extremely low thermal conductivity and high hydrophobicity was mixed with soil to provide the thermal insulator. Silica aerogel was mixed with soil in ratios of 0.5, 1 and 2% and the properties of these mixtures such as thermal conductivity, hydrophobicity, permeability, moisture content in saturated state and durability against freeze-thaw cycles were studied. In this study, it was observed that due to the hydrophobicity of silica aerogel, soil-aerogel mixtures also become significantly hydrophobic. For this reason, their water absorption is significantly reduced; So that the moisture content in the saturated state in the soil without silica aerogel is about 4 times the moisture content in the soil-aerogel mixture. As a result, wetting soil-aerogel mixtures do not have much effect on increasing their thermal conductivity. On the other hand, it was observed that the permeability of the soil without silica aerogel is about 21 times the permeability of the soil-aerogel mixture, which indicates a significant decrease in the permeability of the soil-aerogel mixtures. Moreover, wetting-drying and freezing-thawing cycles as well as exposure to water flow had no effect on the thermal conductivity of the soil-aerogel mixtures. Considering the set of the thermal and hydraulic characteristics of the soil-aerogel mixtures, they can be introduced as a suitable choice for use on the soil surface as a moisture-compatible thermal insulation in order to deal with the adverse effects of frost in the soil.