Effects of A low-carbon emission additive on mechanical properties of fine-grained soil under freeze-thaw cycles

Abstract

The microstructural and resistance properties of fine-grained soils can remarkably alter under freeze-thaw cycles in seasonally frozen regions. Although treated soils have better mechanical properties than natural ones to withstand severe environmental damage, CO2 emitted from additives is not usually regarded. In this research, by analyzing the amount of carbon dioxide releases from some widely used materials, glass fiber was selected as an eco-friendly and low-carbon reinforcement additive. The strength properties of natural and reinforced samples were studied under freeze-thaw conditions via a series of unconfined compression and direct shear tests. The microstructural changes and interfacial interaction of fiber-clay particles was also evaluated by Brunauer-Emmett-Teller (BET) and scanning electron microscopy (SEM) analyses. The results revealed that increasing freeze-thaw cycles reduces the resistance properties of the soil. Despite the favorable impact of glass fiber on compressive strength and elastic modulus, its effect on preventing the resistance reduction due to freeze-thaw cycles was not significant and the best performance of fiber was achieved for shear strength. After 12 cycles, natural clay and soil treated with 2.5% fiber showed 42 and 19% reduction in shear strength, respectively. The results of BET test showed a 30 and 42% increase in total pore volume and mean pore diameter of clay sample due to the freeze-thaw cycle. Adding fiber had no effect on reducing the number and size of micro-voids. However, the mechanical effect of entanglement and high strength of fiber against tensile stresses improved tensile strength of the soil. The stresses were caused by external loading or internal pressure due to water volume changes which were triggered by ice lenses. SEM images showed that glass fiber prevented the formation and expansion of micro-voids and crack lines during freeze-thaw conditions. The presence of fiber preserves integrity, improves bonding and solidarity, and widens the contact surface between the soil particles, finally leading to enhanced frictional resistance between soil particles. Furthermore, glass fiber produces less strength than popular additives such as lime and cement, but it was found to emit very low carbon dioxide to the environment compared to other additive materials.