Evaluation of Unconfined Compressive Strength and Durability of Carbonate and Silicate Sands Treated with Persian Gum Biopolymer and Calcium Chloride Binding Agent

The constraints such as altering soil acidity and environmental concerns stemming from the use of traditional soil stabilizers like cement have justified the exploration of environmentally friendly, cost-effective materials with fewer secondary risks, such as biopolymers. This study focuses on examining the effect of adding Persian gum and calcium chloride to two types of soils, silicate sand from Firoozkooh and carbonate sand from Hormuz. For this purpose, initial parameters such as the weight percentage of Persian gum and the molarity of calcium chloride were evaluated through an unconfined compressive strength test, identifying optimal additive percentages. Then, the impact of factors such as curing time, curing place, and wetting-drying cycles on the compressive strength and durability of the optimized treated specimens was investigated. The results of this research indicate that the compressive strength of Persian gum-treated Firoozkooh and Hormuz sands increases up to 2.75 and 3 MPa, respectively, after a 28-day curing period at 40°C with the optimal Persian gum percentage (2.5% and 3%). Under dry conditions, Persian gum and calcium chloride-treated Firoozkooh and Hormuz sands at the optimal percentage (1.5% Persian gum and 3 molar calcium chloride for Firoozkooh sand and 2.5% Persian gum and 2 molar calcium chloride for Hormuz sand) achieve compressive strengths of 6.2 and 5.1 MPa, respectively, after 28 days, representing a 125% and 70% improvement compared to specimens treated with Persian gum. Persian gum exhibits acceptable durability against wetting and drying cycles, demonstrating initial dry and wet uniaxial compressive strengths (after immersion in water) for Firoozkooh and Hormuz sands treated with Persian gum, which were initially 2200 and 200, 2250 and 240 kPa, respectively. After undergoing 10 wetting and drying cycles, these strengths decreased to 750 and 110, 600 and 80 kPa, respectively, and will maintain this resistance in subsequent cycles.