The impact of raspberry fiber and xanthan gum in improving the mechanical properties and freeze-thaw durability of bentonite soil subgrade

Currently, the application of enhancement techniques with natural additives for soil stabilization is crucial due to growing urbanization and environmental concerns. Contemporary construction methods increasingly need eco-friendly and cost-effective materials, such as natural fibers. Reinforcing the soil sublayers with fibers improves layer quality and increases its load transfer capacity over a larger surface, thereby reducing the required thickness of upper layers. This study utilized raspberry stalks and xanthan biopolymer as natural additives for the first time to improve the mechanical qualities of bentonite expansive soil. Different tests, including compression and indirect tensile strengths, swelling potential, freeze-thaw (F-T) cycles, California bearing ratio (CBR), and scanning electron microscopy (SEM), were performed on samples comprising 0.2, 0.4, and 0.6 % of raspberry fibers and 0.5, 1, and 2 % of xanthan gum, with curing durations of 1, 7, 14, and 28 days. The test results revealed that the combination of 1 % xanthan and 0.4 % fibers, subjected to 28 days of curing, showed the best performance in increasing the mechanical properties of bentonite. The hydrogel structure and the locks and links formed in the soil by the additives led to increases of 353 % and 103 % in compressive and tensile strengths, respectively. The results also indicated that the free-swelling potential of the unstabilized bentonite soil diminished from 280 % to 74 % when stabilized with optimum percentages of xanthan and fiber. Furthermore, the investigation showed that even after exposure to 10 F-T cycles, the durability of xanthan-fiber-stabilized bentonite soil was significantly higher compared to the unstabilized soil. Moreover, the CBR value of the stabilized soil improved by 143 % compared to the unstabilized soil, indicating a significant increase in soil layer quality. The SEM results verified that the additive combination significantly impacted the strength of the samples. The data indicate that the incorporation of xanthan gum as a bio cohesive agent and raspberry fiber as tensile strands enhances soil strength, hence augmenting the viability of these additives in practical applications, including shallow foundations, adobe brick, and subgrade. • Raspberry fibers improved xanthan-stabilized clay compressive and tensile strength. • Adding raspberry fibers enhanced xanthan-stabilized bentonite soil durability. • Adding raspberry fiber to xanthan-stabilized bentonite soil decreased swelling. • Enhancing clay subgrade with raspberry fibers reduces pavement layers thickness. • The optimal amount of raspberry fibers for reinforcing bentonite soil is 0.4 %.