Evaluation of mechanical properties and durability of biopolymer-cement-treated silty sand

Biopolymers like xanthan gum (XG) are increasingly explored as an environmentally friendly soil binder; however, their combined use with conventional binders and response to moisture-induced effects have received limited attention. This study evaluates the mechanical properties of a silty sand treated with XG, cement, and their combinations under varying moisture states and durability conditions. Tests such as compaction, unconfined compressive strength, and wet–dry durability were conducted. Results revealed decreasing dry densities with increasing XG content, and XG-only treatments exhibited negligible strength with swelling on 24 h of water immersion. Conversely, cement–XG (3% cement + 0.5%–1.5% XG) treatments showed substantial wet strength and sustained six wet–dry durability cycles – exceeding XG-only (0.5%–1.5%) and cement treatments (3%). Fourier transform infrared spectroscopy indicated ionic-cross-linking interactions among biopolymer and Ca2+ ions, and X-ray diffraction analysis evidenced cementitious phase formations. Morphological insights into the strengthening mechanisms through field emission scanning electron spectroscopy exhibited distinct XG gel features due to cement incorporation. Overall, the findings demonstrate cement–XG combinations offering better moisture resistance compared to XG-only treatments, potentially presenting a viable soil treatment strategy for applications prioritising environmental sustainability.