Biopolymer stabilization of rammed earth based on native and ionic crosslinked xanthan gum: Mechanical, microscopic, and environmental durability assessment

Unstabilized rammed earth (URE) is a low-carbon construction technique, but its broader adoption is constrained by limited mechanical performance and environmental durability. This study introduces an ionic crosslinked biopolymer stabilization strategy based on xanthan gum (XG) and trivalent chromium (Cr 3+ ) to improve in-situ soil with low clay content for rammed earth (RE) construction. Specimens containing 0.5–1.5 wt% XG were produced by dry mixing and evaluated using unconfined compression, Brazilian tensile testing, SEM-EDS, XRD, and accelerated environmental cycling. Initial moisture content strongly governed performance, with strength-optimizing values of 10% for XG-treated RE (XRE) and 12% for Cr 3+ -crosslinked XRE (CXRE) reflecting coupled effects of dry density and polymer hydration/crosslinking. At an optimum of 1.5% biopolymer concentration, XRE achieved a 28-day compressive strength of 5.01 MPa, significantly higher than URE (1.86 MPa), while also increasing elastic modulus from 146.8 to 301.8 MPa, energy absorption capacity from 18.5 to 60.1 kJ/m 3 , and tensile strength from 0.132 to 0.335 MPa. Although CXRE showed slightly lower 28-day compressive strength (4.41 MPa) than XRE, it exhibited superior tensile performance (0.425 MPa) and exceptional durability. After exposure to rigorous accelerated environmental cycles, strength losses were 29.28% for URE, 19.36% for XRE, and only 1.13% for CXRE. Microstructural analyses attributed these improvements to biopolymer coatings and interparticle bridges, while Cr 3+ crosslinking produced a denser, more climate-resistant three-dimensional network without altering the mineralogical framework. These findings demonstrate that XG and CX are effective stabilization strategies for producing structurally robust and environmentally durable RE from low clay in situ soils.