Multi-scale characterization of acacia gum as an alternative plant-based biopolymer binder for CO₂ sequestering earthen soil composites

The construction industry is under increasing pressure to adopt sustainable, low-carbon alternatives to conventional materials such as cement. Biopolymers derived from natural sources offer a promising pathway, combining environmental compatibility with functional performance. This study explores the use of acacia gum, a naturally exuded, biodegradable polysaccharide from acacia senegal and acacia seyal, as a stabilizing agent in earthen soil composites across 12 united states department of agriculture (USDA) classified soil textures. A fixed dosage of 1 wt.% acacia gum was incorporated into each mix, and a comprehensive multi-scale characterization was performed, including scanning electron microscopy (SEM), energy-dispersive spectroscopy (EDS), X-ray photoelectron spectroscopy (XPS), thermogravimetric analysis (TGA), mechanical strength testing, and shrinkage measurements. Results show that texture plays an important role in acacia gum–soil interaction. Clay-rich soils exhibited strong chemical bonding through hydrogen and electrostatic interactions but suffered from high shrinkage up to 20%. Sand-rich mixes demonstrated weak van der waals-based adhesion with minimal thermal or mechanical improvement. Silt-rich and silty clay loam soils provided an optimal balance, achieving up to 5.8 MPa compressive strength and 1 MPa flexural strength, and moderate shrinkage between 6 to 10%, with TGA indicating ~ 8.3% mass loss due to moisture retention and gum decomposition. These properties are important not only for mechanical durability but also for supporting plant growth and microbial life, enabling biopolymer-soil composites to contribute to vegetation development and potential CO₂ sequestration. The findings demonstrate acacia gum’s viability in climate-adaptive construction, including green facades, vernacular housing, and regenerative soil systems in arid or disaster-prone areas.