Physicochemical Interactions of Clays and Polysaccharides for High-Performance Biopolymer-Stabilized Earthen Materials

As the climate crisis intensifies, the demand for more sustainable construction materials, such as biopolymer-stabilized earthen materials, has become increasingly urgent. This study elucidates fundamental physicochemical interactions between five polysaccharide biopolymers (i.e., guar gum, locust bean gum, methylcellulose, sodium alginate, and xanthan gum) and two common clays, namely bentonite and kaolinite, using Fourier-transform infrared spectroscopy, thermogravimetric analysis, and zeta potential. In addition, this study investigated the effect of these biopolymers on the fresh-state rheological and hardened-state properties of the clays. The results demonstrate that the two nonionic galactomannans, guar and locust bean gums, bind to both clays, while methylcellulose binds primarily to bentonite. In contrast, the two anionic biopolymers, sodium alginate and xanthan gum, bind to neither clay. Clay–biopolymer binding affinity was observed to correlate directly to stiffening (binding) or plasticizing (nonbinding) effects in rheological testing. While all biopolymers led to an increase in unconfined compressive strength, the highest strengths were achieved in bentonite (13.7 ± 1.3 MPa) and kaolinite (8.0 ± 0.5 MPa) using sodium alginate, a low molecular weight anionic biopolymer with nonbinding, plasticizing effects on both clays. Collectively, these findings provide mechanistic insights that can be leveraged in the production of high-performance biopolymer-stabilized earthen materials for the 21st century.