Assessing the durability of biopolymer-treated soil under weather cycles

Biopolymers, as eco-friendly alternatives to traditional inorganic chemicals or synthetic polymers, have significant potential applications for sustainable soil stabilization and ground improvements. This study investigated the weather durability of xanthan gum (XG), an emerging biopolymer, and sticky rice (SR), a biopolymer used in construction for millennia. The performance of biopolymer-treated soils was evaluated through laboratory experiments focusing on their behavior under wet–dry (W-D) and freeze–thaw (F-T) cycles. The basis of comparison includes untreated soil as the baseline, and soil treated with lime, a conventional non-renewable chemical soil stabilizer. The underlying mechanisms for their performance were assessed by microstructural analysis using Scanning Electron Microscopy (SEM) and elemental composition assessment via Energy-Dispersive X-ray Spectroscopy (EDS). Results indicated that soil treated with biopolymers demonstrated different resistance to weather-induced degradation. In terms of susceptibility to W-D cycles, SR-treated soil exhibited higher resilience under W-D cycles, remaining intact after eight cycles with only 1.1% mass loss by the sixth cycle; while XG-treated soil lost 14% mass after the first W-D cycle and collapsed in W-D cycles. In terms of susceptibility to F-T cycles, SR-treated soils showed a 27.2% decrease in unconfined compressive strength (UCS) after six F-T cycles, while XG-treated soils experienced 18.1% reduction of UCS. The observed behaviors are attributed to the interactions between SR or XG with water, i.e., hydrophobicity versus hydrophilicity. SEM and EDS analyses revealed SR’s hydrophobic coating and XG’s fibrous network in the microstructure of treated soils as potential underlying mechanisms for observed behaviors. To leverage the resilience of SR in W-D cycles and XG in F-T cycles, a hybrid SR-XG treatment is recommended to utilize the complementary advantages of these biopolymers to provide sustainable soil improvements across diverse climate cycles.