Soil improvement with biopolymers is an emerging sustainable geotechnical engineering practice. Its long-term durability, however, can be compromised by microbial degradation, which reduces their strength over time. The addition of lime potentially preserves the biopolymers by inhibiting microbial growth. This study investigates the synergistic use of xanthan gum (XG) and sticky rice (SR) together with hydrated lime to enhance both the mechanical strength and microbial resistance of clayey sand. Soil pH, microbial DNA concentration, scanning electron microscopy (SEM) images, and unconfined compressive strength (UCS) were evaluated after 7 and 28 days of treatment. Sticky rice-treated soil (SRTS) and xanthan gum-treated soil (XGTS) exhibited high microbial activity, particularly XGTS (up to 1.014 ng/g DNA), compared to untreated soil (0.022 ± 0.004), indicating its susceptibility to biodegradation. Lime addition markedly reduced microbial activity (>80% reduction at 3-5% lime), as evidenced by lower DNA concentrations and denser soil microstructures. Consequently, lime-sticky rice (LSR) and lime-xanthan gum (LXG) composites achieved substantially higher UCS compared to biopolymer-treated soils (BPTS) or lime-treated soil (LTS). At 28 days, LSR and LXG composites with 5% lime increased UCS by 127% and 119%, respectively, relative to untreated soil (UTS).These findings indicate that addition of even low-dosage of lime can simultaneously suppress microbial degradation and preserve biopolymer-induced strength through coupled chemical and microstructural mechanisms, providing a laboratory-scale framework for enhancing the microbial resistance of biopolymer-stabilized soils.
Ullah et al. (2026) studied this question.