Strength Improvement of Silica Sand Treated with a Fungi-Soybean Flour Bio-Composite

Aswin Lim, Octavianus Arvin Sukiwan, Athaya Zhafirah, Alfrendo Satyanaga, Brian Prakasa Saputro, Alexander Owen

Biogeotechnics, 2026

Full text Open access: Gold Metadata (CSL-JSON)
DOI 10.1016/j.bgtech.2026.100271
Data confidence 70 medium
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Abstract

This study investigates a novel fungal-biopolymer bio-composite for improving silica sand by combining Tempeh inoculum containing Rhizopus oligosporus and Rhizopus oryzae (ROO) with soybean flour (SF). Unlike previously used additives, soybean flour offers a dual function as both a nutrient source for fungal growth and a binder-forming material, which functions both as a nutrient source and a binding agent. The effects of SF dosage, water content, and curing time on the strength development of treated silica sand were evaluated through unconfined compression tests on SF-treated and bio-composite-treated (BC-treated) specimens cured for up to 62 days. SEM and XRD tests were performed to examine the strengthening mechanism. The results showed that SF-only enhanced strength by forming soy-binder coatings and interparticle bridges between sand particles. Moreover, SF alone improved strength through soy-binder coatings and interparticle bridges, while the ROO–SF bio-composite developed a hybrid bonding mechanism involving soy-based biopolymer films and fungal hyphae. Water content was the dominant factor controlling bio-composite performance, and the optimum mixture of 5% ROO + 5% SF + 15% water achieved the highest unconfined compressive strength of approximately 378 kPa after 62 days. Compared with previously reported ROO-only and ROO-rice flour treatments, the ROO-SF bio composite reached higher strength, although it remained weaker than ROO-Xanthan gum mixtures. These findings demonstrate that soybean flour is a promising, locally available material for fungi-based soil improvement and that the proposed bio-composite has potential for sustainable engineering applications requiring moderate strength and reduced water infiltration.