Mechanical Behaviour of Soil Treated with Chitosan and Calcium Metasilicate Considering the Fungal Growth

Biopolymers have been widely experimented with as organic stabilizers in the last decade for improving soil properties. However, the high nutritional value of some biopolymers like chitin, carrageenan, casein, and chitosan can also promote microbial growth which can affect the improvement in the strength of biopolymer-stabilized soil. This study investigates the mechanical behaviour of clay treated with chitosan at dosages of 0.5, 1.0, 1.5, and 2.0% at various curing periods of 7 d, 28 d, 56 d, and 90 d and also observes the fungal growth, the conditions favourable to fungal growth, and the effect of an inorganic secondary additive on the mechanical behaviour of treated soil. The study shows that fungal growth is higher with the time and dosage of chitosan. The strength of chitosan-treated samples increased with both dosage and age despite the fungal growth observed on the treated soil, as did the fungal growth. On treating the soil with 2% chitosan, the percentage increase in strength was nearly 14.39%, and on the 56th day, it was phenomenally increased to 1534.39%. In an attempt to control the fungal growth, a secondary additive, calcium metasilicate (calsil), was added to various dosages of chitosan-treated soil (CTS). The secondary additive did not completely stop the fungal growth but certainly controlled fungal growth. Chitosan and calsil are hydrophilic, increasing OMC by 67% and 150% for the high CTS and calsil–chitosan-treated soil (CCTS) doses. Calsil coated the soil particles and prevented closer packing under compaction, reducing MDUW by 7.8% and 18% for CTS and CCTS at maximal dosage. The development of hydrated cementitious products made the soil brittle, causing the post-peak strength of CCTS samples to diminish significantly with age. FTIR spectroscopy showed hydrogen bonding strengthening CTS, while XRD revealed cementitious compounds in CCTS. The strength of the soil treated with chitosan and calsil showed a higher strength than soil treated with only chitosan.