Evaluation of Cracking in Biochar-Amended Clayey Soil Under Freeze–Thaw Cycles

Biochar has been identified as an efficient soil amendment, and it shows promising results in inhibiting desiccation cracks. However, the effects of biochar on soil freeze–thaw cycle behavior on surface cracking have not been considered. This study focuses on the influence of wood biochar dosages on surface cracking under freeze–thaw cycles on clayey soils, and the mechanism was investigated through image analysis and water evaporation. Samples were prepared with different biochar dosages of 0%, 5%, 10%, and 15%, and maintained for 12 h constant temperature freeze (−20°C) and thaw (21°C) cycles. Every 12 h, sample weight, 2D images, and 3D scans were taken. Also, a parallel desiccation experiment was conducted at room temperature for comparison purposes. Results show that with an increased dosage of biochar for the freeze–thaw samples, the crack ratio, fractal dimension, total crack length, and average crack width decrease. Also, the crack propagation rate decreased with the increased amount of biochar. Further, the water evaporation rate decreased with increasing biochar for the freeze–thaw samples; the reasons can be correlated with the reduced thermal conductivity of soil with added biochar, and the reduction in bulk density causing reduced thermal conductivity. Results indicate that the final crack patterns are associated with the initial ice crystal patterns. Samples with low biochar produced larger-sized parallel layered texture ice crystals, and increased biochar content caused homogeneous massive ice crystal texture; these responses can be correlated with changes in soil hydraulic conductivity.