Influence of biochar with varied pyrolysis temperatures on soil desiccation cracking under dry-wet cycles
摘要
Climate change can lead to soil moisture loss and shrinkage, forming crack networks that reduce soil strength and impermeability, hence posing serious risks to engineering safety. This study aims to investigate the influence of biochar on controlling soil cracking through laboratory tests, considering different soil dry densities, biochar pyrolysis temperatures & contents, and dry-wet cycles. The selected biochar was derived from corn straw at two pyrolysis temperatures of 200 °C and 500 °C. Mechanisms of biochar in controlling soil cracking were revealed by using the methods of scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), liquid-plastic limit tests, and image analysis. The results showed that biochar under pyrolysis temperature at 200 °C was more effective than that pyrolyzed at 500 °C in inhibiting soil cracking. The greatest reduction in soil cracking rate was 81.0% for the samples treated with 200 °C biochar and 63.0% for the samples treated with 500 °C biochar. Cracks in the soil became pronounced as the dry density decreased. The 500 °C biochar was more effective in reducing crack width, decreasing it by 59.2%, whereas the 200 °C biochar had a greater effect on limiting crack length, achieving a reduction of 82.0%. This is because biochar at 200 °C had better water retention properties, while biochar at 500 °C promoted soil expansion. The effectiveness of biochar with varied pyrolysis temperatures on resisting soil cracking depended on the relative dominance of three mechanisms, namely enhanced soil water retention, diminished shrinkage space, and modified soil expansion properties. This study provided guidance for applying biochar in earthen infrastructures.