Effect of biochar on desiccation cracking characteristics of clayey soils

Abstract

Biochar is a promising material for soil remediation. However, the influence of biochar on soil cracking has not been clearly understood to date. Soil cracking can significantly change the mobility of contaminants in soil and consequently the remediation performance of biochar. This study investigates the effect of a wood biochar on the desiccation shrinkage characteristics of two clayey soils (PKE and XS). The biochar dosages selected are 0%, 0.5%, 2%, 4%, 6%, and 10% (w/w). The results indicate that biochar affects the desiccation cracking characteristics of clayey soils by changing the evaporation process. For PKE, the evaporation rate decreased by 6.56% and 5.59% with 0.5% and 2% biochar addition, respectively, and increased by 2.11% and 17.20% with 4% and 6% biochar addition. Similarly, with the biochar dosage ranges from 0.5% to 10% for XS soil, the evaporation rate decreased by 8.57%, 8.73%, 4.56%, and increased by 0.96% and 41.06%, respectively. Image processing analysis on the cracks indicates that the addition of biochar decreases the quantitative parameters such as the crack ratio, the number of soil mass and the fractal dimension for both treated soils. The crack ratio, the number of cracks and the number of soil mass were reduced by 16.85%, 32.26% and 39.22% for 4% biochar addition in PKE. The value of XS soil with 6% biochar addition decreased by 30.80%, 8.28%, and 11.61%, respectively. Furthermore, biochar can effectively reduce the width of cracks. The role of biochar in the development of desiccation cracking may include (1) occupying the shrinkage space of soil particles; (2) weakening the bonding between soil particles and (3) providing hydrophobic channels. In general, the application of 4% and 6% biochar in PKE and XS respectively has the best performance in inhibiting soil cracking.