Experimental study on improving the performance of imitation earthen site soil in carbon dioxide environment

This study aims to explore the performance of lime-treated soil for repairing the lime soil of the earthen city wall of Kaifeng and to standardize the construction technology of lime-treated soil. The research comprehensively considered factors such as carbonation time, lime particle size, aging conditions, and lime content, and conducted various tests and analyses including triaxial mechanical properties, surface crack analysis, particle size distribution, pH measurement, composition analysis, and electron microscopy on different samples. The results indicate that the significant effect of high-concentration CO2 carbonation enhances the chemical reactions of lime soil, and an appropriate carbonation process can strengthen the bonding and density between soil particles. Under the maintenance condition of 5 % CO2, with increasing carbonation time, the crack ratio, average crack length, and average crack width of the samples decreased. Cohesion and internal friction angle of the samples exhibited an initial increase followed by a decrease, while shear strength of the samples increased by 22.93 %-75.09 %. The lime particle size has a critical impact on the formation of cracks in lime soil. With increasing lime particle size, the crack ratio, average crack length, and average crack width of the samples increased. Cohesion and internal friction angle of the samples gradually increased with increasing lime content. The increase in crack ratio, average crack length, and average crack width during natural curing of lime-treated soil samples was proportional to the lime content. Appropriate carbonation time, smaller lime particle size, and curing conditions with 5 % CO2 contribute to improving the particle size distribution of lime-treated soil samples, reducing surface cracks, and enhancing performance. However, prolonged carbonation may lead to larger lime particle size, resulting in rough and loose particles, disorganized arrangement of CaCO3 crystals, and the inability to form a cross-linked network skeleton, causing a reduction in shear strength of the samples. These research findings provide important theoretical basis and construction technology guidance for the application of lime-treated soil combined with CO2 carbonation in repairing earthen city walls.