Engineering properties and microscopic mechanism of clay improved by XG-Cr³⁺ hydrogel

This study aims to verify the improvement effect of Cr³⁺ -induced xanthan gum (XG) cross-linking (referred to as XG-Cr³⁺ hydrogel for short) on clay. Firstly, the physical properties such as water sensitivity and viscosity of XG-Cr³⁺ hydrogel were studied. Subsequently, the influence of Cr³⁺ on the improvement effect of XG hydrogel on clay was investigated through unconfined compressive strength tests and water stability tests. Finally, the microscopic mechanism of XG-Cr³⁺ hydrogel in improving clay was revealed by means of SEM and FTIR tests. The results show that: (1) The incorporation of Cr³⁺ can significantly reduce the gelation time of the XG solution, and the hydrogel state is firm. It can also effectively improve the water sensitivity of the XG hydrogel, reduce the viscosity, and accelerate the gelation process. (2) With the increase of Cr³⁺ dosage and curing time, the compressive strength of the improved clay is significantly enhanced, showing obvious strain softening characteristics. The specimens are mainly damaged by through fractures, and the fractures are mostly in the shape of "Y". (3) The incorporation of Cr³⁺ can significantly improve the water stability of the improved clay, prolong the disintegration time of the soil sample (the XG-Cr³⁺ hydrogel improved clay maintains structural integrity within the test time), significantly reduce the disintegration index (SI) value, and the SI values at different times gradually decrease with the increase of Cr³⁺ dosage and curing time. (4) After adding an appropriate amount of Cr³⁺ to the XG solution, it promotes intermolecular and intramolecular cross-linking of XG through metal coordination with the functional groups on the XG molecular chain, enhances the hydrogel strength of XG, reduces water sensitivity, and thereby increases the strength and water stability of the clay in a wet state. This effect of XG-Cr³⁺ hydrogel is closely related to the concentration of XG, the dosage of Cr³⁺ and the curing time. In this study, the clay reinforcement effect was more significant when 30%Cr³⁺ was added to 1%XG and cured for 14 days.