Mechanical characteristics and microstructure of salt-rich cement-soil

In order to examine the effect of Mg²⁺, Cl⁻ and ${\mathrm{S}\mathrm{O}}_4^{2-}$ on the strength of salt-rich cement-soil, a series of unconfined compression tests of salt-rich cement-soil with different curing ages are carried out to analyze the change of the strength with different contents of soluble salt ions. The techniques of X-ray diffraction (XRD) and environmental scanning electron microscopy (ESEM) are used and the effects of soluble salt ions on the microstructure and chemical compositions of the salt-rich cement-soil are also studied. The interaction mechanism between the soluble salt ions and cement soil is revealed from the macro and micro perspectives. The research results indicate that Mg²⁺, Cl⁻ and ${\mathrm{S}\mathrm{O}}_4^{2-}$ have negative influence on the strength of cement soil. The strength of the cement soil decreases with the increasing soluble salt ion content and that the coexistence of multiple corrosive ions has a greater effect than any single ion. The reason for this phenomenon is that the high contents of soluble salt ions participate in the chemical reaction. C-S-H gel and C-A-H gel are consumed in the process of reaction. Meanwhile, M-S-H, M-A-H and a large amount of crystals are also generated. M-S-H and M-A-H are dispersed in C-S-H gel and C-A-H gel, which reduces the cementing force of cement soil and makes the strength of salt- rich cement-soil decrease.