Bound water is an important factor in controlling the physical, chemical and mechanical properties of clayey soils, and it plays an important role in geotechnical engineering disaster prevention and environmental protection. There are many factors (such as soil texture, mineral composition, specific surface area (SSA), organic matter content, porosity and so on) that affect bound water in natural clayey soils. However, the main factors are mineral composition and specific surface area (SSA). Experimental tests on specific surface area and isothermal adsorption of a series of artificial mixed clayey soils were carried out to determine the different types of bound water. On this basis, the relationship between the bound water of mixed clayey soils and influencing factors of mineral composition and specific surface area are discussed. The results show that relative humidities of RH = 0.90 and 0.98, in an isothermal adsorption method, are the boundary-dividing points between strongly bound water and weakly bound water, and between weakly bound water and free water, respectively. The bound water content of the mixed clayey soils increased linearly with the montmorillonite content and specific surface area. Clay’s mineral composition (montmorillonite) was found to be the most fundamental influencing factor.
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