Classification and characterization of bound water in marine mucky silty clay

Purpose: Bound water has a large impact on physical and chemical properties of clay. The objective of this study was to investigate the contents, types, and physical properties of bound water and provide insights for understanding the thermal behavior and hydration process of the marine mucky silty clay under the control of bound water. Materials and methods: An integrated approach incorporating isothermal adsorption, thermogravimetric analysis (TGA), and specific gravity testing were developed to determine the contents and the boundaries of different types of bound water in Qingdao clay and investigate their physical characteristics. Results and discussion: Adsorption isotherm can be divided into two phases, which are the formation of strongly bound water and some capillary water under condition of p/p(s)< 0.9 and the formation of weakly bound water in the coverage for p/p(s)>0.9. The initial dehydration temperatures of strongly bound water range between 87 and 92 degrees C in the hydrated clays under condition of p/p(s) < 0.98. Weakly bound water starts to be released at temperatures near 60 degrees C and is completely removed at temperatures between 90 and 108 degrees C. Capillary water and free water are evaporated before 60 degrees C. The specific gravity of hydrated clay decreases linearly with adsorbed water contents. The volume of hydrated clay, volume of adsorbed water, and thickness of water film approximately linearly increase with adsorbed water contents. Conclusions: Quantitative determination and classification for bound water can be implemented through thermogravimetry (TG) and derivative thermogravimetry (DTG) curves. The physical properties of hydrated clay and bound water film are directly affected by the adsorbed water contents. The results may contribute to environmental and engineering risk assessment.