Determination of Bound Water Content of Loess Soils by Isothermal Adsorption and Thermogravimetric Analysis

Loess is a wind-blown deposit generally low in clay content. Despite being strongly hydrophilic, there is a lack of detailed investigation of bound water on loess particle surfaces. An integrated approach incorporating isothermal adsorption and thermogravimetric analyses was applied to determine the content of different types of bound water on the surfaces of four loess soil samples with clay contents varying between 12.2% and 26.9%. At 25 degrees C, strongly bound water was found at a relative humidity (RH) lower than 11% and was released at temperatures between 135 degrees and 210 degrees C, whereas weakly bound water was found at an RH between 11% and 75% and was released at temperatures ranging between 75 degrees and 135 degrees C. Capillary water formed by water vapor condensation when RH was greater than 75% and completely evaporated at 75 degrees C. The amounts of strongly and weakly bound water on the loess particle surfaces ranged from 0.5% to 0.8% and from 1.4% to 2.2%, respectively. Total bound water content ranged from 1.9% to 3.9%, and the fractions of strongly and weakly bound water were about 26% and 74%, respectively. We found a linear relationship between the content of clay minerals and the amount of bound water.