Mass change of bound water in clays under compression

Abstract

In general, reliability of industrial and civil units is determined by strength and deformation properties of foundation soils of structures. On the one hand, calculated values of mechanical properties largely depend on technogenic load on a ground base, and on the other hand, on content of bound water in soils, especially clays. Many Russian and foreign scientists were engaged in evaluation of bound water in clays. Their works describe an effect of mineral composition, initial moisture and composition of clay exchange cations on thermal dehydration of bound water. It was found that the smaller the size of clay particles, the sharper dehydration curves diverge in a high-temperature area. The conclusion is drawn that there is no significant discontinuity in values of energy, corresponded to active centers on basal facies and crystal chips. The paper presents results of studies of change of properties of bound water in clays under influence of high temperatures and pressures. To researchers' mind, during compaction of clays saturated with water, free water of large pores is first to be removed, then under 1–3 MPa load osmotic water, and under pressure of more than 10 MPa structured hydrate layers begin to be removed. Closest to a hard surface water layers, which determine moisture content in clays, are not squeezed out at tens of megapascals, when monolayers at loads of hundreds of megapascals. As a result of studies conducted it was experimentally established that in kaolinite and montmorillonite clays content of film and absorbed water of the colloid, as well as surface water and water of hydroxyl groups of minerals varies with change in pressure magnitude. It is established that studied parameters influence total water loss differently, which is confirmed by various mathematical models. However, in all cases, except for montmorillonite subjected to pressure of more than 1000 MPa, the most important factor determining the overall loss of water mass is adsorbed water of minerals.

Keywords

• montmorillonite
• kaolinite
• clay
• pressure
• mass loss
• thermal analysis
• x-ray phase analysis
• correlation matrix
• regression analysis
• colloid
• mineral