From Technical - Clay
Minerals of clay are highly reactive due to his great area superficial and because commonly they take a load that must to the ionic substitution in the tetrahedral and octahedral leaves, according to the described thing above.
The water that is lost in the low temperatures can classify in three general categories. (Fig. 2):
1.- The water in the volume of pores and capillaries (absorbed water).
2.- The water in the surfaces and around the edges of particles of minerals of the clay as well as in the surfaces of pores (water fixed by absorption).
3.- The water of the interlayer (water fixed by absorption) that causes the expansion of montmorillonite.
The absorbed water (type 1) requires very little energy to be removed (e.g. the curing in a temperature slightly superior to the room temperature).
The water fixed by absorption (types 2 and 3) requires defined energy to be removed completely. The particle of the clay when it is suspended in water could be surrounded by a hydrosphere of the water fixed by adsorption, within which they are the soluble ions of diverse loads.
Around the last clay particle there is an ion layer of negative load (due to the fact that oxygen forms the composition of silicates) and these are balanced by a cluster of the cations that spread through the hydrosphere.
These 'opposite' cations provide connections between particles with the clay obtaining with it plasticity. The plasticity is associated with the formation of water films absorbed with certain thickness around each particle, and is therefore a function determined by the water content.
The Maximum plasticity of the clay is obtained in a specific water content that corresponds to a film of density around each particle of approximately 2 000 Å.
For most of clays, this would be in the operational range of 15 - 25 percent of the weight. An attempt to compact so material will cause a total reduction in the graduation, which will give rise to a later increase of the plasticity. This is due to the development of the hydrostatic pressure within the material during the compaction.