A model of plastic shrinkage

The proposed model of plastic shrinkage is based on the idea that the capillary pressure in a saturated mixture, exposed to drying, depends on the geometry of the spaces between the solid particles near the surface of evaporation and the difference between the amount of evaporated water and the amount of water transferred from inside the mixture to the surface. The geometry of the pores at the surface and the factors affecting the amount of water transferred to the surface are studied by investigating the development of capillary pressure in three groups of materials with different behaviour when mixing with water: fine sand beds, silica fume and fly ash slurries, and cement pastes. It is shown that the total relative deformation of a sample depends on the rate of evaporation and the development of capillary pressure. Furthermore, the capillary pressure is a function of the water loss, the pore structure near the surface, the thickness of the sample and the modulus of plastic shrinkage.