Calculation and analysis of capillary tension and disjoining pressure in cementitious materials

During the hydration process water in cementitious materials is consumed and the internal relative humidity of the pore system drops. Due to the self-desiccation, autogenous deformation – which plays an important role in early-age macroscopic volume change of cementitious material – will occur. While there is general agreement about the existence of a relationship between autogenous deformation and internal relative humidity changes in the pore system, the actual mechanism is still under discussion. Surface free energy of solid particles, disjoining pressure and capillary tension are the three frequently discussed mechanisms. This paper presents models for calculation of the disjoining pressure and capillary tension of cement paste. In the model of disjoining pressure, the disjoining is divided into three components, namely, van der Waals force, the electrostatic force and the structural force. Portland cement paste (CEM I 52.5 R) with water/cement ratio 0.37 is studied to compare the roles of the disjoining pressure and capillary force on the autogenous deformation.