Modeling of hydration kinetics and shrinkage of Portland cement paste

A mathematical hydration kinetics model and a constitutive model for the shrinkage of Portland cement paste are developed, calibrated and validated in this dissertation.; First of all, a hydration kinetics model for Portland cement is formulated based on the thermodynamics of multiphase porous media, in which the effects of chemical composition and fineness of cement as well as water-cement ratio are taken into account. In particular, the influences of elevated curing temperature and high applied pressure are considered. An equation for the diameter of the largest water-filled capillary pore that is a function of the degree of hydration is also presented. The hydration kinetics model is calibrated against the experimental data for eight different Portland cements. Simple relations between the model parameters and the chemical composition of cement are obtained. This model is then used to predict the degree of hydration, chemical shrinkage, adiabatic temperature rise, and autogenous relative humidity of different cement pastes in various curing environments.; A multi-scale micromechanical constitutive model that can simulate the effective elastic properties of hardened and hardening Portland cement paste is then formulated based on the theories of poromechanics and mechanics of composites. The effective elastic properties of cement paste are captured by applying the up-scale approach with the appropriate basic modeling schemes at four different scales, viz. calcium silicate hydrate (C-S-H), hydration products, solid phase of cement paste, and cement paste. The stress redistribution in the solid phase of hydrating cement paste is simulated by considering both stress equilibrium and deformation compatibility of the composite materials. This model is validated against available experimental data with the intrinsic elastic properties of the constituent components of cement paste obtained from the literature.; The micromechanical constitutive model is further extended to describe the nonlinear and creep behavior of cement paste. A constitutive model that describes the time-dependent properties of the C-S-H matrix is developed and used in the multi-scale modeling with intrinsic model parameters. This constitutive model together with the aforementioned hydration kinetics model are successfully used to simulate the autogenous shrinkage of different Portland cement pastes.; The proposed constitutive framework can be extended to simulate the volume changes of cement paste at high curing temperatures and high applied pressures, if and when pertinent experimental data become available.