Simulation of Volume Changes of Cement Paste at Early Age

The evolution of early age mechanical properties and volume change of cement paste is performed through Finite Element analysis on a 3D computer-generated cement paste. The time evolution of the hydrating microstructure is generated by μic(mike), a vectorial hydration model which takes into account the Particle Size Distribution (PSD) of anhydrous cement particles, the w/c ratio, the filler content and different hydration kinetics mechanisms such as nucleation, growth and diffusion. The microstructure geometry is then discretized into a finite element mesh. At each hydration step, the capillary depression is computed according to Laplace-Kelvin equation and applied on the pore space generated by the hydration model. Then, the autogenous shrinkage corresponds to the overall load-free deformation of the computational volume. Two constitutive models are used. The first one is a purely elastic model where macroscopic stress depends on the total porosity only. The second one is a poroelastic model which takes into account the fluid-solid interaction and the de-saturation effect. In parallel to the modeling work, a systematic experimental study has been performed on series of white cement pastes prepared different finenesses and various water-cement ratios. Many characterization techniques were used in the experimental study: chemical shrinkage, evolution of relative humidity, mercury intrusion porosimetry (MIP), x-ray diffraction (XRD), linear and volumetric autogenous shrinkage and ultrasonic wave propagation measurements. The numerical results are compared with experiment data and it is shown that the poroelastic model provides the best agreement to the experimental results. The remaining gap between the modeling and the experiment is discussed and future developments are outlined.