Shrinkage of hardened cement paste is a direct result of its desorption isotherm. The relationship between the desorption isotherm and the relative humidity in a hydrating cement paste is mainly controlled by the pore size distribution (nanopores to micropores). There are several hydration models to describe the microstructure of cement paste, but the desorption isotherm and self-desiccation are not direct outputs from those models as they are usually given as constitutive inputs. In this study an attempt was made to fill this gap by predicting the sorption isotherm, the drying shrinkage and the self-desiccation of cement paste directly from the evolution of its microstructure. A simple hydration model was developed to predict the microstructure of Portland cement pastes, as well as the nanostructure of calcium silicate hydrate (C-S-H), considering its densification during cement hydration. Predictions from the model were compared with some recent experimental findings from studies in the literature where the influence of the water-to-cement ratio was evaluated. The main contribution of this work is the integration of nanoscale and microscale material models towards determining the macroscopic properties of cement paste.

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The development of the elastic properties of a hardening cement paste results from the microstructural evolution due to cement hydration. The elastic behaviour of cement paste can be predicted by a combination of the hydration model and micromechanical analysis, which originates from a microstructural representative volume where the elastic behaviour of different hydrating cement products can be recognised. In this paper, the formation of the microstructural volume is simulated with the computational code HYMOSTRUC3D for cement hydration. The obtained microstructure is an input for a micromechanical modelling. A 3D regular lattice model is proposed to predict the elastic modulus of the microstructure, considering a water-to-cement (w/c) ratio within the range [0.30-0.50]. In addition, the Finite Element Method (FEM) is used to compare and validate the results from the lattice model. Predictions from these two modelling approaches are then compared to the experimental results provided by the EMM-ARM (Elasticity Modulus Measurement through Ambient Response Method) testing technique, the latter allowing measurement of the elastic modulus of hydrating cement pastes. Finally, the above-referred numerical models are used to evaluate the influence of the following features: the particle size distribution of the cement grains, the microstructure discretisation refinement and the elastic modulus of the C-S-H cement hydration product.

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Exposing reinforced concrete (RC) structures to aggressive environmental conditions is one of the main reasons that may limit their service life. Diffusion of chloride ions through concrete cover is one of the most damaging environmental actions, since it may cause corrosion of steel reinforcement. Therefore, modelling this phenomenon allows supporting a better durability assessment of RC structures. In the present study, a modelling strategy considering a 3D cement paste microstructure, which is obtained using HYMOSTRUC3D software, is adopted to compute the diffusion process in saturated sound and cracked cement pastes. The diffusion process is calculated as a statistical result of random walkers (representing ionic species) through the porosity of the cement paste microstructure. The simulation is implemented using a random walk algorithm (RWA), which is compatible to be used in sound and cracked cement paste microstructures. Additionally, the proposed modelling strategy aims to establish a relation between the diffusion coefficient of cement paste and the level of tensile damage in the microstructure, which is obtained by considering the microcrack development in the cement paste. A lattice fracture model is employed to simulate the microcracks. The primary results of the proposed model are presented and discussed in the present paper. @en