Growth and porosity of C-S-H phases, development of the `Sheet Growth Model` and coupling with experimental data (1H NMR, SEM)

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Understanding the micro-structure and process of formation of Calcium-Silicate-Hydrates (C S H) which are the main products of cement hydration is the key to understand properties and performance of concretes. Improved experimental evidence and parallel development of high resolution modelling allows simulating structural changes and to assess their impacts on macroscopic properties of concrete (shrinkage, strength, durability etc.). During the preceding part of the project the boundaries of fundamental knowledge could be pushed forward significantly. The formation of C S H phases were analysed by high-resolution scanning electron microscopic (SEM) investigations, proton nuclear magnetic resonance spectroscopy (1H-NMR), X ray diffraction analysis (XRD) and mercury intrusion porosimetry (MIP). These experimental results were used to develop the microstructural ‘Sheet Growth’ model further and to tune model parameters. This approach enabled us to simulate the growth of C S H phases that closely resembles microstructural findings (SEM, 1H-NMR) at a scale from 0.5 to 500 nm in three dimensions. In the extended project, the modelling will be based on the strong foundation laid by the previous part of the project. Our model will be extended towards other unhydrated (alite and belite) and hydrated phases (inner C S H, outer C-S-H, CH). Further on we will adjust the morphology and density of the hydrates to real structures and significantly enlarge the modelled domain. This is achieved by combining the ‘Sheet Growth’ model with the ‘Level-Set’ approach. The ‘Level Set’ approach is able to simulate multi-phase transformations over time. We will use the combined models to describe the development of pores, structures and spatial phase distribution in a scale from 0.5 nm to 1000 µm in three dimensions. To make this study complete, the model output will be verified, and parameters will be further calibrated with the following experimental data.Nanotomography investigations using X-Rays and SEM with Focused Ion Beam (FIB) will depict porosity and volume development of the phases three dimensionally and time depended. The combination of these techniques with 1H-NMR spectroscopy and low temperature differential scanning calorimetry on wet and dried samples will allow us to evaluate the development of the pore size distribution at full scale and the water saturation of capillary and larger pores. This data is used directly to make the modelling realistic. In the future, the model obtained in this way can offer the possibility of predicting characteristic values (shrinkage, creep, permeability) of concretes.