Visualization of Cement Paste Hydration and Microstructure Development
Understanding the complex chemical changes that occur when cement powder is mixed with water is a long-standing but extremely challenging technological goal. These changes are termed hydration. Fundamental computational modeling of the hydration of cement is difficult because it involves a large number of coupled nonlinear rate equations that must be solved on a random three-dimensional spatial domain. To address these challenges, we are applying a new computational model called HydratiCA, which has several advantages over previous attempts to model cement paste hydration.
Visualization is important for validation of the model as development proceeds. It is also important to facilitate understanding the distribution of phases in 3D.
The HydratiCA model is based on concepts of transition state theory and uses stochastic cellular automaton algorithms to simultaneously model 3-D reaction and transport phenomena. This allows us to track the detailed kinetics and equilibria that occur in a diverse range of cementitious systems. At the length scales required to finely resolve the reaction mechanisms and microstructure changes in cement paste, HydratiCA must take small time steps (approximately 10-5 seconds) to remain numerically stable. In other words, tens of millions of time steps are required to simulate the behavior of cement paste for just one hour. Therefore, parallelization of the model is important so that we can model systems that are large enough to be realistic, avoiding finite size effects, and still be able to complete the simulations in a reasonable amount of time.
The output of the hydration numerical simulation is a 3D volume of data with percentage values for each of multiple material phases at each voxel location. Over the course of the simulation time, a series of data volumes is produced at the time intervals of interest. For each data set, an over all Volume Fraction is computed for each phase and plotted as a 2D graph using the R statistical and graphics software:
From the Volume Fraction values, a series of Isosurface Values is computed and also displayed as a 2D graph:
For each material phase a series of isosurfaces is generated using VTK. Here is the isosurface for the C3S phase at timestep 32:
Here is the isosurface for the CSH phase at the same timestep:
These time series of isosurfaces are combined into a 3D animation utilizing DIVERSE and in-house developed software. These components (3D animation, 2D plots, interactions) are combined into a complete application for interactive exploration and analysis in the immersive visualization environment by the domain scientists. Here is a single frame from this combined interactive time-varying visualization:
Future work in the area will evolve this application into a Virtual Cement Analysis Probe (VCAP). The immersive visualization environment will be used to interactively probe the data and create application specific analysis and measurements. Additional software enhancements will allow alternate data representations such as volume rendering to augment the current isosurface representation.
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