Understanding the complex chemical changes that occur when cement powder is mixed with water is a long-standing but extremely challenging technological goal. 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. HydratiCA 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 (See Figure 1)
using the R statistical and graphics software (www.r-project.org).
From the Volume Fraction values, a series of Isosurface Values is computed and also displayed as a 2D graph. (See Figure 2)
For each material phase (Figure 3 and 4) a series of isosurfaces is generated using VTK
(www.vtk.org). These time series of
isosurfaces are combined (Figure 5) into a 3D animation utilizing DIVERSE (diverse.sourceforge.net)
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.
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.
