Multi-scale hydration modeling of calcium sulphates

Computer models for cement hydration has been proven to be a useful tool for understanding the chemistry of cement hydration, simulating the microstructure development of hydrating paste and predicting the properties of the hydration process /1/. One of these advanced models is CEMHYD3D, which is used and extended within the University of Twente for the last 12 years with pore water chemistry /2/, slag cement /3/ and multi-time modeling /4/. Chen and Brouwers /5/ pointed out that the smallest size handled in CEMHYD3D, called the ‘system resolution’ is important for a digitized model. Features smaller than the voxel sizes cannot be represented since the model works based on the movement and phase change of each discrete voxel. Furthermore, the system resolution determines the amount of computing time needed for a specific task, a higher system resolution will lead to longer computational time. Due to better computational possibilities, the use of higher resolutions is possible nowadays. This article shows the effects of using different resolutions with CEMHYD3D. This is done for the ‘fresh’ mixtures as well as during hydration modeling of the binder. The model has been modified to cope with several different resolutions from 0.20-2 μm (or 500-50 voxels in the system in a box of 100 μm x 100 μm x 100 μm). This paper shows two methods for the multi-scale modeling. The first method consists of a system, which use a modified PSD-line for each resolution. The second method uses the same digitized initial microstructure, but in stead of 1 voxel of 1 x 1 x 1 μm3 for 200 μm-system 8 voxels of 0.5 x 0.5 x 0.5 μm3 are used and for the 300-μm system 27 voxels of 0.33 x 0.33 x 0.33 μm3.