2.1 Methodology

To evaluate the consequences of the leaching of CH, AFm and AFt on the cement paste elastic modulus, we used two NIST models: CEMHYD3D and ELAS3D. The first one is a three-dimensional cement hydration and microstructure development modelling package. The second one is a finite element linear elastic program developed for computing the linear elastic properties of random materials whose microstructure has been stored in a 2D or 3D digital image. Several steps were followed:

1. The first step consisted in building the three-dimensional microstructure of the unleached paste by using the CEMHYD3D program. This program has been previously described in detail (Bentz 1997). The cubic hydration volume is 100³ µm³ or 10⁶ voxel elements. Among other results, this program computes the hydrate volume fractions and capillary porosity.
2. The second step consisted in simulating the leaching of CH, AFt and AFm by replacing the pixels representing these phases by those of water. The hydrate volume fractions and the capillary porosity of the unleached and leached material were provided by the program. This simulated leaching was done globally, in order to see material response, and so would not set up leached zones, as in Fig. 1, since there was not a surface where leaching started. The CEMHYD3D model has periodic boundary conditions (Bentz 1997).

3. The third step consisted in computing the Young's modulus of the unleached and leached microstructures using the ELAS3D program. This code is described in detail elsewhere (Garboczi 1998). The microstructures obtained in steps 1 and/or 2 were used as input data for the program (Garboczi 1998). The elastic moduli of each voxel were defined by its corresponding phase.

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