In order to check the relevance of this modelling, a comparison with an experimental result is necessary. Based on physico-chemical characterization and compression test results, (Carde 1996) found that total dissolution of CH caused a reduction of 55 % in the Young's modulus of portland cement paste with w/c= 0.5.
The different modelling steps described in section 2.1 were applied to Carde's cement paste and the simulated value of the elastic modulus reduction after CH leaching was compared to the experimental one. The mineralogical composition of the cements studied is presented in Table 1. These values were used in the CEMHYD3D model. Table 2 gives the elastic modulus and Poisson’s ratio values of the principal phases used in the ELAS3D code (1 % to 2 % uncertainty in all values). The used water phase properties are the bulk modulus (K) equal to 2.2 GPa and shear modulus (G) equal to 0.0 GPa (Lide 1997).
| Table 1. Mineralogical composition of Carde's Portland cement using Bogue method (% weight content) (Carde 1996). |
||||
|---|---|---|---|---|
| C3S | C2S | C3A | C4AF | Gypsum |
| 57.4 % | 14.7 % | 8.2 % | 9.2 % | 5.4 % |
| Phases | E (GPa) | v | References |
| C3S | 117.6 | 0.314 | Boumiz et al. 1997 |
| C2S | 117.6 | 0.314 | |
| C3A | 117.6 | 0.314 | |
| C4AF | 117.6 | 0.314 | |
| Gypsum | 45.7 | 0.33 | Choy et al. 1979 , Bhalla 1984 |
| Portlandite | 42.3 | 0.324 | Monteiro & Chang 1995 |
| C-S-H | 22.4 | 0.25 | Damidot et al. 2003 |
| C-S-Hpozz | 22.4 | 0.25 | |
| Afm | 42.3 | 0.324 | |
| Aft | 22.4 | 0.25 | |
| Empty porosity | 0 | 0 |
The model values of the Young's modulus of unleached and leached cement pastes are given in Table 3. If the random hydration and leaching simulations were run several times, there would only be about a 1 % or lower value of the standard deviation in these moduli. The results show the important effect of CH dissolution on the decrease of the elastic modulus. The effect of the dissolution of the sulfoaluminates, AFm and AFt, appears less important than does dissolution of CH, with the dissolution of AFm being the least important in reduction of the Young's modulus. A reduction of 49 % was found after only CH leaching. This model value is in good agreement with the experimental value of 51 %.
| Table 3. Hydrate dissolution effect on the Young's modulus - numerical results using ELAS3D. | ||
|---|---|---|
| Young's Modulus | ||
| Gpa | % of unleached cement paste | |
| Unleached | 19.0 | 100 |
| CH dissolution | 9.8 | 51 |
| CH and AFm dissolution | 9.8 | 51 |
| CH, AFm and AFt dissolution | 8.3 | 43 |