The two main goals of the modelling study on the six leached cement pastes were to quantify the dissolution effect of CH, AFm and AFt on the value of the elastic modulus, and develop a simple equation to relate the reduction in the Young's modulus to the increase in the capillary porosity. Table 8 summarizes the model values of Young's modulus for the unleached and leached cement pastes. Results clearly show an important decrease of this parameter in the leached cement pastes. The reduction rate depends on the water-to-cement ratio and silica fume addition.
| Table 8. Young's modulus, E, value for the various cement pastes according to the rate of degradation - numerical results obtained by ELAS3D program. | |||||||
|---|---|---|---|---|---|---|---|
| E (GPa) | |||||||
|
CEM I paste |
CEM II/A paste |
||||||
| w/c = | 0.5 | 0.4 | 0.25 | 0.5 | 0.4 | 0.25 | |
| unleached | 18.6 | 23.0 | 32.7 | 17.8 | 21.9 | 30.8 | |
| without CH | 8.7 | 11.9 | 19.0 | 11.6 | 14.9 | 23.9 | |
| without CH and AFm | 8.6 | 11.9 | 18.7 | 11.5 | 14.7 | 23.1 | |
| without CH, AFm and AFt | 7.8 | 10.8 | 17.0 | 10.7 | 14.3 | 22.6 | |
Figure 6. Dissolution effect of CH, AFm and AFt on the Young's modulus decrease of the six cement pastes.
To further quantify the effect of the hydrate dissolution on the reduction in the Young's modulus, we calculated the leached-to-unleached cement paste elastic modulus ratios, as shown in Fig. 6. The results clearly indicate the important effect of portlandite dissolution in the decrease of this parameter value. This reduction increases with the water-to-cement ratio.
For the two other hydrates, AFm and AFt, whose original volume fraction was low (see Table 6), their dissolution caused a much lower decrease in the Young's modulus of the different cement pastes. The system with silica fume has a higher residual elastic modulus value. It is due to the lower initial content of CH, which in turn is due to the pozzolanic reaction of the silica fume. Much less CH originally means that much less CH could be leached. In all the cases, the value of Young's modulus found after leaching decreases as w/c increases.