## 3 Results and Discussion
### Scaling under Freezing and Thawing
#### 3.3.4 Influence of Prolonged Hydration before the Start of the Freeze/Thaw Test  
Figure 18 compares the results of the specimens of Mix 3 and Mix 5 tested according to the standard procedure, and hydrated for 14 more days. As previously explained, the test specimens subjected to prolonged pre-treatment were sawn from the unused half of the cubes used in the standard freeze/thaw test of the same concrete qualities. Since the test specimens result from the same cube, the results obtained for the same mix with different pre-treatment procedures are not, therefore, significantly affected by mechanical properties and different air pore structures. As seen in Figure 19, the specimens subjected to prolonged hydration before the freeze/thaw test generally present a lower mass of scaled material than the specimens tested at 31 days of age, for both Mixes 3 and 5. The specimens of Mix 3 subjected to prolonged pre-treatment show a better performance than the specimens pre-treated according to the standard at all ages. In fact, the specimens of Mix 3 pre-treated according to the standard fail after 112 cycles, whereas the mix that was allowed to hydrate longer presents acceptable frost resistance at the end of testing. Figure 19: Comparison between the scaled material of Mixes 3 and 5, pre-conditioned according to the standard procedure and hydrated in the climate chamber during more 14 days. As for Mix 5, the specimens tested at 45 days of age reveal a slight better frost resistance throughout the test, but not as evident as for Mix 3. However, at the end of the test, the accumulated scaled material is approximately the same for both cases. These results were somewhat expected. On the one hand, the specimens that remained 14 more days in the climate chamber were allowed to cure (moist curing at 20 \({}^{\circ}\)C, 65% R.H.) for a longer period before the first freeze/thaw cycle. This means that the hydration degree of these specimens was higher at the start of the test, i.e., the specimens presented higher compressive (and tensile) strength, and reduced amount of capillary porosity, which positively influences the salt-frost resistance of concrete. On the other hand, the specimens subjected to prolonged pre-treatment in the climate chamber were not in contact with water, which may have allowed prolonged drying of the test specimens before the first freezing took place (21 days, instead of 7 days for the specimens pre-conditioned according to SS 13 72 44). In fact, according to [PERSON] [4], drying of concrete before the exposure to freeze/thaw cycles improves its scaling resistance, as long as adequate wet curing was provided prior to drying, in order to ensure extensive hydration. Drying of the specimens lowers the degree of saturation of concrete, which means that the critical degree of saturation is not reached as early as for mixes which were not allowed to dry, and, therefore, less damage is obtained. This may, in turn, explain why the mass of scaled material of the specimens tested at 45 days of age is significantly lower than the specimens tested at the 31 st day of age in the first freeze/thaw cycles, but not as much in the last cycles. As seen in Figure 18, the mean accumulated scaled material of the concrete qualities subjected to prolonged pre-treatment increases significantly after 56 cycles, with Mix 5 with prolonged hydration reaching the same value of Mix 5 without prolonged hydration after 112 cycles. This may be related to the lower degree of hydration of the mixes tested at 31 days of age at the start of the test, which critical degree of saturation is achieved earlier, resulting in increased damage in the early cycles. After the critical degree of saturation is reached also for mixes tested at 45 days of age, the effect of the freeze/thaw cycles in the presence of salts is similar for mixes tested at both ages. The positive influence of the prolonged pre-treatment in the climate chamber seems more pronounced for Mix 3 than for Mix 5. This fact may be related with the different air content of the two mixes.