## 3 Experimental Results and Discussion
### Variation of Porosity and Porosimetric Curves along the Depth  
Voids are not equally distributed along the depth. The distance to the exposed surface, where evaporation and water interchange occurs, is relevant to understand how the porosity is distributed along the depth. Next, the porosity curves of the different mixtures and curing conditions are shown for the different depth ranges (Figure 8).  
It is highlighted that the thickest graphs represent the complete porosity curves (the ones shown in Figure 7a) which are, in fact, the average of the rest of the curves.  
Figure 8 shows some interesting data. First, it is observed that, in general, curves belonging to the lower half of the specimens are placed over the full curve, while the curves belonging to the upper half are placed below the full curve. This phenomenon is observed in all cases, both in fiber-reinforced concrete and plain concrete, as well as in moist-cured concrete and air-cured concrete. This means that, mainly the porosity is concentrated in the lower half of the specimens. This is because they are far from the free surface and, in consequence, it is more difficult for the trapped air to get off while the concrete paste remains fresh.  
In the case of plain concrete, curves belonging to the depth ranges 0.4-0.5 and/or 0.5-0.6 show an abnormal behavior, different from their neighbors. This is because the cylinders were cast in two times and a small horizontal construction joints appeared. This phenomenon is less clear in fiber-reinforced concrete because fibers act as stitches between the two faces of the joint.  
Additionally, the curves belonging to the depth range 0.0-0.1 show a behavior different from the rest of curves. In this range, the porosity is small and also shows lower porosity in all the pore sizes.  
Next, the porosity curves of the different mixtures and curing conditions are shown for the different depth ranges (Figure 9).  
Figure 9: Porosimetric curves along the depth: (**a**) SFRC moist-cured, (**b**) SFRC air-cured, (**c**) PC moist-cured and (**d**) PC air-cured.  
Analogously, in this case, the thickest graphs represent the complete porosimetric curves (the ones shown in Figure 7b), which are, in fact, the average of the rest of the curves.  
Figure 9 shows some interesting data. Firstly, it is observed that there are not relevant differences between the curves belonging to the upper half of the specimens and the ones belonging to the lower part: All of them are close to each other, and they are also close to the full curve. This means that the percentages of pore volume are similarly distributed along the depth. Pore size distribution is strongly related to the spaces that remain in the concrete matrix that are also related to the composition of the concrete matrix. As this composition is uniformly distributed along the depth, the spaces available for voids are uniformly distributed and, in consequence, the porosimetric curves are similar.  
In the case of plain concrete, it is observed that the porosimetric curve belonging to the depth 0.4-0.5 in one case and the one belonging the depth 0.5-0.6 in the other case are significantly displaced to the right. These curves show the effect of the horizontal construction joint. In this zone, a higher pore volume is observed (Figure 8c,d) and greater pores, too (Figure 9c,d).  
In general, porosimetric curves belonging to the range 0.0-0.1 (exposed surface) are slightly displaced to the left. This means that, in this region, the smaller voids are more dominant, since they are easier to retain.