# Porcelain Tile Polishing Residue in Concrete as an Additive or Replacement for Portland Cement
## 3 Results and Discussion
### Hardened State Properties
#### 3.2.2 Durability Indicators
The electrical resistivity increases as there is a decrease and refinement of pores because the ion flow is hindered [53]. The average electrical resistivity values of the concrete with a partial replacement of cement by PPR were 18.71% for S10, 23.23% for S20, 23.87% for S30, and 16.13% for S40. The exception was S50, which is caused by greater porosity, and it showed a lower result of 8.37%; further, with a high content of PPR, the particles may have agglomerated, which minimized its effect. All concretes presented average values of electrical resistivity that were higher than the reference concrete, 20.65% for A10, 25.16% for A20, 38.71% for A30, 45.61% for A40, and 48.97% for A50. The electrical resistivity increased as the PPR content in the mixture increased. In addition to porosity, another factor contributing to higher resistivities in concretes with PPR incorporation was pozzolanic reactivity because mineral additions can reduce hydroxyl ions that are one of the main components responsible for charge transport [54]. Figure 10: Relation between electrical resistivity and compressive strength. Figure 9: Electrical resistivity of concrete. Carbonation  
Carbonation depth results are shown in Figure 11. All concretes with the partial replacement of cement by PPR showed higher average carbonation depths compared to the reference concrete (41.95% for S10, 51.71% for S20, 17.91% for S30, 41.82% for S40, and 234.20% for S50). The results obtained are similar to those reported by [PERSON] et al. [17], who used PPR as a supplementary cementitious material in concrete. According to the authors, this is attributed to two reasons: (1) the reference concrete has more clinker, and therefore, it has a higher amount of Ca(OH)\({}_{2}\) when compared to mixtures with partial cement replacement; (2) the pozzolanic action of PPR can partially consume the Ca(OH)\({}_{2}\) formed by cement hydration. Ca(OH)\({}_{2}\) reacts with CO\({}_{2}\), which penetrates the concrete in the context of carbonation. This forms CaCO\({}_{3}\) that promotes the clogging of the pores, which reduces the CO\({}_{2}\) ingress and consequently the carbonation depth. The lower production of Ca(OH)\({}_{2}\) achieved by reducing the clinker or its consumption by pozzolanic activity reduces the occurrence of this phenomenon. Further, the carbonation depth of concrete S50 is considerably higher than that of the others, and it can be explained by the high porosity of the composite (higher water absorption among the concretes, Figure 6) together with the lower cement content and consequently lower Ca(OH)\({}_{2}\) formation. In concretes with added PPR, there was a tendency of equality (A10) or reduction (A20-A50) in the carbonation depth with increasing residue content. Although pozzolanic activity was observed in concrete with added PPR, the improvement in compactness promoted by the addition of waste reduced the ingress of CO\({}_{2}\) through the voids. This trend agrees with the results of water absorption and compressive strength (correlation presented in Figure 12), which indicated lower porosities in the concretes with the addition of PPR.