## 3 Infrastructure Inspection and Monitoring Carried Out
### Pathologies Detected in the Visual Inspection Initial Phase
Furthermore, sectional cuts in the transverse reinforcement bars were observed with a crack alignment coinciding with some of the longitudinal cracks and with a macroscopic appearance of brittle fracture, according to Figure 7. For the observation of the reinforcement, small test cuts were made in the alignment of the deck cracks. Figure 5: Longitudinal cracks in the deck’s upper face. Figure 6: White halos around aggregates detected in the cores without microscopy needed. Figure 2:0 Sectional cuts in the transverse reinforcement bars. This type of brittle fracture is probably the most relevant damage observed in the structure under study, due to the extraordinary and unexpected nature of the phenomenon. As can be seen in Figure 7, necking is not observed in the breakage of the bars. In this sense, this fact points directly to a brittle fracture compatible with a corrosion fatigue phenomenon, which suggests the existence of a localized corrosion attack by chlorides coming from the winter maintenance treatments. Chlorides can easily penetrate inside the concrete mass through the existing cracks in the deck's upper face until they reach the reinforcement bars. Multiple factors such as the width or depth crack affect that penetration. However, the paper does not focus on internal chloride diffusion. Consequently, the modeling of chloride penetration is out of the scope of this paper, and we direct the reader to the listed references [17,18]. Lastly, signs of possible injection defects of the post-stressed sheaths were observed by examining the uncovered venting pipes in the milled area, by inserting a tape measure or a screwdriver inside them to check if they were clogged, as detailed in Figure 2:1 In this preliminary check it was observed that several of the venting pipes were not grouted up to the top face of the slab and that, therefore, it would be likely that there could be an inadequate injection of the prestressing sheaths. This led to the subsequent inspection with a borescope in the auscultation and testing campaign carried out in the structures. In addition to the above pathologies, it should be noted that the presence of any waterproof treatment on the upper face of the deck was not observed. It certainly contributes to aggravating and accelerating any degradation process of the structure. Thus, the above damages, detected in the initial study phase of the state of conservation of the structure, pointed to the existence of a concrete process degradation by an aggregate-alkali reaction, which gave rise to several longitudinal cracks. Additionally, significant vertical deflections appeared because of the loss of stiffness of the concrete characteristic due to advanced stages of the process of arid-alkali degradation. Additionally, and as will be seen below, the appearance of brittle failure of the upper transverse reinforcing bars with a failure alignment coinciding with the longitudinal cracks was observed. It suggests that the bar's failure is the consequence of a corrosion fatigue phenomenon. This phenomenon occurred as a result of chloride from the frequent use of de-icing salts that go into the slab cracks and the presence of cyclic traffic loads. In addition, the presence of wetting and drying cycles can affect the concrete internal movements of chlorides toward the surface [19]. The use of de-icing salts in post-stressed slabs without waterproof treatment could contribute to the progression of serious damages in the prestressing such as corrosion or even wires breakage. Although these defects were not observable in the initial inspection phases, they could be detected using borescope inspection in the following auscultation phases, as detailed in the following sections. Figure 2:2 Venting pipes check to verify the clogged conditions (see the handle of the screwdriver inserted into the hole).