Non-Destructive Testing in the Strategic Research on the Performance of Bridges

The main purpose of bridges is to overcome physical obstacles and improve territorial mobility, therefore, knowledge of their particularities is required, such as project design, inspection and execution, maintenance service plans and others. The aim of the research is to carry out a survey of the main pathological manifestations in three reinforced concrete highway bridges (HB) – built in different years, namely: 1927, 1960 and 2018. The qualification and quantification of the anomalies were carried out and, after that, the prioritization matrix was used, which allows obtaining strategies to ensure the safeguard of the HBs. The methodology used, data collection and detailed inspection of the structure, i.e., non-destructive testing, proved to be appropriate to assess the conditions of the HBs, and also allowed to present results related to recovery services and the necessary maintenance. The pathological manifestations in older bridges are the result of project and building errors, as well as lack of maintenance service.


Introduction
Several accidents happen on bridges and viaducts, mainly due to changes in conditions of use and lack of structural maintenance, which cause social, environmental, and economic damage. Many authors (Campos et al., 2018;Fowler, 2018;Alexander et al., 2017;Azenha et al., 2016;SINAENCO, 2016;Dyer, 2014;Moo, 2011) mention the following pathological manifestations as the main ones found: cracks, reinforcement corrosion, efflorescence, flaking, infiltrations, implementation failures, among others.
The bridges located in the state of Minas Gerais (Brazil) show cracks, exposed concrete reinforcement and carbonated concrete, as well as unevenness between the bridge decks due to the differential settlement of the bridge and the vegetation between pillars, among other aspects (SINAENCO, 2016). Most of these bridges were built in the early 1990s, i.e., a long time ago. Furthermore, it is important to consider the failures related to maintenance services, which allow the emergence and development of several anomalies.
In this context, many countries, including Brazil, have developed procedures for inspection, maintenance, and repair of bridges. The frequencies of their inspections vary in intervals from 3 months to 6 years, according to each country (AASHTO, 2019;Chen et al., 2021). This is what happens in the United States of America (AASHTO Manual for Bridge Element Inspection), where the standards for the inspection of bridges require that all critical elements of fracture in bridges must be inspected in periods shorter than 24 months (ALAMPALLI; PH; ASCE, 2010). This survey is carried out from the upper part of the bridge to its lower part. Notes are used to assess the state of conservation of each element. The default condition of the bridge is divided into 4 elements, namely the general descriptions: Good, Fair, Poor, and Severe. They consider factors such as the performance of the elements, deterioration rates, viable actions and preservation costs (AASHTO, 2019;Chen et al., 2021;Rafael et al., 2017;Yoseok et al., 2018;Heng et al., 2009).
In Brazil, stands out the inspection and classification processes applied to pathological manifestations in highway bridges (HBs), to consolidate a database on the conservation of these infrastructures, allowing the updating of the inspection manual developed for the Brazilian territory (Binder, 2018;Teixeira, Nogal, & jms  The h the on of n 1% ing a ng in les of llized area ndary l and n the planning for the conservation and repair, i.e., the GUT prioritization matrix identifies problems through 3 criteria: Gravity, Urgency and Tendency, and is widely used in the business sector to assist in the definition of priorities and decision-making. Gravity is defined as the intensity, the depth of the damage that the problem may cause if there is no intervention on it, the urgency refers to the time for the results to be undesirable if there is no intervention and, finally, the tendency is the development that the problem will have in the absence of action. Therefore, the calculation of GUT (= G x U x T) indicates the highest or lowest priority for a given demand (Braga et al., 2019;Silva Neto et al., 2021), see Table 2. h) Estimated life cycle: analyzing the repair and conservation services and boundary conditions that result from errors in the quality of the project and/or in the choice of material, as well as the environmental conditions, i. e., the durability and life cycle of the bridges, it is possible to estimate the durability of concrete structures, as shown in Equation 1 (Barbosa; Rosse; Laurindo, 2021): where: LC ESTIMATED the estimated life cycle of the bridge; LC R is the minimum life cycle, which is usually prescribed in the standardization, i.e., 50 years with regard to the NBR 15575 (Residential Buildings -Performance Part 1: General Requirements, 2021); X, Y, Z are the indicators given in Table 3.  The purpose is to insert the concept of the GUT matrix in the life cycle, and thus better understand the effect of the anomalies. This procedure will allow evaluating the effect of the current state of conservation of the HBs.

Watertightness Problems
Transverse joints are intended to transfer the vertical and horizontal load from the vehicles to the beams, which can adapt to the displacements of the bridges (Ma et al., 2020). HB A and B showed a lack of such joints, Figures  5 and 6, and this compromises the structural system, as well as compromises their life cycle, since it favors the development of cracks and allows the infiltration of residues and other hazardous agents (Shi et al., 2019;Allard et al., 2018;Karthik et al., 2016). HB -C showed a good state of conservation. It is important to consider that inefficient joints and encounters facilitated the appearance of cracks that allow the percolation of water through concrete structure (Figures 6 and 7). jms.ccsenet

Safety
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Conclusions
If we consider the progress of urbanization in cities, it is easy to observe the need for improvements in the infrastructure of the highway bridges (HBs), which, in turn, need inspection and maintenance services throughout their life cycle. This inspection must encompass technical activities ranging from data collection (project and building), detailed structural inspection and reporting, to the evaluation of the state of the work and recommendations. The procedure introduced in this study enables the management of maintenance services to ensure better performance and a longer life cycle, in addition to influencing economy and functionality factors. Therefore, this methodology was appropriate to lead to results capable of supporting the identification of defects and the quantitative measurement of recovery and maintenance services.
The main pathological manifestations were associated with the corrosion of steel bars due to project flaws, coating specifications and execution, exposed bars, concreting nests, overload caused by high traffic volume, and problems in the drainage system -which led to several anomalies associated with humidity. Accordingly, and based on the evaluation process, it was possible to observe the need to recover bridges A and B, based on structural reinforcements to improve the load capacity and meet regional demand, and the need to install adequate and updated safety, drainage and waterproofing systems. Besides, all HBs require a carefully elaborated use, operation and maintenance manual including maintenance and inspection procedures and schedule. If necessary, future interventions must be set to ensure the capacity of the HBs to operate.  1016/j.proeng.2017.06.197