PSI - Issue 26

Petr Konečný et al. / Procedia Structural Integrity 26 (2020) 430 –438 Author name / Structural Integrity Procedia 00 (2019) 000–000

431

2

1. Introduction In the last decades, the evaluation of the durability of concrete bridges is of high interest in the Czech Republic and countries as well. Bridges are the typical constructions that are exposed and affected by the combined effect of environmental (especially the carbonation and chloride ingress) and mechanical load. These phenomena are significant threats to the concrete and for the reinforcement, which is prone to corrosion. The corrosion of the reinforcement leads to bearing capacity and durability reduction, and therefore the service life of the structure is decreasing. Nowadays, the design of the structural elements is executed by the deemed-to-satisfy rules prescribed by Eurocode 2 and 206. These standards also consider the exposure conditions of the elements. Still, when the service life should be determined, the engineering knowledge given in these standards is not sufficient to quantify durability with expected precision. Therefore, the design of these specific structures and their details itself requires significant research and effort to precisely determine the assessment of carrying capacity concerning durability issues. It is necessary to take into account the history of designing and use the most appropriate knowledge to achieve a high quality of design. Thus, it is desirable to attain the knowledge of the possible threats to our infrastructure, such as corrosion of reinforced steel in concrete bridges, and provide and educate engineers on how to deal with such phenomena related to the environmental, or human activities. Moreover, it is essential to focus on the application of best practices, inspections, and maintenance of infrastructure, as well as to foster research in numerical modelling and predictive capabilities. For mitigation of the threats, it is necessary to identify and describe them with sufficient precision. Therefore, the essential question is, what is the primary influence on corrosion in the case of reinforced concrete bridges? It is generally accepted that the durability is affected by structural properties, load, environment, and human factors related to reliability issues. The structural properties are related to the type of concrete (e.g., Portland cement-based, binary, or ternary mixtures, see Seitl et al. (2018), Konečný et al. (2018), Ghosh et al. (2015), type of reinforcement - conventional steel, stainless steel, etc., see Darwin et al. (2009), protection strategies - epoxy-coated reinforcement, see Weyers et al. (1998), or waterproof membrane). The load influences the carrying capacity and safety of the bridges directly, and the influencing parameters are described more explicitly compared to the environmental parameters (e.g., construction in the marine environment or usage of de-icing agents used in winter). Therefore, the environmental effects still deserve great attention from the research groups. It is worth mentioning that the human factor related issues are a significant topic, however, it is out of the scope of the presented article. Chloride ions from the external environment penetrate through the structure of the concrete. After they penetrate to the level of reinforcing steel in a sufficient amount, they support the conditions for the corrosion initiation and corrosion progress itself. It is a well-known fact that besides chlorides, there is also the carbonation effect due to CO 2 . The carbonation process changes the alkaline environment that naturally protects the reinforcement. It is the reaction between carbon dioxide and free hydroxyl ions, which leads to a reduction of the pH. However, the combined effect of carbonation and chloride ingress is usually neglected. In the combination of those phenomena, the risk of corrosion induced by the actions of chlorides is higher when comparing the carbonated concrete with the non-carbonated concrete with a higher pH, see Raharinaivo et al. (1986), Vořechovská et al. (2018). Even though the models for the evaluation of the corrosion of reinforcement in concrete are developed and improved for decades, the sufficiently effective model has not been defined yet, see Helland et al. (2016). Although the physical laws for a description of the diffusion of aggressive agents were already defined and generally accepted, the modeling still contains many unspecified parameters, especially when the material is heterogeneous. The tools for modeling are of high interest to many research groups around the world. This development is connected to the preparation of Performance-Based Design (PBD) for the assessment of the durability of structures, that are under service, to improve the available numerical tools, some of those are described in Novák et al. (2007), Boddy et al. (1999), Stewart et al. (1998), Ghosh et al. (2011), Lehner et al. (2014), Vořechovská et al. (2009), Bentz and Thomas (2013). Considering the correctness of the input parameters, even more questions related to the modeling arise. The recommendations are prepared, e.g. in fib Bulletins, such as 34 from 2005, and also Joint Committee for Structural Safety has prepared a draft of chapter 2.19 called Environmental Attack, but they are not available yet.