PSI - Issue 11

Esequiel Mesquita et al. / Procedia Structural Integrity 11 (2018) 138–144 Author name / Structural Integrity Procedia 00 (2018) 000–000

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1. Introduction Features as workability, high durability and low cost of production have contributed for the concrete to be the material most employed in the industry of the construction in the world, namely over around 12 billion of tones per year (Mehta & Monteiro 2008). Essentially in emerging economies, as Brazil and South Africa, for instance, a large part of the existing structures are based in reinforced concrete (RC) that, in no rare cases, the first buildings constructed in the XX century also present cultural value. The values and the main recommendations for preservation of the recent constructions were recognized recently by Madrid Letter’s (ICOMOS 2011). Fundamentally in recent nations, as the found in the American continent, the age of heritage constructions (HC) are shortest than the historical buildings found in Europe. Sometimes this can give the wrong idea that the employment of modern building materials, as cement, can disfigure the cultural value of a HC. However, this fact cannot mean that the cultural value of the recent HC is less than another one. In truth, historical RC structures have their values recognized by Madrid’s Letter, where it is evident that the cultural value is not related with the building age or the material employed, but with the importance of the building for the community development (ICOMOS 2011). Thus, the development of studies related with safety maintenance of recent HC has become a relevant research topic. In fact, the adherence between concrete and reinforcing bars is the essential characteristic to the existence of RC. Although this adherence is not a simply mechanical phenomenon, in general terms, this can be understanding and described by the chemical, mechanical and frictional adhesion between reinforcing bars and the concrete. In tension zones, two aspects must be considered for the bond control, namely, mechanism of transference of tensions between the reinforcing bar and concrete, and the RC resistance to pull-out solicitations (Dahou et al. 2009). In the same line to the one presented by Daoud, Maurel and Laborderie (2013), the bond between the reinforcing bars and the surrounding concrete considerate the fundamental factor for the RC performance, being its existence conditioned by some factors as: steel bars performance, concrete resistance to loads, and by the tension transfer mechanism between reinforcing bars and the surrounding concrete. According to Silva et. al. (2013), the study of the RC adherence is important for the definition of the structure safety. This can be used to estimate the concrete axial strength, reducing the waiting time necessary to realize the compressive tests, across the traditional methods (see NP EN 12390-3: Ensaios do betão endurecido - Parte 3: Resistência à compressão dos provetes de ensaio, 2003). However, the authors highlight some restrictions of that method, when the experimental tests are performed in laboratories or in samples collected in field, due to the length and loads actions limitations. Another way to analyze the adherence zone between the reinforcing bars and the concrete is through crack analysis, based in the opening and cracks spacing. Additionally, numerical and experimental proceedings can also be used to predict the bond state of reinforcement bars with the concrete (Torre Casanova et al. 2013). The crack evolution is influenced by different parameters, including tension distributions on the surrounding area between reinforcing bars and concrete, age, material, geometrical and loading. This can be used to analysis the steel concrete adhesion through the bond stress-slip evolution obtained, often, by pull-out tests. In this testing method the crack emergence on the specimen is influenced by the pulling of the reinforcing bars and the cracks in the specimen surface are not visible. Nevertheless, the maximum bond stress limit (also called by bond strength) can be achieved through the results of the pull-out test. The maximum bond strength can be estimated through the ratio between the necessary applied force to promote the slip of the reinforcing bars inside the concrete, and the lateral surface area of the bars (RILEM 1970). Examples of this testing application can be found in (RILEM 1970; Torre-Casanova et al. 2013; Silva et al. 2013). Studies considering the effect of the corrosion process in different levels using 3D chemo-hydro-thermo mechanical model on emergence of cracks in the adherence zone of rebar-concrete were recently developed by Ožbolt, Oršanić and Balabanić (2014). Basically, the model proposed by the authors considered the physical and electrochemical characteristics of the corrosion process with the concrete properties. The modeling was based on finite element method (FEM), and the modeling of the RC adherence was characterized according to results come from standardized tests carried-out in RC samples (Daoud et al. 2013). However, the authors highlight that the recurrence to pull-out tests is the simplest way to collect accuracy data on adherence zone, nevertheless its performance on real structure is really complicated. In fact, the recurrence to pull-out tests is a good way to characterize the mechanical adherence of the RC. However, especially in RC heritage constructions, the collection of samples for characterize the adherence zone between reinforcing bars and concrete is not always possible, and the