Checking concrete cover during construction

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The provision of sufficient cover thickness is a fundamental aspect of preventing corrosion of steel reinforcement. Arguments range over concrete quality specification, formula for calculating design life and the definition of design life itself but if cover is not achieved with reasonable consistency, structures will fail prematurely, possibly spectacularly.

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... If a building with a 50-year design life has a minimum cover of 20 mm, a cover reduction of only 2 mm reduces the expected life by ten years. In an extreme case reducing the cover to 10 mm reduces the life from 50 years to 12 years (Papworth et al., 2005). ...
... When dissolved in water, sodium chloride forms a highly corrosive solution of sodium ions and chloride ions. The very mobile chloride ions penetrate through the concrete pores and where they reach the reinforcing steel they attack its passive layer (Papworth et al., 2005). Thus, achieving the specified cover is of primary importance. ...
Purpose This paper aims to report a case study regarding the combined use of several non‐destructive techniques (NDTs) as a tool in the management of diagnosis and refurbishment of a damaged reinforced concrete building. Design/methodology/approach Four types of NDTs have been selected and carried out on the pillars of the building: visual inspection, electromagnetic rebar location, sonic test and rebound hammer test. The campaign has been planned and run in order to get the highest amount of reliable data about materials degradation and structural safety with limited costs and limited interference with the functionality of the building. Findings The diagnostic campaign highlighted the usefulness of the selected techniques in the diagnosis of the type and the amount of degradation, thus permitting a plan of refurbishments to be defined, and to get a realistic estimation of restoration costs. Practical implications NDTs' ability to specifically identify a type of damage may be viewed as a reliable tool in assessing and managing the structural life‐cycle cost. Originality/value The presented case study highlighted that NDTs are very likely to locate and quantify the damage of materials and buildings, so that they can be considered as one of the most important parts of health monitoring of civil structures and infrastructures.
... Um dos maiores problemas relacionado à execução de estruturas de concreto armado é a incapacidade de posicionar a barra de aço com o correto cobrimento de concreto, afetando diretamente o comportamento mecânico e a durabilidade da estrutura (SHAW, 2007), fato que exige ações corretivas envolvendo reparos caros (MERRETZ, 2010). ...
... Contudo, a falha na obtenção do cobrimento geralmente não é percebida pelos engenheiros como um problema, logo não lhe é dado prioridade [4]. Sendo assim, um dos maiores problemas relacionado a estas estruturas é a incapacidade de posicionar a barra de aço com o correto cobrimento de concreto, afetando diretamente o comportamento mecânico e a durabilidade da estrutura [5], exigindo ações corretivas envolvendo reparos caros [6]. Contudo, muitos estudos ao redor do mundo têm mostrado que o cobrimento alcançado na execução normalmente não atende às expectativas de projeto [3], ou seja, o cobrimento mínimo projetado não tem sido alcançado em sua totalidade nas atuais obras que adotam esta solução estrutural [4][7] [8]. ...
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The durability of reinforced concrete structures is highly dependent on the characteristics of the concrete cover to reinforcement and its thickness. The failure to obtain cover thickness is the factor with the largest influence on the premature corrosion of the reinforcement, which in turn is the main deterioration form of reinforced concrete structures. Studies indicate that the designed cover is not reached in the current constructions that adopt this structural solution, configuring a chronic, and not a sporadic problem. One of the observed causes for the failure in obtaining the minimum standardized cover is the incorrect use of spacers and the use of inadequate spacers. This is made more serious by the absence of a Brazilian standard to regulate the product and its use and, consequently, the absence of a quality certification from the responsible regulating agency. Focusing on spacers, requirements and performance criteria were proposed, in addition to methods for their assessment, with most being taken and adapted from international standards. Subsequently, some spacers available on the market were effectively tested according to the proposed methodology. No spacer model proved to be satisfactory according to the established performance approach. However, for each criteria and assessment methods proposed, there was, at least, one spacer model at the market which satisfied them, so it can be said that the criteria and methods are suitable for spacers performance evaluation. Faced with the performance diversity of the spacer models on offer, the need for a regulatory Brazilian standard for this product was confirmed in order to delimit the quality of spacers available on the market and to eliminate this variable as one of the causes for not obtaining the correct covering.
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