Performance evaluation of plastic spacers: proposal and development of evaluation methods

Abstract

ResumoThe 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.A durabilidade de estruturas de concreto armado é altamente dependente das características do concreto de cobrimento das armaduras e sua espessura. O fracasso na obtenção do cobrimento é o fator de maior influência na corrosão prematura de armaduras que, por sua vez, é a principal forma de deterioração de estruturas de concreto armado. Pesquisas indicam que o cobrimento projetado não tem sido alcançado nas atuais obras que adotam esta solução estrutural, tratando-se de um problema crônico e não esporádico. Uma das causas observadas para falha na obtenção do cobrimento mínimo normalizado é o uso incorreto de espaçadores e a utilização de espaçadores inadequados. Isso se agrava pela falta de uma norma brasileira que regulamente o produto e seu uso e, consequentemente, a falta de certificação de qualidade pelo órgão responsável. Tendo como foco os espaçadores, foram propostos requisitos e critérios de desempenho, assim como métodos para avaliação dos mesmos, sendo a maioria compilada e adaptada de normas internacionais. Em seguida, alguns espaçadores disponíveis no mercado foram efetivamente testados segundo a metodologia proposta. Nenhum modelo de espaçador provou-se satisfatório segundo a abordagem de desempenho estabelecida. Entretanto...

Computational and experimental simulation to analyze loss in concrete cover by reinforcement deformation in solid slabs

“…The cover protection provided is only achieved by the adequate quality of the concrete (composition, production, transport, concreting, thickening, finishing and curing) and sufficient thickness (quality and distribution of the spacers) [10], [11].…”

“…Despite its importance, limited studies have investigated the effect of spacers on the concrete structures [25], [26]. Some aspects should be considered when choosing the spacer type to be used, such as the product performance [11], the structural element to be concreted, the reinforcement characteristics [10]. Also, the spacer correct quantity and position are essential because the distance between them has a significant influence on the final cover in slabs [27].…”

“…Among the structural elements, the slabs are one of the most damaged elements as a result of insufficient cover thickness [27]. Unsatisfactory covers could be a consequence of uneven placement or insufficient quantity of spacers, lack of formwork leveling [35], [36], spacers with a poor performance [11], wrong choice of spacers, or workers walking through the reinforcement meshes [34]. Furthermore, the minimum cover execution tolerance value of 5 mm, which is related to a good execution quality control, are not met, being directly related to the reduction of building durability [32], [34].…”