Caracterização do comportamento da ligação entre betões de distinta classe de resistência

Comunicação apresentada no Encontro Nacional Betão Estrutural 2004, Porto, Portugal, 17 - 19 Nov. 2004.O incremento do momento flector resistente que a técnica de reforço baseada na fixação de laminados de CFRP no betão de recobrimento de estruturas laminares de betão armado, por vezes, fica limitado pela extensão máxima de compressão aplicável ao betão. Nestes casos, a conjugação deste sistema de reforço com a aplicação de uma camada de compressão de betão reforçado com fibras de aço (BRFA) permite aumentar significativamente a resistência à flexão deste tipo de estruturas. Este trabalho é dedicado ao estudo da ligação entre camada de BRFA e o betão da estrutura a reforçar.Fundação para a Ciência e Tecnologia - SFRH/BD/11232/2002. “Companhia Geral de Cal e Cimento S.A. (SECIL)”. Sika S.A. “Central do Pego”. “Pedreiras Bezerras”. Bekaert NV. “Bettor MBT Portugal Produtos Químicos para Construção S.A.”

On bonding repairing steel fibre reinforced concrete to hardened concrete

In the last years an emerging repair and strengthening technique for concrete slabs has been used, consisting of applying a thin layer of steel fibre reinforced concrete (SFRC) onto the existent concrete slab. The performance of the structural system depends on the bonding behaviour between old and new concretes. Adhesives based on epoxy resins currently make this liaison. The prices of these adhesives are quite different depending, mainly, on the percentage of pure resin that they include. In the present paper, three commercial adhesive compounds of distinct prices and properties were selected to bond concrete base and repairing SFRC overlay. The bond behaviour was assessed from pull-off tests and the influence of the strength class of concrete base and repairing SFRC was analysed. Finally, the performance of the adhesives was evaluated, considering both the bond strength and their prices.Fundação para a Ciência e a Tecnologia (FCT) - PhD grant SFRH/BD/11232/2002

Sistema híbrido em materiais compósitos para reforço de lajes de betão armado

O desempenho em termos de aumento da resistência à flexão da técnica de reforço que combina laminados de CFRP à tracção com camada de compressão em betão reforçado com fibras de aço (BRFA), foi avaliado experimentalmente, efectuando-se ensaios em faixas de lajes maciças sem reforço (controlo), reforçadas apenas com laminados de CFRP, e duplamente reforçadas com laminados de CFRP e camada de BRFA. Os resultados obtidos permitem concluir que esta estratégia de reforço é eficaz, tanto para o estado limite de serviço (ELS) quanto para o estado limite último (ELU)

Efficient strengthening technique to increase the flexural resistance of existing RC slabs: NSM CFRP laminates and compressive thin bonded SFRC overlay

Technical report 09-DEC/E-0

Concrete slabs strips reinforced with epoxy-bonded carbon laminates into slits

A promising strengthening strategy, using carbon fiber reinforced polymer (CFRP) materials, consists in applying CFRP laminate strips into pre-cut slits opened in the concrete cover of the elements to strengthen. Since both faces of the laminate are bonded to concrete by epoxy adhesive, the maximum attainable strain in the CFRP at the failure of the strengthened element is higher than when the CFRP is externally bonded. This strengthening technique is designated by Near Surface Mounted and has been successfully used to increase the flexural and the shear resistance of concrete and masonry structures. In the present work, the effectiveness of this technique to increase the service and ultimate load carrying capacity of reinforced concrete slabs is assessed by an experimental program. A numerical strategy was developed to predict the load-deflection relationship of this type of elements. The results are presented and analyzed, and the performance of the numerical model is appraised.Fundação para a Ciência e a Tecnologia (FCT) - PhD grant number SFRH/BD/11232/2002.S&P® Reinforcement.Degussa Construction Chemicals Portugal SA.Companhia Geral de Cal e Cimento SA (SECIL).Pedreiras Bezerras

Efficient strengthening technique to increase the flexural resistance of existing RC slabs

Composite materials are being used with notable effectiveness to increase and upgrade the flexural load carrying capacity of reinforced concrete (RC) members. Near-Surface Mounted (NSM) is one of the most promising strengthening techniques, based on the use of carbon fiber-reinforced polymer (CFRP) laminates. According to NSM, the laminates are fixed with epoxy based adhesive into slits opened into the concrete cover on the tension face of the elements to strength. Laboratory tests have shown that the NSM technique is an adequate strengthening strategy to increase the flexural resistance of RC slabs. However, in RC slabs of low concrete strength, the increase of the flexural resistance that NSM can provide is limited by the maximum allowable compressive strain in the compressed part of the slab, in order to avoid concrete crushing. This restriction reduces the effectiveness of the strengthening, thus limiting the use of the NSM technique. A new thin layer of concrete bonded to the existing concrete at the compressed region is suitable to overcome this limitation. Volumetric contraction due to shrinkage and thermal effects can induce uncontrolled cracking in the concrete of this thin layer. Adding steel fibers to concrete (Steel Fiber Reinforced Concrete - SFRC), the post cracking residual stress can be increased in order to prevent the formation of uncontrolled crack patterns. In the present work, the combined strengthening strategy, a SFRC overlay and NSM CFRP laminates, was applied to significantly increase the flexural resistance of existing RC slabs. Experimental results of four-point bending tests, carried out in unstrengthened and strengthened concrete slab strips, are presented and analyzed

Influence of the spacing between NSM-CFRP laminates on the flexural strengthening efficacy of RC slabs

Fundação para a Ciência e a Tecnologia (FCT) - bolsa de doutoramento SFRH / BD / 11232 / 2002

Efficient strengthening technique for reinforced concrete slabs - SFRC and CFRP laminate strips

A promising strengthening strategy, using carbon fiber reinforced polymer (CFRP) materials, consists in applying CFRP laminate strips into pre-cut slits opened in the concrete cover of the elements to strengthen. This strengthening technique is designated by Near Surface Mounted (NSM) and has been successfully used to increase the flexural and the shear resistance of concrete and masonry structures. The present work describes an efficient strategy, using steel fiber reinforced concrete (SFRC) and NSM CFRP laminates, for the strengthening of existing reinforced concrete (RC) slabs. The use of a SFRC compression overlay can provide the necessary ductility for attaining high level of tensile stress in the CFRP strengthening system and therefore preventing the concrete crushing failure mode. In the present work, the effectiveness of this technique to increase the service and ultimate load carrying capacity of RC slabs is assessed by an experimental program. A numerical strategy was developed to predict the load-deflection relationship of this type of elements. The results are presented and analyzed, and the performance of the numerical model is appraised.The authors acknowledge the Portuguese Science and Technology Foundation (FCT) for the PhD grant number SFRH / BD / 11232 / 2002. Thanks also for the companies “Companhia Geral de Cal e Cimento S.A. (SECIL)”, Sika S.A., “Central do Pego”, “Pedreiras Bezerras”, Bekaert NV, “Degussa Construction Chemicals Portugal S.A.”, S&P® Reinforcement, which have supplied cement; overlay bond product; fly ash; aggregates; steel fibres; superplasticizer and CFRP adhesive; and CFRP laminate, respectively