Hygrothermal durability of bond in FRP-strengthened masonry

Fiber reinforced polymers (FRPs) are accepted as an efficient material for external strengthening of masonry structures. Previous researches have shown that the bond between FRP and the substrate plays an important role in the effectiveness of this strengthening technique. Extensive investigations have been devoted to the characterization of the short-term bond behavior, while its durability and long-term performance requires further studies. In this regard, a full experimental program for investigating the environmental durability of bond in FRP-strengthened masonry is crucial for understanding the degrading mechanisms. This paper presents the results of an experimental program aimed at investigating the hygrothermal durability of bond in FRP-strengthened bricks. Accelerated ageing tests were performed on the FRP-strengthened brick elements and the bond degradation was periodically investigated by visual inspection and by conventional single-lap shear bond tests. The changes in the properties of material constituents have also been monitored. The obtained results are presented and critically discussed.This work was developed within the framework of the RILEM Technical Committee "223-MSC: Masonry Strengthening with Composite Materials". The financial support from the project FP7-ENV-2009-1-244123-NIKER of the 7th Framework Program of the European Commission is gratefully acknowledged. The first author also acknowledges the financial support of the Portuguese Science Foundation (Fundacao de Ciencia e Tecnologia, FCT), through grant SFRH/BD/80697/2011

Produtos de hidratação em argamassas geopoliméricas à base de argila da Tunísia para reparação de estruturas de concreto

A reparação de estruturas degradadas de concreto representa uma oportunidade para a indústria da construção mas também um desafio para a comunidade científica. O desenvolvimento de novas argamassas de reparação constitui por isso uma importante área de investigação. Os geopolímeros são ligantes inovadores alternativos ao cimento Portland pelo que as argamassas à base destes materiais, geopolíméricas, apresentam algumas potencialidades no campo da reparação das estruturas de concreto. O presente artigo apresenta resultados de uma investigação sobre o desenvolvimento de argamassas geopoliméricas à base de uma argila da Tunísia sujeita a tratamento térmico. É incluída uma análise da argila e também dos produtos de hidratação da argamassa os quais apresentam fases geopoliméricas típicas

Behavior of fiber-reinforced composite beams with mechanical joints

The fundamental behavior of the fibre reinforced composite beams with mechanical joints was examined using coupon and full-scale specimens. The effect of applied bolt torque, the contribution of adhesive bonding, and the number and configuration of bolts on the load capacity and failure mode of the double-lap bolted joints were investigated. The results showed that at different levels of applied bolt torque (10, 15, 20 and 25 N-m), little friction resistance developed. A slight increase on the load capacity was however observed with increasing tightening torque. On the other hand, the mechanical joints using bolts accompanied by adhesive bonding provided resistance against slipping. The flexural behavior of full-scale fibre composite beams with joints at midspan connected with bolts alone and a combination of bolts and epoxy was further examined. The beams connected using bolts and epoxy exhibited the same strength and stiffness as the beams without joints while using bolts alone resulted to a beam with only 65% of the stiffness of those without joints. This showed that the combination of bolts and epoxy adhesives could provide a reliable connection method for fibre reinforced composite beams

Strengthening of an artificially degraded steel beam utilising a carbon/glass composite system

To rehabilitate damaged or sub-standard steel structures, techniques utilising the lightweight, high strength and corrosion resistance of fibre reinforced polymer (FRP) composites have been proposed. The flexural load carrying capacity of a steel girder can be increased significantly by adhesively bonding carbon fibre polymer (CFRP) composites to its tension flange. This paper discusses the experimental results to investigate the effectiveness of an ultra-high modulus, and a high modulus, CFRP prepreg in strengthening an artificially degraded steel beam of rectangular cross-section under four-point loading. Four beams were upgraded, two utilising U-shaped prepreg units, which extended up the vertical sides of the beam to the neutral axis height, whereas the other two beams used a flat plate prepreg. All beams had an identical hybrid lay-up of CFRP and glass fibre reinforced polymer (GFRP) composite but for each of the geometrical shapes either an ultra-high modulus or a high modulus CFRP was used. Fabrication of the prepreg material was undertaken in situ and all the prepregs were bonded to the steel substrate utilising an adhesive film. The composite containing the ultra-high modulus CFRP failed when the ultimate strain of the carbon fibre was reached in the pure moment region. The failure load exceeded the plastic collapse load of the undamaged beam, thus demonstrating the effectiveness of the proposed upgrading scheme. On re-loading the failed beams, the U-shaped hybrid upgrade continued to act compositely with the steel beam outside of a well confined region close to the original failure location, whereas the beams with the flat plate upgrade exhibited the typical response of a steel beam, owing to debonding having taken place over practically the entire length of the prepreg. The beams using the high modulus CFRP reached even higher ultimate loads and exhibited ductile response leading to very high deflections; neither fibre breakage nor adhesive failure was observed in either the U-shaped or the flat plate strengthened beam. © 2005 Elsevier Ltd. All rights reserved

Selection of carbon-fiber-reinforced polymer systems for steelwork upgrading

This paper examines the effectiveness of a high and an ultrahigh modulus carbon-fiber-reinforced polymer (CFRP) composite prepreg, both of which have been specifically developed for the civil engineering industry. A film adhesive, compatible with the matrix material of the CFRP composite, has been introduced. The bonding characteristics of this film adhesive have been compared with those of a standard two-part adhesive - widely used in the construction industry - with those of a two-part adhesive - frequently used for high-grade bonding applications in the aerospace industry. The results have shown that when bonding carbon fiber composites to steel, the film adhesive has more favorable characteristics compared to those of the standard civil engineering adhesive, though the high-grade, and higher-cost, aerospace adhesive has superior bonding qualities. It has also been demonstrated that a good understanding of the full load-deformation response of relevant joints, including load-strain and load-extension characteristics, as well as failure mode characterization, is essential. © 2006 ASCE