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

A Novel Structural Assessment Technique to Prevent Damaged FRP-Wrapped Concrete Bridge Piers from Collapse

Repairing deteriorated concrete bridge piers using externally wrapped fiber reinforced polymer (FRP) composites have been proven as an effective approach. This technique has also been applied to low-rise building structures. Failures in FRP-wrapped concrete structures may occur by flexural failures of critical sections or by debonding of FRP plate from the concrete substrate. Debonding in the FRP/adhesive/concrete interface region may cause a significant decrease in member capacity leading to a premature failure of the system. In this chapter, a novel structural assessment technique aiming at inspecting the near-surface FRP debonding and concrete cracking of damaged FRP-wrapped concrete bridge piers to prevent the structures from collapse is presented. In the first part of this chapter, failure mechanisms of FRP-wrapped concrete systems are briefly discussed. The second part of this chapter introduces a novel structural assessment technique in which far-field airborne radar is applied. In this development, emphasis is placed on inspection of debonding in glass FRP (GFRP)-wrapped concrete cylinders, while the technique is also applicable to beams and slabs with bonded GFRP composites. Physical radar measurements on laboratory specimens with structural damages were conducted and used for validating the technique. Processed experimental measurements have shown promising results for the future application of the technique. Finally, research findings and issues are summarized.National Science Foundation (U.S.) (Grant CMS-0324607)Lincoln Laborator

FRP-to-masonry bond durability assessment with infrared thermography method

The bond behavior between FRP composites and masonry substrate plays an important role in the performance of externally bonded reinforced masonry structures. Therefore, monitoring the bond quality during the application and subsequent service life of a structure is of crucial importance for execution control and structural health monitoring. The bond quality can change during the service life of the structure due to environmental conditions. Local detachments may occur at the FRP/substrate interface, affecting the bond performance to a large extent. Therefore, the use of expedite and efficient non-destructive techniques for assessment of the bond quality and monitoring FRP delamination is of much interest. Active infrared thermography (IR) technique was used in this study for assessing the bond quality in environmentally degraded FRP-strengthened masonry elements. The applicability and accuracy of the adopted method was initially validated by localization and size quantification of artificially embedded defects in FRP-strengthened brick specimens. Then, the method was used for investigating the appearance and progression of FRP delaminations due to environmental conditions. GFRP-strengthened brick specimens were exposed to accelerated hygrothermal ageing tests and inspected periodically with the IR camera. The results showed environmental exposure may produce large progressive FRP delaminations.Fundação para a Ciência e Tecnologi

Behavior of composite material instrumented by optical fiber

International audienceThe efficiency of an optical sensor embedded in a composite structure strongly depends on the interfacial adhesion between the optical fiber coating and the surrounding solid material and on the environment humidity. Moisture diffusion can induce a decrease of the mechanical stiffness and strength of organic matrix composites. The present work reports on the study of the interfacial adhesion of an optical fiber embedded in a composite material. A sample composed of optical fibers embedded in an epoxy vinylester resin or polyester resin with glass fibers was studied to evaluate the influence of the water diffusion and the glass concentration on fiber bonding. © 2020, Cefin Publishing House. All rights reserved