Experimental Investigation on Bond Behavior of Cement-Matrix–Based Composites for Strengthening of Masonry Structures (original) (raw)
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This paper presents the results of an experimental study and discusses the applicability of a fracture mechanics based approach to understand the stress transfer mechanism of fiber reinforced cementitious matrix (FRCM) composites externally bonded to a concrete substrate. The FRCM composite was comprised of polyparaphenylene benzobisoxazole (PBO) fibers and polymermodified cement-based mortar. This research aims to gain insight into the fundamental behavior of the bond between concrete and FRCM composites, which is critical in structural strengthening applications because complete loss of bond (debonding) generally initiates structural member failure. Single lap shear tests were conducted on specimens with composite strips bonded to concrete blocks. Parameters varied were composite bonded length and bonded width. Results were analyzed to understand the effective bond length, which can be used to establish the load-carrying capacity of the interface to design the strengthening system...
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Due to demands on higher loads, degradation, re-construction etc. there is a constant need for repair or strengthening of existing concrete structures. Many varying methods exist to strengthen concrete structures, one such commonly used technique utilizes surface epoxy bonded FRPs (Fibre Reinforced Polymers). The method is very efficient and has achieved world wide attention. However, there are some drawbacks with the use of epoxy, e.g. working environment, compatibility and permeability. Substituting the epoxy adherent with a cement based bonding agent will render a strengthening system with improved working environment and better compatibility to the base concrete structure. This study gives an overview of different cement based systems, all with very promising results for structural upgrading. Studied parameters are structural retrofit for bending, shear and confinement. It is concluded that the use of carbon FRPs provides the highest strengthening effect and that the fibres should be imbedded into a matrix for enhanced utilisation of inherent strain capacity.
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Textile reinforcement is used nowadays in many applications. Fibre reinforced concrete is also well understood. The use of textiles as reinforcement for cementitious composites, however, is a relatively new field for which some detailed research is needed. Moreover, if textiles will be used as a prestressing element further, knowledge is required. This paper discusses the bond behaviour of textiles used for reinforcement or prestressing in cementitious materials under different conditions. The presented results are based on experiments with textiles made out of carbon and aramid, which are mostly chemically compatible with the cement matrix. Some of these textiles were uncoated, others were impregnated with an epoxy resin or coated with SBR (Butadien-Styrol). Pullout tests and tensile tests show that resins and coatings strongly influence bond behaviour and tensile strength of the textile and therefore the load bearing capacity of the composite element. The different temperature coefficients of the textiles used compared with the cement in the concrete test specimens were accounted for by storing the specimens in different environments before testing. On the basis of the preliminary results reported in this paper the efficiency of the different textile reinforcements will be discussed.
Proceedings of the Fifteenth International Conference on Civil, Structural and Environmental Engineering Computing
Fibre-reinforced polymers (FRP) have shown to be an effective solution for retrofitting and strengthening of existing masonry structures, although some drawbacks related with the use of organic resins have been found. A newly developed alternative to FRP, known as fibre reinforced cementitious matrix (FRCM) composites, may overcome the drawbacks. This paper provides a better insight into the bond behaviour of FRCM when applied to masonry substrates and highlights possible differences with the behaviour of FRP composites by means of push-pull single-lap direct-shear tests for two types of fibres (glass and basalt). Additionally, the sustainability of this strengthening system was evaluated by means of a life cycle assessment (LCA). The experimental data suggests that the effective bond length for basalt FRCM composites is lower than 260 mm and that for basalt and glass composites the initial response is highly dependent on the elastic behaviour of the fibres. The FRCM system provides environmental benefits in all the analysed categories with respect to the reference FRP technique, based on the analysis performed.
2020
Fabric Reinforced Cementitious Matrix (FRCM) is a relatively new material used for strengthening applications of reinforced concrete structures. Several studies reported in the literature have indicated that the bond between FRCM layers and the concrete substrate is one of the main factors that affect the performance of the system. Few studies have attempted a combined approach of analyzing the surfaces between the three layers of this composite (fibres-matrixconcrete). An investigation of the bond behavior is studied in this thesis with an emphasis on the fibre-matrix and the concrete-matrix interfaces. The efficacy of surface preparation methods and the existing concrete strength were used to evaluate the bond at the concrete-matrix interface. The fibre-mortar width ratio was used to analyze the bond at the fibre-matrix interface. This experiment was completed in two phases: 72 concrete blocks (150x150x165mm) in double shear testing and 12 small concrete beams (150x150x500mm) in flexural testing. For double shear, the varying parameters included 1) surface preparation (untreated, grinding, sandblasting, shotblasting, and combination), 2) fibre-mortar width ratio (1:1 and 1:2) with fibre widths of 120mm and 60mm, and 3) concrete strength (30MPa and 50MPa). The double shear test results indicated that the bond strength increased with enhanced methods of surface preparation. Surface grooving reduced the debonding response, and combined surface preparation methods were effective at eliminating debonding failures. Also, the fibre-mortar ratio of 1:2 exhibited higher bond strength and reduced bond failure than the 1:1 ratio. The concrete strength had an insignificant effect on the bond strength and failure mode. For flexural specimens, the surface preparation method was examined. The surface preparation had a significant effect on the bond strength, and all failures occurred at the fibre-matrix interface. The bond strength was on average 44.5% higher for the flexural than for the double shear specimens. v PREFACE This thesis is based on the original, experimental work completed in whole by the author in the School of Engineering at the Okanagan campus of the University of British Columbia. The author was responsible for completing all aspects of the project including literature review, material acquisition, experimental work, data collection and analysis, and thesis writing. Considerable guidance and supervision throughout the thesis work were contributed by Dr. Ahmad Rteil. Major portions of chapter 3 and 4, and a minor portion of chapter 2, have been submitted to peer-reviewed journals and conferences for publication. The following is a list of publications based on the thesis:
Materials
In recent years, inorganic-matrix reinforcement systems, such as fiber-reinforced cementitious matrix (FRCM), composite-reinforced mortars (CRM), and steel-reinforced grout (SRG), have been increasingly used to retrofit and strengthen existing masonry and concrete structures. Despite their good short-term properties, limited information is available on their long-term behavior. In this paper, the long-term bond behavior of some FRCM, CRM, and SRG systems bonded to masonry substrates is investigated. Namely, the results of single-lap direct shear tests of FRCM-, CRM-, and SRG-masonry joints subjected to wet-dry cycles are provided and discussed. First, FRCM composites comprising carbon, polyparaphenylene benzobisoxazole (PBO), and alkali-resistant (AR) glass textiles embedded within cement-based matrices, are considered. Then, CRM and SRG systems made of an AR glass composite grid embedded with natural hydraulic lime (NHL) and of unidirectional steel cords embedded within the same li...
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