Interfacial bond characteristics of fiber reinforced cementitious matrix for external strengthening of reinforced concrete members (original) (raw)
Related papers
ACI Materials Journal, 2014
This paper presents the results of an experimental study conducted to understand the behavior and stress-transfer mechanism of fiber-reinforced cementitious matrix (FRCM) composites externally bonded to a concrete substrate for strengthening applications. The FRCM composite was comprised of a polyparaphenylene benzobisoxazole (PBO) fiber net embedded within two layers of polymer-modified cement-based mortar. Single-lap shear tests were conducted on specimens with composite strips bonded to concrete prisms. Parameters that varied were bonded length and width of composite. Additionally, the external coating layer of matrix was omitted on a limited number of specimens to examine the interfacial behavior between fibers and matrix and the role of the matrix in the stress transfer. Strain measurements along the composite bonded length were used to investigate the stress-transfer mechanism. Results suggest that the effective bond length of this composite is within the range of 250 to 330 mm (10 to 13 in.). Unlike with fiber-reinforced polymer (FRP) composites, no width effect was observed in terms of the maximum load. Finally, the stress-transfer mechanism at the matrix-fiber interfaces on either side of the fiber net was found to be unequal.
Experimental Investigation of FRCM-Concrete Interfacial Debonding
2014
This report presents the results of an experimental study conducted to understand the stress-transfer mechanism of fiber reinforced concrete matrix (FRCM) composites externally bonded to a concrete substrate for strengthening applications. The FRCM composite was comprised of a polyparaphenylene benzobisoxazole (PBO) fiber net and polymer-modified cement-based mortar. Direct 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 bonded length, which can be used to establish the load-carrying capacity of the interface to design the strengthening system. The normalized load carrying-capacity was plotted against the width of the composite strip to study the width effect. Finally, strain gage measurements along the bonded length were used to investigate the stress-transfer mechanism.
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:
Effects of Defects on Bond Behavior of Fiber Reinforced Cementitious Matrix Materials
Materials
High-strength fibers embedded in inorganic matrix i.e., Fiber Reinforced Cementitious Mortar materials (FRCM) are commonly used as strengthening technique for existing masonry structures, due to the low sensitivity to debonding phenomena between substrate and matrix. Nevertheless, the use of lime or cement-based matrix instead of epoxy adhesive implies that attention has to be paid to the bond behavior between the fibers and the matrix, since sliding phenomena and cohesive failures in the mortar matrix can occur. The paper aims to investigate the effect of the mechanical properties of fiber and matrix on the FRCM efficiency, and potential geometrical defects, typical of real applications. The aim is to analyze the mechanical behavior of the FRCM system by simulating hypothetical bond tests, as they are usually performed in laboratories. The bond test has a significant role, as it is used for the qualification of the material, providing sometimes very scattered results. Hence, it is ...
Journal of Composites for Construction, 2016
Despite the current awareness of the high seismic risk of earthen structures, little has been done so far to develop proper strengthening solutions for the rammed earth heritage. Based on the effectiveness of TRM for masonry buildings, the strengthening of rammed earth walls with externally bonded fibers using earth-based mortar is being proposed as a compatible solution. In this context, the investigation of bond behavior was conducted by means of direct tensile tests, pull-out tests and single lap-shear tests. The specimens were prepared using earth-based mortars and two different types of meshes (glass and nylon) while considering different-bonded lengths. The direct tensile tests on TRM coupons showed the high capacity of the nylon mesh in transferring stresses after cracking of the mortar. The pull-out tests highlighted that in the case of glass fiber mesh, the bond was granted by friction, while the mechanical anchorage promoted by the transversal yarns granted the bond of the nylon mesh. Finally, the single lap-shear tests showed that the adopted earth-based mortar seems to limit the performance of the strengthening.
Journal of Civil Engineering and Architecture, 2017
Strengthening of RC structures with externally bonded FRP (fiber reinforced polymers) has become an important challenge in civil engineering. Epoxy is the main bonding agent used so far, but in the case of a fire, it is subjected to complete loss of his bonding capabilities. Mineral based composites strengthening systems consist of FRPs and a cementitious bonding agent which form a repair or strengthening system that is more compatible with the concrete substrata, and roved its efficiency. The current research introduces the use of a special cementitious material "Grancrete" as a bonding agent. Test results of 32 T-section RC beams strengthened with various FRG (fiber reinforced Grancrete) strengthening systems are presented. The results demonstrated that most of the specimens were likely to fail by debonding of the FRP from the concrete either at the ends or at intermediate flexural cracks. This paper presents an in-depth study aimed at the development of a better understanding of debonding failures in RC beams strengthened with externally bonded FRP systems. Different analytical models, published in the literature for plate end debonding, are reviewed and compared to test results. The results also demonstrated that when using U-wraps, the specimens were likely to fail by FRP sheet rupture.