Flexural Strengthening of RC Beams with Cement-Based Composites

Abstract

In this paper, the effectiveness of fiber-reinforced cementitious matrix (FRCM) materials for the strengthening of reinforced concrete (RC) beams is experimentally investigated. Bending tests on RC beams strengthened with different FRCM materials, made out of (1) carbon fiber nets; and (2) poliparafenilenbenzobisoxazole (PBO) fiber nets embedded in cement-based matrix, are performed. For case (2), different net shapes, cementitious matrices, and a number of net layers were considered. Depending on the type of fibers and matrix, different flexural debonding failure modes are identified. The fiber strain at debonding is evaluated by comparing the experimental results with those obtained with two different theoretical models. The results obtained in this study confirm the effectiveness of FRCM materials for the strengthening of RC structures and encourage further experimental and theoretical work on the topic. A better understanding of the debonding phenomenon is crucial for an optimal design of the strengthening material. The way in which the nature of fibers and matrices and the number of layers control the performance of the strengthened members is also investigated in the present paper

Effect of the Fiber Type and Axial Stiffness of FRCM on the Flexural Strengthening of RC Beams

“…Furthermore, some research works were performed to evaluate the effectiveness of FRCM for the flexural strengthening of RC beams. D'Ambrisi and Focacci [4] investigated the effect of fiber net material (PBO and carbon FRCM), the type of mortar matrixes and the strengthening scheme (different U-wrapping configurations) on the flexural behavior of FRCM-strengthened beams having an internal reinforcement ratio of 0.11…”

“… It was found that RC concrete beams reinforced with two layers of PBO FRCM, which yields an axial stiffness of approximately 83% of one layer of carbon FRP sheets, provided about a 30% increase in the ultimate load, which was almost the same increase as the CFRP strengthening. Meanwhile, two layers of carbon FRCM with an axial stiffness of about 75% that of CFRP, enhanced the ultimate load by only 15% [4].…”

“…However, externally-bonded FRP sheets still suffer from many disadvantages. For example, FRP sheets lack permeability, trapping moisture at the interface and, therefore, affecting the bonding integrity to RC [4]. In addition, low temperature conditions also affect the bond integrity [5].…”

“…Due to the presence of cementitious bonding material, the FRCM system, unlike FRP, is less affected by temperature fluctuations and possesses porous properties that allow moisture to diffuse through RC structures where FRCM is applied [5]. In comparison to FRP, FRCM is inherently incombustible [4], hence making it a much safer and a convenient alternative to the commonly-used FRP. In addition, research has shown that FRCM can be applied to concrete structures and columns in low temperature conditions and onto wet surfaces [6].…”

Flexural behaviour of reinforced concrete beams strengthened with a composite reinforcement layer: BFRP grid and ECC

“…However, the bonding behaviour at the FRP-to-concrete interface may deteriorate due to environmental factors, such as moisture, high temperature and fire [8,9] because of the organic property of the epoxy material. Therefore, some scholars have attempted to utilize inorganic cementitious materials to replace the epoxy resin to develop new fibre composite systems, such as dry fibre sheets bonded with cementitious materials [10][11][12][13][14][15], fibre-reinforced inorganic polymer (FRIP) composites [16,17] and textile reinforced mortars (TRM) [18][19][20][21] for strengthening RC members. The advantages of the inorganic bonding materials are their high resistance to ultraviolet (UV), reduced environmental impact, better resistance to elevated temperature and moisture, as well as better compatibility with the substrate concrete.…”