Reinforcing bars adhesion

If concrete removal is not required or supplementary reinforcing bars cannot be used, external reinforcement can be applied. For instance, steel bars may be encased in a shotcrete layer or steel plates may be bonded onto the concrete surface. Recently, the use of steel plates has been substituted by fibre-reinforced plastics (F. R.P.), that are composite materials with glass, aramide or carbon fibres embedded in a polymeric matrix (usually an epoxy system). F. R.P. are available in the form of laminates or sheets that are bonded to the concrete surface using an epoxy adhesive [11]. They are typically used to improve the flexural and shear strength or to provide confinement to concrete subjected to compression. The... 

The adhesion or bond of latex-modified mortars to reinforcing bars is found to be very important for their use in repair work for damaged reinforced concrete structures. Figure 4.54l l illustrates the bond strength of the latex-modified mortars to the reinforcing bars, determined under direct tension by pull-out method. In general, the bond strength of the latex-... 

M. A. R. Bhutta, Y. Ohama and K. Demura Underwater adhesion of pol5miethyl methacrylate concretes to reinforced steel (reinforcing bars). ACI Materials Journal Vol.96, No.l (1999), pp.90-94. 

Covering of reinforcing bars with resin, apphed as an anti-corrosion protection, can lower their adhesion to cement paste. Worsening of adhesion occurs in the case of vinyl polychloride, but it does not occirr if the epoxy resins are used. However, some epoxy resins reveal the creep effect [56]. 

Bonding of hem flanges is now practiced for more than 30 years. At the beginning the reason was more corrosion protection than increase in stiffness. Meanwhile, the hem flange bonding contributes to the structural stiffness of hoods. And it is an important element for the resistance of the doors against side impact. The adhesive prevents the inner door panel with the reinforcement bar to slip out of the hem flange upon impact. 

RubCon structures reinforced with steel-ribbed bars have a high bond stress due to adhesion and forces of mechanical bond. 

In the presence of special devices for the bonding of the extreme ends of sheets and laminates, the aforementioned verifications can be neglected, as long as a proper certification of the experimental surveys of these devices is available. The certification should involve the employed materials (adhesives and reinforcements), the specific systems used to improve the bonding (covered cross-bars, cross-strips with sheets, etc.), the sequence of stages provided by the manufacturer to prepare the surfaces, the application time, and the environmental conditions. 

Four mechanisms contribute to the shear resistance at the interface concrete-to-concrete adhesion, concrete-to-concrete friction (Fig. 4a), the connecting action from either steel bars placed across the interface between the old and the new concrete (Fig. 4b), and bent-down bars welded between the bars of the old and the new crmcrete (Fig. 4c Dritsos 2007). These four mechanisms can be subdivided into the two groups of unreinforced and reinforced interfaces, depending on whether or not additional steel is placed across the interface or welded between the bars of the old and the new concrete (Dritsos 2007). 

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