Composites rebars

Polymers, after their combination with fibres to form special composites produces some materials with enhanced properties, enabling them to be used as structural members and units, competing with metals. The use of polymeric fibres in concrete to replace steel frame (as composite rebars) has many advantages which has been in use for a long time with an ever increasing trend in use, if the material costs involved are decreased in the future, as expected. However, proper materials characterisation in addition to development of new standard test methods still appear to be the immediate needs to be fulfilled in the near future. 

Key words damage-controllable structures, existing RC structures, seismic retrofit, FRP steel-fiber composite rebars. 

Steel-fiber composite rebars for damage-controllable structures... 

Even if the validity of the basic unit costs and hours has been established, the Project Manager must ascertain that the composition of each unit price is consistent with the scope of units i.e., if the unit is cubic yards of concrete and includes excavation, rebar, and forms, the cost and hours per cubic yard must include a reasonable pro rata of all the cost components. Chapter 19 provides enough data to make this analysis. 

In non-carbonated and chloride-free concrete, the passivity of low-alloyed steels is not influenced appreciably by their composition, stracture or surface conditions. Therefore, the usual thermal or mechanical treatments or the roughness of the surface of the rebars have negligible influence on their corrosion behaviour. 

Galvanized rebar is used successfully in structures where carbonation is a risk such as cladding panels. Galvanizing can easily be carried out in most countries although the quality and composition of the coating can affect its durability. It suffers from fewer problems when handled roughly because the coating is sacrificial and protects bare areas. 

S V Kumar, S S Faza, H V S GangaRao and M A1 Megdad, Fatigue performance of concrete slabs with glass fiber reinforced plastic (RP) rebars , Proceedings 50th Annual Conference, Composites Institute, SPI, New York, 1995, Paper 21-C. 

Abbasi, A. and P. J. Hogg (2004). Fire testing of concrete beams with fibre reinforced plastic rebar. In Advanced Polymer Composites for Structural Applications in Construction, ed. L. C. Hollaway, Cambridge, UK, Woodhead Publishing, pp. 445-456. 

Katz, A., N. Berman and L. C. Bank (1999). Effect of high temperature on the bond strength of FRP rebars. Journal of Composites for Construction 3(2) pp. 73-81. 

Concrete is extremely stiff and good in compression, but quite poor in tension. Steel rebar reinforcement is normally used to make a stronger structure, but because steel is subject to atmospheric corrosion, it has to be shielded with a relatively thick protective layer of concrete, which with time, is removed by weathering and erosion, eventually exposing the steel to attack. Carbon fiber has very good corrosion resistance and would not be affected by any alkalis in the cement. Hence it should be possible to utilize a carbon fiber composite such as carbon fiber/epoxy pultruded rods that would only require a relatively thin coating of concrete. Alternatively, carbon fiber can be incorporated directly into the concrete mix [9]. 

Abbasi, A. and Hogg, P.J., Temperature and environmental effects on glass fibre rebar modulus, strength and interfadal bond strength with concrete, Composites Part B 26 (2005)394-404. 

The average effective strain in which the composite jacket is activated in the lateral direction decreases as the ratio IJdi, increases. Hence, a rational design of the jacket thickness, to provide that steel yielding will precede bond failure of the rebar, is possible if one incorporates the dependence of the transverse jacket strains on the ratio IJd. The most reliable approach for doing so relies on using the design Eqs. (12.9c) and (12.9d). 

In this context, general information about polymer composites are presented in Chapters 5 and 8, while more detailed information for FRP rebars and retrofitting/rehabilitation of concrete as well as several applications are presented in Chapters 2, 4 and 6. 

Rebars are polymer fibre reinforced-concrete composites, and they are used as primary structures. It is estimated that replacement of steel reinforcing bars by non-corrosive polymer fibres, i.e., by Kevlar or carbon fibres (which gives rise to Kevlar or C-composite bars) for concrete structures produces structures with one-quarter the weight and twice the tensile strength of the steel bar. It is known that, corrosion of steel reinforcement from carbonation or chloride attack can lead to loss of the structural integrity of concrete structures, and such a danger is non-existent for rebars. Thermal expansion coefficient (TEC) values of these fibres are closer to concrete than that of steel, which provides an another advantage and they have the same surface deformation patterns as the steel bars. In addition, they can provide more economy than epoxy-coated steel bars. 

In the earlier Nestehous , Concept House of Neste, Finland, the development of new on-site processing techniques were aimed at. Concrete casting moulds that stayed on the construction site were prepared from GFRP composites of polyester and they were used to prepare concrete rebars (prepared with concrete and PP fibres) used as the main load bearing material in the house. 

Results of the experimental studies have indicated very clearly for both RC bridges and bnildings that fiber composites (FRP sheets and rebars) are promising strengthening tools that can be nsed to alter the critical failure modes in deficient elements of the existing structures. Furthermore, fiber composites can be employed to control the behavior of those deficient elements hence, the reqnired seismic performance of the entire structure could be achieved. 

Fahmy, M.F.M., and Wu, Z.S. (2012). Seismic performance of RC bridge columns retrofitted with smooth and deformed near-surface-mounted basalt FRP rebars . 6th Int. Conf. on FRP Composites in Civil Engineering (CICE 2012), Rome. 

Fahmy, M.F.M., Wu, Z.S., Wu, G., and Sun, Z.Y. (2010b). Post-yield stiffnesses and residual deformations of RC bridge columns reinforced with ordinary rebars and steel fiber composite bars . Journal of Engineering Structures, 32 2969-2983. 

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