Fraunhofer Institute for Casting, Composite and Processing Technology IGCV
Fraunhofer Institute for Casting, Composite and Processing Technology IGCV

Rebar 3D – Process routes for the production of FRP reinforcement bars in concrete

Development of innovative, large-scale technical process routes for different matrix systems for the production of FRP reinforcement bars with different bending radii and their implementation in semi-finished concrete products

Fiber composite reinforcement in the construction industry

Concrete reinforced with steel is currently the standard in construction. It is inexpensive and structurally flexible. However, this system is increasingly reaching its limits. Steel corrodes, resulting in considerable costs for monitoring, repair, and reinforcement. To protect the reinforcement, large concrete coverings are necessary, which makes components heavy and increases materials and energy requirements.
In addition, the production of cement and steel is one of the most CO₂-intensive industrial processes. More concrete and more steel directly mean higher greenhouse gas emissions – both in production and in the transport of heavy prefabricated parts. The high thermal conductivity of steel further reduces the energy efficiency of buildings, and its electrical conductivity limits its use in EM-sensitive sections. Its poor machinability is also problematic, for example in tunnel construction, when openings have to be created retrospectively.

Fiber-reinforced plastics (FRP), in particular glass-fiber-reinforced plastics (GFRP), have established themselves in recent years as a promising alternative to steel reinforcement. They are corrosion and chemical resistant, significantly lighter, less thermally conductive, electrically non-conductive, and much easier to machine. Because FRP does not corrode, the concrete cover can be reduced. This saving in concrete lowers CO₂ emissions and conserves resources.

Process routes suitable for series production of FRP reinforcement bars

Roboterunterstütztes Umformen von FVK
Bending technology for fiber-reinforced plastics at Fraunhofer IGCV: HotBend 35 bending system

The aim of the “Rebar 3D” project is to develop innovative process routes suitable for large-scale production for the manufacture of FRP reinforcement bars with different matrix systems and bending radii, and to implement these in semi-finished concrete products. To this end, both thermosetting and thermoplastic matrix systems are being considered and the respective manufacturing and forming processes are being optimized to enable high-speed, automated production. For thermoplastic bars, the focus is on the development and optimization of efficient bending processes that make targeted use of the formability of these systems. In addition, a process for the production of molded thermoset bars is being developed. The straight and curved profiles produced in this way can then be combined to form application-specific reinforcement structures and used in precast concrete elements.

Bending processes for thermoplastic FRP reinforcements with optimized thermal management

In the “Rebar 3D” project, Fraunhofer IGCV is developing a bending process for thermoplastic FRP reinforcement bars. Unlike thermoset variants, these bars can be reheated and reshaped after pultrusion. This opens up great design freedom and better recycling options, but poses challenges for process technology: With the current status of bending processes, it is virtually impossible to implement targeted thermal management during forming. This requires high bending forces, which place a heavy strain on the tools and often lead to fiber damage and inaccurate bending radii.

 

To solve this problem, Fraunhofer IGCV is designing an improved thermal management system for thermoplastic bending technology. The bending point is brought to forming temperature locally and energy-efficiently, bent immediately afterwards in the heated tool, and cooled down again in a targeted manner. This preserves the fiber architecture, allows matrix properties to be adjusted, and enables the bending area to be precisely fixed and tight bending radii for different diameters to be set reproducibly.

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