Schöck Combar glass fibre reinforcement is fast becoming the preferred choice over traditional steel rebar for a variety of new projects in unusual and demanding environments.
Combar (composite rebar) is a ribbed reinforcing bar made of corrosion resistant glass fibres that are bound by a vinyl ester resin. The high quality components and the unique manufacturing process result in an outstanding material.
One of the latest applications is for a sonar test tank facility for assessing detection apparatus performance. There were two main considerations in the selection process. Primarily, Combar was chosen for its non-magnetic properties, as the product offers no risk of any electromagnetic interference with the test results. Hydroacoustic devices are measured over a range of frequencies and tests are highly diverse, ranging from the acoustic characteristics of a transducer, to the reflective characteristics of acoustic materials. So, electromagnetic sensitivity is a critical issue and normal steel rebar would interfere with the results due to its magnetic properties – and even stainless steel would also compromise the test results.
The secondary issue involved the ability to overcome loading issues within the structure itself. The tensile strength of Schöck Combar is far better than that of reinforcing steel and there is also the ability to design the product to different shaped bar types. The ‘Z’ bar within the wall structure on this project is a very unusual bar shape and also radiused.
A special two-part manufacturing process
It is the two-part manufacturing process that enables the ribbed GRP bars to meet the reinforcement requirements.
First, in the pultrusion process, densely bundled high-strength glass fibres are pulled through a closed chamber and impregnated with a synthetic resin. The parallel alignment of the fibres results in optimum strength of the material. The ribs are then cut into hardened bars and given a final coating. As the vinyl ester resin is diffusion tight and every glass fibre is embedded in resin, the result is a durability of up to 100 years in concrete.
Schöck Combar application examples include taking advantage of its easy machinability in tunnel construction, whereby boring machines used in shaft walls of tunnels, cannot drill through steel reinforced walls. With Combar, the machine can cut directly through the head wall. In high voltage transformers and power plant reactors, inductive currents are generated within the reinforcing steel. The heat will affect the rebar strength if too close to the coils, but Combar remains unaffected. And its corrosion resistance – even from salt – is unrivalled when building bridge, marine and harbour constructions.
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