Technische Universität Dresden (TU Dresden), in partnership with textile machinery manufacturer Karl Mayer Malimo, has carried out a special project to produce concrete reinforcement from carbon fibre heavy tows (CFHT). A specially modified, industrial Malitronic Multiaxial warp knitting machine developed by Karl Mayer was used in the research work.

Carbon fibre CFHT are opening up more and more applications for textile reinforcing materials in the building sector, with each heavy tow consisting of 50,000 individual filaments that can reduce material costs for a higher fibre volume in each textile concrete-reinforcing layer. This, the researchers say, represents a considerable economic advantage over alkali-resistant glass fibres and conventional carbon fibre materials comprising 12,000 individual filaments, which are currently used in textile-reinforced concrete for maintaining and restoring buildings.

The modifications to the Malitronic Multiaxial machine related primarily to the elements for delivering the CFHT material in the main reinforcing direction, i.e. the warp yams and the delivery units were modified to permit extremely accurate positioning of the yarns with no damage. The improvements also included developing gentle warp yarn brakes for reducing filament breakages and installing combined warp yarn/holding-down sinkers for placing the warp yarns accurately between the needles.

Special components were also integrated for processing the carbon material gently in the adjacent reinforcing direction. These are runners, or transport chains, which use the tension of the weft yarns to guarantee that the CFHT lies parallel and at right-angles to the adjacent reinforcing direction. A weft yarn laying device developed specially for processing 50K carbon filament tows is also said to guarantee large openings and deflection angles which, together with suitable combinations of materials, was a prerequisite for feeding-in the material with minimum damage.

The technical improvements resulted in the development of a Malitronic Multiaxial machine, which is said to enable the CFHT material to be processed extremely accurately and gently to produce multiaxial reinforcement layers. The warp yarns are fixed without being pierced and the weft yarns are fixed in a reduced width during the warp knitting process. According to the researchers, both yarn systems lie completely parallel and stretched in the reinforcing textiles, which has a positive effect on the strain characteristics.

The research team says it was possible to improve other relevant, mechanical properties by integrating inline coating and drying processes and thanks to the modular construction of the Malitronic Multiaxial, it was possible to incorporate the coating and drying system directly into the industrial multiaxial warp knitting machine.

As well as improving the properties of the reinforcement, the improvements made to the Malitronic Multiaxial also increased the productivity with the machine was running at speeds of up to 560 rpm during the project.

Source: New findings on the processing of 50K carbon fibre tow on the Malitronic® MULTIAXIAL, TUDALIT® Magazine, No. 7, p. 27, September 2012.