Günter Grabher (Source: Grabher Group)
There are approx. 36,300 publicly managed bridges in Austria. 43 % of these were built between 1960 and 1990, a situation that is comparable throughout Western Europe. Increasing traffic loads, increased durability problems and changes in standardization pose great challenges to maintainers, engineers and construction companies alike. The question arises as to how a safe and stable traffic network can continue to be guaranteed in the future.
In the meantime, a group of embroidery manufacturers
and members of the Smart Textiles Platform Austria also addressed this issue more than 5 years ago. That textile concrete with carbon grid reinforcements can offer potential was known from various successful research projects, especially from Germany. Especially in bridge remediation, however, not only carbon grid structures are needed, but also arch and stabilization structures with different arrangements of radii and fiber strands in order to be able to replicate all load cases and load profiles of a bridge. Of all textile processes, only embroidery technology offers the possibilities to meet these requirements.
After initial rudimentary self-experiments with embroidered carbon structures and concrete, it very quickly became clear to the development group that successful development would hardly be possible without scientific support. A partner was found in the Department of “Solid and Bridge Construction” at the University of Innsbruck/Austria to generate the foundations for the industrialization of embroidered textile concrete structures in funded research projects.
The research efforts ended in a granted patent (EP3684985A1) for the production of these special textile reinforcement structures, which is the basis for the first pilot project for the remediation of a large bridge in Austria (Damüls) with textile concrete.
Durable and high-performance reinforcement, a very low design deadweight and installation by means of field-tested construction sequences are the particular advantages of this development.
However, there is still no set of rules for this construction method in Austria or worldwide. Therefore, the use of these pilot applications is an essential milestone for the future of textile concrete in widespread application.
The starting point was a required individual approval
by destructive bulk testing at the TU Dresden, the stitched carbon reinforcement for the approval was thereby manufactured by RAC GmbH (riedmann advanced composite), Lustenau/Austria.
This was followed by the next steps: Bridge investigation, static recalculation, concept development, investigations on small and large component tests, cost estimation, life cycle costing and risk management by identifying opportunities and threats. Furthermore, a comparison of variants with a conventionally steel-reinforced shotcrete layer was developed.
This 5-year preliminary work formed the basis for the decision of the Vorarlberg state government to approve the use of textile concrete for transverse force and torsion reinforcement of a plate girder bridge, and also to commission it for the remediation.
The Krumbach Bridge in Vorarlberg
is a 3-span, longitudinally pre-stressed reinforced concrete bridge which was opened to traffic in 1983. It is an important connecting bridge for the tourist resort of Damüls in Vorarlberg. The decisive factor for the decision to remediate the bridge with textile-reinforced concrete was, of course, also the cost for the public authorities in the form of the Vorarlberg state government. For static reasons due to the increase in weight, a conventional remediation of the bridge would not have been possible. The alternative, apart from all the hardly soluble traffic obstructions, was to demolish and rebuild the bridge at a cost of approx. € 4 million or to remediate it with textile concrete at a cost of approx. € 2 million.
The bridge lies in a circular arc with a mean radius of 100 m and has a length of 120 m. Both edge spans, each with a span of 36 m, are designed with a 4-web plate girder cross-section. Currently, severe deformations and diagonal cracks are visible on the web surfaces. The aim is to carry out a remediation of the bridge that will allow a remaining service life of approx. 50 years. The concept to accommodate the deficiencies of the plate girders consists of 2-3 cm thin textile concrete U-shells, depending on the load. In addition, a textile concrete collar is continued over a length of 60 cm, laterally to the web faces, on the underside of the deck. In combination with an anchoring system consisting of an anchor plate and a composite anchor system, the final anchoring of the textile is thus made possible. The textile reinforcement structures consist of more than 300 different, form-fitted, partly curved carbon embroidery components. In total, over 6,000 m2 of these reinforcement structures are required for the remediation.
The installation of the textile concrete layer on site at the bridge will be carried out in layers, using the dense-phase wet-spraying method. Due to corona, the start of remediation has already been postponed several times, but will now start in May 2022 in 2 phases, and should be completed by October 2022.
Parallel to this, intensive research is currently
being carried out together with Dr. Wolfgang Fiel from the University of Vienna, V-trion textile research GmbH, the start-up Basalt+ GmbH and the Smart-Textiles Plattform Austria, and investors, into alternative possibilities of how the use of stitched basalt fibers as reinforcement structures in combination with clay could become a recyclable low-CO2 construction material of the future.