High-temperature resistant basalt-carbon hybrid textiles

Projektdaten

Report in the yearbook 2012

Basalt Fibres – an Alternative for Textile Reinforced Concrete ?

Until now different high performance fibres in combination with concrete have been examined for bearing concrete components. High-tensile carbon fibres will be implemented into the market shortly but are still quite expensive. Although promising results have been obtained with alkali resistant glass, it suffers from reservation in the construction industry concerning its costs and characteristics e.g. regarding its durability in the concrete and the temperature resistance being relevant in terms of constructional fire protection.

For a long time basalt has therefor been repeatedly considered. With 500 °C it has a comparable temperature resistance to carbon fibres. Nevertheless its practical use has failed until now owing to the unsufficient or rather varying quality, alkali resistance of the fibres and its limited availability.

The development of industrial-suited production processes for basalt fibres though has made it available in potentially large amounts. Compared to AR-glass they are around 20-40 % less expensive and at the same time about 15 % more tensile. Questions concerning the industrial availability and coating, the resistance in case of fire as well as its durability and the composite behaviour in combination with concrete are yet to be examined. Thus the first aim of this research project is the development and providing of high temperature resistant basalt reinforcements for the subsequent strengthening of existing building substances with focus on precisely adjusted and application-orientated formed textiles and their coating under consideration of durability and fire protection.

Stationary and transient strain specimen tests at temperatures of up to 600 °C are supposed to provide insights regarding load-bearing capacity and the strain-stress behaviour. Pull-out tests under temperature load can determine the composite parameters between filament yarn and fine-concrete matrix and give information about required anchorage and lap lengths. Thermogravimetric analyses and warm creep tests at the textile reinforcement are supposed to provide evidence concerning the loss of mass in relation to the temperature as well as the transformation temperature. Large-scale component tests with flame impingement will complete the project.

Report in the yearbook 2014

Basalt fibers for temperature-steady textile concrete

© Harald Michler

Given the extreme stiffness of carbon fibers, a very efficient reinforcement material is available for composites comprised of textile and concrete. Carbon is relatively cost-intense, but it is sturdy and not susceptible to alkaline reaction in a concrete environment. Reinforcing with AR-Glass fibers is somewhat more economical, but there are, however, disadvantages regarding the load-carrying capacity and durability. Basalt is also a feasible reinforcing material. In contrast to other materials, basalt has the advantage to occur naturally in large quantities. In the context of this project, a high-temperature resistant yarn should be developed. A composite resistant to high temperatures is adequate to strengthen existing reinforced concrete buildings.

Research on the mechanical properties of textile reinforced concrete samples with basalt textiles layers showed a quite tidy performance. The carrying capacity was somehow higher than that of AR-Glass reinforcement. The behavior of the composite correlated to that of the AR-Glass reinforcement, with a short bond length and an adequate crack distribution.

However, to be able to use basalt textiles under the desired specified conditions, a high-temperature resistant coating is required, which must additionally guarantee the durability and fulfill safety requirements under fire resistance. In case of a fire, basalt, as well as AR-Glass and reinforcing steel, clearly loses stiffness, even at relatively low temperatures from approx. 150 °C. Therefore, the basalt-yarns must also be protected against high temperatures to ensure a significant load carrying capacity in case of a fire.

It is an advantage that the basalt textiles are able to hold together the existing reinforcing in a structure even under high temperatures. In fire tests, there was not lost of concrete cover, and the heat insulation effect provided by the composite was maintained. Basalt is, in terms of fire loading, a good construction reinforcement material with a very good crack distribution behavior.

However, the tested basalt materials were still not resistant enough to the alkaline reaction in concrete, which is why additional research is needed in this area. Suitable storage facilities are required, natural mineral deposits should be available. The application is feasible, however, when the alkaline resistance of the material is of subordinated meaning, for example in extremely dry surroundings or also for components with a limited service life.