Topic of the month July 2010

Figure 1: An intelligent package makes concrete ductile: The newly developed fibres are packed in such ways that they can simply be worked into the concrete. Image: Empa.

Innovation in GREY: Concrete Convinces with Tailor-made Properties

Solid foundations, massive constructions, pipes, ducts, casings or even entire football stadiums are just some examples, which demonstrate that concrete is a material, which is of central importance for the realisation of industrial projects. In 1753, concrete was mentioned by the French scientist Bernard de Bélidor in his book "Architecture hydraulique" as a construction material for the first time and since then it is increasingly being used for various construction projects. The multitude of application areas can be justified by the fact that the property profiles of various concrete materials are customizable to the requirement profiles. Due to this central feature, this material class will also provide interesting features in the future, in order to offer solutions for current issues such as resource conservation, lightweight construction and material and energy efficiency – particularly in the context of the international trade fairs wire and Tube.

Ductile Concrete: The Right Mix is the Key

Concrete is basically a simple mixture of the components gravel, sand, water under addition of cement as a binding material. Once this mixture is hardened, it can withstand extremely high pressures – in contrast the material fails, even at relatively low tensile stresses. Because of this fact concrete is being armed with steel, because steel can absorb the occurring tensile forces. The scientists Josef Kaufmann, Jörn Walter and Lübben Trindler of Empa in Dübendorf in cooperation with fibre specialists of the company fibrotec ag in Mollis have recently developed an innovative method to provide additional ductility to concrete without steel reinforcement. Therefore the developers use a novel fibre, consisting of two different plastic materials, which are reliably worked into the mineral matrix. For the production of this fibre, the researchers apply a new manufacturing process, which allows the intelligent combination of two specific components. The "trick" here is that the fibre core is built up of low-cost polypropylene (PP) while the fibre surface consists of a high quality polymer, whose chemical resistance, surface quality and mechanical stability is ideal for the use of cement bonded building materials. The results after first application tests are impressive – with only five kilograms of these fibres, thirty kilograms of steel fibres can be replaced, whereas the bicomponent fibres are about ten percent cheaper than conventional steel fibres, which are normally used for this application.

Concrete: Stable and Acid Resistant like Ceramic

Figure 2: Ultraporcrete – a building material that combines the advantages of conventional concrete and aerated concrete. Image: TU Dortmund.

By adjusting nanoscale binders to concrete, scientists at the University of Kassel aim to make concrete as robust and acid resistant like ceramics materials. This would open up many other fields of application for the industry. The concrete production is growing worldwide, particularly in emerging markets like China. Concrete is relatively inexpensive and it is a building material, which can be well processed. Nevertheless concrete also has significant disadvantages compared to other materials. Its relatively low chemical resistance to acidic media and chloride or sulphate containing solutions limits the lifetime of many applications, such as pipes, tanks and walls. Scientists led by Dr. Dietmar Stephan from the Institute of Structural Engineering at the University of Kassel are working on a new formula to make concrete more resistant to such chemical attacks. In order to replace cement, due to its climate damaging production processes, slag sand, a waste product of raw iron production, and fly ash, a waste product from coal-fired power plants as well as sodium silicate, are being used as novel binders for the concrete. Sodium silicate is an intelligent function owner in this process, because it binds the components and compacts the micro structure at the same time. Investigations performed by scanning electron microscopy show almost no pores in the new concrete – so the harmful chemicals can not penetrate into the material. Currently, the material is subjected to a permanent stress test in an acid bath – if the results are satisfying, initial tests under real conditions are planed. The possibility to use the new material as air-blown mortar is also assessed to be very promising by the scientists. By this method already existing concrete constructions could be coated with a protective layer, in order to lengthen their life cycle.

Ultraporcrete: A Novel High-strength Foam Concrete

Researchers led by Prof. Dr. Bernhard Middendorf at the TU Dortmund have the objective to develop a building material, which combines the strength and application flexibility of conventional concrete with the low density and the positive thermal insulation properties of aerated concrete. The result of their research is: "Ultraporcrete.” The material is the world's first foam concrete, whose physical-mechanical properties allow the application as a building material for load bearing components. Because of the high porosity of this building material, it also has good heat insulating properties. Another advantage of "Ultraporcrete" is its low weight, which is only one third in comparison to a component made from conventional concrete. Furthermore the possibility to regulate the dispersion of the pores accurately enables the flexible adjustment of properties, like for example compressive strength and density, to the requirements of the built object. “Ultraporcrete is consequently opening entirely new possibilities in concrete construction", Middendorf explains. "This material also enables the cost-effective production of roof constructions, which are still mainly made out off wood today.” The TU Dortmund has filed a patent for “Ultraporcrete" and the industry has already shown great interest.

Dr.-Ing. Christoph Konetschny
Material and Nano Expert

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