Is less flammable

Lighter and thinner: vacuum-insulated facade elements made of textile-reinforced concrete

The energetic and ecological requirements for the building envelope will continue to grow over the next few years. Using conventional materials and systems, this leads to a continuously increasing thickness of the outer skin. Slimmer cross-sections, lower weight and an improved ecological balance are just three key words that make a new facade construction material a popular product in this situation. Especially in the area of ​​prefabricated facade elements, the advantages of a new development increase due to the high number of elements. But how can demands for energy efficiency, durability, noise and fire protection be satisfied with slim, lightweight components? One possible solution is provided by Prof. Frank Hülsmeier and his team from the Building Technology, Energy Concepts and Building Physics department at the HTWK Leipzig in the form of vacuum-insulated facade elements made of textile concrete.

"The development of a facade system that is as resource-efficient as possible while meeting all requirements," is how Prof. Hülsmeier describes his research goal. At the same time, the individual facade element should be made from components that correspond to all the latest developments. At the beginning of the investigations, there was initially the question of suitable materials. In view of the increasing global population and the associated food shortage, the researchers decided against renewable raw materials and instead chose mineral building materials. With the combination of textile concrete, a glass fiber reinforced fine concrete, and vacuum insulation panels, two new types of building materials come together in the facade elements.

The structure of the new elements consists of a textile concrete plate on the outside and inside. In between there are air or protective layers in front of the two layers of vacuum insulation. Two vacuum panels, explains Prof. Hülsmeier, are not absolutely necessary, but would still ensure the statutory minimum thermal protection in the event of a failure of an insulation layer. In comparison with a conventional, energetically equivalent reinforced concrete facade element in the passive house standard, the advantages of the new facade system become apparent. Compared to the reinforced concrete element with a thickness of 44 cm, the vacuum-insulated facade elements made of textile concrete can achieve savings of over 30 cm and only require a cross-section of 11 cm. In addition to material and space, another advantage is the reduction in component weight to a fifth compared to the reinforced concrete structure, which leads to savings in transport and heavy equipment on the construction site, shorter assembly times and lower loads for the support system.

The new facade system had to meet the four criteria of architecture, construction and technology, ecology and economy in all stages of development. The vacuum panels used are sensitive, have to be made to measure and cannot be cut to size later or react to necessary structural changes. In return, they enable narrow system widths with a high insulating effect. Correspondingly protected, their lifespan is 30 years, a technical failure of the building material is currently only assumed after 50 years. In terms of sound insulation, the facade system reaches 47 dB, which corresponds to sound insulation class 3. In addition, the new building material is not flammable.

In comparison with various facade systems, the vacuum-insulated facade elements made of textile-reinforced concrete do quite well. Only wooden stand constructions, which were out of the question as a renewable raw material for the researchers, can achieve better results in terms of aspects such as environmental risks, water consumption, sustainable material extraction, surface drainage or primary energy use. The greatest disadvantage of the new building materials, the high investment costs of currently around € 500 per square meter, is invalidated by Prof. Hülsmeier with a simple comparison of the usable area gained. In view of the lack of space in the city centers and the associated increasing costs in the real estate sector, this shows a particular advantage of the new building material.

There is still a need for development in the area of ​​joining techniques. The individual layers are currently being bonded with fiberglass. Despite all the optimization of the connecting webs, the losses in the area of ​​the panel joints are considerable. Instead of a U-value of 0.12 for the undisturbed element, the U-value, taking into account the connecting joints, is 0.18 W / (m² · K). In addition, the use of carbon fibers instead of glass fibers is currently being researched. Here, a new integration of use in the form of climate-neutral radiant heating offers itself. For a better ecological balance, the new building material will not only be lighter and thinner, it will also provide additional warmth in future. Further information on the funded research project:
Research initiative Zukunft Bau
HTWK: Architecture Institute LeipzigLecture by Prof. Frank Hülsmeier, Department of Building Technology, Energy Concepts and Building Physics at the HTWK Leipzig, as part of the event series "The Future of Building" by Detail research and the research initiative Zukunft Bau of the BMUB and BBSR on March 13, 2014 at the University of Stuttgart Topic "Energy-efficient building".

To person
Prof. Frank Hülsmeier holds the professorship in the field of building technology, energy concepts and building physics at the HTWK Leipzig. He is the dean of architecture studies and head of the Leipzig ai: L architecture institute and the energy design research group. He also runs the hülsmeier architects office in Leipzig. After studying architecture at the Technical University of Berlin and at the Istituto Universitario di Architettura di Venezia, he worked as an employee for Hascher and Partner, Berlin, and von Gerkan, Marg and Partner, Hamburg, before founding his own architecture office. From 1997 to 2002 he worked as a research assistant at the TU Darmstadt, department of design + building technology, from 2000 to 2001 as a lecturer at the University of Applied Sciences Hildesheim for building materials science, building services + technical expansion and from 2001 to 2002 at the TU Darmstadt for technology the building envelope. He has been working at the HTWK Leipzig since 2002.