Non-metallic reinforcement for sandwich facades

Sandwich constructions, consisting of two concrete face layers and an insulating core, are increasingly used as facade elements in office and commercial buildings. Due to the use of reinforced concrete and the required concrete cover for corrosion protection, the concrete surface layers must have a thickness of approx. 80 mm. Stricter specifications regarding the energy quality of buildings also require thick insulation layers. However, this has an unfavorable effect on the lever arm between the load-bearing and facing shells, resulting in greater stress on the composite means. This can be remedied on the one hand by new types of insulating materials that provide a higher insulating performance for the same insulation thickness, or on the other hand by reducing the thickness of the facing layer. The aim of the first project phase is to compile the consortium’s current findings and experience in the field of concrete sandwich facades with slender facing shells. The focus is to be on the targeted supplementation of standard designs (reinforced concrete and mineral wool) with a slender textile concrete facing shell. Together, the CBI will work with Nesseler and Solidian toward this goal.

In addition to the general trend in the construction industry to use prefabricated system components for the erection of buildings, sandwich elements are becoming increasingly important. A predominant role is played by facade elements, which as standard consist of two reinforced concrete face layers and an insulating core layer of mineral wool. In addition to load transfer (dead weight, ceiling or roof loads and wind loads), sandwich facade elements must also meet requirements in terms of thermal insulation of the building and the architectural design of the surfaces. However, when using inlaid insulation layers without a frictional connection to the face layers, bonding agents must be installed to activate the composite load-bearing effect between the two face layers (sandwich load-bearing effect). Typically, the thicknesses of the face sheets are between 80 mm (facing layer) and at least 200 mm (load-bearing layer) and of the insulation layer between 60 mm and 250 mm. In combination with a reinforced concrete facing layer (t≥80 mm), high forces act on the fasteners between the two facing layers. Equally problematic is the thickness of the overall structure of up to 500 mm, which makes space-saving construction and the largest possible usable area with the same building cubature difficult.

By using textile concrete, the concrete cover thicknesses can be significantly reduced, which reduces both the dead weight and the consumption of resources. As a result of the lower dead weight, the stress on the sandwich anchor is also reduced. Depending on the appearance of the facade and the desired joint pattern, large-format facade elements may also be required. However, larger elements tend not to remain flat, and so-called “bowling” occurs. This effect can be intensified by the arrangement of thin facing sheets. In addition, cracking due to shrinkage and constraining stresses resulting from temperature fluctuations can occur, especially in thin facing shells. These effects can be avoided by a suitable arrangement of the textile composite materials.

This project was successfully completed.