Project topic

Project description

The structure of a classic sandwich element in solid construction consists of a reinforced concrete or textile-reinforced concrete facing shell, a rigid foam layer and a reinforced concrete load-bearing shell. The bond between the two concrete shells is ensured by mechanical bonding agents made of steel, glass fiber reinforced plastic (GRP) or a spatial textile fabric.

In a joint research project with the Chair of Structural Design atthe University of Siegen
of the University of Siegen, a new type of sandwich structure was developed in which glass panels are connected to a reinforced concrete load-bearing shell as a facing shell without additional composite materials via the insulation layer. The transfer of tensile and shear forces, which result from the dead load of the glass panels and the insulation layer, from the wind load or from constraint loads, takes place in the boundary layers between the three materials exclusively via adhesion bonding.

In order to characterize the bond between normal strength concrete (OPC) or ultra-high performance concrete (UHPC) and various rigid foam panels bonded with concrete, 120 adhesive tensile tests and 30 shear tests were carried out at the Chair of Concrete and Masonry Structures. The rigid foam panels consisted of expanded polystyrene (EPS), extruded polystyrene (XPS) and polyurethane (PUR) and had different surface textures.

In the case of OPC, the type of rigid foam and the surface texture had no significant influence on the adhesive tensile strength in the rigid foam-concrete composite joint. In composite joints with UHPC, higher adhesive tensile strengths were measured than with OPC, unless cohesive failure in the insulation material was decisive. In addition, a clear influence of the surface texture on the test results was recognizable. The adhesive tensile strength for OPC was between 0.135 and 0.156 N/mm² on average for the various rigid foam boards, while average values between 0.193 and 0.251 N/mm² were achieved for UHPC.

In light microscopic examinations of the interface between rigid foam and concrete, a higher molding accuracy of the UHPC could be determined, which explains the better micromechanical interlocking between rigid foam and UHPC. The reason for this appears to be the higher fines content and the more flowable consistency of the UHPC.

In the shear tests on rigid foam concrete samples, only composites with PUR were examined. The PUR rigid foam slabs were milled smooth, either with or without milled grooves. In the tests, the grooves were aligned both longitudinally and transversely to the direction of loading. Almost without exception, cohesive fractures occurred in the PUR, so that for both OPC and UHPC only a minor influence of the surface texture of the rigid foam panels on the shear strength of the composite joint was observed. The series average shear strength was between 0.155 and 0.177 N/mm² (OPC) and between 0.157 and 0.182 N/mm² (UHPC).

The bond joint between glass and rigid foam was examinedat the Chair of Load-bearing Structures.
was investigated.

The production of the glass-rigid foam-concrete sandwich can be easily integrated into the production process of a plant for the production of sandwiches for lightweight metal construction and into the usual work processes of precast concrete plants.

Publications

WEIMAR, T.; HAMMER, C.; LEUTBECHER, T.; METJE, K., 2021. Study on Glass-Rigid Foam Composite for Innovative Concrete Sandwich Elements. Civil Engineering Design. 3(1-2), 3-12. doi:10.1002/cend.202000010

METJE, K.; LEUTBECHER, T.; WEIMAR, T.; HAMMER, C., 2020. Bond between concrete and rigid foam in precast concrete sandwich construction. Civil Engineering Design. 2(5-6), 182-192. doi:10.1002/cend.202000011

METJE, K.; LEUTBECHER, T.; WEIMAR, T.; HAMMER, C., 2019. Bond in glass-rigid foam-concrete sandwich elements. Part 1 - Experimental investigations on the bond between concrete and rigid foam. Bautechnik. 96(10), 731-739. doi:10.1002/bate.201900016

WEIMAR, T.; HAMMER, C.; LEUTBECHER, T.; METJE, K., 2019. Bond in glass-rigid foam-concrete sandwich elements. Part 2 - Experimental investigations on the bond between glass and rigid foam. Bautechnik. 96(10), 740-748. doi:10.1002/bate.201900017

LEUTBECHER, T.; WEIMAR, T., 2019. composite-free concrete sandwich element with glass facing. In: Congress documents 63rd BetonTage: Innovation in concrete. Neu-Ulm, February 19-21, 2019. Betonwerk und Fertigteil-Technik/Concrete Plant and Precast Technology. 85(2), 91.