In this thesis project a concrete sandwich wall element of 250 mm insulation of Kooltherm has been resulted to have U-values and ψ-values closer to the passive housing recommendations. However, by using 180 mm thick insulation, no significant difference in the annual energy consumption is observed. Using a metal sheet in the window connection and small concrete brackets, low thermal bridge values are achieved. Low thermal bridge coefficient values were also observed with thick insulation in the foundation and the roof structure, although, it is impossible to achieve values below 0,01 W/mK in the corner connections. Airtightness of the building envelope is more important than the thickness of the wall in the energy consumption simulations. Therefore, the thermal bridging and the U-values of the wall are, in most cases, dependent on the thickness of the element. No conclusions on the structural reliability of the solutions can be extracted from this thesis project. In order to conclude the statements above, this thesis project has been focused on the evaluation and design of a concrete sandwich wall panel. The design of the wall element, including its reinforcement and connectors, while achieving values according to passive housing regulations, is the initial goal of this project. Subsequently, connections between the building components and the wall element are analyzed and designed through several simulations according to the passive housing regulations respectively. Simulation tests took place in Sweco Structures AB offices with the valuable contribution of experts. An existing building project was used and evaluated in order to present the simulation results in a more realistic manner. Several insulation materials have been tested for the thermal and moisture reliability. Using the existing building as a base for information, energy simulations generated the energy consumption results in order to compare different wall thicknesses, and thermal bridging effects. This project is inspired by the needs of building sustainability and efficiency, which has become a significant part of the worldwide effort on reducing the energy consumption on the planet. Regulations regarding building technology have been completely changed and adjusted in the passive housing design. Particular effort has been put on the commercial and multi-residential buildings, in which the energy consumption is usually higher than in small family houses. Concrete sandwich wall panels have been introduced in the building market as an alternative and more efficient way of constructing. Prefabrication has been proved to be less time consuming, although issues on the thermal behavior appear in this kind of structure. The evaluation of the thermal efficiency of the concrete sandwich wall elements has been a significant issue in the civil engineering society and research.

Sandwichelemente mit Betondeckschichten besitzen gute bauphysikalische Eigenschaften, einen hohen Vorfertigungsgrad, geringe Montagezeiten und eine gute architektonische Gestaltbarkeit. Werden die Deckschichten mit einer Betonstahlbewehrung ausgeführt, ergibt sich ihre Dicke aufgrund der in EC 2 [1] geforderten Mindestbetondeckung zum Korrosionsschutz der Bewehrung zu etwa 80 mm [2]. Weiterhin wird bei der Bemessung von Stahlbetonsandwichelementen die Verbundtragwirkungen zwischen den einzelnen Schichten nicht angesetzt, sodass das volle Potenzial der Sandwichbauweise bei Stahlbetonsandwichelementen nicht ausgeschöpft wird. Das Forschungsvorhaben beschäftigte sich daher, aufbauend auf den Ergebnissen aus den Projekten HE 2637/16-1 und HE 2637/16-2 [3], s. S.356 ff ., mit der praxisnahen Umsetzung von weitspannenden Sandwichelementen mit dünnen Deckschichten unter Ausnutzung der Sandwichtragwirkung. Ein analytisches Berechnungsmodell, das im Zuge des Vorhabens entwickelt wurde, berücksichtigt die Verbundtragwirkung zwischen den einzelnen Schichten und kann das Trag- und Verformungsverhalten zutreffend abbilden. / Sandwich elements with concrete facings have excellent physical properties, a high level of prefabrication, short assembly times and various architectural design options. The facings are usually produced with steel reinforcement, which leads to a thickness of about 80 mm due to the minimum concrete cover required in EC 2 [1] for corrosion protection of the reinforcement [2]. Furthermore, the bond between the single layers are not taken into account in the design of sandwich elements, so that the full potential of sandwich constructions with reinforced concrete facings is not completely exhausted. Based on the projects HE 2637/16-1 and HE 2637/16-2 [3], see page 356 et seq., the focus of the transfer project was set on wide-span sandwich elements with thin facings made of carbon reinforced concrete and their practical production. An analytical model, which was developed during the project term, takes into account the bond between the single layers and can accurately represent the load-bearing and deformation behaviour of the novel sandwich elements.

As part of the work in this project, a literature review is conducted to determine the optimal thickness of the outer concrete layer in prefabricated concrete sandwich elements. These elements are used as exterior walls in buildings and consist of a load-bearing inner concrete layer, an intermediate insulation layer, and an outer concrete layer that forms the building's facade. The focus is on optimizing the sandwich wall in precast concrete by reducing the thickness of the outer skin compared to the current standard thickness of 80 mm. This could potentially reduce the weight of the elements by approximately 1.5-2 tons by reducing the thickness from 80 mm to 30 mm. This weight reduction can have a significant impact, for instance, on the crane capacity in large construction projects, allowing a crane to handle all the elements on a construction site without the need for relocation. Additionally, this optimization of the sandwich wall will result in cost savings by using less material in the elements, as well as impacting other aspects of the construction process, such as energy consumption and transportation costs. In this project, test specimens of size 400mm x 400mm have been used, and to draw comprehensive conclusions, full-scale experiments are required to account for factors such as temperature variations and shrinkage in the outer skin. In this work, compressive strength tests have also been conducted to determine the strength of the concrete used in the outer skin of the tested sandwich walls. The concrete used in the tests was a fiber-reinforced concrete from Finja, and the reinforcing mesh was a hot-dip galvanized plaster mesh. Initially, samples were cast to test the laboratory equipment and evaluate the testing methods. Subsequently, the remaining samples were cast and tested according to a predetermined schedule to ensure relevant testing conditions. Samples on the wall elements were made with both diagonal and straight anchoring and were tested under tensile load parallel to the outer layer as well as tensile load perpendicular to the outer layer. In total, 20 samples were conducted in the study, testing various combinations of anchoring systems, loads, reinforcement, and recesses. Samples 1-10 were tested with diagonal anchoring and parallel load, while samples 11-20 were tested with perpendicular anchoring and perpendicular in combination with parallel load. The samples exhibited a variation in failure types, such as grain failure in the outer layer, anchor pull-out, adhesion, and outer layer failure. The highest load values were observed in sample 2 (8.7 kN) and 6 (7.6 kN) for samples 1 to 10, and sample 12 (10.6 kN) and 15 (9 kN) for samples 11 to 20. In summary, it can be stated that the trials have yielded initially positive results regarding the practical use of a thinner outer panel for prefabricated concrete sandwich elements.