Optimerad sandwichvägg i prefabricerad betong

Sammanfattning: 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.