The outer layer of concrete can, as with the initial model with PUR foam, be kept very thin through the reinforcement with textile fibers. The result is a lightweight element with very good insulation properties and load bearing capacities. The lightweight construction saves material and transport energy. The sandwich element is recyclable and should be particularly flame-resistant, due to the materials applied
At the Fraunhofer WKI, we had already developed a wood foam in an earlier project, which can be utilized in the same ways as classic plastic foams. The application for which the new sandwich element can be used in construction depends on the adjustable properties of the wood foam. Particularly as regards compressive strength and thermal conductivity, the wood foams must exhibit certain properties in order to ensure fulfilment of the requirements for the load-bearing capacity and insulation value with the smallest possible component thicknesses. Through previous investigations at the Fraunhofer WKI, it is known that the species of wood from which the wood foam is produced and the bulk density of the foam heavily influence the thermal conductivity. Broadly speaking, the lower the bulk density, the better the thermal conductivity. Simultaneously, the compressive strength of the foam decreases with the bulk density. An optimal compromise needs to be found here in order to achieve the widest possible range of application for the sandwich element. For this reason, we initially produce wood foams using differing wood species and bulk densities and characterize the foam properties such as strength, thermal conductivity and moisture behavior.
We subsequently develop a manufacturing process for the sandwich element. The wood foam core and the textile concrete top layer must form a solid bond in order for the positive mechanical properties of these two materials to be utilized. We hereby follow two different approaches:
- The individual constituents (wood foam and textile concrete) are produced individually and then brought together. The bonding of the two materials following preceding surface treatment has the advantage that by means of selected adhesives, which are to be identified during the project, loads in the component can be specifically deduced.
- The concrete top layer is poured around the wood foam core following preceding surface treatment. It is hereby very important to examine the resistance of the wood foam to alkaline fluids.