Structural elements made of wood-based lightweight concrete

The researchers developed various recipes for wood-based lightweight concrete and assessed them in terms of their load-bearing properties. They examined various interface connections, conceived slab and wall elements made of wood-based concrete and tested them in large-scale load tests. In addition to the load and rupture behaviour, they also evaluated their long-term properties, both experimentally and analytically. Based on this work, structural design methods were deduced for practical use. The load-bearing properties allow for the use of such slab elements in residential, office and school buildings. In addition to their static functions, slab and wall elements made of wood-based concrete were assessed in terms of their thermal insulation and storage properties, their sustainability and economic competitiveness.

Cement-bonded wood products have been used for non-load-bearing purposes for a long time, e.g. as noise or fire protection panels. In principle, structural elements made of wood-based concrete could also be used in load-bearing slab and wall elements and their non-structural properties (thermal and acoustic insulation, fire protection) could also prove useful. That said, knowledge about load-bearing elements made of wood-based concrete is still too limited for practical application to go ahead. The following questions are particularly pertinent: What is the best composition of wood-based concrete for a certain use? What connection types should be used? What conception will make slab and wall elements most economical? What dimensioning methods can be applied to these elements? What are their ecological advantages?

The project aimed to develop different lightweight concrete mixtures with wood components and to assess their suitability as load-bearing materials in composite wood/wood-based concrete elements.

Load-bearing elements from wood-based concrete are lighter in weight than traditional timber-concrete composite elements. They offer integrated noise and fire protection and act as thermal insulation and storage. Thanks to the high share of wood, these innovative building elements are largely based on renewable resources. They can be combusted once they are no longer used and therefore offer ecological advantages compared to other construction materials. The project results show that it is feasible to build with wood-based concrete and that this approach could make the Swiss wood reserves more competitive.

Recipes for wood-based lightweight concrete (WBLWC) can be defined such thata new pourable, self-compacting, lightweight and economical building material is available. Tests showed that wood-based concrete has high thermal storage capacity. Its thermal insulation properties are comparable to other lightweight concretes.

However, the mechanical properties of WBLWC, such as elastic modulus or compressive strength, are not good enough for it to be used as a substitute for usual lightweight concrete. If used in structural elements, WBLWC has to be used in composite action with other components. Its long-term deformation is significant and has to be considered in the structural design and verification.

WBLWC can also be used as screed or for fire protection, e.g. to encase timber elements. Despite its fire protection properties, it can be recycled in waste incineration, offering significant heat value. Burning WBLWC does not require special flue gas treatment or firefighter equipment. Because it creates high combustion residues, it should be combusted with other fuels and a further use of its ashes should be explored.

Wood and wood-based concrete: The building material of the future?