Wood-based concrete building constructions (WooCon 2)

The proposed follow-up project Wood-based concrete building constructions (WooCon 2) aims at developing a multi-layer wall and floor system composed of cement bonded wood particles and full size timber elements in composite action. The load bearing composite elements can transmit bending (e.g. floors), compression and shear (in the case of walls). The proposed technology combines concrete construction tradition with organic renewable resources as an alternative to conventional concrete or masonry, also opening opportunities to reduce carbon emissions through the increased use of wood for construction (since the carbon dioxide stocked in the wood is preserved for several decades instead of burning it). This opens new application fields for a smarter wood-based construction, with an increased volume and use of locally available wood from renewable resources. The partial substitution of energy consuming industrialized construction materials may lead to a more ecological, economic and sustainable building technology. The follow-up project focuses on three main questions w.r.t. composite elements made of timber and pourable st wood-concrete compounds (WCC) which could not be treated in the 1 project phase: Fire safety of timber-WCC composite wall elements Long-term serviceability limit state (SLS) behavior of timber-WCC composite floor slabs Development of two-span timber-WCC composite floor slab Fire safety shall be evaluated by pilot testing on a limited number of small-scale elements, supported by thermo-mechanical FE-simulations, simplified into fire design rules, and be compared to traditional configurations of timber and composite elements. nd The 2issue complements current research w.r.t. creep and shrinkage behavior of WCC. The long-term behavior of different conceptual designs of complete floor slabs is of elementary interest since SLS verifications usually govern the structural design of timber and timber-concrete composite (TCC) structures. It shall be predicted analytically, be evaluated in full-scale tests over minimum 12 months, and be compared to the long- term behavior of traditional TCC structures. rd The 3issue regroups several problems, e.g. conceptual design of structural details and elements of continuous systems in line with the needs of prefabrication/construction, suitable approaches for structural modelling, and bond behavior in the hogging moment area and its impact on SLS and ULS design of continuous timber-WCC composite systems. Analytical approaches shall be developed and verified experimentally on a small number of full-scale specimens. nd All work packages of this 2 phase are coordinated with and complemented by parallel work at ETH Zurich and College of Eng. and Arch. Fribourg on elements made of cross-laminated timber (CLT) panels in composite stnd action with adhesively bonded prefabricated WCC products. The whole project (i.e. 1 and 2 phase) will profit from appropriately targeted KTT activities, and also provides the basis for following CTI projects.

IntroductionThis research project focuses on the development of new conceptions for structural elements made of wood and wood-cement compounds. Besides a load-bearing function, these innovative construction elements also offer economic and ecological advantages, as they contribute to thermal and acoustic insulation.Project descriptionThe project deals with applications of lightweight wood-cement compounds in combination with timber elements on several levels and to a depth of proofing associated concepts: as a structural material (recipes, constitutive laws, long-term behavior, production issues) in slab and wall elements (conceptual design, connections, short- and long-term behavior, structural design methods) with additional building-physical benefits (thermal insulation, heat storage, acoustic insulation), leading to economic and ecological advantages.BackgroundToday, cement-bonded wood products are mainly used for non-structural purposes, e.g. as noise or fire protection. However, wood-cement compounds possibly in new mixtures could potentially be used in slab and wall elements and thus, contribute to load-bearing capacity. Currently, knowledge about load-bearing elements involving wood-cement compounds is too limited for practical application. In particular, data is lacking on the appropriate composition of wood-cement compounds for specific uses, on the nature of appropriate structural joints, on how whole slab and wall elements can be designed economically and on dimensioning methods to be applied.AimDifferent mixture recipes of lightweight wood-cement compounds are developed and assessed for their suitability as load-bearing material. Complemented by experiments on different types of joints for individual components, the results flow into the conceptual design of slab and wall elements. Using dimensioning methods rarely applied before in timber construction, the structural behavior of entire elements up to rupture is predicted, studied in large-scale short- and long-term load tests, and practice-oriented dimensioning approaches are derived. Based on further pilot testing and case studies, other expected advantages are assessed, e.g. thermal insulation and thermal storage capacity, fire and sound protection properties, and economic and ecological competitiveness.ResultsWood-cement compounds (WCCs) were developed as a new structural material, formulated such that they are pourable, self-compacting, lightweight, and economically viable. WCCs contribute significantly to thermal storage capacity of structural elements, and their thermal insulation properties are equivalent to other lightweight concretes (Lecca-Beton). Their mechanical properties (e.g. elastic modulus or compressive strength), however, are very low, impeding their use as a substitution material for regular lightweight concrete.In structural elements, WCCs need to collaborate with other components in composite action. Practice-oriented proposals for modelling the compressive behavior of WCC and timber were developed, derived from mechanically more sophisticated considerations. Long-term deformation properties of WCCs were identified as rather important and need to be considered in structural design. WCCs further provide excellent fire protection (e.g., for enclosed timber elements). Still, WCCs can be thermally recycled (e.g. in waste incineration), providing significant thermal energy and requiring no particular smoke treatment, nor special fire-fighting equipment. Due to important combustion ashes, WCCs shall be combined with other combustible matter.Slab elements were conceived, tested experimentally and their structural behavior verified analytically, up to rupture but also for long-term behavior. Practice-oriented recommendations for structural design and detailing were developed. Slab elements made of timber and WCC provide structural performance apt for residential, office and school buildings. They also provide significant acoustic insulation. Timber-WCC wall elements were also conceived and tested experimentally, providing sufficient performance for buildings up to six stories. Practical structural design approaches were identified, in analogy to well-known methods. Such wall elements also contribute significantly to thermal insulation of buildings skins, al-lowing to reduce (non-structural) insulation.Implications for research and practiceLoad-bearing elements containing wood-cement compounds are lighter in weight than traditional timber-concrete composite elements and offer integrated sound and fire protection as well as beneficial thermal properties. Thanks to the high share of wood, these elements are largely based on renewable resources. Moreover, they can be recycled as a combustible in heat production after dismantling, thereby contributing to the economic and ecological performance. The developed dimensioning methods could make construction with wood and wood-based products more efficient and thus, contribute to the appropriate and more competitive use of Austrian forests and Austrian wood.