Tailor Made Concrete Structures – Walraven & Stoelhorst (eds) © 2008Taylor & Francis Group, London, ISBN 978-0-415-47535-8 Infra-lightweight concrete M. Schlaich & M. El Zareef Institute of Structural Engineering,Technische Universität, Berlin, Germany ABSTRACT: Fair-faced concrete does not only possess high visual qualities. Monolithic concrete structures are also particularly durable, and the fact that no plastering or cladding is required leads to cost savings and makes buildings more sustainable and easier to recycle. However, due to the high thermal conductivity of normal concrete, fair-faced concrete without insulation causes prohibitive heating costs in cold countries. Infra- lightweight concrete with a dry bulk density of less than 800 kg/m 3 and the corresponding advantageous thermal properties promises to overcome this problem while maintaining the advantages. At the Technical University in Berlin such infra-lightweight concrete was developed and to prove its practicality a single family house was built with it using glass fiber bars as reinforcement. This paper describes this new concrete mix and its properties. It elaborates on the structural implications when working with infra-lightweight concrete. Design and construction of the house will also be presented. 1 INTRODUCTION Monolithic structures of fair-faced concrete not only have a high architectural potential but also are very durable. Since no plaster and cladding is needed cost is saved and recycling is made easier. Unfortunately, the heat conductivity of normal con- crete (NC) is so high that in cold countries like Germany monolithic fair-faced concrete buildings have virtually disappeared. Since the oil crisis of the seventies of the last century it is either necessary to construct exterior walls as complicated and costly double-layer structures with interior insulation that is difficult to inspect, or one contents himself with fair- faced concrete on one side only and uses conventional thermal insulation on the other side of the wall. Therefore, engineers and architects have started try- ing to develop concrete with low thermal conductivity quite a while ago.Already in the 80s of the last century, insulated “foam concrete” with a dry density below 1000 kg/m 3 was studied as a part of a project funded by the German Ministry of Investigation and Technol- ogy (BMFT). Weight reduction was achieved by using pre-mixed protein foams (Widman, H. et al. 1991). Since the only prototype building with this concrete showed unacceptable cracking due to strong shrinkage deformations the project was not continued. Recently, in Switzerland and Germany, some buildings made of monolithic fair-faced insulating lightweight concrete have been constructed. Con- crete mixes with densities above 1000 kg/m 3 were used (Faust, T. 2003, Filipaj, P. 2006 & Baus, U. 2007). Worthy of mention is a residential house in Chur, Switzerland, where the architect Patrick Gart- mann used expanded clay and glass as lightweight aggregates to get insulating concrete with heat con- ductivity of λ = 0.32 W/mK and concrete strength of LC 8/9. Even lighter concrete mixes using only expanded clay are used in shipbuilding and were devel- oped by Professor Christian Thienel (Thienel, K.C. et al. 2007) of the “Universität der Bundeswehr” in Munich. Inspired by the Swiss house and based on the Munich findings the departments of “Conceptual and Structural design” and “Construction and Build- ing Material Testing”, both belonging to the Institute of Structural engineering at the Technische Univer- sität in Berlin, started in the summer of 2006 to jointly develop infra-lightweight concrete with very low thermal conductivity (Schlaich, M. et al. 2007). Why the term infra-lightweight concrete (ILWC)? The German concrete code DIN 1045-1 defines lightweight, normal and heavy weight concretes according to their densities. Lightweight concrete is defined as concrete with dry densities in the range 800–2000 kg/m 3 . We define particularly lightweight concrete as that which has dry densities below the 800 kg/m 3 -limit as Infra-Lightweight Concrete, adding the Latin preposition “infra” which means “below”. Rather than the low weight it is the good ther- mal properties resulting from the high air void content of the concrete that are of interest here. The concrete mix that was developed at the Tech- nische Universität (TU) Berlin consists only of water, cement, light expanded clay as a lightweight aggre- gate, and an air-entraining agent. The concrete strength of this mix comes close to that of a lightweight 707
Infra-lightweight concrete
Apr 22, 2023
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