conductivity, monolithic construction elements, cast-in-site concrete, simple construction details, low cost, environmental construction elements, and easy to recycling are the main parameters that push engineers and architects to restart trying to develop the LWC quite a while ago. Recently, the virtual results of these trying can be presented through number of new buildings in Switzerland, Netherland and Germany. Table 2.2 summarized some of these recent buildings.
Table 2.2: Recent applications of lightweight concrete and infra-lightweight concrete
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Project LC [N/mm²] ρ [g/cm³]
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MPU Heavy Offshore Lifter, Rotterdam, Netherland, 2009 35/38 1.58
Schlaich Family House, Berlin, Germany, 2007 8/9 0.76
Amts- and Landgericht, Frankfurt/Oder, Germany, 2006 LB 15 1.20
Continue Table 2.2: Recent applications of lightweight concrete and infra-lightweight concrete
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Project LC [N/mm²] ρ [g/cm³]
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Gartmann Family Hause, Chur, Switzerland, 2004 8/9 1.00
German Technical Museum, Berlin, Germany, 2001 25/28 1.40
Youth Center Anna-Landsberger-Haus, Berlin, Germany, 2001 LB 15 1.20
Auditorium Maximum, TU München, München, Germany, 1994 25/28 1.60
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0 10 20 30 40 50 60 70 80 90 100
0.8 1.0 1.2 1.4 1.6 1.8 2.0
Concrete dry density [kg/dm³]
Cylinder compression strength [N/mm²]
0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0
0.8 1.0 1.2 1.4 1.6 1.8 2.0
Concrete dry density [kg/dm³]
Thermal conductivity [W/m.K] .
Figure 2.13: Spectrum curve for LWC density against Figure 2.14: Relation between lightweight concrete its compression strength [Faust T., 2003]. density and its thermal conductivity [Faust T., 2003].
Generally, for the LWC structures that are mentioned in previous literature review and even that are applied in the recent structures, it can be concluded that there were big varieties in concrete density with relative to concrete strength and concrete thermal conductivity.
Figures 2.13 & 2.14 [Faust T., 2003] show the spectrum line that controls the relation between LWC density and its compressive strength as well as its thermal conductivity respectively.
In spite of this variety for LWC and its favourable mechanical and thermal properties, nowadays, the spread of LWC is considered limited. This may be due to the lack of experimental and analytical studies in this field. Therefore, in this study, two new LWC mixtures and their conceptual and structural design aspects will be presented.
- Infra-Lightweight Concrete (ILWC) is developed with dry density under 800 kg/m³, low thermal conductivity under λ = 0.2 W/mK, and enough strength to resist bearing stress from floor slabs.
- Lightweight Concrete (LWC) is developed with minimum dry density as half as normal concrete, low thermal conductivity, and maximum compression strength comparable to strength of normal concrete and adequate to be used in construction of floor slabs and beams.
Many issues such as the development of these new materials, the structural details for the connections between ILWC walls and NC floor slabs, and the structural behaviour of LWC beams and its interaction with NC columns under dynamic loads will be presented in the following chapters.
CHAPTER 3
INFRA-LIGHTWEIGHT STRUCTURAL CONCRETE
3.1 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 concrete (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 trying 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/m³ was studied as a part of a project funded by the German Ministry of Investigation and Technology (BMFT). Weight reduction was achieved by using pre-mixed protein foams [Widmann 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 LWC have been constructed. Concrete mixes with densities above 1000 kg/m³ 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 Gartmann used expanded clay and glass as lightweight aggregates to get insulating concrete with heat conductivity 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 developed 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 Building Material Testing”, both belonging to the Institute of Structural engineering at the “Technische Universität Berlin”, started in the summer of 2006 to jointly develop ILWC with very low thermal conductivity [Schlaich M., et. al., 2007].
The concrete mix that was developed at TU-Berlin consists only of water, cement, light expanded clay as a lightweight aggregate, and an air-entraining agent. The concrete strength of this mix comes close to that of a lightweight concrete LC 8/9. Mixes which yield a closed fair-faced concrete surface, a dry density of ρdry < 800 kg/m³, and a thermal conductivity of λdry,10 < 0.2 W/mk, are consistently achieved in the concrete lab at TU-Berlin.
In Berlin, a recently built single family house with outside walls made of ILWC proves the practical value of this material. It was an interesting challenge to adjust typical structural and insulation details used for normal concrete to the properties of this material. To reduce the unavoidable cracks due to shrinkage, glass-fibre reinforcement bars were used. Glass-fibre reinforcement also solves the corrosion problem conventional steel reinforcement might have in a porous material such as infra-lightweight concrete. Further, compared to steel reinforcement fewer thermal bridges are produced, however this effect was not quantified.
Figure 3.1: Finished house with infra-lightweight concrete walls.
The experience gained so far shows that ILWC allows well insulated fair-faced concrete buildings (Fig. 3.1), and that it has the potential to play a role in the future of building with concrete. In this chapter, the properties of ILWC and the experience gained with this material will be presented. Aspects of conceptual and structural design with ILWC will be discussed in the last section.