Building with Infra-lightweight Concrete: Design, Planning, Construction 9783035619263, 9783035619256

Citation preview

Building with Infra-Lightweight Concrete

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Claudia Lösch  |  Philip Rieseberg Edited by Mike Schlaich  |  Regine Leibinger

Building with ­ Infra-Lightweight ­Concrete Design | Detailing | Construction

Birkhäuser Basel

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Acknowledgments

This manual was created by numerous authors and with the assistance of many others. Special thanks go to Dr. Alexander Hückler, who contributed a large part of his research results on deflection measurements and the bonding, cracking, and deformation behavior of infra-lightweight concrete and made a significant contribution to this book with corrections and comments. Max Bauer and Prof. Matthias Schuler (Transsolar Energietechnik GmbH) wrote the chapter on dynamic simulations (Chapter 6.4). Dr. Arndt Goldack provided assistance with corrections and comments on Chapter 7. We would also like to thank the many members of staff, students, and tutors of the Chairs of Conceptual and Structural Design and of Building Construction and Design at Berlin Technical University who, with great personal commitment, were involved in simulations, designs, studies, test series, and the construction and testing of prototypes. Berlin, December 2017 Claudia Lösch, Philip Rieseberg, Mike Schlaich, Regine Leibinger

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Contents

Acknowledgments

5

1 Introduction

11

2 Theoretical Background

13

2.1

Definition and Classification of Infra-Lightweight ­Concrete

14

2.2

The Development of ­Lightweight and Infra-­Lightweight Concrete

14

2.3

Conceptual Design ­Potential of the Material

19

3 Material Technology 3.1

Composition and Bulk ­Density Classes

3.2 Properties 4 Building Typologies

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25 26 27 31

4.1

Example Design of a Building

33

4.2

Infill Building

38

4.3

Linear Buildings

43

4.4

Single-Family House

45

4.5

High-Rise Building

49

5 Key Building Construction Details

55

5.1

Wall Construction Details

58

5.2

Floor Slab Connections

60

5.3

Balconies and Cantilevers

64

5.4

Window Connections

68

5.5 Foundations

78

5.6

86

Detail of Joint between Parapet and Flat Roof

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6 Fundamentals of Design 6.1

Table of Parameters for ­Initial Design ­Considerations

92

6.2

Infra-Lightweight Concrete in the Context of the Energy Conservation Directive (EnEV)

94

6.3

Building Physics Properties

95

6.4

Dynamic Simulation-Based Investigations

104

6.5 Eco-Balance

110

6.6 Costs

112

6.7

113

Legal Background

7 Calculation Procedures for Structural ­Design 7.1

Structural Design Principles

7.2 Durability

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91

117 118 120

7.3

Ductile Building ­Component Behavior

122

7.4

Base Values for Structural Design

123

7.5

Structural Design for the ­Ultimate Limit State

126

7.6

Structural Design for the Serviceability Limit State

133

7.7

Special Considerations for the Design of Components with GRP Reinforcement

141

7.8

Bonding Behavior and ­Concrete Cover

142

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8 Practical Construction Aspects

145

8.1

Suitable Formwork

146

8.2

Surface Design

146

8.3

Production and Building with ILC

154

8.4

­ fter-Treatment Stripping Times and A

155

8.5

Surface Protection – W ­ ater-Repellent Coating

156

8.6

Concrete Cosmetics and After-Treatment

156

9 Selected Buildings

161

9.1

Single-Family House in Infra-Lightweight Concrete, Berlin

162

9.2

Betonoase, Berlin

164

9.3

Single-Family House, Aiterbach

166

9.4

Small House I, Kaiserslautern Technical University

168

10 Appendix

171

10.1 Calculation of Design Values – Examples

173

10.2 ω-tables with Design Values

182

10.3 Editors and Authors

202

10.4 Literature

203

10.5 Index of Figures

209

10.6 Index of Tables

212

10.7 Index of Keywords

213

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1 Introduction

On the Use of This Manual This manual is the result of the interdisciplinary research project, entitled Infra-lightweight Concrete in Multistory Residential Buildings (INBIG), at the Chair of Conceptual and Structural Design of Prof. Mike Schlaich and that of Building Construction and Design of Prof. Regine Leibinger and Prof. Matthias von Ballestrem at Berlin Technical University, which received funding from the Future of Building research initiative of the Federal Institute for Research on Building, Urban Affairs, and Spatial Development (BBSR). This research project at TU Berlin focuses on infra-lightweight concrete, a thermally insulating lightweight concrete, which can be used for the construction of buildings without additional layers of insulation. A monolithic material that combines load transfer and thermal insulation can be used in robust, durable, and straightforward constructions and provides a high degree of conceptual design potential. These properties make this ­material a competitive alternative in terms of conceptual ­design, fire protection, and recyclability compared with the multilayer wall constructions common today. Infra-lightweight concrete has been the subject of research and development at the Chair of Conceptual and Structural Design at TU Berlin since 2006. During the first research phase [1], basic knowledge was established for the production and processing of the material and a first building was constructed. During the second phase [2], further significant development of the original infra-lightweight concrete was achieved, new information was obtained, and the basis for various research projects was created – such as the INBIG project. The findings from research activity carried out over a period of ten years are also included in this manual. The content is based on investigations in the context of thirdparty-funded projects, doctoral theses, and student projects and dissertations. It goes without saying that research is continuing; currently work is being carried out on optimizing the composition of the material. For this reason it is advisable to search for the latest research results when designing an actual project. This manual is aimed at illustrating the constructive and ­architectural possibilities of infra-lightweight concrete and at providing detailed help in the design of buildings with an envelope consisting of this new type of material.

The spectrum of subjects reaches from the technical introduction to the composition, manufacture, and properties of the material, through to approaches to the structural design, practical application details, and processing methods, as well as the design possibilities. The manual is conceived as a reference book and is sub­ divided into ten chapters. References to other chapters, external publications, and built examples help with the search for further information. The book provides a short overview of the historical development of the material and a short list of some exemplary buildings built of infra-lightweight concrete that are worth mentioning in the context of this publication. The authors’ emphasis is not on a comprehensive historical review or the compilation of all completed buildings using thermally insulating lightweight concrete for construction; instead, their aim is to include some exemplary applications of the material. The construction details illustrated are intended as a design aid and as inspiration for conceptual and construction design. These details reflect the current state of construction technology to the best of our knowledge. The practical suitability of the material for buildings has been convincingly demonstrated in several completed projects. In spite of this, infra-lightweight concrete does not  – as of 2017 – have the benefit of general building control approval. As of that date, any projects require individual approval as a prerequisite for the use of the material. The approaches presented here can be used in the context of this procedure; however, in each individual case they should be checked, adjusted and, if necessary, modified to reflect the requirements of the respective building project. This manual is intended to promote the wider use of this useful building material and to make a contribution to the sustainable use of globally limited resources. The authors and publishers hope that the result of the multidisciplinary research presented here will encourage many readers to pursue similar courses of action.

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2 Theoretical Background

2.1 Definition and Classification of Infra-Lightweight Concrete 2.2 The Development of Lightweight and Infra-Lightweight Concrete 2.3 Conceptual Design Potential of the Material

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2  Theoretical Background

2.1 Definition and Classification of Infra-Lightweight ­Concrete

are limited, which is why industrially manufactured aggregates are important.

Infra-lightweight concrete is a constructive lightweight concrete with very low bulk density [1] that combines the load-bearing and thermally insulating functions of the building envelope in a monolithic material. In contrast to complex, multilayer wall constructions, building with infra-lightweight concrete results in straightforward, robust structures that are durable, require very little maintenance, and can therefore contribute to a sustainable use of resources. In spite of ever more strict energy conservation regulations, exposed concrete buildings involving sophisticated free-form designs can make a contribution to our building culture. Generally, different types of lightweight concrete (LC) are classified in terms of their structure, making a distinction between porous particulate and dense-structure (constructive) lightweight concrete. Porous particulate lightweight concrete types are characterized by a matrix of rock particles, which are bonded together with cement paste only at the points of contact; they are usually used for prefabricated components or building blocks [3]. By contrast, dense-structure lightweight concrete has a similar structure to that of normal concrete (NC). Its low bulk density is mainly achieved by ­using more lightweight rock particles, which can be manufactured industrially or are quarried from natural resources. Industrially manufactured aggregates include expanded clay, foam glass, and expanded slate. Natural alternatives include natural pumice stone, which does not need to be expanded – a process which does require a large amount of energy – and therefore has comparatively good properties in terms of ecology. However, natural pumice stone reserves

Infra-lightweight concrete 800 kg / m3

In addition to the dense structure and porous particulate lightweight concrete types there is also the group of porous lightweight concrete (foam concrete) and porous concrete, both of which are manufactured without coarse rock particles. The porous lightweight types of concrete use foaming agents for foaming the cement matrix, whereas porous concretes are manufactured in porous concrete works using air-entraining agents such as aluminum [4]. Infra-lightweight concrete is considered part of the group of dense-structure lightweight concretes. Owing to its low bulk density of less than 800 kg/m³, it is distinguished from the lightweight concretes defined in DIN EN 206 [5] (dry bulk densities of between 800 kg/m³ and 2,000 kg/m³). This gives rise to the prefix “ultra” (see Figure 2–1). Dense-structure lightweight concretes that have good compressive strength and low thermal conductivity and can therefore perform structural and insulating functions are referred to as insulating concretes [6]. Ultra-lightweight concrete is such an insulating concrete, which is characterized by a very good combination of compressive strength and thermal properties and, in accordance with Faust [7], is to be classified as High Performance Lightweight Aggregate Concrete (HPLWAC).

2.2 The Development of ­Lightweight and Infra-­ Lightweight Concrete Even though concrete has been used for two thousand years and modern reinforced concrete, in the last one hun-

Lightweight concrete

Normal concrete

γDR = 2,000 kg/ m3

Infrared

Heavyweight concrete 2,600 kg/ m3

Ultraviolet

[infra (Latin prefix) = beneath, under]

Figure 2-1  Classification of infra-lightweight concrete in accordance with dry bulk density ρDR [1]

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2.2  The Development of ­L ightweight and Infra-­L ightweight Concrete

dred years, has been established as the most important building material, these developments indicate that the potential of this material has by no means been exhausted. In terms of lightweight concrete, infra-lightweight concrete can meet load-bearing and thermal insulation requirements, which have arisen as a result of the energy turnaround and the discussion on sustainability and climate change. The research at Berlin Technical University has resulted in infra-­ lightweight concretes with a bulk density of less than the normal bulk density of lightweight concretes, which makes it possible to build houses with exposed concrete walls without additional thermal insulation material. Below follows a short history of lightweight concretes through to infra-lightweight concrete. For the history of concrete, please refer to the specialist literature.

Lightweight Ships Interestingly, modern lightweight concrete construction started in shipbuilding: one of the early concrete structures includes a ship, the concrete barge by Joseph Louis Lambot. In order to save on expensive steel and weight, the United States started to manufacture lightweight concrete ships during the First World War. The USS Selma, a tanker, weighed about 7,500 tons and was 425 feet long! This was based on the patented idea of Stephen J. Hayde, who managed to produce lightweight rock particles from shale in the rotary furnaces used by his company, Haydite. The USS Selma was not completed until after the war, and was then successfully used for peaceful purposes for many years. These first successes led to the US Marines producing more than 100 cargo ships of lightweight concrete during the Second World War [8].

Antiquity The best-known early lightweight concrete structure is probably the roof of the Pantheon in Rome, which was started in AD 114 by Emperor Trajan and was completed about ten years later by Hadrian. In order to reduce the weight of the spherical shell, the Romans used tuff stone as a lightweight rock particulate for their opus caementicium.

Lightweight Concrete in Building Construction The experience gained in shipbuilding led to lightweight in situ concrete being first used in the USA in the 1920s and then also worldwide in building construction. The reduction in weight of the load-bearing structure led to savings in the foundations and a reduced mass in the case of earthquakes. The first high-rise building in lightweight concrete is thought to be the Park Plaza Hotel in St. Louis dating from 1929; better known are probably the 60-story-tall towers of Marina City in Chicago. The low weight of lightweight concrete and its good resistance to frost and thawing and to frost and de-icing salt can be beneficial in bridge construction. Particularly attractive examples are the Dyckerhoff pedestrian bridge in Wies­ baden-Schierstein designed by Ulrich Finsterwalder in 1967 and Maintenance Hall V at Frankfurt Airport by Helmut Bomhard, a stressed-ribbon construction from 1972 that is covered with lightweight concrete. In spite of their low bulk density, modern lightweight concretes can have high structural strength. The recently completed widely cantilevering roofs of the tramway stops in front of Berlin Main Railway Station were built using LC45/50 concrete that only weighs 1,600 kg/m³.

Figure 2-2  Roof of the Pantheon in Rome

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2  Theoretical Background

Figure 2-3  Tramway stop at Berlin Main Railway Station (source: Hans Joosten)

Figure 2-5  Dyckerhoff bridge at Schierstein Rhine Port (source: Cengiz Dicleli)

Figure 2-4  Marina City Towers

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2.2  The Development of ­L ightweight and Infra-­L ightweight Concrete

Bridges Offshore structures

Industrial buildings, roofs, stadiums TU Kaiserslautern

Buildings

TU Berlin Oil crisis 1973

HPLWAC

Modified static resistance αHP

200 180 160 140 120 100 80 60 40 20 0 1950

1960

1970

1980

1990

2000

2010

2020

Year Figure 2-6  Historical development of the performance characteristics of lightweight concrete ([9], based on [10])

The Oil Crisis and New Lightweight Concrete

Figure 2-7  Lufthansa Maintenance Hall V (source: Yoshito Isono)

Expanding clay or glass to produce lightweight rock particles requires very high temperatures and therefore a high consumption of energy. As shown in Figure 2–6, the shock of the 1973 oil crisis and rising energy prices led to an almost twenty-year standstill in lightweight concrete construction. Naturally, lightweight concrete was, and continues to be, used in building and bridge construction owing to its low weight. Interestingly though, for some years, the idea of saving energy has once again led to lightweight concrete becoming attractive for building construction. The thermal properties of lightweight concrete were primarily rediscovered by Swiss architects, leading to the increased use of lightweight concrete in residential building. In his important book Architektonisches Potential von Dämmbeton [6], Patrick Filipaj demonstrates the diversity of modern Swiss exposed concrete construction.

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2  Theoretical Background

Figure 2-8  Single-family house in Berlin, 2007

Research on Infra-Lightweight Concrete in Berlin The thermal conductivity of lightweight concretes with dry bulk densities of over 1,000 kg/m³, as were used in Switzerland, is however too high, which means that the requirements included in the new Energy Conservation Directives cannot be met. For this reason, infra-lightweight concretes with a dry bulk density of less than 800 kg/m³ have been investigated at Berlin Technical University since 2006 [11]; these types of concrete can achieve values for thermal conductivity of significantly less than λ10°,dr = 0.2  W/(m · K). A first house was built as early as 2007 using this material [1], and in 2012 the research results of a more developed version received a Holcim Innovation Prize [12]. Nowadays, infra-lightweight concrete has been explored in theory and practice to such an extent that there are now fewer and fewer obstacles to its use in practice.

State of Research Research at TU Berlin is continuing. Third-party-funded projects include:

nn INBIG – Infra-Lightweight Concrete in Multistory Residential

Buildings, with funding from Future of Building, a project that was worked on by architects and engineers in cooperation. nn A DFG project for investigating the load-bearing and deformation behavior of infra-lightweight concrete components that are subject to bending stress. nn A subproject (C3 B4) of the C3 – Carbon Concrete Composite project supported by the Federal Ministry for Education and Research (BMBF) that investigated carbon-­ reinforced infra-lightweight concrete, and nn the MultiLC project, also supported by the BMBF, that looks at multifunctional lightweight concrete components with nonhomogeneous properties. The latter is aimed at developing building components based on infra-lightweight concrete with varying properties across the cross section and at adding other functionalities such as active insulation or photocatalytic cover layers for improving air quality. nn The ILVO research project that focuses on the manufacture of prefabricated components in infra-lightweight concrete, funded by the DBU, in which prefabricated infra-lightweight concrete (ILC) components are developed and then used in a multistory residential building of HOWOGE Wohnungsbaugesellschaft mbH.

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2.3  CONCEPTUAL DESIGN P ­ OTENTIAL OF THE MATERIAL

In addition, numerous internal research projects exist on ­various subjects. Generally speaking, there is much interest in insulating concrete, which is also why there is much research activity in this area. In the field of lightweight concrete and infra-lightweight concrete, the extensive work of Prof. Karl-Christian Thienel, Department for Construction Materials at the Bundeswehr University Munich, and the research of Prof. Wolfgang Breit in the field of construction materials at Kaiserslautern Technical University, should be emphasized. Prof. Thienel has been focusing on lightweight concrete for decades and has also significantly contributed to the development of infra-lightweight concrete for the Thalmaier single-family house in Aiterbach in 2016 (see Chapter 9.3 and [13]). During the initial work on infra-lightweight concrete at TU Berlin in 2006, Prof. Thienel, together with Prof. Hillemeier (TU Berlin), provided help and advice. Prof. Breit has developed an infra-light architectural lightweight concrete, which was used in 2012 to build the Small House I experimental building in Kaiserslautern (see Chapter 9.4 and [14]). Figure 2-9  Prototype smart material house, infra-lightweight concrete

Further development also benefits from the research as well as from the work required to obtain approval in individual cases. Such approvals have already been given for the infra-lightweight concrete used in the Thalmaier house and for the Be­ tonoase youth center in Berlin (see also Chapter 9.2).

amount of gray energy used in the production of cement, the concrete aggregates, and the lightweight rock particles in infra-lightweight concrete. Building with thermal insulation will not become less of an issue until we have clean, renewable, and cheap solar energy permanently available.

Does Infra-Lightweight Concrete Have a Future? Of course, infra-lightweight concretes cannot compete with the low thermal conductivity of non-load-bearing thermal insulation. Filipaj wrote in 2013: “For this reason, the significantly stricter thermal insulation regulations with U-values of 0.2  W/(m² · K) ) have become an almost insurmountable obstacle when trying to use insulating concrete for the envelope of buildings …” [15]. However, when we look at the building as a whole, including its floor slab, roof, and facade, and take into account alternative heating and cooling methods, or even consider innovative approaches such as the use of capillary tube mats as a form of wall heating and cooling using groundwater, then there are no limits to building with infra-lightweight concrete. Even so, the need for research continues. It is imperative to continue reducing the CO² footprint resulting from the

2.3 Conceptual Design ­Potential of the Material Infra-Lightweight Concrete – From Material to Form If we approach the architectural design of a project with a certain building material in mind rather than adopting a completely free and open attitude with regard to form, structure, and material, we have to be aware of the specific logic that comes with the specific material. Therefore when we design a building with a load-bearing and insulating envelope of infra-lightweight concrete, we have to ask ourselves how we deal with the material convincingly and appropriately, and what form would result from that.

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2  Theoretical Background

Louis Kahn is well known for having told the following story. In 1963, when talking to his students, he answered the architectural question about the interaction between building material, form, and construction principle using the example of brick masonry, as follows: “If you think of Brick, you say to Brick, ‘What do you want, Brick?’ And Brick says to you, ‘I like an arch.’ And if you say to Brick, ‘Look, arches are expensive, and I can use a concrete lintel over you. What do you think of that, Brick?’ Brick says, ‘I like an arch.’” [16] Similarly, we should also ask a new building material such as infra-lightweight concrete what it would like to be. We have to find out what form of appearance most corresponds to its inner logic. In architecture, expression and form are directly related to the material used or the building product it has been transformed into. Material and form are directly interdependent. In his article “Stoff, Form, Hylemorphismus  – Zum Verhältnis von Konstruktion und Philosophie” [17] the architectural theorist Jörg H. Gleiter describes the relationship between matter and form as described by Aristotle, who uses the term hylomorphism: “However, with our senses we can experience matter only when it is manifest in form. In form, one of the possible potentials inherent in the matter is expressed.” The building materials manifest in archaic basic forms, socalled epistemic objects. In the case of clay, the dried and later fired brick is the basic module; in steel construction it is the double-T beam, at least since Ludwig Mies van der Rohe. When we are building and designing with infra-lightweight concrete, we have to clarify what the epistemic object of the material is.

The Thick Wall as an Epistemic Object Infra-lightweight concrete is a composite material consisting of concrete and steel, similar to normal reinforced concrete, that is, a composite consisting of two base materials. However, infra-lightweight concrete amplifies the properties of reinforced concrete: the property of thermal insulation is added to the already existing ones, that is, the transfer of loads, the spanning of open spaces, and the free formability. Despite its enormous performance capability, concrete is a

heavy construction material in terms of its relative density. By contrast, insulation materials are always particularly lightweight and usually achieve their insulation effect through a high proportion of air voids. Infra-lightweight concrete combines the positive properties of a heavy material with those of a light one. It is this very combination of opposed properties that results in one of the primary characteristics of the material: unlike reinforced concrete, infra-lightweight concrete is used in large material thicknesses and volumes. It needs to be used in these volumes to develop its benefits compared to other construction materials. This leads us to the hypothesis that the thick wall turns out to be a primary architectural element, as an epistemic object that is inherent in the material. The simple, thick monolithic external wall is the basic module in the design of a building made of infra-lightweight concrete.

Simple, Monolithic, Robust “Thus, every time I had the sense of perceiving the deepest sense of the world, I was stunned above all by its simplicity.” (A. Camus [17]) The longing of many architects for simplicity and the desire for harmony between expression and construction are often driving forces in the architectural design process. It is not a new idea resulting from this to develop building materials with a higher degree of complexity that fulfill different requirements. As an example, let’s just mention the brick with its cavities, which are filled in addition with highly insulating materials, or the solid wall made of lightweight clay that has been reinforced with natural fibers. Compared with these building materials, infra-lightweight concrete appeals not only because it can be used as a building material for monolithic, smooth, and thick walls, thereby radically reducing the number of layers in the wall, but also because it lends itself to free-forming and can be surface-treated in a wide range of different ways, including even ornamentation. Owing to its high load-transfer potential and also its good resistance to bending moments, it can be used in monolithic construction, which means that even cantilevering components can be built using a single building material without additional auxiliary constructions and special connection details.

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2.3  Conceptual Design P ­ otential of the Material

In contrast to many highly adaptive high-tech building materials, infra-lightweight concrete nevertheless represents an approach to minimizing technology and to deliberate simplicity. This idea also gives rise to the hope that buildings can be put up that have low maintenance requirements and that, due to their durability and robustness, are ecologically sustainable in the long term.

The Thick Wall – Layout and Detailing So, when we design a building with external walls made of infra-lightweight concrete, our main focus is on the primary element of the thick wall. The reduction in the thickness of the external envelope – which took place during the phase of architectural modernism and resulted in a slender building element that is hardly distinguishable in plan from other internal separating walls – does not provide much help in developing an architecturally pleasing conceptual design with the thick external wall. For this reason, many authors advise architects and designers to rely on previous epochs of architecture with their thick external walls as architectural design elements, which in those days still had to be employed as a constructive necessity. In contemporary architecture with insulating concrete, Baroque architecture with its common pochés has often been cited as a reference. In this context, pochés are additional space situations that result from the variation in wall thickness. “Through porosity or as space-­ containing walls, architectural masses that function as poché may in turn contain interior spaces which remain in the background in relation to the main rooms as subsidiary chambers, ancillary rooms, cabinets, etc.” [18] Owing to its high load-bearing capacity and, at the same time, relatively good thermal insulation, infra-lightweight concrete furthermore offers the opportunity to build floor decks or roofs with low thermal conductivity using the material and to construct a house using the same material throughout. However, the thick wall also requires special detailing for adjoining elements such as windows, doors, and roof connections. It challenges us to reevaluate these interfaces with respect to their spatial effect. For example, in a thick wall the window can be arranged in a number of different ways:

Figure 2–10  San Lorenzo, Turin, Guarino Guarini (source: Architettura civile, plate 4, Torino, 1737)

“The cross sections of insulating concrete elements literally call for the insertion of additional functions, for example window openings with seating on the sides or niches for cabinets and shelves that finish flush with the wall.” [19]

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2  Theoretical Background

Figure 2–11  Private house in Leymen, Herzog & de Meuron (photo: Margherita Spillutini)

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2.3  Conceptual Design P ­ otential of the Material

The design for a residential tower block in Berlin, which received an award in a competition (see Chapter 4.5), displays some aspects of the design possibilities offered by infra-­lightweight concrete. In this case, the external shape of the building is reflected on the inside. The window opening with its deep reveal is utilized as an adaptive thermal buffer by including an additional glass pane. The material determines the shape of the building in a decisive way, and this shape is repeated analogously on the inside.

The Lightness of the “Heavy” Envelope When we think of examples of buildings in solid concrete, the concrete architecture of later work by Le Corbusier readily comes to mind (Notre-Dame-du-Haut in Ronchamp, or Sainte-Marie de la Tourette near Lyon) or the archaic-seeming buildings by Marcel Breuer. Another example of the many ways in which architectural design can benefit from the free-formability of a material are the concrete buildings of the Spanish architect Miguel Fisac with their textile appearance or the sculptural creations of the Italian architect Angelo Mangiarotti. However, we should always remember that, by definition, infra-lightweight concrete is not an element associated with heaviness. In contrast to conventional reinforced concrete, infra-lightweight concrete weighs significantly less than water. Any building made of infra-lightweight concrete, irrespective of the thickness of its walls, feels more like a lightweight building than one in solid construction. It is this duality of the material in particular – that is, the presence of heaviness and lightness at the same time – which we need to use appropriately and for which we need to find diverse architectural expressions. The architectural potential inherent in the material, and hence the range of conceptual and constructive design options, is great. We are now faced with the task of exploring its boundaries.

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3 Material Technology

3.1 Composition and Bulk Density Classes 3.2 Properties

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3  Material Technology

Lightweight concrete is classified in accordance with a number of different criteria. These include dry bulk density, compressive strength, and type of structure, among others. The capability of lightweight concrete is measured in terms of structural performance, in which strength and bulk density play a part (see [7]). Owing to its capability, infra-lightweight concrete is classed as a High Performance Lightweight Aggregate Concrete (HPLWAC [7]) and, with its dry bulk density of ≤ 800 kg/m³, does not fall within the lightweight concretes specified in Eurocode (EC) 2 [20]. In spite of its very low dry bulk density, ILC has a closed structure and therefore does not belong to the porous particulate concretes but to the dense-structure or constructive lightweight concretes (see Chapter 2.1).

3.1 Composition and Bulk ­Density Classes Infra-lightweight concrete in the composition developed at TU Berlin [2] consists of cement, water, lightweight rock particles, silica fume, plasticizer, and stabilizer. The compositions, which are based on expanded clay as lightweight rock particles, can be found in various publications (see, for example, [1, 2, 21]). The compositions are continually being developed at Berlin Technical University. For this reason, it is recommended to carry out research for improved compositions when collecting information for a new design project. At the time of writing this book, compositions are available for concretes with dry bulk densities of between 600 and 800 g/m³, referred to as ILC600 to ILC800 (Table 3-1), which have average compressive strengths of between approximately 5 and 13 MPa (Table 3-2). The bulk density classes of ILC compare with those of lightweight concrete as defined in accordance with the EC2 [20].

Figure 3–1  Components of infra-lightweight concrete (source: Alex Hückler)

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3.2 PROPERTIES 2.3  Conceptual Design P ­ otential of the Material

3.2 Properties

The most important parameters for the various ILC classes have been compiled below. The information is based on extensive test series carried out by Hückler [21] and are valid for the composition stated. Detailed data can be found in Chapter 7.

The properties described below and the findings explained in later chapters refer to the compositions listed in the doctoral thesis “Trag- und Verformungsverhalten von biegebe­ an­ spruch­ten Bauteilen aus Infraleichtbeton” (Load-bearing and deformation behavior of infra-lightweight concrete [ILC] components exposed to bending moments) by Hückler [21]. Infra-lightweight concrete ILC600

ILC650

ILC700

ILC750

ILC800

0.60

0.65

0.70

0.75

0.80

1.0

1.2

1.4

1.6

1.8

2.0

551 to 600

601 to 650

651 to 700

701 to 750

751 to 800

801 to 1,000

1,001 to 1,200

1,201 to 1,400

1,401 to 1,600

1,601 to 1,800

1,801 to 2000

Bulk density class Dry bulk density class ρdr [kg/m³]

Lightweight concrete as specified in EC2 [20]

,

Table 3–1  Bulk density classes of infra-lightweight and lightweight concrete [21]

Parameters ILC600

ILC650

ILC700

ILC750

ILC800

CEM III/A N – 32.5 LH/NA

190

225

260

296

333

Silica fume

74

72

70

68

66

Effective water

144

154

164

175

185

25; 139; 243

42; 132; 227

59; 126; 212

76; 120; 196

93; 114; 180

Plasticizer

2.86

3.03

3.19

3.36

3.52

Stabilizer

0.27

0.36

0.45

0.53

0.63

Composition [kg/m³]

Lightweight rock particles (expanded clay) w60-damp 0/2;1/4; 2/6

Experimentally determined properties (weighted averages; detailed statistical evaluation, dimensions of test specimen, and test description are documented in Hückler [21]) Fresh concrete bulk density ρfresh [kg/m³]

872

906

947

1,009

1,075

Slump flow sm [mm]

624

664

637

629

591

Air void content AV [ %]

25

25

23

21

21 800

Intended dry bulk density ρdr [kg/m³]

600

650

700

750

Achieved dry bulk density ρdr [kg/m³]

619

674

711

766

809

Mean cylinder strength filcm,cyl [MPa]

5.3

7.4

9.4

11.3

13.0

Tensile strength filctm [MPa]

0.65

0.71

0.76

0.82

0.87

Modulus of elasticity Eilcm [MPa]

2,300

2,700

3,100

3,500

3,900

Thermal conductivity λ10°, dr [W/m · K]

0.141

0.153

0.166*

0.178*

0.193

*  from linear interpolation

Table 3–2  Composition and associated properties of infra-lightweight concrete based on [21, 22]

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3  Material Technology

Consistency/Workability Infra-lightweight concrete in accordance with Table 3-2 is almost self-compacting. This means that ILC is self-leveling and that spaces, such as those between the reinforcement and the formwork, are filled; however, in contrast to common self-compacting concretes, it will not de-air itself. This would be counterproductive since the increased air void content is wanted for its thermal insulation.

to minimize the temperature gradient in the building component between core and surface, it is necessary to apply careful after-treatment (see Chapter 8.4). Another option for reducing the development of the temperature is the partial replacement of the water with ice shards, as has already been successfully practiced in the Thalmaier project in Aiterbach (see Chapter 9.3 and [13]).

Consequently, it is not necessary and not recommended to use classical compaction methods such as vibrating when installing ILC, because this would significantly change the properties of the concrete, such as its strength, raw density, and thermal conductivity. In certain cases it may be helpful to carry out compacting in specific places (for example, external vibration, poking in the corners) for optical reasons, for example in order to avoid surface marks in the concrete (see Chapter 8.3).

Temperature Development The temperature increase T in the fresh concrete during hydration depends on the cement content z, the hydration heat H of the cement, and the heat stored (product of the bulk density ρ and the specific heat capacity c) [7]. T = z ∙ H / (c ∙ ρ)

(1)

From the above we can conclude that the temperature rises more in lightweight concrete compared to normal concrete, because the bulk density ρ is lower, whereas the specific heat capacity c is of a similar order in both normal and lightweight concrete [7]. In addition, owing to the low thermal conductivity of lightweight concrete, the discharge of its hydration heat takes place more slowly. In infra-lightweight concrete too we find a stronger temperature increase owing to hydration. In order to counteract this effect, cement CEM III for ILC was selected for the formulations discussed here, because this cement produces a relatively small amount of heat. Owing to the different cement content, the various ILC formulations in Table 3-2 must be expected to have different temperature development behaviors. For example, for ILC800 in a 45 cm thick wall, temperatures of up to 82 °C were measured. It follows that in order 28

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4 Building Typologies

4.1 Example Design of a Building 4.2 Infill Building 4.3 Linear Buildings 4.4 Single-Family House 4.5 High-Rise Building

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4  Building Typologies

The objective here is to illustrate the basic principles in the conceptual and constructive design of a building using infra-lightweight concrete. Basic design options will be presented, including initial information about some basic parameters such as wall thicknesses, proportion of window area, opening widths, etc. The objective is not to present concrete design patterns for dealing with infra-lightweight concrete as a building material. The sketches deliberately omit conceptual design details  – such as plinth stories, roof details, or surface finishes – in order to give readers and users a maximum of space for the development of their own aesthetic and technical approaches. So as to keep the scope manageable, we will be mainly considering multistory apartment buildings, since these are particularly suitable for the application of infra-lightweight concrete owing to their demanding requirements in terms of energy and structural design. However, we do not wish to convey the impression that infra-lightweight concrete is only suitable for housing. Infra-lightweight concrete also offers many advantages and opportunities for application in nonresidential buildings, which should be explored in the future.

Figure 4-1  Freestanding apartment building

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4.1  EXAMPLE DESIGN OF A BUILDING

4.1 Example Design of a Building

Example of Initial Questions to Be Asked When ­Designing a Freestanding, Multistory Apartment Building in Infra-Lightweight Concrete From the point of view of the designer, some basic information is required in response to the questions below in order to approach the design of a building in infra-lightweight concrete: nn What is the basic structure of the building? Which ele-

ments are made of infra-lightweight concrete and which of other conventional building materials? nn How high can I build, and what combination of strength and wall thickness is needed for the load-bearing external walls? nn What is the combination of bulk density and wall thickness of infra-lightweight concrete I need to meet the energy conservation requirements? nn What types of openings are possible? What is the proportion of openings? nn Will I build using in situ concrete, a hybrid construction method, or only prefabricated components? The design of the basic structure of a building (freestanding apartment building) is shown as an example in order to provide the parameters for the conceptual and structural outline design of a sample building. The parameters are summarized in Chapter 6.1 in table form (see Table 6-1 for initial sizing). Figure 4-2  Example of the structure of a building in infra-lightweight concrete: nnExternal envelope in the form of a load-bearing monolithic wall in infra-lightweight concrete (black) nnIntermediate floors in concrete, solid timber, or similar supported on the load-bearing external wall nnLoad-bearing internal core of normal concrete (see Figure 4-4) nnRoof made of lightweight concrete with insulation and weatherproofing layer nnCellar built of conventional building materials (here, unheated cellar of waterproof prefabricated components)

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4  Building Typologies

ILC800 7 full stories

ILC750 6 full stories

ILC700 4 full stories

ILC600 2 full stories

Figure 4-3  Maximum building heights achievable with different ILC strength classes

Height of Building, Thickness and Strength of Wall

Energy Conservation Requirements

The building chosen here as an example is a freestanding apartment building measuring 14.2 m × 20.8 m with variations in building height. The building consists of a load-bearing external building envelope of infra-lightweight concrete with a consistent wall thickness of 60 cm. The openings at lower floor level have larger spans.

The thermal transmittance (U-value) of the respective wall is calculated from the bulk density in combination with the wall thickness necessary to fulfill the relevant thermal insulation requirements.

Depending on the number of floors, it is possible to use different strength classes of ILC.

As a rule, the key criterion for the wall thickness is the thermal insulation requirement; therefore, the wall thickness required is usually determined on the basis of the calculation of the necessary U-values (see Details 5-1 and 5-2 of wall thicknesses and U-values).

Using concrete with a bulk density of 800 kg/m³, buildings can be designed with up to eight full stories without recourse to additional structural elements.

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4.1  EXAMPLE DESIGN OF A BUILDING

Scale 1:200

Figure 4-4  Design of freestanding apartment building, standard floor plan

Possible Dimensions of Openings

Thermal Insulation in Summer

With an opening width of approximately 1.6 m, the openings shown in Figure 4-4 are quite manageable from a structural point of view. The only really large openings on the first floor are those with a clear opening width of 4.90 m. As a general principle, openings should be limited to a clear span of 3.0 m for both technical and economic reasons.

The thickness of the walls offers the opportunity to utilize the walls for thermal insulation in summer. Windows can be placed in the openings such that the reveal is used as a natural shading element. For windows facing south, the glass panes should preferably be fitted flush with the inside surface of the wall; windows facing north, east, and west can be installed centrally. It is currently not recommended to install windows flush with the outside of the walls because it is possible for the inner reveals to suffer from ­excessive moisture (see Details 5-7 to 5-11 on window connections).

Larger window openings would be very possible; however, this would make construction more complex and increase costs.

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4  Building Typologies

Figure 4-5  Detail of ILC balcony connection with back-anchoring

Balconies/Cantilevers Balconies can be connected using conventional systems with decoupling devices and with back-anchoring to the floor slab. However, it is also possible to design the balconies as projecting infra-lightweight concrete elements. This removes the necessity of fitting additional thermal decoupling devices. It also means that the technical complexity of the building and building process is reduced (see Detail 5-6).

The load-bearing and deformation behavior of infra-lightweight concrete components subjected to bending moments was investigated at TU Berlin. The results demonstrated that the material can be used when exposed to bending moments and is also suitable for components such as balconies and canopies. The prototype of a projecting infra-lightweight concrete balcony slab (gray) and an inner floor slab of normal concrete (light gray) shown in Figure 4-6 illustrates this construction principle. Load tests have already been carried out to prove the functionality of this construction.

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4.1   EXAMPLE Example DESIGN Design OF of A a BUILDING Building

Figure 4-6  Load test of a balcony prototype using a slab bending machine

In Situ Concrete or Prefabricated Component Generally speaking, both in situ concrete and prefabricated component constructions are possible with infra-lightweight concrete. The choice depends on design considerations (in prefabricated component construction joints are unavoidable) as well as other factors, such as the site logistics and the benefits of prefabrication. At this stage, the use of infra-lightweight concrete in prefabricated components has not been researched extensively. However, research projects on this subject are in the pipeline.

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4  Building Typologies

4.2 Infill Building

Building volumes Position of stairwells

Joist layout Also optional position of main walls

Optional position of corridors

Figure 4-7  Design of infill building using in situ concrete, standard floor plan

The classical inner-city gap between buildings with two sides of the external envelope exposed to the outside, that is, facing the street and the rear, and two thermally neutral side walls (which do not have to be taken into account in the design of the envelope) is a type of building that is predestined for innovative building and insulation materials. In this case, the proportion of wall surface in relation to the overall envelope of the building is relatively small; also, these buildings are usually treated preferentially in terms of thermal calculations. Furthermore, the favorable ratio of envelope surface to building volume means that the global impact of thermal bridges on the building is reduced. Both preliminary studies for an infill building using infra-lightweight concrete presented here are initially based on the classical construction principle used for Berlin tenements. These buildings are usually 12 to 13 m deep.

Loads are mainly transferred via the two load-bearing external facades (facing the street and facing the yard) and a load-bearing spine wall. The span of the floors from the spine wall to the external wall is approximately 6 m. Both buildings shown here are very similar in the design of the north facade facing the street. They appear like a straightforward urban facade with individual windows, without any other particular details of interest. The design of the south facade facing the yard was more elaborate. Here, the subject of shading the large window areas played an important role, as did the general design and construction considerations (smaller windows facing north, larger windows facing south).

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  Example Design 4.2  INFILL of a BUILDING Building

Scale 1:200 Figure 4-8  Design of infill building using prefabricated components, standard floor plan

Scale 1:200 Figure 4-9  Floor plan of tenement in Leinestrasse around 1910 [23]

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4  Building Typologies

Figure 4-10  Rendering of infill building in in situ concrete construction

Figure 4-11  Prototype of a wall section with ILC balcony without back-anchoring

The Facade in In Situ Concrete Construction – ­Potential for Self-Supporting Free-Form Applications

balcony constructions that is appropriate for the material. In spite of the projecting building elements, this design still ­allows for a monolithic wall construction (see also Chapter 6.4.3, Thermal Bridge Simulation).

Infra-lightweight concrete offers the opportunity to produce facades using the same material throughout. This means that elements such as balconies or oriels do not have to be added to the facade, but instead can be developed out of the facade itself. Formally, this can be achieved in a number of different ways. In the example shown here, the forces are transferred directly into the load-bearing wall via arch-like canopies. This means that the floor slab is no longer used for back-anchoring the projecting balcony slab. Rather, the facade becomes a sculptural component, and recesses and projections are inherent parts of the construction (see ­Detail 5-6).

A facade of this design is probably more convincing as an in situ concrete construction than as a prefabricated component construction, because in the latter it is not possible to avoid the joints between the elements. Owing to the large wall cross sections needed when building with infra-lightweight concrete, large quantities of concrete are required, which no doubt is a disadvantage on inner-city construction sites with complicated site logistics. Here again, an infill building has a clear advantage compared to a freestanding building owing to the lower proportion of external envelope.

Of course there will still be a thermal bridge, which cannot be avoided at points where the cross section of the building component is reduced in size. The version shown here illustrates an alternative to conventional thermally decoupled 40

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4.2  INFILL BUILDING

Figure 4-12  Rendering of infill building in prefabricated element construction

Prefabricated Element Facades – Potential for ­Applications in New Building and Refurbishment­ In the directly adjoining infill building in Figure 4-12, a very different design principle was used for the design of the south-facing facade compared to Figure 4-10. This is determined by a system of identical loggia modules. The building components are delivered prefabricated and are manufactured of infra-lightweight concrete throughout. In contrast to a balcony, this loggia can be used as such or as an interior space that has the benefit of insulation all round. This additional functionality makes the facade a space element in its own right. This principle of a facade consisting of prefabricated space elements can be applied in new building as well as in refurbishment. In a new building the elements would also contribute to the load transfer from the floor slabs of the building. In a refurbishment situation, the modules can be placed in front of the building as an additional facade layer. In that case, this

facade layer provides an energy upgrade to the existing building envelope, as well as an extension of the space in the apartments. In the 2016 refurbishment project in the Quartier du Grand Parc, Bordeaux, by architectural practice Lacaton & Vassal, an additional functional layer is created, which can be erected on one side in front of the building or even on two sides. Standardized apartment buildings with their serial construction logic involving many identical floor plans seem to be particularly suited to this situation. When using infra-lightweight concrete elements, the additional space created can be used as a thermal buffer zone and also fulfills the same requirements as those for normal interior space. This construction method appears particularly suited to climate zones with exacting requirements ­regarding the building insulation.

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4  Building Typologies

Figure 4-13  Schematic of the Quartier du Grand Parc, Bordeaux (source: Anne Lacaton & Jean Philippe Vassal; photo: Frédéric Druot, Christophe Hutin)

Figure 4-14  Subsequently added loggias at the Quartier du Grand Parc, Bordeaux (source: Anne Lacaton & Jean Philippe Vassal; photo: Philippe Ruault)

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4.3  Linear Buildings

4.3 Linear Buildings

The example shown here, a linear development at Kracauerplatz, is located on a site along the heavily trafficked east– west connection of Berlin’s S-Bahn. The north elevation of the building forms a kind of attenuation wall facing the existing railway line, whereas the open south side faces the urban square. In order to do justice to the specific urban location, the rear facade of the building consists of an almost completely closed infra-lightweight concrete construction and the facade facing south consists of large open areas constructed in timber and glass with continuous shading balconies. In this example, the material’s sound insulation value based on the mass per area is to be used to good advantage (see Chapter 6.3.8). At the same time, this approximately 60 m long in situ concrete wall was used to investigate the theoretical effects of creep and shrinkage of the material (see Chapters 7.4.4 and 7.6.4).

Figure 4-15  Site plan with linear building using in situ concrete construction

Since the beginning of architectural modernism at the latest, long rows of linear buildings have become a common building typology in the urban housing of the twentieth and twenty-­ first centuries. Infra-lightweight concrete is a material that can also be used for this typology in a number of different ways.

The rear wall of the building facing north is used for a zone in which secondary rooms are located. The building has a clear orientation, with a more public part facing the city and a more private zone at the rear. This includes toilets, kitchens, work rooms, and also some bedrooms. The wall varies in its thickness and, in some places, has small pockets (pochés), which can be used to integrate cabinets or even small functional units.

The example here shows an application option for this typology that is based on the specific urban situation as well as on the combination with other building materials, such as the use of timber for the floor construction.

Figure 4-16  Design of linear building using in situ concrete construction, standard floor plan

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4  Building Typologies

Scale 1:200

Scale 1:500

Figure 4-17  Rendering of linear building in in situ concrete construction

Scale 1:500

External wall in ILC 60 cm

Load-bearing structural element Concrete/steel/masonry

Downstand beams Floor joists

Figure 4-18  Construction principle of linear building using in situ concrete construction

The small openings in the rear wall (see Figure 4-17) m ­ easure 65 cm × 65 cm and are spread across the entire wall surface in an irregular pattern. Shuttering is carried out with standard formwork panels measuring 2.5 m × 2.5 m. This rigid formwork pattern fashions the guiding motif for the rear facade. The floors in the building are constructed using timber joists laid perpendicular to the rear wall (see Figure 4-18). These joists penetrate the south facade of the building, thereby

forming the base for the meandering balconies along the city square. So here we also see a combination of infra-lightweight concrete with timber construction. It is therefore necessary to provide structural calculations for the connection between the timber joists and the load-bearing ILC wall, as well as to prove the suitability of the material in the chosen configuration in terms of building physics.

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Single-Family HOUSE House 4.4  SINGLE-FAMILY

4.4 Single-Family House

Figure 4-19  Rendering of design for single-family house

To date, the freestanding residence is the type of building in which infra-lightweight concrete or other insulating concretes have been used most. As a rule, the reason for this was the lower load-bearing capacity of the material in early formulations of the time. Also, the proportional risk relating to the cost of building of a single-family house is of course significantly lower, which means that motivated individuals were able to implement such ambitious individual projects. In terms of load-bearing capability, infra-lightweight concrete does not present any technical problems when applied to the construction of a single-family house. As before, this type of building lends itself to various design solutions using infra-lightweight concrete. In view of the fact that, in a single-­ family house in particular, the wall thicknesses can be varied, surfaces differentiated, and connection details designed more radically, we can conclude that the scope for design with this material has not yet been fully exhausted in this type of building. The design shown here is intended to illustrate one of the key design themes when building with the “primary element of the material,” that is, the architectural element of the thick wall (see Chapter 2.3).

The many completed buildings, some of which are introduced at the end of this publication, adequately demonstrate the design potential of a monolithic material for this type of building. In this example, the facades shown and the overall external appearance of the building are of secondary importance and are only shown for better understanding. In our discussion below, the main focus is on the floor plan of the building.

The Inside Face of the External Wall In contrast to multistory apartment buildings, which tend to be designed with generic, economically optimized solutions for apartment floor plans, the single-family house offers the opportunity to find specific space solutions that meet the needs of individual users. At the same time, in this type of project there is less pressure to find the most economic and efficient solutions compared to collective housing projects. The wall, with its extra thickness, is not subject to the same economic restrictions, and can therefore be sculpted more freely.

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4  Building Typologies

Scale 1:200 Figure 4-20  Rendering of single-family house, floor plans

This means that we can focus on the architectural subject of designing spaces enclosed by thick walls, including projections, niches, or pochés (pockets). As part of this process, the thick wall is no longer just a component designed to meet technical requirements (those of structure and building physics) but becomes a key conceptual design element. This goes beyond trying to produce perfect exposed concrete surfaces inside and out. Beyond the aesthetics of a minimalist building with exposed concrete surfaces all round, the scope of design of insulating concrete has not as yet been particularly well explored (see also Chapter 8.2). We conclude that the wall can be utilized in many different ways. Window niches can accommodate seats; walls have niches for cabinets and fitted furniture; the wall can be strictly orthogonal, smooth, and straight, but it can also be designed in concave and other free shapes. Even the horizontal surfaces, such as the roof and floor, can become part of the interior design concept.

Large Spans and Cantilevers When studying examples of houses built with insulating concrete, it is apparent that architects like to transfer the technical possibilities of applying the large spans and cantilevers common in reinforced concrete buildings to buildings made of insulating concrete. We need to stress at this point that although it is possible to achieve spans of certain dimensions with both infra-lightweight concrete and insulating concrete, these materials soon reach their limits when the spans become too wide. It is possible to cope with larger spans as well, for example by including more reinforcement or integrating steel beams, but these additions are costly, may reduce the insulating properties of the construction and therefore may not comply with the principles of material-­ appropriate building.

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4.4  Single-Family House

Figure 4-21  Interior of the Birg mich Cilli project, Peter Haimerl (photo: Edward Beierle)

However, it is not intended here to query the rationale of designing a building that goes beyond the inherent technical feasibility of its materials. In fact, such design approaches seem to be a natural fit with infra-lightweight concrete, a material that lends itself to free sculptural forms. 47

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4  Building Typologies

Figure 4-22  Well-designed, technically sophisticated example of a building in insulating concrete, new construction of the Meisterhäuser in Dessau (Bruno, Fioretti, Marquez Architects; photo: Christoph Rokitta)

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HIGH-RISE Building BUILDING 4.5  High-Rise

4.5 High-Rise Building

In accordance with the findings of current research, infra-lightweight concrete can be used as a load-bearing material for up to a maximum of about seven to ten stories, depending on the design and structural system. This raises the question as to whether, in future, high-rise buildings in infra-lightweight concrete may be possible. In 2014 an ideas competition for housing fit for the future was organized in Berlin under the name Urban Living Competition. The high-rise building at Karl-Marx-Allee, which was designed by Barkow Leibinger Architects and schlaich bergermann partner, won one of the first prizes in the competition. This scheme is of interest to the INBIG project, because in the design the material is used far beyond its inherent limits and its possible applications for high-rise buildings with monolithic facade structures are demonstrated.

Design Concept The curved load-bearing external wall construction of the building is based on a single wall type with several curvatures that is deployed repeatedly, thereby forming the monolithic exterior envelope of the building. The wall components are separated by story-high window areas. Balconies and exterior areas are created in the spaces left by the curvature of the facade elements.

Figure 4-23  Competition entry, Urban Living Competition, Berlin

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4  Building Typologies

Scale 1:200 Figure 4-24  Design of high-rise building, standard floor plan

The shape of the facade is also apparent in the interior and determines to a large degree the atmosphere of the internal spaces. By exposing the structure of the inside wall, the material of the envelope presents itself differently to the outside.

Structural Concept In view of the fact that the load-bearing capability of ILC on its own is not sufficient for the number of stories in this project, reinforcement bars known as pressure bars are inserted in the center of the cross section, which will transfer the bulk of the load. In this case, the surrounding infra-lightweight concrete does not so much transfer vertical loads, but rather has the function of preventing the bars from buckling by adding additional stiffness. A separate research project has been planned to investigate this structural concept involving what have been called “Stabwände” (bar walls).

Figure 4-25  Prototyp smart material house, infra-lightweight concrete

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4.5  High-Rise Building

Figure 4-26  Construction principle of reinforcement bars placed in infra-lightweight concrete (bar walls)

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4  Building Typologies

Figure 4-27  Detail of walk-in loggia window

Energy Performance – Consideration of Proportion of Window Area While the project was being developed, the EnEV calculations were carried out in parallel; this soon revealed that, in terms of heat loss from the envelope of the building, the solid walls with a thickness of 60 cm had less impact on the overall outcome than in other forms of building. Instead, relatively speaking, the larger energy losses occurred through transparent building elements. Although a case can be made for a window area proportion of approximately 35 percent, in this case, that is, a freestanding high-rise block, the effect is particularly pronounced. A common solution in such a case is to reduce the proportion of window area, which would

have fairly drastic consequences for the appearance of the facade. Instead the designers tried to find a new solution that does justice to the thick, solid ILC wall and makes the most of its potential. The selected solution was the installation of a back-ventilated triple glazing system that creates space for a walk-in loggia. The system utilizes the thickness of the wall and creates a usable, variable intermediate space, which is closed in winter. At that time this intermediate space acts as an additional thermal buffer that significantly enhances the efficiency of the glazing. In summer however, either the external single glazing or the triple glazing on the inside face of the wall is used to close off the interior space.

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5 Key Building Construction Details

5.1 Wall Construction Details 5.2 Floor Slab Connections 5.3 Balconies and Cantilevers 5.4 Window Connections 5.5 Foundations 5.6 Detail of Joint between Parapet and Flat Roof

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The often cited quote “God is in the details” has frequently been credited to the architect Mies van der Rohe, though he is likely to have borrowed it from the art historian Aby Warburg. Mies van der Rohe seizes on the statement in the sense of an architectural principle that is effective between the overall appearance of a building and its constituent individual elements. Every detail of a construction reflects the spirit of the overall building. During the design process, the architect or designer always faces the same seemingly banal question: How do I actually do that in detail? The examples presented here are intended to provide basic answers to that question. An attempt is made to reflect the basic simplicity of a building made of infra-lightweight concrete. These details reflect the current state of construction technology to the best of our knowledge.

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5  Key Building Construction Details

5.1 Wall Construction Details

ETICS, standard U = 0.27 W/(m² · K)

Curtain wall facade U = 0.29 W/(m² · K)

Poroton S10 U = 0.26 W/(m² · K)

Scale 1:20

Infra-lightweight concrete ILC600 U = 0.30 W/(m² · K) (λ10°,dr) U = 0.34 W/(m² · K)

Infra-lightweight concrete ILC800 U = 0.36 W/(m² · K) (λ10°,dr) U = 0.41 W/(m² · K)

(λ: rated value)

(λ: rated value)

Detail 5-1  Comparison of different wall constructions in accordance with EnEV 2016 (external walls with an average thermal transmittance of U = 0.28 W/m² · K)

Comparison of different wall constructions in accordance with EnEV 2016 (external walls with an average thermal transmittance of U = 0.28 W/m² · K) Whereas in Germany no fixed requirements exist regarding the thermal resistance of individual building components because the transmission heat loss H'T relating to the entire heat-transferring envelope surface is considered instead, specific values must be achieved in other countries. In those cases, the necessary U-value can only be achieved with the thickness of the external wall.

In Germany it is possible to compensate for any inadequacy in the thickness of a building component with other compo-

nents (such as windows, roof, foundation slab, exposed parts of floor slabs, etc.). In the assessment of ILC, the rated value for thermal conductivity (λrv) was chosen as the parameter. This is approximately 20 percent above the measured value of the thermal conductivity (λ10°,dr) of ILC at 10 °C in dry condition. Note: Where complex building components contain a high proportion of reinforcement, the reinforcement may have to be included in the calculation of the U-value of the external wall.

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5.1  WALL5.1  CONSTRUCTION DETAILS High-Rise Building

ETICS, standard U = 0.21 W/(m² · K)

Curtain wall facade U = 0.21 W/(m² · K)

Poroton S10 U = 0.22 W/(m² · K)

Scale 1:20

Infra-lightweight concrete ILC600 U = 0.27 W/(m² · K) (λ10°,dr) U = 0.30 W/(m² · K)

Infra-lightweight concrete ILC800 U = 0.31 W/(m² · K) (λ10°,dr) U = 0.35 W/(m² · K)

(λ: rated value)

(λ: rated value)

Detail 5-2  Comparison of different wall constructions in accordance with EnEV 2016 less 20 percent (external walls with an average thermal transmittance of U = 0.21 W/m² · K)

Comparison of different wall constructions in accordance with EnEV 2016 less 20 percent (external walls with an average thermal transmittance of U = 0.21 W/m² · K) It is likely that, with the future introduction of the new Building Energy Act, the requirements relating to the building envelope will be made more demanding. The examples in the diagram show the effects of an approximately 20 percent change which, for the external wall, would mean an average thermal transmittance of U = 0.21 W/m² · K.

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5  Key Building Construction Details

5.2 Floor Slab Connections

Scale 1:10

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5.2  Floor FLOOR Slab SLAB Connections CONNECTIONS

Detail 5-3  Connection of a normal concrete floor slab with a load-bearing wall in infra-lightweight concrete (ILC), with the face of the slab insulated 1 External wall: ILC, 50–60 cm Reinforcement, corrosion-proof 2 Floor slab: normal concrete, 2,400 kg/m³ 3 Bearing: expanded rubber pad 4 Face insulation to reduce the thermal bridge effect 5 Formwork 6 Floor construction: – Loose layer of expanded clay (installations) –  Impact sound insulation –  Screed (underfloor heating) –  Floor finish

Standard section, floor slab bearing Alternative to continuous bearing: bearing pockets

Connection of a normal concrete floor slab with a load-­ bearing wall in infra-lightweight concrete (ILC), with the face of the slab insulated In principle it is possible to achieve a rigid connection; however, a flexible soft connection as used in a connection with a brick wall is normally preferred. The face of the floor slab is fitted with additional insulation in order to reduce the inevitable thermal bridge. In the detailed thermal bridge calculation this insulation reduces the effect of thermal bridges on the external envelope.

Optionally it is possible to rest the floor slab in bearing pockets with a length of about 0.8 to 1.0 m, for example. These pockets are used partly in an effort to reduce thermal bridging and partly to create areas for the direct vertical load transfer. In order to reduce the risk of spalling in the area of the bearing, a strip of expanded rubber is inserted in the formwork. The casting joint is located at the lower edge of the adjoining floor slab. To reduce the risk of edge breakages it is possible to insert an added horizontal arris rail.

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5  Key Building Construction Details

4

5

Scale 1:10

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5.1  5.2  Floor FLOOR Slab SLAB Connections CONNECTIONS

Detail 5-4  Connection of a normal concrete floor slab with a load-bearing wall in infra-lightweight concrete (ILC), without insulation on the face of the slab 1 External wall: ILC, 50–60 cm Reinforcement, corrosion-proof 2 Floor slab: normal concrete, 2,400 kg/m³ 3 Bearing: expanded rubber pad 4 Formwork 5 Floor construction: – Loose layer of expanded clay (installations) – Impact sound insulation – Screed (underfloor heating) – Floor finish

Standard section, floor slab bearing Alternative to continuous bearing: bearing pockets

Connection of a normal concrete floor slab with a load-­ bearing wall in infra-lightweight concrete (ILC), without insulation on the face of the slab In principle it is possible to achieve a rigid connection; however, a flexible soft connection as used in a connection with a brick wall is normally preferred. The thermal bridge created at the face of the floor slab due to the geometric reduction in the thickness of the material is not fitted with additional insulation. From a building physics point of view, this

detail is possible. In accordance with the calculations, there is no formation of condensate even though the influence of the thermal bridge is more pronounced than in the insulated version. As shown in the detail with the insulation applied to the face of the slab, it is possible to build the floor slab with bearing pockets (see Detail 5-3).

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5  Key Building Construction Details

5.3 Balconies and Cantilevers

Scale 1:10

Cantilevering balcony slab (prefabricated ILC component) with back-anchoring to the floor slab and an external wall of infra-lightweight concrete The balcony has been back-anchored to the reinforced concrete floor slab over its entire length. This construction is similar to the system of back-anchoring with thermal separation, except that here no insulating element is inserted but rather the entire balcony slab functions as an insulating ­element.

The balcony slab is shown with a decreasing thickness ­towards the edge; this is not a structural requirement, but results in a saving of material and in a narrower front face of the balcony edge.

The balcony can be prefabricated and then fitted on the construction site. Because of the low weight of ILC, it is possible to transport and fit very large elements. However, it is important to consider the differential expansion of the balcony slab and the floor slab when there are big differences between the outside and inside temperatures; this should be accommodated with appropriate expansion joints in the balcony slabs. In order to meet the requirements of the directive on the sealing of flat roofs [24, 25], the balcony is finished with concrete slabs placed on gravel and a sealing layer. Owing to the high porosity of the material it is recommended not to use infra-lightweight concrete balcony slabs without an additional sealing layer.

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5.1  Floor Slab 5.3  BALCONIES ANDConnections CANTILEVERS

Detail 5-5  Cantilevering balcony slab (prefabricated ILC component) with back-anchoring to the floor slab and an external wall of infra-lightweight concrete 1 Balcony slab: ILC800, 14–25 cm Reinforcement: glass-fiber, ­corrosion-proof 2 External wall: ILC, 50–60 cm Reinforcement, corrosion-proof 3 Floor slab: normal concrete, 2,400 kg/m³ Reinforcement: steel bar 4 Continuous reinforcement, ­corrosion-proof 5 Terrace construction: – Sealing layer – Liquid membrane – Gravel bed – Concrete slab 6 Insulation wedge 7 Windows: wood windows with triple glazing 8 Edge insulation strip 9 Floor construction, interior: – Loose layer of expanded clay – Impact sound insulation – Screed (underfloor heating) – Floor finish 10 Bearing: expanded rubber pad

Scale 1:20

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5  Key Building Construction Details

Scale 1:10

Cantilevering balcony slab (in situ ILC) without back-­ anchoring to the floor slab, with an external wall of ­infra-lightweight concrete The balcony is not back-anchored to the reinforced concrete floor slab but has been formed as an independent building element from the plane of the wall, in the shape of a console.

The balcony slab is shown with a decreasing thickness toward the edge; here too, this is not a structural requirement, but results in a saving of material and in a narrower front face

of the balcony edge. In this construction detail the balcony is seen as part of the external wall rather than as a floor slab element. Therefore the use of prefabricated balcony components is not an obvious choice in this version (see Chapter  4.2 Infill Building, The Facade in In Situ Concrete ­Construction  – P ­ otential for Self-Supporting Free-Form Applications). In this detail again, the balcony is finished with concrete slabs placed on gravel and a sealing layer (see Detail 5-5).

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5.3  Balconies and Cantilevers

Detail 5-6  Cantilevering balcony slab (in situ ILC) without back-anchoring to the floor slab, with an external wall of infra-lightweight concrete 1 Balcony slab: ILC800 Reinforcement: glass-fiber, ­corrosion-proof 2 Floor slab: normal concrete, 2,400 kg/m³ Reinforcement: steel bar 3 Terrace construction: – Sealing layer – Liquid membrane – Gravel bed – Concrete slab 4 Insulation wedge 5 Windows: wood windows with triple glazing 6 Edge insulation strip 7 Floor construction, interior: – Loose layer of expanded clay – Impact sound insulation – Screed (underfloor heating) – Floor finish 8 Bearing: expanded rubber pad

Scale 1:20

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5  Key Building Construction Details

5.4 Window Connections

Scale 1:20

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5.3  Balconies 5.4  WINDOW andCONNECTIONS Cantilevers

Detail 5-7  Window placed centrally, with window rabbet and metal windowsill dressing 1 External wall: ILC, 50–60 cm Reinforcement, corrosion-proof 2 Windows: wood windows with triple glazing 3 Slanted metal dressing (zinc) 4 Windowsill inside: solid wood

Window placed centrally, with window rabbet and metal windowsill dressing The diagram shows a window fitted centrally to the wall including a typical 6 to 8 cm wide window rabbet. The window rabbet helps to reduce the thermal bridging effect in the window reveal so that it is possible to omit additional insulation.

In order to avoid additional shuttering costs and long-term building damage, the inside windowsill is fitted with a conventional window board. On the outside, metal dressing is applied to the sloping sill surface.

Scale 1:10

It is also possible to form the lintel over the window with a slight angle in order to ensure that any water will drain off to the outside at the top of the window. 69

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5  Key Building Construction Details

Scale 1:20

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5.4  Window Connections

Detail 5-8  Window placed centrally, without window rabbet, with stone sill element 1 External wall: ILC, 50–60 cm Reinforcement, corrosion-proof 2 Windows: wood windows with triple glazing 3 Solid sill element (waterproof fiber cement) 4 Lining of inside reveal: – Solid wood –R  eveal insulation board, 20 mm, thermal conductivity group 020, fully bonded

Window placed centrally, without window rabbet, with stone sill element The diagram shows a window fitted centrally to the wall without a window rabbet. In order to reduce the risk of condensate forming in the area of the inner window reveal, the window should be fitted with an insulated internal reveal lining all round. The insulation should be 20 to 25 mm thick. Depending on the insulation material, an additional vapor barrier should be used.

On the outside, a sloping stone sill element can be used as  an alternative to the metal windowsill dressing (see ­Detail 5-7). Additional sealing can be applied beneath the sloping stone sill element.

Scale 1:10

As an alternative to the sloping detail of the window lintel (see Detail 5-7), the lintel is cast with a drip, which is achieved by inserting an arris rail in the formwork. 71

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5  Key Building Construction Details

Scale 1:20

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5.4  Window Connections

Detail 5-9  Window placed on the inside face, with window rabbet and stone sill element 1 External wall: ILC, 50–60 cm Reinforcement, corrosion-proof 2 Windows: wood windows with triple glazing 3 Solid sill element (waterproof fiber cement) 4 Window frame inside: wood with reveal insulation board, 30 mm, thermal conductivity group 020, fully bonded

Scale 1:10

Window placed on the inside face, with window rabbet and stone sill element The window is fitted flush with the inside face of the wall. In order to reduce the risk of condensate forming in the area of the window reveal, the window should be fitted with an insulated internal frame all round. Various details are possible for the design of the external sill and lintel (see Details 5-7 and 5-8).

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5  Key Building Construction Details

Scale 1:20

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5.4  Window Connections

Detail 5-10  Window placed centrally, with window rabbet, sloping concrete surface and additional metal dressing 1 External wall: ILC, 50–60 cm Reinforcement, corrosion-proof 2 Windows: wood windows with ­ triple glazing 3 Slanting metal dressing in the area of the horizontal window rabbet, outside windowsill of waterproofed exposed concrete

Window placed centrally, with window rabbet, sloping concrete surface and additional metal dressing Here the window is fitted centrally to the wall to a window rabbet, and the windowsill consists of ILC with w ­ ater-­repellent treatment. The window rabbet helps to reduce the thermal bridging effect in the window reveal so that it is possible to omit additional insulation.

In order to avoid the need for an external window board, the monolithic external windowsill features a very steep draining angle. The flatter area of the sill (3) is protected by an angled metal sheet that is tucked into a recess in the window frame and has a slope of approximately 3°. It is strongly recommended to apply additional water-repellent treatment to the surfaces.

Scale 1:10

Note: This detail has been implemented in similar form in prototypes and its performance under heavy rain has been simulated. Practical experience has not yet obtained. Due to the high propensity of the material to absorb water, it is suggested that sill details with metal dressing or high-density concrete should be chosen.

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5  Key Building Construction Details

Scale 1:20

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5.4  Window Connections

Detail 5-11  Window fitted on the outside face of the wall, without rabbet 1 External wall: ILC, 50–60 cm Reinforcement, corrosion-proof 2 Windows: aluminum windows with triple glazing 3 Inside reveal lined with solid wood, reveal insulation board, 20 mm, thermal conductivity group 020, fully bonded

Scale 1:10

Window fitted on the outside face of the wall, without rabbet Windows fitted flush with the outside of the wall are a special case in our discussion. In spite of the doubtless architectural qualities of this solution, it must be viewed with strong caution, particularly where windows are fitted in an infra-lightweight concrete wall. It is the authors’ view that otherwise, heavy moisture saturation may occur in the area of the inner reveal due to the high water absorption capability of the material in the case of driving rain directly hitting the facade. For this reason this solution is not recommended, taking into account the current state of technology and material development.

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5  Key Building Construction Details

5.5 Foundations

Groundwater

Scale 1:10

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5.5 FOUNDATIONS 5.4  Window Connections

Detail 5-12  The building has a cellar; the external ILC wall starts from the foundation slab 1 External wall: ILC, 50–60 cm Reinforcement, corrosion-proof 2 Foundation slab: waterproof concrete and insulation layer 3 Metal barrier plate 4 Cellar wall: waterproof concrete 5 Vertical damp-proofing 6 Calcium silicate brick up to groundwater level 7 Drainage to suit ground conditions 8 Layer of gravel 9 Floor slab: normal concrete, 2,400 kg/m³ 10 Floor construction: – Loose layer of expanded clay – Impact sound insulation – Screed (underfloor heating) – Floor finish

The building has a cellar; the external ILC wall starts from the foundation slab A cellar extends beneath the entire building. The external infra-lightweight concrete wall is placed as an insulating external skin in front of the cellar wall of waterproof concrete.

Owing to the high water absorption capability of the material, the entire surface of the cellar wall should be sealed on the outside. Any differences in level between the first floor and the cellar depend on the respective design. The concrete wall of the building runs into the ground without transition.

Where a building has no cellar, the detail should be adapted accordingly. Note: In the detail shown here it is possible that the external wall will be saturated by splash water in the area just above the ground. Depending on the detailing of the roof edge/roof overhang, the detail can be adjusted accordingly (for example, by applying water-repellent treatment to the plinth or raising the external wall sealing to above ground level,  see Detail 5-13).

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5  Key Building Construction Details

Groundwater

Scale 1:10

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5.5 Foundations

Detail 5-13  The building has a cellar, the external ILC wall starts from the foundation slab; the plinth has been sealed 1 External wall: ILC, 50–60 cm Reinforcement, corrosion-proof 2 Foundation slab: waterproof concrete and insulation layer 3 Metal barrier plate 4 Cellar wall: waterproof concrete 5 Vertical damp-proofing 6 Calcium silicate brick up to groundwater level 7 Drainage to suit ground conditions 8 Fiber-cement board reaching into the ground 9 Floor slab: normal concrete, 2,400 kg/m³ 10 Floor construction: – Loose layer of expanded clay – Impact sound insulation – Screed (underfloor heating) – Floor finish

The building has a cellar, the external ILC wall starts from the foundation slab; the plinth has been sealed A cellar extends beneath the entire building. The external infra-lightweight concrete wall is placed as an insulating external skin in front of the cellar wall of waterproof concrete.

Owing to the high water absorption capability of the material, the entire surface of the cellar wall should be sealed on the outside. In order to prevent the plinth being saturated

with water from splash-back, the sealing is raised to approximately 30 cm above ground level. A fiber-cement panel reaches down into the ground, protecting the lowest part of the building. Any differences in level between the first floor and the cellar depend on the respective design. Where a building has no cellar, the detail should be adapted accordingly.

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5  Key Building Construction Details

Scale 1:10

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5.5 Foundations

Detail 5-14  The building has a cellar, cellar wall of ILC 1 External wall: ILC, 50–60 cm Reinforcement, corrosion-proof 2 Foundation slab: waterproof concrete and insulation layer 3 Metal barrier plates optional 4 Cellar wall: ILC 5 Vertical damp-proofing 6 Drainage to suit ground conditions 7 Layer of gravel 8 Bearing: expanded rubber pad, 10 mm 9 Floor slab: normal concrete, 2,400 kg/m³ 10 Floor construction: – Loose layer of expanded clay – Impact sound insulation – Screed (underfloor heating) – Floor finish

The building has a cellar, cellar wall of ILC A cellar extends beneath the entire building. The external infra-lightweight concrete wall functions as a load-bearing and insulating external building component from the bottom up.

Owing to the high water absorption capability of the material, the entire surface of the cellar wall should be sealed on the outside.

Where a building has no cellar, the detail should be adapted accordingly. Note: In the detail shown here it is possible that the external wall will be saturated by splash water in the area just above the ground. The detail can be adapted to suit the detail of the roof edge/roof overhang.

Any differences in level between the first floor and the cellar depend on the respective design. The concrete wall of the building runs into the ground without transition. 83

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Scale 1:10

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5.5 Foundations

Detail 5-15  The building has a cellar, the ILC wall starts from ground level 1 External wall: ILC, 50–60 cm Reinforcement, corrosion-proof 2 Foundation slab: waterproof concrete and ­insulation layer 3 Metal barrier plate 4 Cellar wall: waterproof concrete 5 Cellar insulation: expanded polystyrene 6 Floor slab: normal concrete, 2,400 kg/m³ 7 Floor construction: – Loose layer of expanded clay – Impact sound insulation – Screed (underfloor heating) – Floor finish 8 Artificial stone slab as spray protection

The building has a cellar, the ILC wall starts from ground level A cellar extends beneath the entire building. The external infra-lightweight concrete wall starts from the transition between the first floor and the cellar. The cellar wall consists of waterproof concrete and is fitted with external insulation of extruded polystyrene; this does not require any additional sealing.

Any differences in level between the first floor and the cellar depend on the respective design. Where a building has no cellar, the detail should be adapted accordingly. Note: In the detail shown here it is possible that the external wall will be saturated in the transition area just above the ground. This is due to the effect of water splash-back.

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5  Key Building Construction Details

5.6 Detail of Joint between Parapet and Flat Roof

Detail 5-16  Parapet with exposed concrete surface on the inside 1 External wall: ILC, 50–60 cm, reinforcement ­corrosion-proof 2 Flat roof construction: – Normal concrete slab, 210 mm – Vapor barrier – Insulation, average 160 mm – Insulation wedges at the edges – Damp-proofing – Gravel layer, 100 mm – Concrete slabs, 40 mm 3 Bearing: expanded rubber pad, 10 mm 4 Metal flashing on parapet

Scale 1:10

Parapet with exposed concrete surface on the inside The parapet shown here has an exposed concrete finish on the inside, such as a terrace parapet. From the point where the normal concrete flat roof slab rests on the wall, the parapet is thinner.

The waterproofing of the roof can either be applied on top of the insulation or underneath it, that is, directly on the flat concrete roof (inverted roof not shown here). At the transition

between the flat roof covering and the parapet, the waterproofing is continued up the parapet. Note: If snow accumulates, leakage can occur. For this­ ­reason, the top of the parapet should be sealed with suitable materials (shown here is metal flashing). Alternatively, it is possible to use a prefabricated concrete element, for example.

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5.6  Detail of Joint between Parapet and Flat Roof

Detail 5-17  Parapet with waterproofing on the inside and metal flashing on top 1 External wall: ILC, 50–60 cm Reinforcement, corrosion-proof 2 Flat roof construction: – Normal concrete slab, 210 mm – Vapor barrier – Insulation, average 160 mm – Insulation wedges at the edges – Damp-proofing, drainage layer – Roof greening, 170 mm 3 Bearing: expanded rubber pad, 10 mm 4 Metal flashing includes inside face of parapet

Scale 1:10

Parapet with waterproofing on the inside and metal flashing on top The detail shown here is a parapet with waterproofing on the inside and overlapping metal flashing; the thickness of the parapet is reduced from the point where the flat normal concrete roof rests on the wall.

The waterproofing of the roof can either be applied below the insulation, on top of the insulation, or on the flat concrete roof (inverted roof not shown here).

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5  Key Building Construction Details

Detail 5-18  Parapet with waterproofing on the inside 1 External wall: ILC, 50–60 cm Reinforcement, corrosion-proof 2 Flat roof construction: – Normal concrete slab, 210 mm – Vapor barrier – Insulation, average 160 mm – Insulation wedges at the edges – Damp-proofing – Drainage layer – Roof greening, 170 mm 3 Bearing: expanded rubber pad, 10 mm 4 Metal flashing (zinc) Multiplex plywood bearing Zinc metal sheet, 0.7 mm

Scale 1:10

Parapet with waterproofing on the inside This detail shows a parapet with waterproofing on the inside, carried up vertically to the top of the parapet (plastic or bitumen); the thickness of the parapet is reduced from the point where the flat normal concrete roof rests on the wall. Where the waterproofing is exposed to solar radiation it must be protected against the effects of UV radiation.

The waterproofing of the roof can either be applied below the insulation, on top of the insulation, or on the flat concrete roof (inverted roof not shown here). In order to compensate for inaccuracies in the concreting process, conventional parapet flashing is applied on Multiplex plywood bearing.

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6.1

Table of Parameters for Initial Design Considerations

47

6.2

Infra-Lightweight Concrete in the Context of the Energy Conservation Directive (EnEV) 51

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6 Fundamentals of Design

6.1 Table of Parameters for Initial Design Considerations 6.2 Infra-Lightweight Concrete in the Context of the Energy Conservation Directive (EnEV) 6.3 Building Physics Properties 6.4 Dynamic Simulation-Based Investigations 6.5 Eco-Balance 6.6 Costs 6.7 Legal Background

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6  Fundamentals of Design

Infra-lightweight concrete is a very lightweight concrete used in construction that resembles conventional lightweight concretes in many ways but also differs significantly with regard to some properties. These properties must be taken into ­account in the design. In addition to load-bearing capability, construction details, and durability, this also affects building physics (thermal insulation, sound insulation, fire protection, etc.) and other issues such as the formwork striking time and of course costs. The next two chapters are intended to provide approaches to the design with infra-lightweight concrete. The information given here largely relies on ILC-specific findings that are research results from TU Berlin. Where no explicit results have yet been obtained for infra-lightweight concrete, we have relied on relevant literature as a source of design details. Infra-lightweight concrete is neither covered by the currently applicable standard nor has general building control ­approval been obtained for it. This means that all design approaches shown here must be checked, adjusted and, if necessary, adapted to the respective building project as part of a procedure for individual building control approval.

6.1 Table of Parameters for ­Initial Design ­Considerations When starting the design of a building with monolithic infra-lightweight concrete walls, many designers always face the same questions. For example, one of the architect’s first questions will be what wall thickness is required for meeting structural and building physics requirements. When this information is not readily available, the architect, structural engineer, and energy consultant need to spend a considerable amount of time in the quest for this information and relevant details. Often this lack of basic experience and the associated extra work input required are important reasons for both client and designer to avoid infra-lightweight concrete as an option for the envelope of a building. In order to fill this information void, at least in parts, several sample designs for residential buildings have been established, including the relevant structural calculations and building physics details, in accordance with the current state of knowledge (see also Chapter 4). The results of this study have been compiled in a table of parameters that is aimed at helping designers make initial decisions for the design of future buildings. It goes without saying that the table only provides a starting point for the continuing work and the details cannot be summarily applied; rather, the full design process needs to be carried out for each project. The table includes the possible number of stories of a building when using different bulk density classes of infra-lightweight concrete with wall thicknesses of 50 and 60 cm, taking the example of the freestanding apartment building described in Chapter 4.1. In view of the fact that the number of stories possible largely depends on the design and structural concept of a building, the details given should only be understood as guide values. More stories in a building are also feasible if the structural system and other design features are adjusted accordingly, for example, applying different ILC bulk densities across the height of the building.

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6.1  TABLE OF PARAMETERS FOR ­INITIAL 6.1 DESIGN TableCONSIDERATIONS of Parameters

7

7 6

6

6 5

5 Number of stories

Possible number of stories in the sample building for wall thickness d = 50 cm* Possible number of stories in the sample building for wall thickness d = 60 cm*

4 4

4 3 2

2 2

2 2

ILC650

ILC600

* Calculated on the basis of the boundary conditions of the sample building in Chapter 4.1, calculation of stress in concrete for centrally applied compression

1 0

ILC800

ILC750

ILC700

Figure 6-1  Number of possible stories in the sample building in Chapter 4.1 for different classes of ILC

The next diagram shows the U-values of the external walls for different bulk density classes and wall thicknesses. This information is based on the rated value for thermal conductivity (see Chapter 6.3.1).

0.45

0.45 ILC800 0.42

Thermal transmittance U W/(m 2·K)

0.40

0.39 0.36

0.35

Finally, the table of parameters shows the possible effects on a concrete project, taking into account the requirements resulting from EnEV 2016 [26].

0.34

0.41 ILC750 0.38 0.35 0.33 0.30

0.30

0.37 0.35

0.34

0.32

0.32

0.30

0.30

0.28

0.28

ILC700

ILC650 ILC600

0.26 0.25

0.20

45

50 55 Wall thickness d [cm]

60

Figure 6-2  U-values for different wall thicknesses and ILC classes (based on the rated value for thermal conductivity, see Chapter 6.3.1)

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6  Fundamentals of Design

Selected construction method

Proportion of window area

U-value, wall W/(m² · K)

U-value, window W/(m² · K)

U-value, roof W/(m² · K)

H'T permiss. EnEV 2016 W/( m² · K)

H'T permiss. Refe­rence build. W/( m² · K)

H'T existing W/(m²· K)

Thermal bridge correction factor

Ratio of surface-­­­ to-­volume A / Ve

Primary energy factor Heating + HW

4.1 Example of building type Free-standing building

ILC800 ILC700 ILC600

60

7

In situ concrete/ prefabricated part

34%

0.34

0.88

0.14

0.50

0.56

0.47

0.05

0.32

0.7

4.2 Infill building, free-form

ILC800 ILC700 ILC600

50

7

In situ concrete

44%

0.41

0.87

0.14

0.65

0.50

0.46

0.10

0.23

0.7

4.2 Infill building, loggia facade

ILC800 ILC700 ILC600

50

7

Prefabricated part + in situ concrete

36%

0.41

0.96

0.14

0.65

0.48

0.48

0.10

0.19

0.7

4.3 Linear row of buildings, Rear wall in ILC

ILC800 ILC700 ILC600

60

7

In situ concrete

30%

0.30

0.95

0.14

0.50

0.54

0.50

0.10

0.31

0.7

4.4 Single-family house Villa

ILC800 ILC700 ILC600

60

3

In situ concrete

22%

0.34

0.95

0.14

0.50

0.61

0.49

0.10

0.53

0.7

4.5 High-rise building with bar walls

ILC800 ILC700 ILC600

60

17

Prefabricated part + bar wall

34%

0.30

0.67

0.14

0.50

0.62

0.48

0.10

0.24

0.7

Project / Parameter

Formulation

Selected number of full stories

Thermal insulation details/Requirements as per EnEV 2016

Selected wall thickness ILC [cm]

General parameters, ILC

Table 6-1  Table of parameters for sample buildings designed using ILC [27]

6.2 Infra-Lightweight Concrete in the Context of the Energy Conservation Directive (EnEV) Infra-lightweight concrete has both insulating and load-bearing properties. The lower the bulk density of a lightweight concrete, the lower its thermal conductivity, but as a rule its compressive strength is also reduced. This implies that thermal conductivity through concrete can only be avoided to a certain degree, because a certain degree of load-bearing capability must also be ensured. Even though the development of the material has by no means reached the end of the road, such a material implicitly cannot compete with non-load-bearing thermal insulation that has been designed for insulation only. In wall thicknesses of 55 to 60 cm, which

are just about still acceptable, this results in U-values above those for common multilayer wall constructions such as composite thermal insulation systems. In contrast to other EU countries, Germany does not impose special requirements for individual building components, which means that the relatively “poorer” values of an external infra-lightweight concrete wall can be effectively compensated for with other building components. Following the introduction of the Building Energy Act (GEG) [28], which as of 2017 has been submitted to the respective German Federal Ministry, new requirements for residential buildings are likely to apply in Germany from 2021. In particular, the stationary consideration of the transmission heat loss H'T regarding the heat-transferring building envelope will be omitted. From then on, the requirements for the reference building will apply.

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In this context, the use of active wall insulation systems powered by renewable energy would appear the most sensible solution in order to fulfill the often stationary requirements for building components in other EU countries or to comply with generally increased insulation standards. The infra-lightweight concrete mixtures available at the time of the publication of this manual already have a significantly lower thermal conductivity than conventional lightweight concrete mixtures. We can assume that the values currently being achieved for thermal conductivity can be further improved in future by optimizing the formulation (see also [15]).

6.3 Building Physics Properties 6.3.1 Thermal Conductivity / Thermal T ­ ransmittance Requirements In the current EnEV, the U-value for the external walls of the EnEV reference building for target temperatures in heated rooms of ≥ 19 °C is stated as U = 0.28 W/m² · K [26]. However, as explained in the previous section, in contrast to other EU countries, in Germany no special requirements are stipulated for individual building components (as of 2017). This means that the specified U-value of 0.28 W/m² · K is not mandatory but should be understood as a guide value. Instead, the requirements relating to transmission heat loss and to primary energy for the building as a whole must be met.

Test Values and Calculation Basis The thermal conductivity of infra-lightweight concrete was determined by KIWA GmbH, an approved inspection body in Berlin, using the guarded hotplate method [29]. As part of this process, the test specimen was first dried and then tested at a temperature of 10 °C. The measured value is expressed as λ10°,dr. The test was carried out for ILC800, ILC650, and ILC600 and the values for ILC700 and ILC750 were calculated by linear interpolation. In real-life conditions, it is common for building components to have a certain moisture content, which increases the thermal conductivity compared to the dried test specimen and

thereby reduces the insulating effect. In order to be able to take real-life conditions into account, the measured value λ10°,dr is converted into the rated value for thermal conductivity λrv in accordance with DIN EN ISO 10456 [30]. The conversion also takes into account the statistical quality of the measured data, allowances for temperature and for moisture content, as well as for aging. The calculation of the rated value λrv was carried out for ILC800 in accordance with the composition in Table 3-2 as an example, and the calculated increase over the measured value λ10°,dr was then adopted for the other ILC classes. The following should be noted regarding the calculation of the rated value of ILC800: nn The statistical quality is taken into account via the number

of measured values obtained (here n = 3). It may be possible to achieve an improvement, that is, a reduced allowance, by carrying out further testing to increase the number of measured results. This has been planned as part of the ongoing research activities at TU Berlin. nn The conversion factors for temperature and moisture ­content were determined for an ambient temperature of 23 °C and 80 percent relative humidity. For this condition,  DIN  EN ISO 10456 states a moisture content of u = 0.03 kg/kg for lightweight concrete with expanded clay aggregate. This value was confirmed in experimental investigations with ILC800, which means that the values in the DIN can be used for ILC. nn There is no clear definition of the effects of aging. The standard does not contain any references to conversion rules. In this respect, no long-term data is as yet available for infra-lightweight concrete. From what we know to date, we assume that ILC is not subject to significant aging processes that affect thermal conductivity. We therefore propose to use the factor of 1.0 for aging. We would like to point out here that, where other compositions than those in Table 3-2 are under consideration, the rated value has to be determined separately on the basis of the respective test results for thermal conductivity, and that the allowances/ values listed here are not transferable. As an alternative to the calculation of the rated value, it is possible to carry out a test at the appropriate test levels, that is, at an ambient temperature of 23 °C and 80 percent relative humidity. 95

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For the composition shown in Table 3-2, the rated values λrv listed in the following table have been established, as well as the associated thermal transmission values for wall thicknesses of 50 to 65 cm. The U-value was determined using the following formula: U=

1

Rsi +

d rv

+ Rse

[W/(m2 K)]

(2)

whereby Rsi = 0.13 [m² · K/W] internal heat transmission resistance with a horizontal flow of heat [31] Rse = 0.04 [m² · K/W] external heat transmission resistance [31] d: wall thickness [m] λrv: rated value of thermal conductivity [W/m · K]

Conclusion The current EnEV (as at 2017) does not stipulate mandatory limit values for the thermal transmittance of external walls. The U-value of ILC walls measuring between 50 cm and 65 cm in thickness lies between 0.41 and 0.24 W/m² · K. This means that, in most cases, the external ILC walls exceed the guide value of U = 0.28 W/m² · K of the EnEV reference build-

Property

ing. However, this can be effectively compensated for with other building components.

6.3.2 Resistance to Frost and Thawing Requirements As a rule, infra-lightweight concrete is used as an external building component, the vertical surface of which is exposed to rain and frost; in accordance with the informative examples of EC2 [20], this would mean exposure class XF1 (moderate water saturation without deicing agent). Exposure class XF3 refers to environmental conditions that lead to high water saturation without deicing agent. With respect to normal concrete, EC2 mentions the informative example of horizontal surfaces directly exposed to the weather. The latter is not very likely / should be avoided when using infra-­ lightweight concrete in construction. However, it should be noted that, in accordance with findings to date, ILC tends to retain water for longer than normal concrete owing to its structure, which can also lead to a higher degree of saturation in vertical building components. Therefore it may be worth considering whether ILC used in a vertical external wall directly exposed to the weather should be classified as XF3 rather than XF1.

Test Result and Allocation to Exposure Classes In order to investigate in detail the frost-thawing resistance of infra-lightweight concrete, experiments [32] were carried

ILC600

ILC650

ILC700

ILC750

ILC800

Thermal conductivity λ10°,dr [W/m)]

0.141

0.153

0.166*

0.178*

0.193

Rated value of thermal conductivity** λrv [W/m · K]

0.160

0.174

0.189

0.202

0.219

U-value for 50 cm wall thickness [W/m² · K]

0.30

0.33

0.35

0.38

0.41

U-value for 55 cm wall thickness [W/m² · K]

0.28

0.30

0.32

0.35

0.37

U-value for 60 cm wall thickness [W/m² · K]

0.26

0.28

0.30

0.32

0.34

U-value for 65 cm wall thickness [W/m² · K]

0.24

0.26

0.28

0.30

0.32

*by linear interpolation **allowance for ILC800 calculated and for ILC600 to 750 adopted

Table 6-2  Thermal conductivity and thermal transmittance of infra-lightweight concrete for different compositions as per Table 3-2

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out with ILC800 and ILC600 in accordance with DIN CEN/ TS 12390-9:2006 [33]. The results showed that ILC800 ­fulfills the acceptance criterion for XF3 as modified in accordance with Faust [7] via the dry bulk density, which is why ILC800 can be considered suitable as XF3 and XF1. However, the results for ILC600 were significantly above the ­acceptance criterion for XF3. It is not possible to make a statement regarding XF1 because no recommendation for an acceptance criterion was given [32]; however, the fact that XF3 was clearly exceeded suggests that XF1 is not achieved without protective surface coating. Property Weathering (mean value) [g/m²] Acceptance criterion for XF3 in acc. with [32] [g/m²]

ILC600

ILC800

1,620

262

275

374

Table 6-3  Frost-thawing resistance of ILC600 and ILC800 in accordance with the composition in Table 3-2, based on [32]

DIN 1045-2 specifies minimum requirements for lightweight concretes for different exposure classes, such as cement content, water/cement value, etc. For example, the minimum cement content for XF1 is 280 kg/m³ and for XF3, 300 kg/m³ (270 kg/m³ in each case when aggregates are taken into account) [34]. As can be seen from the composition in Table 3-2, the cement content of ILC600 to ILC700 inclusive is under 270 kg/m³; only that of ILC800 is over 300 kg/m³, and that of ILC750 is 296 kg/m³. Assuming the transferability of the criteria to infra-lightweight concrete, it follows that ILC600 cannot be assigned to exposure class XF1 (ILC800 fulfills the requirements for XF3, which is borne out by the test results of the frost-thawing test). When assessing the results of the frost-thawing investigations, note should be taken of the fact that the tests were designed for normal concrete and its behavior during the capillary absorption of moisture. By contrast, in accordance with findings to date, ILC will absorb water over a longer period of time, which is why a higher degree of saturation must be assumed especially toward the end of the test, which would indicate more severe damage. Whether such an increased degree of saturation occurs in practice depends on the boundary conditions of the installation, such as the application of water-repellent coating.

Conclusion ILC800 in the composition as listed in Table 3-2 fulfills the requirements of exposure classes XF1 and XF3 also when directly exposed to the weather, that is, without surface protection. By contrast, ILC600 as listed in Table 3-2 should not be used where directly exposed to the weather, but should be given an appropriate surface protection coating. As was also shown in the tests regarding exposure to direct rain in Chapter 6.3.6, water-repellent coating generally makes sense for external ILC building components of all ILC classes. This would result in a significantly reduced risk of frost-thawing damage. Further experiments should be carried out to prove this point.

6.3.3 W  ater Absorption and Depth of Penetration Requirements Regarding the penetration of water, a material can be assessed using two different parameters: the water absorption coefficient that describes the capillary absorption capability, for example during continuous exposure to rain or driving rain, and the water penetration depth that takes into account penetration under pressure. Standards and regulatory instruments with specific requirements for the classification of water penetration depth are not available. Examples are available for waterproof concretes, with limit values of 50 mm (see, for example, [35]). However, this criterion should not be used for ILC since it is not possible to preclude the water penetration depth progressing over time.

Testing for Water Absorption and Depth of Penetration During internal research work, the water absorption coefficient for ILC800 and ILC600 as per the composition in Table 3-2 was tested in accordance with DIN EN ISO 15148 [36].

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6  Fundamentals of Design

Property Water absorption coefficient Ww [kg/m²h0.5]

ILC600

ILC800

Porous concrete

Cement concrete

Calcium silicate block

0.3

0.7

2 to 8

0.1 to 1.0

2.5 to 10

Table 6-4  Water absorption coefficient Ww of ILC600 and ILC800 as per the composition in Table 3-2 compared with other building materials [37]

The results for both compositions showed a coefficient of ≤ 0.7; the value of ILC600 was below the results for ILC800. The reason for this may lie in the different cement content. However, in an earlier test series similar values were obtained – although in that series ILC800 absorbed less water than ILC600 [32]. It is as yet not clear what the reasons are for the differences between the two test series. Further tests are required in order to provide sufficient statistical evidence for the above results. Note should also be taken that, in accordance with the findings in Chapter 6.3.2, water absorption in ILC takes place over a longer period. In view of the fact that the tests for water absorption, in accordance with standard DIN EN ISO 15148 [36], were designed for a short period of time (only 24 hours), it may be the case that the tested water absorption coefficient for long-term water absorption in ILC is not relevant. In the context of internal research work, tests were also carried out on the depth of water penetration under pressure [32] in ILC600 and ILC800 in accordance with DIN EN 12390-8 [38]. In these tests, a water jet with a pressure of 5 bar is directed onto the surface of the test specimens to be tested for 72 ± 2 hours. The specimens are then split in order to measure the maximum depth of water penetration. The test series with ILC800 were carried out in accordance with the standard and throughout the tests no water escaped from the sides of the specimens. During the tests with ILC600 it was not possible to prevent water escaping from the sides; in spite of that, the pressure was kept at 5 bar during testing. The test results obtained in this way were confirmed with additional tests using test specimens with sealed sides.

Figure 6-3  Test specimen for determining the depth of water penetration in ILC800 [32]

Property Water penetration depth (short-term) [mm]

ILC600

ILC800

66

12.5

Table 6-5  Water penetration depth (short-term) of ILC600 and ILC800 in the composition shown in Table 3-2, based on [32]

Conclusion The short-term water absorption and short-term water penetration resistance of infra-lightweight concrete in the composition shown in Table 3-2 are of a similar order of size as those of normal concrete. However, longer-term and therefore increased water absorption and/or penetration depth cannot be precluded. In spite of the relatively good properties of ILC in terms of penetration of moisture, a protective surface treatment is recommended (such as water-repellent coating) in order to prevent the possibility of longer-term water absorption.

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Water vapor diffusion resistance coefficient µ

ILC600

ILC800

Steam-cured porous ­concrete

Concrete (density 2,400 kg/m³)

Lightweight concrete with porous particulate structure (exclusively ­expanded clay)

Calcium silicate brick masonry (density 1,200 to 2,200 kg/m³)

11 (dry)

31 (dry)

5/10

80/130

5/15

15/25

Table 6-6  Water vapor diffusion resistance coefficient of ILC600 and ILC800 in the composition shown in Table 3-2 [41, 42] compared with that of other building materials [31]

Specific heat capacity c [J/kgK]

ILC800

Steam-cured porous concrete

Concrete with bulk density of 2,200 kg/m³

Lightweight concrete with porous particulate structure (exclusively expanded clay)

Calcium silicate brick masonry

863

1,000

1,000

1,000

1,000

Table 6-7  Specific heat capacity of ILC800 in the composition shown in Table 3-2 [43] compared with other building materials [31]

6.3.4 Water Vapor Diffusion Requirements

water vapor diffusion took place through the specimens. By weighing the test specimens regularly it was possible to establish the water vapor diffusion resistance coefficient.

It is desirable to opt for a “diffusive” construction as this ­offers various opportunities in terms of the moisture management in building components. The water vapor diffusion resistance coefficient µ is a parameter that describes the degree of diffusiveness / diffusion resistance. This parameter indicates by which factor the water vapor diffusion resistance of a material is greater than that of a stationary layer of air of the same thickness and same temperature [39]. This means that the lower the water vapor diffusion resistance coefficient, the more the building material tends to be open to diffusion.

Conclusion

Test Result

Requirements

The water vapor diffusion of ILC800 and ILC600 was tested [41, 42] in accordance with DIN EN ISO 12572 [40]. In these tests, specimens were placed on containers filled with drying agent, and these were set up in a defined climate with increased relative humidity. Owing to the differential water vapor pressure on the different sides of the test specimens,

The specific heat capacity indicates how much heat can be stored by a material. This property in combination with the bulk density ρ is mainly of practical relevance in terms of thermal protection during summer. The greater the product of c times ρ, the more the material contributes to keeping the interior cool even when the ambient temperature is high.

The water vapor diffusion resistance (dry) of ILC600 in the composition shown in Table 3-2 is of the same order of size as that of porous concrete or of porous particulate lightweight concrete. The resistance of ILC800 as per Table 3-2 is significantly greater but also significantly below that of normal concrete.

6.3.5 Specific Heat Capacity

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6  Fundamentals of Design

Test Result of Hot Disk Transient Plane Source (TPS) Method The specific heat capacity of ILC800 in the composition shown in Table 3-2 was established using the TPS method [43]. To date, the specific heat capacity of ILC600 to ILC750 has not yet been investigated.

Conclusion The specific heat capacity of ILC800 in the composition shown in Table 3-2 is somewhat below the heat capacity of normal concrete or porous concrete, for example. However, the order of size is similar, which means that the effect on thermal protection during summer compared to normal concrete is less due to the specific heat capacity and more to the low bulk density.

6.3.6 Behavior During Exposure to Driving Rain Requirements The absorption of moisture in an external envelope, in particular during driving rain events, is of special importance for various aspects, such as the insulating effect, the durability, surface cracking, etc. Therefore the absorption of moisture in an external building component should be limited. This in turn raises the need for surface treatment in certain cases or the inclusion of roof overhangs or drip details in the overall architectural concept.

The ILC facade section including the window board was directly exposed to the rain event. The back of the section (= inside of the external wall) was not exposed to the rain but was exposed to the increased relative humidity in the room. The absorption of moisture from the air was checked using regularly weighed test specimen of ILC600 that had been set up at the back of the test rig. The prototype was suspended from the ceiling via a load cell, which made it possible, simultaneously with the test procedure, to measure and document the increase in the weight of the building component as a result of the rain event. Furthermore, measuring points were fitted within the test specimen, which were used to check the relative humidity within the building components using resistance measurements at specified time intervals. Both the recording of the weight and the moisture measurements within showed nearly no change during the course of the test; it therefore appeared that the building component was largely dry on the inside. Following the rain event test, the wall was cut open with a hammer and chisel in order to be able to check the depth of water penetration in the component. The results confirmed that the component was dry inside. The component was only penetrated by moisture on the outside to a depth of approximately 1 to 2 cm. After 24 hours the surface had almost completely dried out. However, when the specimen was cut open to a greater depth it could be seen that the moisture had penetrated approximately 15 to 20 cm into the interior of the wall section; this was also confirmed by the electrical resistance measurements.

Test Result of Driving Rain Test In order to investigate the absorption of moisture in an untreated infra-lightweight concrete surface during a rain event, a driving rain test was carried out with the prototype of a window opening in a 50 cm thick ILC600 wall. The test was carried out using the driving rain test rig of the Department for Building Physics and Building Construction of TU Berlin, which is also used in the context of the certification of sarking membranes in accordance with prEN 15601. The rain event chosen was an event with a duration of three hours that had been developed for sarking membranes.

Conclusion This test showed that initially moisture only penetrates the surface of the ILC during a rain event but that over time penetration progresses to the interior of the building component. This is confirmed by the findings from the frost-thawing resistance tests (see Chapter  6.3.2). For this reason, ILC surfaces should be systemically protected against moisture penetration, such as by applying water-repellent coating (see Chapter 8.5).

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Figure 6-4  Prototype in the driving rain test rig showing the front to be exposed to the rain (left) and the penetration depth of the moisture shortly after exposure to the rain (right) [27]

6.3.7 Fire Protection Requirements The requirements of fire protection are defined in relation to the class of building and the type of building component. As a rule, multistory apartment buildings of infra-lightweight concrete will be assigned to building class 5, below the highrise building limit. This means that load-bearing external walls have to be fire-resistant, that is, complying with fire resistance class F90-AB or REI90 [31].

Fire Behavior of ILC DIN 4102-4 [44] lists building materials that are classified as noncombustible (building material class A1 in accordance with DIN 4102-1 [45]). These include, first and foremost, concretes as per EC2 [20]. Owing to its low dry bulk density and strength, infra-lightweight concrete is not included in this category; however, the general description “Building materials that do not contain more than 1 percent (of mass) of homogeneously distributed organic components” [44] applies to ILC. This means that ILC should be classed as noncombustible.

nn Table-based method (evidence level 1) nn Simplified calculation method (evidence level 2) nn General calculation method (evidence level 3).

The table-based method (evidence level 1) for reinforced concrete specifies requirements for the minimum size of cross sections and the distance of the center of reinforcements from the edge of the building component, which were determined on the basis of standard fire tests [31]. The minimum cross section sizes and the loading take into account that the strength of concrete reduces when exposed to high temperatures; the minimum concrete cover ensures adequate protection of the reinforcement. For walls consisting of lightweight concrete with a closed structure, DIN 4102-4 [44] allows a reduction in the minimum dimensions, which increases as the bulk density decreases. For example, in load-bearing walls of bulk density class 1.0 the minimum wall thickness and the distance of the center of the reinforcement from the edge of the component can be reduced by 20 percent, subject however to minimum dimensions of 150 mm for the wall thickness and a distance of 30 mm of the reinforcement center from the edge of the component [44].

EC2 offers three methods for establishing the load-bearing behavior in the case of fire: 101

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6  Fundamentals of Design

Concrete αT [mm/m · K]

0.01 

Lightweight concrete 0.008 

Reinforcement steel 0.018 – 0.012

GRP reinforcement 0.006 (axial) 0.022 (radial)

ILC800 0.007 – 0.012  αT ≈ 0.01 mm/m · K

Table 6-8  Thermal coefficient of linear expansion αT of ILC800 compared with other materials [24, 31]

As a rule, infra-lightweight concrete walls will be 50 to 60 cm thick (see Chapter  6.1), which means that compliance with the above minimum cross section dimensions should not pose a problem. Furthermore, in view of the fact that ILC has better thermal insulation properties than normal concrete, it can be assumed that the requirements for the distance of the reinforcement from the building component edge in EC2 / DIN 4102-4 are on the safe side. Experimental investigations at TU Berlin with infra-lightweight concrete at high temperatures showed behavior commonly experienced with concrete in the sense that the reduction in compressive strength at high temperatures diminished as the proportion of aggregate to cement increased. A reduction in strength and rigidity was observed from about 200 to 400 °C [46]. However, no investigation was carried out regarding the risk of spalling in infra-lightweight concrete. The reason for spalling can be found in residual and restraint stresses due to uneven heating of the cross section, differential expansion of the reinforcement and concrete, as well as of the lightweight rock particulates and cement stone. Another possible cause may be tensile stresses resulting from hydrostatic water vapor pressure and water vapor escaping [7]. The thermal expansion of ILC was determined experimentally using ILC800 and compared as follows: As can be seen, the thermal expansion of infra-lightweight concrete is not somewhat less than that of normal concrete, as is common for lightweight concrete, but lies in a similar range. This allows the conclusion that, analogously to normal reinforced concrete, no significant restraint stress between reinforcement and concrete must be expected due to changes in temperature.

Conclusion ILC is to be classed as noncombustible. Experimental investigations indicated a behavior at high temperatures that is common for concrete in relation to the reduction in strength and stiffness. The behavior in the case of fire has not yet been adequately investigated, particularly with respect to spalling, which is why further research work/testing may become necessary as part of the application procedure for individual building control approval. Depending on the type of reinforcement material it is possible that special fire protection requirements apply, such as in the case of GRP reinforcement (see Chapter 7.7). The requirements should be checked in each individual case.

6.3.8 Sound Insulation Requirements The sound insulation quality of an external building component can be stated in terms of the evaluated sound insulation value Rw. For this parameter no concrete limit values are in existence, because the sound insulation effect also depends on various other factors such as the proportion of openings, flanking building components, etc. and also because the requirements differ depending on the location and/or ambient conditions. The higher the evaluated sound insulation value of a building component, the better is the sound insulation achievable.

Calculations The evaluated sound insulation value for infra-lightweight concrete classes is calculated below using the example of a 55-cm-thick wall. The calculation is based on DIN 4109-32 of 2016 [47]. The mass per unit area is calculated as follows: m' = d ∙ ρ [kg/m²]

(3)

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In accordance with DIN 4109-32, the mean value for the class as specified in DIN EN 206 should be used for the purpose of calculating the bulk density of lightweight concrete. This procedure is adopted for ILC, which means that for ILC800 (range of bulk density 751 to 800) the mean value of 775 kg/m³ is chosen. The evaluated sound insulation value Rw is calculated in relation to m', the calculated mass per unit area. DIN 4109-32 includes the mass curves for various materials, which were determined on test rig–based test measurements for building acoustics. Equations are available for concrete, lightweight concrete (that has a curve which is 2 dB more favorable than normal concrete with the same mass per unit area), and porous concrete. The mass curve for lightweight concrete is used for infra-lightweight concrete, because the mass per unit area m' of ILC is in a range (140 kg/m² to 480 kg/m²) covered by the formula. The mass curve for porous concrete however only applies to m' ≤ 300 kg/m², the value of which would only exceptionally be less for infra-lightweight concrete walls (for example, ILC600 with a wall thickness of 45 cm). Furthermore, a comparative calculation with the formula for porous concrete revealed that the results were only slightly (< 1 dB) below the results based on the formula for lightweight concrete. Therefore the formula for lightweight concrete is used to calculate the evaluated sound insulation value for ILC: Rw = 30.9 · lg (m'total /m'0) – 20.2  [db],

(4)

whereby 140 kg/m²