Technology Report (unfinished) - Formative Submission Concrete Sam Eadington
Cover page
Contents page
Introduction In this report I will be looking into concrete structures and relating the technologies from numerous precedents to my 1914 project, explaining how and why elements from them can be taken and applied to my design. I will explore the historical importance of the material, it’s impact upon architecture and construction and the properties of concrete that have made it such a popular choice of material for a wide range of structures.
Fig 1.1 Author’s Own Alberto Campo Baeza’s Caja Granada headquarters building is a powerful example of concrete in situ. The building’s materiality reinforces its civic importance.
My Design My design for the 1914 project is a series of walls which are an abstract representation of the unchanging streets of Huddersfield over the past 100 years. The design aims to explore the idea of changing landscapes and question the notions of temporary and permanent. The purpose of the concrete walls is to provide a permanent frame for temporary structures and activities to exist between. My structure will be built using steel reinforced Portland concrete for both the walls and the foundations. This decision was made having taken into account numerous properties of Portland concrete including: it’s structural properties, construction methods, cultural perceptions, aesthetic, maintenance, cost, availability and environmental impact. This report explores the material and how it can be used meet the physical, conceptual and theoretical requirements of my design.
Fig 2.1 Author’s Own A view of my 1914 project
Fig 2.2 Author’s Own A view of my 1914 project
Fig 2.3 Author’s Own The plan for my 1914 project
Concrete Concrete is a synthetic rock made predominantly from cement, aggregate and water. Additives and reinforcements can be added depending on the purpose. Concrete is the most commonly used construction material in the world and is responsible for shaping a large portion of our built environment. Two key reasons for the popularity of concrete in architecture and engineering are it’s high strength under compression and it’s workability. Concrete mixture is fluid when mixed allowing it to be cast into almost any shape imaginable before it hardens and becomes a solid form (simscience.org). The vast majority of today’s concrete is mixed using Portland cement. This cement is made from iron ore, lime, alumina and silica which are ground and fired at a temperature of 700°C - 815°C in a kiln to produce clinker which is cooled then ground into a fine powder which is cement (ce.memphis. edu). To become concrete, cement has to be mixed with aggregate, both fine aggregate such as sand and coarse aggregate such as stones and rocks, and water which reacts with the cement in a process called hydration to cause it to harden into a solid form. Although this particular mix of concrete dominates the world of construction today, throughout history there have been a number of different versions with varying ingredients and today there are new innovative mixtures in development which could see this material continue to evolve.
Fig 3.1 Author’s Own Alberto Campo Baeza’s Centro Cultural in Granada, Spain. A monumental concrete structure boasting a surface finish which reveals the construction process. Public events take place in and around this building which is used as a blank canvas for cultural events.
The
Origins
of
Concrete
Concrete-like structures date back to 6500BC where archaeologists found remains in Syria, yet the concrete we are familiar with today, containing Portland cement, was invented in 1824 by a bricklayer, Joseph Aspdin, from Leeds. Ancient concrete-like mixtures were made from crushed and burned limestone mixed with sand and to produce a mortar, variations of which were used across the world, not only in architectural structures, but also by the Chinese to hold together bamboo in the construction of boats. These early cements were predominately used for building in conjunction with other materials, generally stone, rather than being moulded into forms on its own. In 600BC a major development came as the Greeks discovered a volcanic ash called Pozzolan, a ‘silicatebased materials that react with (consume) the calcium hydroxide generated by hydrating cement to form additional cementitious materials.’ (Girard, 2011), which allowed them to create hydraulic cement, a cement which hardens under water and in the air. This discovery was used to a far greater extent by the Romans who used concrete to construct unprecedented structures such as the Pantheon and the Colosseum.
After the fall of the Roman Empire, the skilled use of concrete was lost until the 15th century when concrete structures began to make a comeback. In 1793 concrete made it’s next major leap forward when John Smeaton discovered a new method for making cement which he used of the rebuilding of Eddystone Lighthouse in Cornwall. This innovation was followed in 1824 by Joseph Aspdin’s invention of Portland Cement. Portland cement requires precise quantities of compounds, this contrasts with natural cement which varies depending on the location and the available ingredients which cause inconsistencies in the mixture. The next step in the development of concrete was the invention of rotary kilns which by the end of the 19th century dominated the production of cement. These replaced vertical stationary kilns as the new horizontal rotary kilns had improved control over the 700°C - 815°C temperature of required for heating the mixture of limestone and clay. Modern day industrial kilns can reach over 150m in length compared to the early rotary kilns which measured less than 20m. These developments in production have allowed concrete to become the world’s most used construction material today, an estimated 3.9 billion metric tonnes of cement were used in 2014 and this figure is expected to grow in the immediate years. The 20th century saw the invention of precast concrete panels by John Alexander Brodie of Liverpool in 1905 (www.gpsprecastconcrete. co.uk) Precast concrete varies from insitu concrete as the concrete form is cast and cured under factory conditions before being delivered to site and installed. Precast concrete has become an important part of the construction industry thanks to the precise and repetitive forms that can be produced. This method also allows for building components to be made before or during the foundations of the structure are being built, then installed quickly as soon as the foundations are ready, saving a lot time in the construction process. The development of precast concrete led to the development of pre-stressing. Pre-stressing is a process which involves the steel reinforcement cables being stretched, or stressed, before the cornet has set in the formwork. Once the concrete has set around the stretched cables, they are cut and therefore contract and compress the concrete further, adding to its strength.
The Future of Concrete Despite Portland concrete remaining the most popular construction material, there have continued to be innovation in concrete technology. 1980 saw the emergence of Ultra High Performance Concrete (UHPC), concrete which is reinforced with ‘high-carbon metallic fibers’ (http://precast.org) has now been developed to achieve compressive strengths of up to 29,000 pounds per square inch (psi) and flexural strengths of up to 7,000 psi (cement.org). These are substantially higher values than standard portland concrete which has a compressive strength of 3000 - 6000 psi and a flexural strength of 400 - 700 psi (engineeringtoolbox.com). These increased strengths could possibly remove the need for conventional steel reinforcements in concrete, freeing up designers create a far wider range of forms. Due to it’s generally specialised and experimental uses, UHPC structures are most frequently pre-cast rather than poured in-situ as the factory conditions allow for far more control over the precise structures. Rudy Ricciotti’s MuCEM in Marseille is a innovative precedent for the use of UHPC. Almost the entire structure is constructed from the material with only small elements of steel. The footbridge onto the roof of the museum spans 76m with a depth of only 1.80m. This is achieved by post tensioning steel cables which run through UHPC sections and are tightened at either end. The solar shading elements are also constructed of UHPC and are structurally self supporting. These construction methods demonstrate the possibilities of concrete in the future with test on attributes such as fire resistance showing that UHPC comfortably meets.
Fig 6.1 E Sumner The organically shaped solar shading elements made from UHPC incorporates prestressed steel fibers.
Fig 6.2 E Sumner The 76m footbridge has gained international recognition as a groundbreaking piece of structural design.
Fig 6.3 E Sumner a section through the footbridge showing the location of the tension cables which allow for the impressive free span of the bridge.
Fig 7.1 Author’s Own Birmingham Central Library by John Madin is a fine example of Br Aesthetic Concrete has been very influential in the evolution of architecture, helping many different movements to express their philosophical and theoretical ideals in build forms, but no movement has been defined by concrete quite as much as Brutalism. Brutalism is an architectural movement which emerged in the 50’s and is ‘synonymous with concrete’(Hopkins, 2014). It’s name comes from beton-brut, or raw concrete in english. Public opinion of concrete is still heavily influenced by Brutalism and its impact on the built environment, often perceived to be imposing, overpowering and disproportionate to the human scale. The simple boldness of brutalist architecture something I am aiming to achieve in my design, albeit at a smaller, more human scale than buildings like John Madin’s Birmingham Central Library. It is my aim the the materiality of my design strengthens the overall concept, therefore concrete, with all it’s associations to Brutalism, is the ideal choice of material to create this sense of permanence and power for the structure which will frame temporary structures within.
Fig 7.1 Author’s Own Delph University is another great example of Brutalist architecture which uses bold geometry and widespeard use of concrete for its aesthetic.
The structural properties of concrete are a key factor in the material’s popularity in the construction world. Concrete is, generally speaking, strong in compression (3000 6000 psi) and weak in tension (400 - 700 psi),therefore, steel reinforcements are often added to provide tensional support to structures. Steel does not change the structural properties of concrete, but it compensates for its weaknesses. Many different factors can have an impact upon the strength of concrete. These include: Time - Concrete gains 90% of it’s final strength within the first 28 days after being poured. The ratio of the mixture of ingredients - The higher the water content the weaker the concrete. Having lower levels of water in the mixture does, however, make the the concrete more difficult to work and manipulate. Size of aggregate - The larger the aggregate, the smaller the ratio of size:surface area, meaning the contact area between the cement and the aggregate is relatively smaller which creates a stiffer mix. Moisture levels - While curing, concrete requires appropriate moisture levels and temperature to reach optimum strength. After curing, concrete which is exposed to moisture in the environment such as rainfall continues to gain strength for many years. Admixtures - Chemicals added to the mixture can manipulate the concrete’s properties, making it, for example, more workable without having to add as much water which would compromise the final strength of the concrete.
Concrete skeleton frames such as this one are a fast and simple way of constructing a building’s structure and have therefore become a very standard way of construction residential buildings in southern Spain, with the vast majority of apartment blocks using this method which resembles Le Corbusier’s Dom-ino system. Using structural columns to support the floor planes frees up the facades of the structure for greater architectural expression.
Fig 9.1 Author’s Own An abandoned concrete structure in southern Spain reveals construction techniques such as the exposed reinforcement bars to tie into the floor above
Fig 9.2 http://www.oxfordreference.com/ Le Corbusier’s Dom-ino system
Fig 10.2 shows an abandoned and unfinished concrete structure in Spain which I have photographed, and above, drawn the next level of the structure. This type of concrete structure, precast beam and block, employs both in-situ and precast concrete elements working together to create a more efficient structure and quicken the construction time. Trenches for the foundations are dug from the ground which act as formwork before then being filled with steel reinforced concrete which is cast in-situ. The concrete poured above ground requires formwork, a mould into which the concrete is poured to give it its form. The next stage in the construction of this concrete frame involves casting the beams to support the first floor. These are made from concrete which is cast in-situ and reinforced with steel bars. Steel reinforcement bars are left to protrude from the concrete columns below in order to tie into the next layer of concrete when it is poured, forming a homogenous structure. The space between these beams is then bridge by a number of precast prestressed concrete beams. Precast concrete blocks are placed between the beams. On top of this bed of precast beams and blocks a slab of concrete is poured in-situ and reinforced with a mesh of steel bars. Once this concrete has set the process is repeated for the floors above.
Fig 10.1 Author’s Own An existing precast beam and block structure with services attached.
Fig 10.2 Author’s Own Exploded perspective drawing of conventional precast beam and block structure in southern Spain.
The surface finish of concrete is dictated by texture of the formwork used for the casting of the concrete. The texture can also be affected by air bubbles trapped in the concrete as it is poured, as well as the mixture of the concrete. These air bubbles can be reduced by vibrating the concrete before it has set. Innovative and thoughtful examples which show how the concrete formwork has been a deeply considered part of the finished architecture are Louis Kahn’s Salk Institute, Peter Zumthor’s Bruder Klaus Field Chapel and Ryue Nishizawa’s Teshima Art Museum. These three case studies are fantastic precedents and inspiration for the construction technology of my 1914 design project, as they are all buildings which use concrete cast in-situ to create the building’s surface finish, it’s structure and to define the form of the architecture.
Fig 11.1 Author’s Own A concrete column in Mecanoo’s Birmingham Library which was cast using a single use card tube formwork designed to give a smooth surface finish to the concrete.
Fig 11.2 Author’s Own The grain of the timber used to cast this concrete in Birmingham Repertory Theatre is clearly visible on the finished surface.
Fig 11.3 E Stefanescu This OSB imprinted concrete is from a renovation of bookstore Carturesti in Bucharest and its tactility invites shoppers to engage with the building’s structure.
Peter Zumthor’s Bruder Klaus Field Chapel employed a very unique system of casting in-situ concrete to create an interior space like no other. Logs from the surrounding woodland were built into the form of the interior void. Formwork was built around this structure of logs and the concrete was poured into the mould at intervals, creating 24 different layers of concrete. Once the concrete had been poured and had set, a fire was ignited in the central void and the logs were burned away, leaving a black smoky surface finish to the interior walls. The ties used to hold the formwork in place have been completely removed, creating small tubes for light to penetrate the walls.
Fig 12.1 S Ludwig The exterior of the chapel clearly shows the 24 different layers of concrete and the holes which remain from tying the formwork in place.
Fig 12.2 openhousebcn.files.wordpress. com Logs from surrounding woodland were used to create the textured formwork which was later burned away to leave the charred concrete finish of the chapel’s interior.
Fig 12.3 S Ludwig The heavily textured surface finish created by the construction techniques employed by Peter Zumthor have defined the atmosphere of this piece of architecture.
Louis Kahn, when constructing the Salk Institute, considered the impact of his choice of formwork down to a very small scale. The architect specified that the plywood for the formwork be sanded and coated with a resin to create a smooth finish and that the concrete be vibrated a specific amount to leave a precise number of air bubbles in the mixture. Kahn was ‘quite content to accept imperfections in his concrete … if they revealed the way the material was poured’ (Wiseman, 2007) which shows the respect he had for the construction process. When constructing my own concrete coffee table I used a plastic coated surface for the formwork, this gave the finished concrete an exceptionally smooth finish, similar to materials such as marble or granite.
Fig 13.1 A Perez Kahn’s Salk Institute is defined by its smooth concrete surface which were highly specified by the architect.
Fig 13.2 & 13.3 A Perez Kahn’s Salk Institute used concrete throughout the whole building, from the large prominent walls to the balustrades of the circulation spaces. The concrete mixture and finish was kept uniform throughout the entire building.
Fig 13.4 Author’s own A concrete table I made by employing similar techniques to Kahn. A smooth formwork surface created the polished, tactile concrete surface of the table top.
Ryue Nishizawa’s Teshima Art Museum is a shallow concrete shell structure. The form tries to maintain the curves of the surrounding landscape while keeping the shell as low and shallow as possible. The cheapest way to construct the shell, it was calculated, was construct the formwork using the earth to make the dome onto which the steel reinforcements were laid and the concrete poured. These images show different stages of process. Nishizawa explained in a lecture how the whole structure had to be poured in one go or else the shell wouldn’t have the structural integrity to support itself. Once the concrete had cured, the earth was dug from beneath the concrete shell to reveal the form of the structure. This sense of a changing and inhabited landscape is something I would like to capture with my design and its construction process. Fig 14.1 I Baan The irregular concrete dome situated within the undulating landscape of Teshima Island Japan.
Fig 14.2 I Baan The hollowed out interior space remains after the excavation of the earth used as the formwork for the concrete. The void in the roof used to excavate the earth also allow light into the space.
Fig 14.3 https://www.youtube.com/watch?v=mwh-LtrQDGU Preparing the steel reinforcement on top of the earth formwork.
Fig 14.4 https://www.youtube.com/watch?v=mwh-LtrQDGU Workers tie the carefully specified steel reinforcements.
Fig 14.5 https://www.youtube.com/watch?v=mwh-LtrQDGU The concrete is poured onto one of the steeper sides of the shell structure. This required temporary fences to hold the concrete mix in place.
Fig 14.6 https://www.youtube.com/watch?v=mwh-LtrQDGU Workers finish the surface of the concrete which was cast in one single pour for structural reasons.
Fig 14.7 https://www.youtube.com/watch?v=mwh-LtrQDGU Once the concrete has set, the earth used to create the form is excavated through one of the holes in the structure.
Fig 14.8 https://www.youtube.com/watch?v=mwh-LtrQDGU As the excavation reveals the space within the structure, work commences on the construction of the floor surface.
These precedents have inspired me into thinking in far greater depth about the construction process of the walls. All three of these structures celebrate the technologies and methods used in their production and therefore create architecture with a fantastic sense of narrative. This sense of narrative created by the innovate and celebratory construction processes, works perfectly with my concept which explores ideas of temporary, permanent and changing landscapes. I have designed a temporary pavilion which allows the public to inhabit the construction process of the final design. The timber scaffolding structure incorporates the formwork in which the concrete used for the walls will be cast. The concrete will be poured into the formwork and when set, the temporary pavilion removed to leave the final structure, which will itself hold numerous tempory structures within it. This detail model shows how the temporary pavilion structure will incorporate the formwork for the concrete to be poured into.
Fig 15.1 Author’s own Scaffolding pavilion a
Fig 15.1 Author’s own Detail model
Fig 15.1 Author’s own Scaffolding removed to reveal walls
Fig 15.1 Author’s own Interior of scaffolding structure
The walls for 1914 design project will employ two different strategies for their foundations. The lower walls will use conventional strip foundations cast directly into the ground, however, this system is not strong enough to resist the forces which may be applied to the taller walls, therefore, the taller walls will use a ground anchoring foundation system. Ground anchoring is commonly seen in concrete retaining walls such as this one in Spain. This drawing shows how an anchor is driven through the concrete structure into the earth. An anchor plate is attached between the exterior surface of the concrete wall and a bolt. This bolt is tightened, anchoring the wall the earth. I plan to adapt this system used for the retaining wall for the walls in my design as shown in this drawing.
Fig 16.1 Author’s own Section through retaining wall showing ground anchor technology Fig 16.2 Author’s own Ground anchor plate tightened on exterior face of wall to tension the steel rod.
Fig 17.1 Author’s own Detail section of wall from my 1914 design showing the ground anchor foundation system applied.
External environments can have an impact on the visual appearance of concrete surfaces. Environmental conditions such as the amount of wind and rain interacting with the concrete will cause the appearance to change over time with the growth of biological organisms and staining. Other factors which can impact the weathering of concrete can include adjoining materials. If other materials which also react to external environmental conditions are situated in a way which allows water to flow from them over the surface of the concrete, the colours from these materials can can stain the concrete. Forms and indentations also have an impact on the aesthetic of the weathering. Indentations in the concrete create ‘rain shadows’ and seams for the water run through, concentrating the stained areas. The way concrete reacts to its environment through time makes it a highly suitable material to link with concept which scrutinises what it means to be temporary or permanent. The concrete walls are designed to be perceived as the permanent structures to frame the temporary structures within, yet the weathering of the concrete will mean that the concrete is itself changing.
Fig 18.1 landscapefocused.tumblr. com Freeway Park, Seattle
For all of its positives, concrete does possess some negative attributes, such as its impact on the environment. The production of Portland cement is responsible for around 7% of the world’s carbon emissions, around 11bn tonnes of aggregate are used along with 1 trillion litres of fresh water in concrete mixtures. Concrete is also a tough material to efficiently recycle. Concrete structures can be ground to create aggregate to be used in new concrete mixes, however, recycled concrete has a higher porosity than virgin aggregates which means the concrete requires a higher water content, diminishing the structural properties of concrete.
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