Concrete is everywhere. It's used more than any other man-made material on the planet. 
It's often seen as relatively modern, a product of the industrial age, but concrete was used extensively by the Romans - the interior dome of the Pantheon in Rome is made from concrete. The substance fell out of use for 13 centuries but resurfaced in Britain in the late eighteenth century, and it has been embraced by the construction industry ever since, due to its versatility and toughness.
In the Fifties, the Brutalist movement embraced concrete, leaving the raw surface exposed as a feature of many of their buildings, like the iconic Barbican Centre in London. The style then fell out of fashion and raw concrete lost its popularity, becoming associated with council estates and urban decay.
Recently, however, concrete is undergoing something of a renaissance. Big name ‘starchitects' such as Zaha Hadid are choosing to use the material extensively and overtly, excited by its design possibilities. And it isn't just big public buildings that are being formed from concrete - it's gaining popularity on a domestic scale too, with practices such as UN Studio, Jamie Fobert and Gianni Botsford designing homes that make concrete a feature.
What is concrete?
We produce five billion cubic yards of concrete every year, making it the second most widely consumed substance on earth, after water. Concrete is a mix of cement, water and aggregates (rock and sand). Varying the mix of the constituent parts can alter the strength and quality of finish of the concrete. The less water in the mix, the stronger it will be. Liquid when first mixed and poured into a mould (called formwork and usually made of wood), concrete then ‘goes off', setting hard.
It's very strong in compression, but needs reinforcement with something else (usually steel) to increase its tensile strength. Even once concrete is set it takes a long time before it reaches full strength; it's assumed to reach half-strength after 28 days.
Concrete is often seen as an industrial material with a very hard edge, used in motorway bridges, underpasses and council flats.
This tough, brutal image is misleading; concrete can be beautiful. The fact it is poured as a liquid and sets means architects can design buildings with sumptuous curves - as you can see in the work of Zaha Hadid. Its huge mass can achieve quiet and tranquil simplicity; just look at the buildings of Japanese architect Tadao Ando, a master of the material. Its huge strength can also achieve cantilevers and huge spans which are full of drama.
Words: Joanna Booth
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 What is concrete?
Concrete is a mix of cement, water and aggregate - rocks and sand. It is liquid when first formed (the less water in the mix, the stronger it will be), and is poured into a mould where it then ‘goes off', setting hard. Though concrete sets relatively quickly, it takes some time for it to reach its full strength; it's assumed to reach half strength 28 days after pouring. Most of the time, it is mixed at a plant, transported by road and poured at the construction site. However, prefabricated concrete panels are growing in popularity.
Though very strong in compression, concrete needs reinforcement with another material - usually steel - to increase its tensile strength. Its load-bearing qualities mean that concrete is often used for foundations and structural walls. However, it needn't be the dirty little secret holding a building up - it can be used decoratively too. You can use concrete to make fire surrounds, bathrooms and even kitchen worktops - though you'll need to make sure the material is properly sealed.
If you think the raw concrete is too harsh under grey British skies then there are plenty of softer options. Decorative shuttering can create beautiful textures for internal feature walls. Concrete Blond produces walls with many different textures and effects. And you don't need to leave concrete grey: the aggregate used will subtly vary the colour and, for vibrant effects, companies such as Crete Designs use pigments and stains to turn concrete any colour under the sun. |
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Concrete usually gets a bad rap from environmentalists, and understandably so, but there are eco pros and cons
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The quarries from which the aggregate is taken can scar the landscape. Because quick delivery is crucial for ready-mix concrete, it goes by road, creating millions of lorry journeys per year. Making cement produces a lot of CO2 emissions, then the chemical process that occurs when concrete sets creates even more.
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These effects can be somewhat mitigated by using a concrete made with pulverised fuel ash or ground granulated blast furnace slag. These are both waste products from power stations, and can be used to replace up to 50 per cent of the cement in concrete. Most ready-mix contractors offer this kind of aggregate - to search for a company near you, go to www.aggregain.org.uk. To find out where pulverised fuel ash actually comes from, the United Kingdom Quality Ash Association has this information on its website, www.ukqaa.org.uk.
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To make your mix more environmentally friendly still, the aggregate could be old concrete, ground up and recycled.
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Concrete is incredibly tough and long-lasting, so using it can increase a building's lifespan.
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Your concrete can also be used in a way that helps the environment. A concrete block wall can store about twice the heat of a plaster stud wall. This is called high thermal mass, and means concrete can work as a heat sink, warming up slowly during the day and then emitting heat in the cool of the night - or vice versa, in summer.
To find out more about the various applications of concrete and how it can be an eco choice, visit www.concrete.org.uk and www.sustainableconcrete.org.uk.
Words: Joanna Booth |
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