About Concrete

Modern ready mix concrete, as supplied by Cambridge-based suppliers Madmix, is an affordable, convenient and durable building material that is widely used in construction projects around the world. But what exactly is concrete, how did it come to be invented and what are its main ingredients?

History of concrete

Concrete tends to be thought of as a modern product, but it was used by the ancient Romans to create buildings including the Pantheon, with its famous dome. However, the technology was forgotten for centuries during the Middle Ages.

A breakthrough came in the mid 18th century, when engineer John Smeaton, from Leeds, made the first modern concrete, using hydraulic lime and powdered brick. His work paved the way for another advance in 1824, when inventor Joseph Aspdin, from the same city, burned clay and limestone together to create Portland cement – still a key ingredient of concrete today. Reinforced concrete was invented in France in the mid 19th century, by Joseph Monier.

After these discoveries, concrete was soon being used for industrial building, including dams, bridges and tunnels. Today, it is the world’s most widely used man-made material. Around ten billion tons are produced globally every year, with concrete being used in everything from homes to airports, car parks and skyscrapers.

Key constituents of concrete

Cement

A basic ingredient of concrete is Portland cement. This is created from limestone, which is heated together with clay and sand in a kiln. The resulting product is known as cement clinker, and is ground together with a small quantity of gypsum to make the finished cement.

Aggregates

The largest volume of a concrete mixture is made up of aggregates, which include gravel, sand and stone. Including aggregate helps to make concrete a far more durable material than cement on its own would be. Modern aggregates are sustainably sourced and recycled concrete is also increasingly being used as a replacement for aggregate from quarries.

Water

Water is the third key ingredient in ready mix concrete. The amount used needs to be strictly controlled, to ensure the proportions are right and that the finished product has the right strength and flow.

Chemical admixtures

Different types of concrete are needed for specific applications. Specialist mixes are created by using a range of additives, known as admixtures, which can be either powders or fluids. These can include corrosion inhibitors to protect any steel structures within the concrete, plasticisers to make the mixture more workable, or pumping agents to create a pumpable concrete.

Steel and fibre reinforced concrete

In some types of construction, steel reinforcement is needed. This will usually be decided during discussions at the planning stage, for instance with the local authority. If you do need to use steel in your project, please let us know before you order, as this could affect the type of mix which is suitable.

For some types of project, fibre reinforced concrete can provide a good alternative to steel mesh. We offer mixes including polypropylene fibres, which make the finished concrete more durable, enhance the surface and mean a reduction in plastic cracking.

Speed of setting and curing

How long does it take for concrete to set? The answer is that it normally stays workable for just over an hour. However, this time can vary, depending on the type of mix and the conditions. For instance, hot weather or the wetter the consistency you have will mean that concrete sets more quickly. If there are special reasons that mean you need your concrete ready mix to remain workable for longer, a retarder can be added to avoid it partially setting too soon.

If new concrete dries out too quickly, it can be weakened and there is more risk of cracks occurring. To avoid this happening, it needs to be cured. The most straightforward method of doing this is to cover the new surface with polythene and ideally kept damp, leaving it there for 10 days in winter, though only 7 days are normally needed in summer. In conditions with a risk of freezing, an air gap can be left.

Certified concrete

Companies which supply concrete can receive the British standard kitemark if their products, processes and procedures are recognised as meeting high quality standards. Madmix is entitled to use the BSI kitemark because of our quality management systems, which meet the requirements of ISO 9001.