Concrete is everywhere in our modern day society. The buildings we live and work in are almost all comprised of some portion of concrete. Foundations, walls and even features can be created using concrete. Modern applications of concrete include self-cleaning mixtures and even translucent concrete. But what actually is concrete? How does it work? What makes concrete the greatest of modern building materials?
Concrete or Cement?
Many people get confused when talking about concrete and cement. Perhaps the easiest way to think about it is that with out cement there is no concrete. Concrete comprises aggregate, water and cement. It is the cement that makes the magical mixture of concrete. But what exactly is cement? How does it work? Let us part the veil of history and look back at the history of cement. About 12 million years ago a shale oil deposit combusted next to a bed of limestone in what is now Israel and created the first cement deposit, another natural cement deposit was found in volcanic Pozzuoli, Italy by the Romans who combined the volcanic ash they found there with water to make a naturally binding agent. From this discovery birthed architectural wonders like the Colosseum and the Pantheon. What a fascinating substance, a fine powder that when combined with simple water has a reaction, and transforms into a binding agent. We take it as commonplace today, and it is commonplace, Cement is the most used man made product in the world. Think about that for a second. The most used substance in the world! The chemical reaction that makes this all possible is an inorganic chemical reaction called Mineral Hydration. That is not about a sport drinks at all, in fact it is about how a mineral reacts with water. Some minerals have no reaction to H2O, yet some like slaked lime, and Pozzolanic materials do have a chemical reaction to water and polymerise to make a dense mortar like material. Today Portland cement is the most used in the world. The blast furnaces run 24 hours a day baking a mixture of limestone and an alumino-silicate clay into ‘Clinker’, which is then ground into a fine powder bagged up and shipped all over the world as cement.
So we have cement, the main ingredient, and water to make a Hydraulic reaction, so all we need now is aggregate. This is the easy part. Aggregate is generally just pebbles or crushed rock that gives the cement something to bind around, giving greater volume, strength and form to the intended structure. There are many different recipes for creating concrete depending on what is required. Mortars contain little or no aggregate as they are designed to bind together large bricks, which form the aggregate in a way themselves. There are also additions like optic fibres to make translucent concrete or even adding Titanium Dioxide to the cement to make a concrete that will self clean and even process toxic smog into easily disposed by products such as water, oxygen, carbon dioxide, nitrates and sulphates which easily wash away.
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