Concrete – An Historic Building Material Concrete is often seen as a very modern substance. The twentieth century saw huge numbers of concrete structures built as modern practices and sciences allowed for larger, stronger, more daring architecture. For the past seventy years almost every major building project has used varying amounts of this incredibly versatile product. It is perhaps surprising then, to learn that humans have been using concrete and cement for pretty much the whole of our civilisation's history. The story begins about twelve million years ago. Limestone and Oil Shale come into contact in what is now Israel and spontaneously burst into flame. Once the fire burnt out, the remaining deposits are the very first cement. Of course at this time they just lay around as piles of dust, as there were no enterprising humans around to take advantage. Nothing else really happens of interest (with regards concrete at least...) until around seven thousand years ago. An early human usage of a concrete like substance was 'Wattle and Daub'. A mixture of clay, sand, straw and cow dung was pasted over wooden slats. Chemical reactions between the clay, sand and lime, which in this case came from the dung, caused the mixture to harden and form wind- and rain-proof walls. The same principle is used today, using high tech ingredients, and thankfully no dung! The ancient Egyptians used a Gypsum based cement in the pyramids 5,000 years ago, and the Chinese held the stone blocks and man-made bricks together on the original Great Wall of China with a similar product. In fact all over the world at this time, people were using wattle and daub, or cemented stone structures. Then came the Romans. From 300BC to 500AD the Romans took what was already known about cement and carried it to an entirely new level. Still based on lime and sand (usually 1:4), they added all kinds of other things to achieve variations in strength, colour, and consistency. Animal fat, milk, and even blood have been recorded! These additives certainly worked though, as incredible structures like the domed roof of the Pantheon prove. This is still the largest unreinforced concrete dome ever made, and it's almost two thousand years old. With the fall of Rome, the best of concrete technology was lost for hundreds of years. The next major breakthrough was in the 17th century, when a process known as Hydration was discovered that underpins the use of concrete to this day. The next few hundred years saw many improvements, including in 1824 the invention of Portland Cement, which was first used in 1828 by Isumbard Kingdom Brunel to fill a breach in the Thames Tunnel. Portland Cement relies on another invention, clinkering, which involves heating the cement to tremendous temperatures, cooling it into nodules, then grinding it up with Gypsum. Yes, thats right, the same Gypsum that the Egyptians were using to hold the pyramids together five thousand years ago. The last hundred years have seen a growth and diversification of the use of concrete that finally lives up to and exceeds the Romans. From small semi-detached houses to skyscrapers hundreds of meters tall, and from roads to gigantic dams like Hoover and Three Gorges. Research and invention continue as we use more and more (six billion cubic meters per year!), so who knows what the future holds for this historic building material.