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Roman Concrete

The first form of concrete. Devised by the Romans over two thousand years ago some of their concrete structures and buildings are still standing so it is also the longest lasting form of concrete.

Roman Concrete: A photograph of the outside of the Pantheon in Rome built around 126 AD. Photo thanks to Wikipedia.

We are forever indebted to the Romans for their discovery of concrete as a new and revolutionary building material. The use of their techniques lead them to be able to construct buildings like the Pantheon that set a standard in size and design that has taken many hundreds of years equal.

The Roman use of concrete or as they called it Opus Caementicium, allowed them to build roads, bridges and viaducts that allowed their civilisation to expand to the corners of the known world.

• The Roman engineers used a mortar that consisted of quicklime, and various types of volcanic ash and aggregates again derived from volcanic rock.
• Their term for the ash is Pozzolana and we still use the term Pozzolanic or fly ash (which is a by product of coal fired power stations which is very similar to the composition volcanic ash) when we are talking about additives to modern concrete.
• The Romans did mix or pour concrete as we do today.
• In essence they mixed a mortar in a box with hoe like tools that was of a VERY DRY consistency.
• This was then carried in baskets to the location where a layer of aggregate (various sized stones) had been prepared.
• The mortar was then pounded into the gaps around the aggregate until they achieved a solid mass.
• There is absolutely no doubt the the use of mortar in this way with an extremely low water ratio is the secret of the success and longevity of this form of concrete.
• They did not pour concrete as we know it today, but they were the first to dry pack concrete or grout.

So when you are tempted to add a bit of extra water to a mix to make it easy to work, think about those early masters of construction, the Romans and the Opus Caementicium that they discovered.

Roman Concrete: The interior of the Pantheon. Photo thanks to Wikipedia.

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"When we build, let us think that we build for ever."John Ruskin 1819-1900