What the Romans are Teaching us about Concrete

What the Romans are Teaching us about Concrete

20th July 2017

We took a look at nano concrete, reinforced concrete, self-healing concrete and even concrete that glows!  The more we looked at concrete and researched it, the more fascinated we became about this versatile building material – we found it being used in art applications and we explained the difference between concrete and cement. 

About eighteen months ago we ran a series of articles on concrete, one of the most common building materials on the planet.  We wrote about the History of Concrete and several articles on innovative new types of concrete which are transforming the way we build. 

Well, concrete has been in the news again recently, but not because of any new, high-tech developments that have taken place – quite the opposite, in fact.  Several online and print news media outlets have been reporting the fact that concrete used by Roman builders to construct piers and harbours still stands today, despite the fact that modern concrete decays in just decades when exposed to salt water. 

Coastal structures constructed by Roman builders more than 1,500 years ago are still standing in many parts of Europe and scientists at the University of Utah have been studying them to find out what the Romans knew that we don’t know when it comes to using concrete on our coastlines.  The concrete made by the Romans has proved so durable that Pliny the Elder was right when he described it in his Natural History as “impregnable to waves and every day stronger”!

As we mentioned in our History of Concrete article, concrete has been used for thousands of years but was first harnessed by the Romans more than two thousand years ago.  At the height of the Roman Empire, an ashy volcanic sand from the Campi Flegrei super volcano was used to mix a mortar strong enough to bind together lumps of rock into an impenetrable load bearing material.  This volcanic sand, named pozzolana by the Romans is a mix of lime and silica oxides (the two main ingredients in cement)

When modern, 21st Century scientists studied the Roman concrete to ascertain why it’s so durable and long-lasting, they discovered that the key to its durability lies in a chemical, reaction caused by the addition of sea water.  When the Roman coastal concrete was analysed it was discovered to contain lime particles within the cores that contained the mineral aluminous tobermorite, a rare substance that is difficult to make.

The lime, seawater and volcanic ash used to form the mortar reacted together to generate heat.  Over time, seawater seeping through the concrete dissolved the volcanic crystals resulting in aluminous tobermorite and phillipsite crystallising in their place.  These minerals have helped to reinforce the concrete, preventing cracks from growing and making the concrete stronger over time. 

Modern concrete is based on Portland cement which does not change after it hardens, which means that any reactions with the material will cause damage and lead to concrete degradation which weakness the structure.  The scientists’ discovery is paving the way for a new concrete recipe which doesn’t rely on the high temperatures and carbon dioxide production of modern cement but will provide a more durable construction material for use in marine and coastal environments.