UTAH-While you might expect 2,000-year-old piers to be on their last legs, ancient structures built by the Romans are now stronger than ever – thanks to seawater.

Researchers have examined Roman structures around Italy, and found that seawater filtering through the concrete leads to the growth of minerals that strengthen the structures.

The team hopes that the findings will help to develop a modern equivalent that could be used to strengthen modern buildings.

Researchers from the University of Utah were interested in understanding why 2,000-year-old Roman piers and breakwaters are stronger now than when they were first built.

Romans made concrete by mixing volcanic ash with lime and seawater to make a mortar, and then adding in chunks of volcanic rock.

This type of concrete was used to build many famous structures, including the Pantheon, and Trajan’s Markets in Rome, as well as huge marine structures to protect harbours.

In contrast, modern cement tends to be made out of sand and gravel, which can turn to paste and crack the concrete over time.

Marie Jackson, who led the study, said: ‘This alkali-silica reaction occurs throughout the world and it’s one of the main causes of destruction of Portland cement concrete structures.’

The researchers wanted to know what made the Roman cement so resilient.

One factor they found was that minerals tended to grow between the mortar and rock, preventing cracking.

In 2009, the researchers discovered a very rare mineral, called aluminous tobermorite in the marine mortar of drill cores taken from around Italy. The presence of the mineral surprised the researchers, as even making it in the laboratory requires very high temperatures, and only results in small quantities.

Ms Jackson said: ‘No one has produced tobermorite at 20 degrees Celsius. Oh - except the Romans!’

Following on from this, the researchers have now studied the drill cores again, and found several other minerals, including zeolite and phillipsite, had formed in the cement.

Ms Jackson said: ‘As geologists, we know that rocks change.

‘Change is a constant for earth materials. So how does change influence the durability of Roman structures?’

The team suggests that when seawater infiltrates the concrete in breakwaters and in piers, it dissolves components of the volcanic ash and allows new minerals to grow from the highly alkaline leached fluids, particularly Al-tobermorite and phillipsite.

They suggest that this Al-tobermorite has crystals similar to those that form in volcanic rocks, which reinforce the cementing matrix, and prevent it from becoming brittle.

Ms Jackson said: ‘We’re looking at a system that’s contrary to everything one would not want in cement-based concrete.

‘We’re looking at a system that thrives in open chemical exchange with seawater.’

While the obvious thing would be to re-create the concrete, unfortunately this isn’t as straight-forward as it sounds.

Ms Jackson said: ‘The recipe was completely lost.’

‘Romans were fortunate in the type of rock they had to work with. They observed that volcanic ash grew cements. We don’t have those rocks in a lot of the world, so there would have to be substitutions made.’

The researchers are now hoping to develop a replacement cement using materials from the western US.