Engineers have cracked the secret behind the strength of Roman water-based structures. The findings, from a team based out of the University of Utah, could help modern builders tackling projects like the Swansea lagoon’s seawall.
It has long been a mystery as to why Roman structures are still standing after more than 1,500 years while modern sea-walls crumble.
However, a team of Geologists from the University of Utah have revealed how Roman material science has stood the test of time.
The traditional Roman mix for concrete included; volcanic ash, lime (calcium oxide), seawater and lumps of volcanic rock.
This held together everything from piers, breakwaters to harbours.
This technology contrast to modern day materials, as these ancient water-based structures became stronger over time.
It has now been revealed that this is the result of seawater reacting with the volcanic material in the cement. This reaction creates new minerals, tobermorite and phillipsite , that reinforce the concrete.
It was previously known that these minerals (which forms early in the life of the concrete) were created as lime, seawater and volcanic reacted together but the team were able to show that over time seawater would continue to dissolve the volcanic crystals; leaving new minerals in their place.
It is this process that helps reinforce the concrete and stops cracks from growing. Allowing Roman structures to become stronger over time as the minerals grow.
Concrete structures in ancient harbours, ‘become a single stone mass, impregnable to the waves, and every day stronger,’ despite being constantly battered by seawater.Pliny the Elder, writing in Naturalis Historia in 79AD
Meanwhile, modern concrete is based on “Portland Cement” and is not designed to change after it initially hardens. This means that any reactions within it in future will cause damage and weaken the concrete rather than reinforcing it.
This new understanding of the process behind Roman concrete could allow material scientists to develop new types of concrete specifically for use at sea.
Published in American Mineralogist, as “Phillipsite and Al-tobermorite mineral cements produced through low-temperature water-rock reactions in Roman marine concrete” by
Marie D. Jackson, Sean R. Mulcahy, Heng Chen, Yao Li, Qinfei Li, Piergiulio Cappelletti, and Hans-Rudolf Wenk
