Modern scientists believe they have discovered the secret to why volcanic sand permitted the creation of concrete buildings capable of outlasting the centuries.
The remarkable ability of the Roman Pantheon to endure the ravages of time for nearly two millennia attests to the extraordinary resilience of ancient recipes for concrete.
The immense concrete building was built in the 2nd century of the Common Era and host to the highest dome in the ancient world, measuring over 43 metres in height.
According to David Moore, author of a book on the ancient structure entitled The Roman Pantheon: The Triumph of Concrete, contemporary building codes would make it impossible to create the Pantheon today, as the entire building was made using concrete without any form of reinforcing structural steel.
Despite the ancient world’s comparative lack of engineering finesse, the Pantheon has managed to withstand centuries of regional earthquakes and weathering by the elements, as well as all the political and military turmoil that has besieged the Italian capital over the course of nearly two thousand years.
It compares extremely favourably to similar structures of far more recent vintage, such as the United States Capital Dome, which was built from cast iron little more than 150 years ago.
The status of the Capital Dome as the defining icon of US political power belies its physical fragility, which has left it with in excess of 1,000 cracks and other defects and prompted the launch of a multi-year restoration project at the start of 2014.
The current overhaul arrives less than 60 years following another complete restoration which was conducted in 1959 – 1960.
What then is the secret to the extraordinary resilience of the Roman Pantheon? Scientists believe it lies in the precise blend of materials employed to produce the concrete from which the entire building was made.
Extant writings by the Roman architect Vitruvius dating from 30BC indicate that the over a century before the construction of the Roman Pantheon ancient engineers were employing volcanic sand as a key ingredient for concrete in order to bolster its strength.
Emperor Augustus subsequently made mortar produced using ash from the Alban Hills volcano as the standard building material for ancient Rome, when he embarked upon a spate of monument creation and restoration at the outset of his reign.
Modern scientists believe they have discovered the secret to why volcanic sand permitted the creation of concrete buildings capable of outlasting the centuries – not just in the form of the Pantheon, but other ancient monuments including Diocletian’s Baths, Hadrian’s Temple, as well as Trajan’s market.
A team of researchers led by volcanologist Marie D. Jackson at the University of California recreated Roman mortar based on Vitruvius’s instructions.
After allowing it to harden for 180 days they examined it using X-ray equipment, and discovered that it was packed with crystals of a material called stratlingite, that had formed as a result of the reaction between the lime and volcanic material.
The material increases the strength of the concrete by reinforcing interfacial zones, which the researchers describe as “the weakest link of modern cement-based concrete,” and preventing the spread of microscopic cracks.
“The pozzolonic mortar perfect by Roman builders during first century AD is key to the durability of concrete components in structurally sound monuments well maintained over two millennia of use,” wrote the researchers in their recently published study entitled Mechanical resilience and cementitious process in Imperial roman architectural mortar.
According to the researchers the material “substantially improved the margin of safety associated with increasingly daring structural designs.”
In addition to strength, another major advantage of concrete made using volcanic ash is that it’s more environmentally friendly than the modern variety made using Portland cement, as it requires lower temperatures and thus less energy to produce.