Almost 2000 years old and virtually intact, the Pantheon in Rome stands as testament not only to the engineering skill of an Empire that accelerated the development and application of concrete, but also to the durability of concrete as a sustainable construction material.

case study 7_photo2.jpgThe Pantheon (“Temple of all the Gods”) was originally built as a temple to the seven deities of the seven planets in the state religion of Ancient Rome. Built of concrete, it has been in continuous use throughout its history, and is the best preserved of all Roman buildings.

The Pantheon’s massive portico, consisting of three rows of eight columns, leads to the rotunda, upon which rests the building’s most distinctive feature – its 43.2m-domed concrete roof.

In order to support the dome, eight-barrel vaults in the massively thick 6.4m rotunda wall carry its downward thrust. In the absence of steel reinforcing, the dome’s weight was minimised through several design features. The dome is configured as five rows of 28 square coffers that diminish in size as they approach the central 8.7m diameter opening (oculus) at the top of the dome. The coffers not only enhance the aesthetic of the building, but more importantly they reduce the thickness and therefore the weight of the concrete dome. At its base the concrete dome is more than 6m thick, but diminishes to about 1.2m at the edge of the oculus.

Also crucial to the dome’s reduced weight are the variances in the type of concrete. Towards the oculus, unglazed to further reduce the dome’s weight, a much less dense concrete mix was used containing a relatively light pumice aggregate.

While the Romans cannot be credited with the invention of concrete, an honour belonging to the Egyptians, they were certainly instrumental in its large-scale uptake. This adoption is based upon the use of volcanic ash from near Pozzuoli, which when combined with lime resulted in a concrete far stronger than anything previously produced.

Pozzolanic cement, as the material became known, quickly established itself as a core construction material in all large-scale Roman construction projects. The theatre at Pompeii, built in 75 BC relied heavily on concrete, as did the Colosseum, built around AD 82. As the largest and most iconic of Roman amphitheatres, the Colosseum made use of dense concrete in its foundations, as well as lightweight concrete in its numerous arches and vaults.  

Hundreds of examples of Roman structures made using concrete still stand today, ranging from magnificent temples and sporting arenas, to functional bridges, aqueducts, reservoirs and sewers. There are even instances of the underwater use of concrete in Roman breakwaters. Their continued existence today embodies not only the enterprise and innovation of their creators, but also the long-term durability of concrete.

Concrete technology has undoubtedly developed over the centuries, but it is not a coincidence that the designers of Te Papa, New Zealand’s national museum, chose concrete as its structural material to achieve a 350-year expected life without significant maintenance.