Roman concrete

Recent research has shown that the incorporation of mixtures of different types of lime, forming conglomerate "clasts" allowed the concrete to self-repair cracks.

For structural mortars, he recommended pozzolana (pulvis puteolanus in Latin), the volcanic sand from the beds of Pozzuoli, which are brownish-yellow-gray in colour in that area around Naples, and reddish-brown near Rome.

[12] The harbour of Caesarea is an example (22-15 BC) of the use of underwater Roman concrete technology on a large scale,[10] for which enormous quantities of pozzolana were imported from Puteoli.

The composition of the aggregate varied, and included pieces of rock, ceramic tile, lime clasts, and brick rubble from the remains of previously demolished buildings.

Concrete and, in particular, the hydraulic mortar responsible for its cohesion, was a type of structural ceramic whose utility derived largely from its rheological plasticity in the paste state.

The strength and longevity of Roman 'marine' concrete is understood to benefit from a reaction of seawater with a mixture of volcanic ash and quicklime to create a rare crystal called tobermorite, which may resist fracturing.

As seawater percolated within the tiny cracks in the Roman concrete, it reacted with phillipsite naturally found in the volcanic rock and created aluminous tobermorite crystals.

[17][18][19] The Roman concrete at the Tomb of Caecilia Metella is another variation higher in potassium that triggered changes that "reinforce interfacial zones and potentially contribute to improved mechanical performance".

[20] For an environment as prone to earthquakes as the Italian peninsula, interruptions and internal constructions within walls and domes created discontinuities in the concrete mass.

One example is the Pantheon, where the aggregate of the upper dome region consists of alternating layers of light tuff and pumice, giving the concrete a density of 1,350 kilograms per cubic metre (84 lb/cu ft).

[23] Because of its unusual durability, longevity, and lessened environmental footprint, corporations and municipalities are starting to explore the use of Roman-style concrete in North America.

picture showing the concrete underside of a large dome
The Pantheon in Rome is an example of Roman concrete construction.
Caesarea harbour: an example of underwater Roman concrete technology on a large scale
Bare concrete dome interior today called the Temple of Mercury with two square windows halfway up the dome on the far side, a circular oculus at the top, and a water level that reaches up to the base of the dome
The so-called "Temple of Mercury" in Baiae , a Roman frigidarium pool of a bathhouse built in the 1st century BC [ 7 ] containing the oldest surviving concrete dome , [ 8 ] and largest one before the Pantheon . [ 9 ]
Example of opus caementicium on a tomb on the ancient Appian Way in Rome. The original covering has been removed.
Crystal structure of tobermorite : elementary unit cell
Another view of the Pantheon in Rome, including the concrete dome