Roman Concrete - Historic References

Historic References

Vitruvius, writing around 25 BC in his Ten Books on Architecture, distinguished types of aggregate appropriate for the preparation of lime mortars. For structural mortars, he recommended pozzolana, which were volcanic sands from the sandlike beds of Pozzuoli brownish-yellow-gray in color near Naples and reddish-brown at Rome. Vitruvius specifies a ratio of 1 part lime to 3 parts pozzolana for cements used in buildings and a 1:2 ratio of lime to pulvis Puteolanus for underwater work, essentially the same ratio mixed today for concrete used at sea.

By the middle of the 1st century, the principles of underwater construction in concrete were well known to Roman builders. The City of Caesarea was the earliest known example to have made use of underwater Roman concrete technology on such a large scale.

Rebuilding Rome after the fire in 64 AD, which destroyed large portions of the city, the new building code by Nero consisted of largely brick-faced concrete. This appears to have encouraged the development of the brick and concrete industries.

In most usage, the raw concrete surface was considered unsightly and some sort of facing was applied. Different techniques were characteristic of different periods and included:

• Opus incertum: small irregular stones.
• Opus reticulatum: small squared tuff blocks laid in a diamond pattern.
• Opus quadratum: regularly laid courses of ashlars.
• Opus latericium: regularly laid courses of brick.
• Opus spicatum: brick laid in a herringbone pattern.
• Opus vittatum: square tuff blocks intersected by brick bands at regular and irregular distances.
• Opus africanum: vertical chains of upright blocks with alternating horizontal blocks.
• Opus testaceum: thick horizontal brick work.