Roman concrete (also called
Opus caementiciumOpus caementicium, also known by the term Roman concrete, was the Roman technique of constructing structures using concrete. Developed in the Concrete Revolution, it was used from the late Republic of the Roman republic through the whole history of the Roman empire.Opus caementicium, like other...
) was a material used in construction during the
Roman EmpireThe Roman Empire was the post-Republican phase of the ancient Roman civilization, characterised by an autocratic form of government and large territorial holdings in Europe and around the Mediterranean. The term is used to describe the Roman state during and after the time of the first emperor,...
. Roman concrete was based on a hydraulic-setting cement with many material qualities similar to modern
Portland cementPortland cement is the most common type of cement in general use around the world, because it is a basic ingredient of concrete, mortar, stucco and most non-specialty grout...
. By the middle of the first century AD, the material was used frequently as brick-faced concrete, although variations in aggregate allowed different arrangements of materials. Further innovative developments in the material, coined the Roman Concrete Revolution, contributed to structurally complicated forms, such as the
PantheonThe Pantheon is a building in...
dome.
VitruviusMarcus Vitruvius Pollio was a Roman writer, architect and engineer , active in the 1st century BC. By his own description Vitruvius served as a Ballista , the third class of arms in the military offices...
, writing around
25 BCYear 25 BC was a leap year starting on Tuesday of the Julian calendar.-Ancient China:*Government gives tributary states 20000 rolls of silk cloth and about 20000 pounds of silk floss.-Rome:...
in his
Ten Books on Architectureright|thumbnail|A 1521 [[Italian language]] edition of De architectura, translated and illustrated by [[Cesare Cesariano]].' is a treatise on architecture written by the Roman architect Vitruvius and dedicated to his patron, the emperor Caesar Augustus as a guide for building projects...
, distinguished types of aggregate appropriate for the preparation of
lime mortarLime mortar is a type of mortar composed of lime, an aggregate such as sand, and water. It is one of the oldest known types of mortar, dating back to the 4th century BCE and widely used in Ancient Rome and Greece, when it largely replaced the clay and gypsum mortars common to Ancient Egyptian...
s.
Roman concrete (also called
Opus caementiciumOpus caementicium, also known by the term Roman concrete, was the Roman technique of constructing structures using concrete. Developed in the Concrete Revolution, it was used from the late Republic of the Roman republic through the whole history of the Roman empire.Opus caementicium, like other...
) was a material used in construction during the
Roman EmpireThe Roman Empire was the post-Republican phase of the ancient Roman civilization, characterised by an autocratic form of government and large territorial holdings in Europe and around the Mediterranean. The term is used to describe the Roman state during and after the time of the first emperor,...
. Roman concrete was based on a hydraulic-setting cement with many material qualities similar to modern
Portland cementPortland cement is the most common type of cement in general use around the world, because it is a basic ingredient of concrete, mortar, stucco and most non-specialty grout...
. By the middle of the first century AD, the material was used frequently as brick-faced concrete, although variations in aggregate allowed different arrangements of materials. Further innovative developments in the material, coined the Roman Concrete Revolution, contributed to structurally complicated forms, such as the
PantheonThe Pantheon is a building in...
dome.
Historic references
VitruviusMarcus Vitruvius Pollio was a Roman writer, architect and engineer , active in the 1st century BC. By his own description Vitruvius served as a Ballista , the third class of arms in the military offices...
, writing around
25 BCYear 25 BC was a leap year starting on Tuesday of the Julian calendar.-Ancient China:*Government gives tributary states 20000 rolls of silk cloth and about 20000 pounds of silk floss.-Rome:...
in his
Ten Books on Architectureright|thumbnail|A 1521 [[Italian language]] edition of De architectura, translated and illustrated by [[Cesare Cesariano]].' is a treatise on architecture written by the Roman architect Vitruvius and dedicated to his patron, the emperor Caesar Augustus as a guide for building projects...
, distinguished types of aggregate appropriate for the preparation of
lime mortarLime mortar is a type of mortar composed of lime, an aggregate such as sand, and water. It is one of the oldest known types of mortar, dating back to the 4th century BCE and widely used in Ancient Rome and Greece, when it largely replaced the clay and gypsum mortars common to Ancient Egyptian...
s. For structural mortars, he recommended
pozzolanaPozzolana, also known as pozzolanic ash, is a fine, sandy volcanic ash, originally discovered and dug in Italy at Pozzuoli in the region around Vesuvius, but later at a number of other sites...
, which were volcanic sands from the sandlike beds of Puteoli brownish-yellow-gray in color near
NaplesNaples in Italy, is the capital of the region of Campania and of the province of Naples. The city is known for its rich history, art, culture, architecture, music and gastronomy, playing an important role throughout much of its existence; it is over 2,800 years old...
and reddish-brown at
RomeRome is the capital of Italy and the country's largest and most populated municipality , with over 2.7 million residents in , while the population of the urban area is estimated by Eurostat to be 3.46 million. The metropolitan area of Rome is estimated by OECD to have a population of 3.7 million...
. 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 first century AD, 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 ADThe Great Fire of Rome was a large fire which struck ancient Rome in 64 AD. According to the historian Tacitus, the fire started on the night of 18 July, among the shops clustered around the Circus Maximus. As many Romans lived in wood houses without masonry, the fire spread quickly through these...
, which destroyed large portions of the city, the new building code by
NeroNero Claudius Caesar Augustus Germanicus , born Lucius Domitius Ahenobarbus, also called Nero Claudius Caesar Drusus Germanicus, was the fifth and last Roman emperor of the Julio-Claudian dynasty. Nero was adopted by his great uncle Claudius to become heir to the throne...
consisted of largely brick-faced concrete. This appears to have encouraged the development of the brick and concrete industries.
Material properties
Roman concrete, like any concrete, consisted of a mortar and an aggregate. The mortar—a hydraulic cement—was a mixture of lime and a special kind of volcanic deposit, called Pozzolana, or "pit sand." The aggregate varied and included pieces of rock, ceramic tile, and brick rubble from the remains of previously demolished buildings. The pozzolanic mortar used had a high content of alumina and silica.
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 setting and hardening of hydraulic cements derived from hydration of materials and the subsequent chemical and physical interaction of these hydration products. This differed from the setting of slaked lime mortars, the most common cements of the pre-Roman world. Once set, Roman concrete exhibited little plasticity, although it retained some resistance to tensile stresses.
The setting of pozzolanic cements has much in common with setting of their modern counterpart, Portland cement. The high silica composition of Roman pozzolana cements is very close to that of modern cement to which blast furnace
slagSlag is a partially vitreous by-product of smelting ore to separating the metal fraction from the worthless fraction. It can be considered to be a mixture of metal oxides; however, slags can contain metal sulfides and metal atoms in the elemental form...
,
fly ashFly ash is one of the residues generated in the combustion of coal. Fly ash is generally captured from the chimneys of coal-fired power plants, and is one of two types of ash that jointly are known as coal ash; the other, bottom ash, is removed from the bottom of coal furnaces...
, or
silica fumeSilica fume, also known as microsilica, is a fine-grain, thin, and very high surface area silica.It is sometimes confused with fumed silica...
have been added.
Compressive strengths for modern Portland cements are typically at the 50 MPa level and have improved almost ten-fold since 1860. There are no comparable mechanical data for ancient mortars, although some information about tensile strength may be inferred from the cracking of Roman concrete domes. These tensile strengths vary substantially from the water/cement ratio used in the initial mix. At present, there is no way of ascertaining what water/cement ratios the Romans used, nor are there extensive data for the effects of this ratio on the strengths of pozzolanic cements.
Seismic technology
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. Portions of the building could then shift slightly when there was movement of the earth to accommodate such stresses, enhancing the overall strength of the structure. It was in this sense that bricks and concrete were flexible. It may have been precisely for this reason that, although many buildings sustained serious cracking from a variety of causes, they continue to stand to this day.
Another technology used to improve the strength and stability of concrete was its gradation in domes. One example included
the PantheonThe Pantheon is a building in...
, where the aggregate of the upper dome region consisted of alternating layers of light tuff and pumice, giving the concrete a density of 1350 kg/m3. The foundation of the structure used travertine as an aggregate, having a much higher density of 2200 kg/m3.
Literature
- Heather N. Lechtman & Linn W. Hobbs, “Roman Concrete and the Roman Architectural Revolution,” Ceramics and Civilization Volume 3: High Technology Ceramics: Past, Present, Future, edited by W.D. Kingery and published by the American Ceramics Society, 1986
- W. L. MacDonald, The Architecture of the Roman Empire, rev. ed. Yale University Press, New Haven, 1982
- Lynne C. Lancaster, Concrete Vaulted Construction in Imperial Rome, Cambridge University Press, 2005