Opus caementicium

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Opus caementicium as the building material for the dome of the Pantheon in Rome
Segment of the Roman Eifel aqueduct made of opus caementicium and a brick segment arch made of natural stone

Opus caementicium (in German, apart from in archaeological specialist publications, mostly written Opus caementitium , also called cast masonry or Roman concrete ) is the Latin name for a concrete-like substance or a certain manufacturing process that the Romans used since the 3rd century BC at the latest. Parts of walls, later whole structures erected.

The similarly composed Opus signinum contained finer aggregates and was used as a waterproof screed mortar and made into decorative screed .

Components

In the opus caementicium there is burnt lime (mostly “white lime” without clay-like components) and aggregates ( quartz , greywacke , sandstone , tuff or broken bricks ) in a ratio of 1: 3. At that time, the limestones were burned in lime kilns or excavated shaft kilns with a diameter of about three meters and a depth of about four meters. The firing temperatures fluctuated between 900 and 1350 ° C depending on the type of stone. In order to obtain a binding agent with hydraulic properties, natural and artificial pozzolans such as tuff, volcanic ash or brick powder were added to the lime . Water-insoluble calcium silicate hydrate is formed from the reaction of the SiO 2 contained in the pozzolans and the Ca (OH) 2 from the burning and extinguishing process of the lime .

I.e. Only when pozzolans or ground bricks are added does the opus caementicium acquire the hydraulic properties that made this mixture harden to form pressure-resistant stone after the addition of water - similar to today's concrete or cement. Opus caementicium therefore also hardens under water. When water is added , the quick lime reacts , generating a lot of heat, and the resulting opus caementicium is shaped and processed hot or warm, whereby the lime components were highly corrosive and could lead to blindness on contact with the eyes.

properties

The compressive strengths of opus caementicium are specified with values ​​of 5 to 40 N / mm² depending on the type of component or type of use and the care taken during installation. With values ​​of approx. 1.53 to 2.59 kg / dm³ for air-dried samples, the gross density is in the range of today's concrete (2.0 to 2.4 kg / dm³). On the other hand, opus caementicium has a significantly higher water absorption capacity than today's concrete with around 20.2 to 54.6% by volume in contrast to 10 to 15% by volume.

Construction and structural development

The construction of the opus caementicium goes back to the Greek model of the so-called 'Emplekton'. Here, a mortar made of rubble and lime was placed between two shells made of masonry, which was supposed to ensure a bond between the masonry. Over time, the Romans used increasingly thinner bowls made of limestone or ceramic bricks, which they filled with a core of lime mortar (the opus caementicium ). Based on the formation of this outer shell, a distinction was made between the forms of opus quadratum (large, hewn limestone), opus incertum (irregular natural stone masonry), opus reticulatum (net-shaped natural stone masonry, stones in pyramid shape with the tip pointing into the interior of the component, approx. 80 BC. ) and opus testaceum (ceramic bricks, around the turn of the ages). They occurred one after the other or in mixed forms ( opus mixtum ). Later, instead of brick shells - similar to today's shuttering elements in concrete construction - wooden beams or boards were used for the duration of the hardening process, which could later be removed and reused.

Opus caementicium was more efficient to work with than masonry made from boulders and hewn natural stone , because it could be poured into molds. For decorative and possibly structural reasons, intermediate layers made of bricks were inserted ( brick penetration ).

Uses

In particular, water pipes and harbor moles were made with the opus caementicium . By adding pozzolanic substances such as tuff , volcanic ash or brick dust , a certain resistance to water was achieved. Large parts (foundation, vault and upper inner walls) of the Colosseum in Rome consist of opus caementicium , and also the Roman domes with huge spans (e.g. the Pantheon in Rome: dome with a diameter of 43.3 meters, approx. 120 AD). BC) only became possible through the use of the opus caementicium . During the construction of the Pantheon, different surcharges were used. Dense travertines were used for the foundation and light aggregates such as tuff or pumice for the dome.

Historical background

Already 1000 BC The Phoenicians mixed their mortars with brick powder and later volcanic sands as pozzolan to achieve solidification underwater. The use of burnt lime also comes from the Phoenicians and was taken over by the Greeks, who used it around 300 BC. Used in southern Italy for the construction of the so-called "Emplekton". This is considered a model for the opus caementicium developed by the Romans .

With the fall of the Roman Empire, there was a decline in the creation of large structures. Hydraulic binders continued to be used in the Middle Ages, and brick flour was used as an artificial pozzolan well into the 19th century. Natural pozzolans such as trass were mainly used in Northern Europe. The search for an alternative to the production of a hydraulic binder finally led to the development of Portland cement in the middle of the 19th century .

literature

  • Heinz O. Lamprecht: Opus caementitium. Construction technology of the Romans. Bau und Technik, 5th edition 2001, ISBN 3-7640-0350-2 .
  • Heinz O. Lamprecht: Buildings made of Roman concrete. Published on the occasion of the permanent exhibition "Opus Caementitium - Roman Building Materials" in the Römisch-Germanisches Museum, Düsseldorf, Beton-Verlag, 1987.
  • Jochen Stark, Bernd Wicht: History of building materials. 1st edition. Bauverlag, Berlin 1998, ISBN 3-7625-3472-1 .
  • Fritz Scheidegger: From the history of construction technology. Volume 1: Basics. 2nd Edition. Birkhäuser, Basel 1994, ISBN 3-7643-5069-5 .
  • Miron Mislin : History of Building Construction and Engineering. From antiquity to modern times. An introduction. 1st edition. Werner-Verlag, Düsseldorf 1988, ISBN 978-3-8041-2684-8 .
  • Stavros K. Kourkoulis: Fracture and failure of natural building stones. Applications in the restoration of ancient monuments. 1st edition. Springer, Dortrecht 2006, ISBN 978-1-4020-5076-3 .

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