For the architectural material actually used by the ancient Romans, see Roman concrete
Roman concrete was a material used in construction during the late Roman Republic through the whole history of the Roman Empire. Roman concrete was based on a hydraulic-setting cement with many material qualities similar to modern Portland cement...
"Roman cement" is a substance developed by James Parker in the 1780s, and finally patented in 1796. It was, in fact, nothing like any material used by the Romans, but was a "Natural cement
In the most general sense of the word, a cement is a binder, a substance that sets and hardens independently, and can bind other materials together. The word "cement" traces to the Romans, who used the term opus caementicium to describe masonry resembling modern concrete that was made from crushed...
" made by burning septaria - nodules that are found in certain clay deposits, and that contain both clay minerals
Clay minerals are hydrous aluminium phyllosilicates, sometimes with variable amounts of iron, magnesium, alkali metals, alkaline earths, and other cations. Clays have structures similar to the micas and therefore form flat hexagonal sheets. Clay minerals are common weathering products and low...
and calcium carbonate
Calcium carbonate is a chemical compound with the formula CaCO3. It is a common substance found in rocks in all parts of the world, and is the main component of shells of marine organisms, snails, coal balls, pearls, and eggshells. Calcium carbonate is the active ingredient in agricultural lime,...
. The burnt nodules were ground to a fine powder. This product, made into a mortar
Mortar is a workable paste used to bind construction blocks together and fill the gaps between them. The blocks may be stone, brick, cinder blocks, etc. Mortar becomes hard when it sets, resulting in a rigid aggregate structure. Modern mortars are typically made from a mixture of sand, a binder...
with sand, set in 5–15 minutes. The success of "Roman Cement" led other manufacturers to develop rival products by burning artificial mixtures of clay and chalk
Chalk is a soft, white, porous sedimentary rock, a form of limestone composed of the mineral calcite. Calcite is calcium carbonate or CaCO3. It forms under reasonably deep marine conditions from the gradual accumulation of minute calcite plates shed from micro-organisms called coccolithophores....
There has been recent resurgence of interest in Natural Cements/ Roman Cements due mainly to the need for repair of facades done in this material in the 19th Century. The major confusion involved for many people in this subject is the terminology used.
Roman Cement - was originally the name given, by Parker, to the cement he patented which is a Natural Cement (i.e. it is a marl(or limestone containing integral clay) dug out of the ground, burnt and ground to a fine powder).
Later, in the 1900s various sources of the correct type of marl - known also as Cement Stone, were discovered across Europe and so there were a range of natural cements (with varying properties) in use across Europe.
It was in 1824 that Joseph Aspdin 'invented' Portland Cement. This was done by adding various materials together to make an artificial version of natural cement. There then followed a number of independently discovered or copied version of this 'Portland Cement' [Also referred to as Proto Portland cement]. Proto Portland cement
Portland 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...
does have a different chemical make up from other Natural Cements being produced at the same time: It was burnt at a higher temperature than other N.C.'s and thus crosses the barrier between traditional Vertical Kiln fired N.C. and the later Horizontal Kiln fired Artificial Cements. This Cement is NOT, however, the same as the modern Ordinary Portland Cement, which can be defined as Artificial Cement.
Artificial Cement: It is with the development in the 1860s of rotating Horizontal Kiln
technology that the properties of cement changed quite dramatically and could be argued to result in modern Cement.
Certainly it is now difficult to actually define whether an old render was a Natural Cement (Single Source Marl) or an artificial one, but there is no doubt if the cement was Vertically kiln fired or Horizontally.
The names Natural Cement or Roman Cement then defines a cement coming from a single source rock
Early or Proto Portland Cement could be used for early cement that comes from a number of sourced and mixed materials.
There is no widely used terminology for these 19th Century cements.
There had been, in order to rediscover this technology, two projects carried out by the European Union ROCEM and subsequently ROCARE http://www.rocare.eu/
(an ongoing project). Both these only deal with Natural Cement - referred to as Roman Cement without reference to the early artificial cements.