The history of Roman cement

The term "cement" is derived from Latin word “caemente”, which Romans used as term for masonry constructed of irregular stone blocks and some binding material. At the beginning of 18th century it was translated to French language as "ciment". This term is used for material solidifying under the water up to now.

The Romans applied above mentioned hydraulic materials very often. They made up concrete for vaults, bridges and another structures with binding material made up of slack lime and 20 – 75 % of volcanic ash of Puzzuola vicinity. The significant structure constructed by Romans of this material is the bridge Port du Gard near Nimes in southern France during the 1st century. The blocks are bound by mortar made up of mix of lime and Puzzolana soil. The ration was probably 1:2 up to 1:5. Application of this material was significantly reduced during the medieval times.

Puzzolana is hydraulic active matter with volcanic origin. They are tuff, volcanic ash, pumice etc. In its broader sense Puzzolana also includes some of sedimentary rocks as radiolarite, diatomite, spongilite, sandy marlstone etc.

The original Puzzolana is volcanic ash. The most famous Puzzolana are "santorin" (Roman and Neapolitan Puzzolana, Rhinish, Bavarian and Romanian trasses[1].

Similar mortars were used during the history also in Czech territory. It is the technological analogy to so called "Romanesque cement". The hydraulic lime from Zlíchov lime works known as "Pasta di Praga" belongs to this group too. This lime was famous in the Europe during the 18th century and was applied also within the construction of moles and some structures in Venice, Amsterdam and London. As a part of Austrian monarchy Czech territories imported hydraulic lime from Kufstein in Austria. This one was baked of marls or clay limestones occurring in the Kufstein vicinity. It was high quality hydraulic lime used for plasters of significant structures in Prague.

Romanesque cement is component of historically used hydraulic mortars. It was baked of "hydraulic" limestone (composition is similar to mixture for production of Portland cement) – clay limestone. These limestones often occur in many regions in Italy (Tuscany, Calabria, Emilia-Romagna) and abroad. They often occur also in the Czech Republic. These limestones are used for production so called "natural cement". The difference between the Romanesque cement and natural cement is in the baking temperature. Romanesque cement is baked below the temperature 900 – 1100°C. Hydraulic active materials contain higher content of reactive SiO2, which at the standard temperature (20°C) reacts with Ca(OH)2 while calcium-silicate phase is formed.

[1] Trass is local Italian term for light coloured mostly trachyte tuff composed mostly of pumice particles
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