Opus caementicium in Roman age: a Revolution in Building Technique

The “opus caementicium” in roman age [IV/III sec aC – IV/V sec dC]: a revolution in the building technique Most monumental Roman constructions that can still be seen today are notable for their solidity, building skill, structural resistance, high degree of specialisation, and complexity. One particularly representative form of construction is that of opus caementicium, a type of concrete that is specifically Roman, in terms of both its choice of ingredients and the methods used to prepare and put it in place. Mortar was of course used before roman time, but only in the creation of the Roman opus caementicium are the quality of the sand and lime and the proportions of the mixture precisely defined, and approximately from the second century aC pozzolana was added causing a chemical reaction that made the mortar much more tenacious, with marked hydraulic characteristics, and with a compressive strength around 120 kg per cmq; about 8 times that of a similar lime and sand mortar. This type of concrete is extremely flexible and suitable for multiple uses, and it could also set underwater. It was used for a wide range of construction elements, from foundations to elevation walls, to ceilings and, with particularly striking effect, vaulted spaces. This encouraged the development of solutions that were innovative not only in technical terms, but also in terms of architectural experimentation. The chronological and geographical extent of the use of opus caementicium – almost a thousand years, from the 4th-3rd century BC to the 4th-5th century AD, and its spread across the entire Mediterranean basin – both testify to its resistance and durability. Variations, improvements and particular solutions did appear over time, but always maintaining a considerable degree of technical uniformity, showing how they were part of a recognised and commonly accepted construction system. The development and carefully targeted use of Roman concrete – both in terms of the choice of ingredients, as in the case of pozzolana, and in terms of method – was undoubtedly a revolution in ancient construction technique. The effectiveness of Roman concrete is still recognised and appreciated today, to the extent that it is the object of special research into its ingredients to see if the results might be of assistance to modern techniques.