Pozzolana or pozzuolana (/ˌpɒts(w)əˈlɑːnə/ POT-s(w)ə-LAH-nə, Italian: [potts(w)oˈlaːna]), also known as pozzolanic ash (Latin: pulvis puteolanus), is a natural siliceous or siliceous-aluminous material which reacts with calcium hydroxide in the presence of water at room temperature (cf. pozzolanic reaction). In this reaction insoluble calcium silicate hydrate and calcium aluminate hydrate compounds are formed possessing cementitious properties. The designation pozzolana is derived from one of the primary deposits of volcanic ash used by the Romans in Italy, at Pozzuoli. The modern definition of pozzolana encompasses any volcanic material (pumice or volcanic ash), predominantly composed of fine volcanic glass, that is used as a pozzolan. Note the difference with the term pozzolan, which exerts no bearing on the specific origin of the material, as opposed to pozzolana, which can only be used for pozzolans of volcanic origin, primarily composed of volcanic glass.
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Pozzolana in the context of Roman concrete
Roman concrete, also called opus caementicium, was used in construction in ancient Rome. Like its modern equivalent, Roman concrete was based on a hydraulic-setting cement added to an aggregate.
Many buildings and structures still standing today, such as bridges, reservoirs and aqueducts, were built with this material, which attests to both its versatility and its durability. Its strength was sometimes enhanced by the incorporation of pozzolanic ash where available (particularly in the Bay of Naples). The addition of ash prevented cracks from spreading. Recent research has shown that the incorporation of mixtures of different types of lime, forming conglomerate "clasts" allowed the concrete to self-repair cracks.
Pozzolana in the context of Pozzolan
Pozzolans are a broad class of siliceous and aluminous materials which, in themselves, possess little or no cementitious value but which will, in finely divided form and in the presence of water, react chemically with calcium hydroxide (Ca(OH)2) at ordinary temperature to form compounds possessing cementitious properties. The quantification of the capacity of a pozzolan to react with calcium hydroxide and water is given by measuring its pozzolanic activity. Pozzolana are naturally occurring pozzolans of volcanic origin.
Pozzolana in the context of Catacomb of Commodilla
The Catacombs of Commodilla or Catacombs of Felix and Adauctus is a three-level underground burial complex forming one of the catacombs of Rome. It is sited on via delle Sette Chiese, not very far from via Ostiense, in the Ostiense quartiere. One name derives from its founder or the donor of the land on which it was built, whilst the other its after the two main martyrs buried there, Felix and Adauctus.
The earliest level is the most interesting in archaeological terms, re-using an ancient pozzolana quarry and housing Felix and Adauctus' tombs in a small underground basilica (which contained the notable Commodilla catacomb inscription). The other two levels were developed out from this level. No remains of monuments connected to the complex survive above ground