Pozzolan

Pozzolan, artificial or natural rocks, from silica, alumina, limestone, iron oxide, and alkaline materials, which are generally formed under heat. In conjunction with calcium hydroxide and water, they are capable of binding.

The name comes from the Italian town of Puteoli (now Pozzuoli) in the Campi Flegrei west of Naples, where in ancient times large amounts were obtained at pozzolanic volcanic ash.

Natural pozzolans ( Puzzolanerden ) are either igneous rocks such as volcanic tuff or in Germany, the Rhenish tuff, but also sedimentary rocks which contain a high percentage of soluble silica and partly reactive aluminum oxide (alumina ). Artificial pozzolans are eg clay ( fired clay) or fly ash from coal -fired or lignite power plants.

Pozzolans are used as additives for the production of mortar or concrete, because together with calcium hydroxide ( hydrated lime ) and water react pozzolana hydraulic and pozzolanic reaction in the form calcium silicate hydrates and calcium aluminate hydrates. These are the same crystalline compounds which are formed also in the hardening of the cement, and which effect the strength and structural resistance of the concrete.

Pozzolan was used already in ancient Roman times as an addition to clays for the ceramic production. You should like other admixtures - as chopped straw or crushed brick - provide a better strength of the final product. After the fire, these admixtures could be seen as a small purple brown and black granules. Furthermore, the pozzolan came as an admixture for concrete the Roman (Latin Opus Caementitium ) and the Phoenicians used.

During the Renaissance, red or black pozzolan was used as an additive to lime plaster with frescoes. For example, Michelangelo used the pozzolan for his cleaning in the design of the Sistine Chapel in the Vatican.