Pozzolans
Pozzolans (also pozzolans ) are artificial or natural rocks from silica , alumina, limestone , iron oxide and alkaline substances that have arisen mostly under the influence of heat. In connection with calcium hydroxide and water they can bind .
The name comes from the Italian town of Puteoli (now Pozzuoli ) in the Phlegraean Fields west of Naples , where large amounts of pozzolanic volcanic ash were extracted in ancient times.
Natural pozzolans (pozzolan earths) are either igneous rocks such as volcanic tuff or, in Germany, Rhenish trass , but also sedimentary rocks that contain a high proportion of soluble silica and, in some cases, reactive aluminum oxide (clay). Artificial pozzolans are z. B. brick meal (burnt clay) or fly ash from coal or brown coal fired power plants.
Pozzolans are used as additives for the production of mortar or concrete, because together with calcium hydroxide (hydrated lime) and water, pozzolans react hydratically and form calcium silicate hydrates and calcium aluminate hydrates in the pozzolanic reaction . These are the same crystalline compounds that are formed during the hardening of the cement and which give the concrete its strength and structural integrity .
Pozzolan earth was used as an admixture to clays for ceramic production as early as Roman antiquity . Like other admixtures, such as chopped straw or crushed bricks, it should ensure better strength of the end product. After the fire, these admixtures could be seen as small purple-brown and black granules. In addition, the pozzolan earth was used as an admixture for Roman concrete (Latin: Opus Caementitium ) and by the Phoenicians .
In the Renaissance , red or black pozzolana was used as an admixture to lime plaster under frescoes . For example, Michelangelo used pozzolana for his plaster for the decoration of the Sistine Chapel in the Vatican .
literature
- Anne Viola Siebert : Story (s) in tone. Roman architectural terracottas (= Museum Kestnerianum 16). Schnell + Steiner, Regensburg 2011, ISBN 978-3-7954-2579-1 , pp. 27-28.
Individual evidence
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- ↑ The material lime and its historical use (PDF; 35 kB).
- ^ Fritz Scheidegger: Brief history of the binders . In: Fritz Scheidegger (ed.): From the history of construction technology . 2nd Edition. tape 1 : Basics. Birkhäuser Verlag, Basel / Boston / Berlin 1994, ISBN 978-3-7643-5069-7 , Chapter 3: Building materials, p. 75-86 .
- ↑ The technical structure of Michelangelo's frescoes in the Sistine Chapel in Rome ( Memento of the original of March 14, 2007 in the Internet Archive ) Info: The archive link has been inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice.
