A pozzolan is a material which, when combined with calcium hydroxide, exhibits cementitious properties. Pozzolans are commonly used as an addition (the technical term is "admixture") to Portland cement concrete mixtures to increase the long-term strength and other material properties of Portland cement concrete. Pozzolans are primarily vitreous siliceous materials which react with calcium hydroxide to form calcium silicates; other cementitious materials may also be formed depending on the constituents of the pozzolan.

The pozzolanic reaction may be slower than the rest of the reactions that occur during cement hydration, and thus the short-term strength of concrete made with pozzolans may not be as high as concrete made with purely cementitious materials. On the other hand, highly reactive pozzolans, such as silica fume and high reactivity metakaolin can produce "high early strength" concrete that increase the rate at which concrete gains strength.

The first known pozzolan was pozzolana, a volcanic ash, for which the category of materials was named. The most commonly used pozzolan today is fly ash, though silica fume, high-reactivity metakaolin, ground granulated blast furnace slag, and other materials are also used as pozzolans.

A pozzolan is a siliceous or aluminosiliceous material, which is highly vitreous. This material independently has few/fewer cementitious properties, but in the presence of a lime-rich medium like calcium hydroxide, shows better cementitious properties towards the later day strength (> 28 days).The mechanism for this display of strength is the reaction of silicates with lime to form secondary cementitious phases (calcium silicate hydrates with a lower C/S ratio) which display gradual strengthening properties usually after 7 days.

The extent of the strength development depends upon the chemical composition of the pozzolan: the greater the composition of alumina and silica along with the vitreous phase in the material, the better the pozzolanic reaction and strength display.

ee also

*Portland cement
*Sodium silicate

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  • pozzolan cement — pucolaninis cementas statusas T sritis chemija apibrėžtis Cementas iš rišamosios medžiagos ir aktyvių mineralinių priedų – pucolanų. atitikmenys: angl. pozzolan cement; pozzolanic cement; puzzolan cement; puzzolanic cement rus. пуццолановый… …   Chemijos terminų aiškinamasis žodynas

  • pozzolan portland cement — pucolaninis portlandcementis statusas T sritis chemija apibrėžtis Pucolaninis cementas, kuriame yra 20–40% pucolanų. atitikmenys: angl. pozzolan portland cement; pozzolanic portland cement; puzzolan portland cement; puzzolanic portland cement rus …   Chemijos terminų aiškinamasis žodynas

  • pozzolan — noun see pozzolana …   New Collegiate Dictionary

  • pozzolan — poz·zo·lan (pŏt sə länʹ) also poz·zo·la·na ( sə läʹnə) or poz·zuo·la·na ( swə ) n. 1. A siliceous volcanic ash used to produce hydraulic cement. 2. Any of various artificially produced substances resembling pozzuolana ash.   [Italian pozzolana,… …   Universalium

  • pozzolan — noun Any material which, when combined with calcium hydroxide, exhibits cementitious properties; often used as an extender with Portland cements. See Also: pozzolanic cement, pozzolanic fly ash cement …   Wiktionary

  • Pozzolan — Poz|zo|lan, Poz|zu|o|lan: ↑ Puzzolan. * * * Poz|zo|lan, Poz|zu|o|lan: ↑Puzzolan …   Universal-Lexikon

  • Pozzolan — Poz|zo|lan 〈n.; Gen.: s, Pl.: e〉 = Puzzolan …   Lexikalische Deutsches Wörterbuch

  • Pozzolan — Poz|zo|lan, Poz|zu|o|lan die; Lehnübersetzung von gleichbed. it. pozzolana, nach dem Ort Pozzuoli am Vesuv> vgl. ↑Puzzolan …   Das große Fremdwörterbuch

  • pozzolan — poz·zo·lan …   English syllables

  • pozzolan — noun see pozzolana …   Useful english dictionary

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