Editing Pozzolan

'''Pozzolans''' are a broad class of siliceous and aluminous materials which, in finely divided form and in the presence of water, chemically react with calcium hydroxide (Ca(OH)₂) at ordinary temperatures to form compounds possessing cementitious properties. The reaction is known as the '''pozzolanic reaction'''.

The term derives from '''pozzolana''', a volcanic ash first exploited by the Romans near the town of Pozzuoli (ancient Puteoli) in Italy. Modern pozzolans include both natural materials and industrial by-products.

== Types of pozzolans ==

=== Natural pozzolans ===
* Volcanic ashes and tuffs (e.g., Italian pozzolana, Santorin earth, Bavarian trass, Japanese shirasu)
* Pumicite and pumice
* Diatomaceous earth (diatomite)
* Calcined clays and shales (metakaolin, burnt clay)
* Volcanic glass

=== Artificial (man-made) pozzolans ===
* '''Fly ash''' (Class F and Class C) – the most widely used artificial pozzolan worldwide
* Silica fume (microsilica)
* Ground granulated blast-furnace slag (sometimes considered a latent hydraulic binder rather than a true pozzolan)
* Rice husk ash
* Metakaolin (produced by controlled calcination of kaolin clay)
* Burnt oil shale ash

== Pozzolanic reaction ==
The general reaction can be expressed as:

:Silica or silica + alumina (from pozzolan) + Ca(OH)₂ + H₂O → Calcium silicate hydrate (C-S-H) and calcium aluminate hydrate (C-A-H)

The primary product, C-S-H, is the same gel responsible for strength and durability in ordinary Portland cement hydration.<ref name="Mehta2006">{{cite book |last1=Mehta |first1=P.K. |last2=Monteiro |first2=P.J.M. |title=Concrete: Microstructure, Properties, and Materials |edition=3rd |publisher=McGraw-Hill |year=2006 |isbn=978-0-07-146289-1}}</ref>

== Benefits in concrete ==
Use of pozzolans in concrete provides several advantages:
* Reduced heat of hydration
* Improved long-term strength and durability
* Lower permeability and increased resistance to sulfate attack and alkali-silica reaction (ASR)
* Reduced calcium hydroxide content (lower risk of efflorescence and chemical attack)
* Lower carbon footprint when replacing part of Portland cement
* Better workability with certain pozzolans (e.g., fly ash)

== Standards and specifications ==
* ASTM C618 – Standard Specification for Coal Fly Ash and Raw or Calcined Natural Pozzolan for Use in Concrete<ref>{{cite web |title=ASTM C618-23 |url=https://www.astm.org/c0618-23.html |publisher=ASTM International |year=2023}}</ref>
* ASTM C1240 – Standard Specification for Silica Fume Used in Cementitious Mixtures
* EN 197-1 – Cement – Part 1: Composition, specifications and conformity criteria for common cements (includes pozzolanic cements)
* EN 450-1 – Fly ash for concrete
* IS 3812 (Part 1) – Indian Standard for Pulverised Fuel Ash as pozzolana

== History ==
The Romans extensively used natural pozzolana mixed with lime to produce hydraulic mortar capable of setting underwater. Notable surviving structures include the Pantheon dome and many Roman harbors (e.g., Portus Cosanus).<ref name="Vitruvius">{{cite book |last=Vitruvius |title=De Architectura (Ten Books on Architecture) |chapter=Book II, Chapter 6 |year=c. 25 BCE}}</ref>

== References ==
{{Reflist}}

== Further reading ==
* Snellings, R., Mertens, G., & Elsen, J. (2012). "Supplementary cementitious materials". ''Reviews in Mineralogy and Geochemistry'', 74(1), 211–278. {{doi|10.2138/rmg.2012.74.6}}
* Juenger, M.C.G., et al. (2019). "Advances in alternative cementitious binders". ''Cement and Concrete Research'', 141, 106344. {{doi|10.1016/j.cemconres.2019.106344}}

[[Category:Cement]]
[[Category:Concrete]]
[[Category:Building materials]]
[[Category:Volcanology]]
[[Category:Ancient Roman technology]]
[[Category:Waste materials]]