HOME

TheInfoList



OR:

Pozzolana or pozzuolana ( , ), also known as pozzolanic ash ( la, pulvis puteolanus), is a natural
siliceous Silicon dioxide, also known as silica, is an oxide of silicon with the chemical formula , most commonly found in nature as quartz and in various living organisms. In many parts of the world, silica is the major constituent of sand. Silica is ...
or siliceous- aluminous material which reacts with
calcium hydroxide Calcium hydroxide (traditionally called slaked lime) is an inorganic compound with the chemical formula Ca( OH)2. It is a colorless crystal or white powder and is produced when quicklime ( calcium oxide) is mixed or slaked with water. It has m ...
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
cement A cement is a binder, a chemical substance used for construction that sets, hardens, and adheres to other materials to bind them together. Cement is seldom used on its own, but rather to bind sand and gravel (aggregate) together. Cement m ...
itious properties. The designation pozzolana is derived from one of the primary deposits of
volcanic ash Volcanic ash consists of fragments of rock, mineral crystals, and volcanic glass, created during volcanic eruptions and measuring less than 2 mm (0.079 inches) in diameter. The term volcanic ash is also often loosely used to refer ...
used by the Romans in
Italy Italy ( it, Italia ), officially the Italian Republic, ) or the Republic of Italy, is a country in Southern Europe. It is located in the middle of the Mediterranean Sea, and its territory largely coincides with the homonymous geographical ...
, at Pozzuoli. The modern definition of pozzolana encompasses any volcanic material (
pumice Pumice (), called pumicite in its powdered or dust form, is a volcanic rock that consists of highly vesicular rough-textured volcanic glass, which may or may not contain crystals. It is typically light-colored. Scoria is another vesicular v ...
or
volcanic ash Volcanic ash consists of fragments of rock, mineral crystals, and volcanic glass, created during volcanic eruptions and measuring less than 2 mm (0.079 inches) in diameter. The term volcanic ash is also often loosely used to refer ...
), 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.


Historical use

Pozzolanas such as Santorin earth were used in the Eastern Mediterranean since 500–400 BC. Although pioneered by the ancient Greeks, it was the Romans that eventually fully developed the potential of lime-pozzolan pastes as binder phase in
Roman concrete Roman concrete, also called , is a material that was used in construction in ancient Rome. Roman concrete was based on a hydraulic-setting cement. It is durable due to its incorporation of pozzolanic ash, which prevents cracks from spreading. By ...
used for buildings and underwater construction.
Vitruvius Vitruvius (; c. 80–70 BC – after c. 15 BC) was a Roman architect and engineer during the 1st century BC, known for his multi-volume work entitled '' De architectura''. He originated the idea that all buildings should have three attribut ...
speaks of four types of pozzolana: black, white, grey, and red, all of which can be found in the volcanic areas of Italy, such as
Naples Naples (; it, Napoli ; nap, Napule ), from grc, Νεάπολις, Neápolis, lit=new city. is the regional capital of Campania and the third-largest city of Italy, after Rome and Milan, with a population of 909,048 within the city's adminis ...
. Typically it was very thoroughly mixed two-to-one with lime just prior to mixing with water. The Roman port at Cosa was built of pozzolana-lime concrete that was poured under water, apparently using a long tube to carefully lay it up without allowing sea water to mix with it. The three
pier Seaside pleasure pier in England.html" ;"title="Brighton, England">Brighton, England. The first seaside piers were built in England in the early 19th century. A pier is a raised structure that rises above a body of water and usually juts out ...
s are still visible today, with the underwater portions in generally excellent condition even after more than 2100 years.


Geochemistry and mineralogy

The major pozzolanically active component of volcanic
pumice Pumice (), called pumicite in its powdered or dust form, is a volcanic rock that consists of highly vesicular rough-textured volcanic glass, which may or may not contain crystals. It is typically light-colored. Scoria is another vesicular v ...
s and
ashes Ashes may refer to: *Ash, the solid remnants of fires. Media and entertainment Art * ''Ashes'' (Munch), an 1894 painting by Edvard Munch Film * ''The Ashes'' (film), a 1965 Polish film by director Andrzej Wajda * ''Ashes'' (1922 film), a ...
is a highly porous
glass Glass is a non-Crystallinity, crystalline, often transparency and translucency, transparent, amorphous solid that has widespread practical, technological, and decorative use in, for example, window panes, tableware, and optics. Glass is most ...
. The easily alterable, or highly reactive, nature of these ashes and pumices limits their occurrence largely to recently active volcanic areas. Most of the traditionally used natural pozzolans belong to this group, i.e., volcanic pumice from Pozzuoli, Santorin earth and the incoherent parts of German trass. The chemical composition of pozzolana is variable and reflects the regional type of
volcanism Volcanism, vulcanism or volcanicity is the phenomenon of eruption of molten rock (magma) onto the Earth#Surface, surface of the Earth or a solid-surface planet or moon, where lava, pyroclastics, and volcanic gases erupt through a break in the su ...
. SiO2 being the major chemical component, most unaltered pumices and ashes fall in the intermediate (52–66 wt% SiO2) to acid (>66 wt% SiO2) composition range for glassy rock types outlined by the
IUGS The International Union of Geological Sciences (IUGS) is an international non-governmental organization devoted to international cooperation in the field of geology. About The IUGS was founded in 1961 and is a Scientific Union member of the Inte ...
. Basic (45–52 wt% SiO2) and ultrabasic (<45 wt% SiO2) pyroclastics are less commonly used as pozzolans. Al2O3 is present in substantial amounts in most pozzolanas, Fe2O3 and MgO are present in minor proportions only, as is typical or more acid rock types. CaO and alkali contents are usually modest but can vary substantially from pozzolana to pozzolana. The mineralogical composition of unaltered
pyroclastic rock Pyroclastic rocks (derived from the el, πῦρ, links=no, meaning fire; and , meaning broken) are clastic rocks composed of rock fragments produced and ejected by explosive volcanic eruptions. The individual rock fragments are known as pyroc ...
s is mainly determined by the presence of phenocrysts and the chemical composition of the parent
magma Magma () is the molten or semi-molten natural material from which all igneous rocks are formed. Magma is found beneath the surface of the Earth, and evidence of magmatism has also been discovered on other terrestrial planets and some natura ...
. The major component is volcanic glass typically present in quantities over 50 wt%. Pozzolana containing significantly less volcanic glass, such as a trachyandesite from Volvic (France) with only 25 wt% are less reactive. Apart from the glass content and its morphology associated with the
specific surface area Specific surface area (SSA) is a property of solids defined as the total surface area of a material per unit of mass, (with units of m2/kg or m2/g) or solid or bulk volume (units of m2/m3 or m−1). It is a physical value that can be used to dete ...
, also defects and the degree of strain in the glass appear to affect the pozzolanic activity. Typical associated minerals present as large phenocrysts are members of the
plagioclase Plagioclase is a series of tectosilicate (framework silicate) minerals within the feldspar group. Rather than referring to a particular mineral with a specific chemical composition, plagioclase is a continuous solid solution series, more pro ...
feldspar Feldspars are a group of rock-forming aluminium tectosilicate minerals, also containing other cations such as sodium, calcium, potassium, or barium. The most common members of the feldspar group are the ''plagioclase'' (sodium-calcium) feld ...
solid solution series. In pyroclastic rocks in which alkalis predominate over Ca, K-feldspar such as sanidine or
albite Albite is a plagioclase feldspar mineral. It is the sodium endmember of the plagioclase solid solution series. It represents a plagioclase with less than 10% anorthite content. The pure albite endmember has the formula . It is a tectosilica ...
Na-feldspar are found.
Leucite Leucite is a rock-forming mineral of the feldspathoid group, silica-undersaturated and composed of potassium and aluminium tectosilicate KAlSi2O6. Crystals have the form of cubic icositetrahedra but, as first observed by Sir David Brewster ...
is present in the K-rich, silica-poor
Latium Latium ( , ; ) is the region of central western Italy in which the city of Rome was founded and grew to be the capital city of the Roman Empire. Definition Latium was originally a small triangle of fertile, volcanic soil ( Old Latium) on ...
pozzolanas.
Quartz Quartz is a hard, crystalline mineral composed of silica ( silicon dioxide). The atoms are linked in a continuous framework of SiO4 silicon-oxygen tetrahedra, with each oxygen being shared between two tetrahedra, giving an overall chemical ...
is usually present in minor quantities in acidic pozzolanas, while
pyroxene The pyroxenes (commonly abbreviated to ''Px'') are a group of important rock-forming inosilicate minerals found in many igneous and metamorphic rocks. Pyroxenes have the general formula , where X represents calcium (Ca), sodium (Na), iron (Fe II) ...
s and/or
olivine The mineral olivine () is a magnesium iron silicate with the chemical formula . It is a type of nesosilicate or orthosilicate. The primary component of the Earth's upper mantle, it is a common mineral in Earth's subsurface, but weathers qui ...
phenocrysts are often found in more basic materials. Xenocrysts or rock fragments incorporated during the violent eruptional and depositional events are also encountered. Zeolite, opal CT and clay minerals are often present in minor quantities as alteration products of the volcanic glass. While zeolitisation or formation of opal CT is in general beneficial for the pozzolanic activity, clay formation has adverse effects on the performance of lime-pozzolan blends or blended cements.


Modern use

Pozzolana is abundant in certain locations and is extensively used as an addition to Portland cement in countries such as Italy, Germany, Kenya, Uganda,Turkey, China and Greece. Compared to industrial by-product pozzolans they are characterized by larger ranges in composition and a larger variability in physical properties. The application of pozzolana in Portland cement is mainly controlled by the local availability of suitable deposits and the competition with the accessible industrial by-product supplementary cementitious materials. In part due to the exhaustion of the latter sources and the extensive reserves of pozzolana available, partly because of the proven technical advantages of an intelligent use of pozzolana, their use is expected to be strongly expanded in the future.


Pozzolanic reaction

The pozzolanic reaction is the
chemical reaction A chemical reaction is a process that leads to the chemical transformation of one set of chemical substances to another. Classically, chemical reactions encompass changes that only involve the positions of electrons in the forming and break ...
that occurs in portland cement containing pozzolans. It is the main reaction involved in the
Roman concrete Roman concrete, also called , is a material that was used in construction in ancient Rome. Roman concrete was based on a hydraulic-setting cement. It is durable due to its incorporation of pozzolanic ash, which prevents cracks from spreading. By ...
invented in
Ancient Rome In modern historiography, ancient Rome refers to Roman civilisation from the founding of the city of Rome in the 8th century BC to the collapse of the Western Roman Empire in the 5th century AD. It encompasses the Roman Kingdom (753–50 ...
. At the basis of the pozzolanic reaction stands a simple acid-base reaction between
calcium hydroxide Calcium hydroxide (traditionally called slaked lime) is an inorganic compound with the chemical formula Ca( OH)2. It is a colorless crystal or white powder and is produced when quicklime ( calcium oxide) is mixed or slaked with water. It has m ...
(as Portlandite) and silicic acid.


See also

* Calcium silicate hydrate (CSH) *
Cement A cement is a binder, a chemical substance used for construction that sets, hardens, and adheres to other materials to bind them together. Cement is seldom used on its own, but rather to bind sand and gravel (aggregate) together. Cement m ...
* Cement chemist notation *
Concrete Concrete is a composite material composed of fine and coarse aggregate bonded together with a fluid cement (cement paste) that hardens (cures) over time. Concrete is the second-most-used substance in the world after water, and is the most ...
* Energetically modified cement (EMC) *
Fly ash Fly ash, flue ash, coal ash, or pulverised fuel ash (in the UK) plurale tantum: coal combustion residuals (CCRs)is a coal combustion product that is composed of the particulates (fine particles of burned fuel) that are driven out of coal-fired ...
* Metakaolin * Portland cement * Pozzolan * Pozzolanic reaction (main page) *
Pumice Pumice (), called pumicite in its powdered or dust form, is a volcanic rock that consists of highly vesicular rough-textured volcanic glass, which may or may not contain crystals. It is typically light-colored. Scoria is another vesicular v ...
* Rice hull ash *
Roman concrete Roman concrete, also called , is a material that was used in construction in ancient Rome. Roman concrete was based on a hydraulic-setting cement. It is durable due to its incorporation of pozzolanic ash, which prevents cracks from spreading. By ...
* Silica fume


References

{{reflist * Cook D.J. (1986) Natural pozzolanas. In: Swamy R.N., Editor (1986) ''Cement Replacement Materials'', Surrey University Press, p. 200. * McCann A.M. (1994) "The Roman Port of Cosa" (273 BC), ''Scientific American, Ancient Cities'', pp. 92–99, by Anna Marguerite McCann. Covers, ''hydraulic concrete, of "Pozzolana mortar"'' and the ''5 piers, of the Cosa harbor, the Lighthouse on pier 5,'' diagrams, and photographs. Height of Port city: 100 BC. * Snellings R., Mertens G., Elsen J. (2012) Supplementary cementitious materials. Reviews in Mineralogy and Geochemistry 74:211–278. Volcanology Cement Concrete