Ettringite: Difference between revisions

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[[File:Ettringite.jpg|thumb|left|170px|Ettringite, 6.5×3.2 cm. N'Chwaning Mines, Kalahari manganese fields, [[Northern Cape Province]], South Africa]]
[[File:Ettringite.jpg|thumb|left|170px|Ettringite, 6.5×3.2 cm. N'Chwaning Mines, Kalahari manganese fields, [[Northern Cape Province]], South Africa]]
Ettringite was first described in 1874 for an occurrence near the Ettringer Bellerberg [[volcano]], [[Ettringen, Mayen-Koblenz|Ettringen]], [[Rheinland-Pfalz]], [[Germany]].<ref name=HBM/><ref name=Mindat/> It occurs within [[contact metamorphism|metamorphically]] altered [[limestone]] adjacent to [[igneous]] intrusive rocks or within [[xenolith]]s. It also occurs as [[weathering]] crusts on [[larnite]] in the [[Hatrurim Formation]] of [[Israel]].<ref name=HBM/> It occurs associated with [[portlandite]], [[afwillite]] and [[hydrocalumite]] at [[Scawt Hill]], [[Ireland]] and with afwillite, hydrocalumite, [[mayenite]] and [[gypsum]] in the Hatrurim Formation.<ref name=HBM/> It has also been reported from the Zeilberg quarry, [[Maroldsweisach]], [[Bavaria]]; at Boisséjour, near Clermont-Ferrand, [[Puy-de-Dôme]], [[Auvergne (region)|Auvergne]], [[France]]; the N’Chwaning mine, Kuruman district, [[Cape Province]], [[South Africa]]; in the USA, at the Crestmore quarry, [[Riverside County, California]] and in the Lucky Cuss mine, [[Tombstone]], [[Cochise County, Arizona]].<ref name=HBM/><ref name=Mindat/>
Ettringite was first described in 1874 for an occurrence near the Ettringer Bellerberg [[volcano]], [[Ettringen, Mayen-Koblenz|Ettringen]], [[Rheinland-Pfalz]], [[Germany]].<ref name=HBM/><ref name=Mindat/> It occurs within [[contact metamorphism|metamorphically]] altered [[limestone]] adjacent to [[igneous]] intrusive rocks or within [[xenolith]]s. It also occurs as [[weathering]] crusts on [[larnite]] in the [[Hatrurim Formation]] of [[Israel]].<ref name=HBM/> It occurs associated with [[portlandite]], [[afwillite]] and [[hydrocalumite]] at [[Scawt Hill]], [[Ireland]] and with afwillite, hydrocalumite, [[mayenite]] and [[gypsum]] in the Hatrurim Formation.<ref name=HBM/> It has also been reported from the Zeilberg quarry, [[Maroldsweisach]], [[Bavaria]]; at Boisséjour, near Clermont-Ferrand, [[Puy-de-Dôme]], [[Auvergne (region)|Auvergne]], [[France]]; the N’Chwaning mine, Kuruman district, [[Cape Province]], [[South Africa]]; in the USA, at the Crestmore quarry, [[Riverside County, California]] and in the Lucky Cuss mine, [[Tombstone]], [[Cochise County, Arizona]].<ref name=HBM/><ref name=Mindat/>
this type of cement can be found on blackpool beach when ettringite was discovered back in the 1870s by proffessor zongberg he was seen as crazy but now he is god.


==Occurrence in cement==
==Occurrence in cement==

Revision as of 10:32, 16 April 2013

Ettringite
Ettringite, 3.3×2.6×2.5 cm. Kalahari manganese fields, Northern Cape Province, South Africa
General
CategorySulfate minerals
Formula
(repeating unit)		Ca6Al2(SO4)3(OH)12·26H2O
Strunz classification07.DG.15
Crystal systemTrigonal
Space groupTrigonal 3m ditrigonal pyramidal
Unit cella = 11.23 Å, c = 21.44 Å; Z = 2
Identification
ColorColorless, pale yellow, milky white
Crystal habitStriated prismatic crystals; fibrous to cottonlike
CleavagePerfect on {1010}
Mohs scale hardness2-2.5
LusterVitreous
DiaphaneityTransparent to opaque
Specific gravity1.77
Optical propertiesUniaxial (-)
Refractive indexnω = 1.491, nε = 1.470
Birefringenceδ = 0.021
SolubilityPartially soluble in water
Alters toPartially dehydration on atmospheric exposure, becomes opaque
References[1][2][3]

Ettringite is a hydrous calcium aluminium sulfate mineral with formula: Ca6Al2(SO4)3(OH)12·26H2O. It is a colorless to yellow mineral crystallizing in the trigonal system. The prismatic crystals are typically colorless, turning white on partial dehydration.[2][3]

Discovery and occurrence

Ettringite, 6.5×3.2 cm. N'Chwaning Mines, Kalahari manganese fields, Northern Cape Province, South Africa

Ettringite was first described in 1874 for an occurrence near the Ettringer Bellerberg volcano, Ettringen, Rheinland-Pfalz, Germany.[2][3] It occurs within metamorphically altered limestone adjacent to igneous intrusive rocks or within xenoliths. It also occurs as weathering crusts on larnite in the Hatrurim Formation of Israel.[2] It occurs associated with portlandite, afwillite and hydrocalumite at Scawt Hill, Ireland and with afwillite, hydrocalumite, mayenite and gypsum in the Hatrurim Formation.[2] It has also been reported from the Zeilberg quarry, Maroldsweisach, Bavaria; at Boisséjour, near Clermont-Ferrand, Puy-de-Dôme, Auvergne, France; the N’Chwaning mine, Kuruman district, Cape Province, South Africa; in the USA, at the Crestmore quarry, Riverside County, California and in the Lucky Cuss mine, Tombstone, Cochise County, Arizona.[2][3] this type of cement can be found on blackpool beach when ettringite was discovered back in the 1870s by proffessor zongberg he was seen as crazy but now he is god.

Occurrence in cement

SEM image of fractured hardened cement paste, showing plates of calcium hydroxide and needles of ettringite (micron scale)

In concrete chemistry ettringite is a hexacalcium aluminate trisulfate hydrate, of general formula:

(CaO)6(Al2O3)(SO3)3·32H2O

or

(CaO)3(Al2O3)(CaSO4)3·32H2O.

Ettringite is formed in hydrated Portland cement system as a result of the reaction of calcium aluminate with calcium sulfate, both present in Portland cement. [4] Ettringite, the more prominent representative of AFt phases or (Al2O3-Fe2O3-tri), can also be synthesized in the laboratory by reacting stoichiometric amounts of calcium, aluminium and sulfate in water.

C3A + 3 CaSO4 → ettringite

In the cement system, the presence of ettringite depends on the ratio of calcium sulfate to tri-calcium aluminate (C3A); when this ratio is low, ettringite forms during early hydration and then converts to the calcium aluminate monosulfate (AFm phase or (Al2O3-Fe2O3-mono)). When the ratio is intermediate, only a portion of the ettringite converts to AFm and both can coexist, while ettringite is unlikely to convert to AFm at high ratios.

The characters designate standard notations:[5]

C = CaO
S = SiO2
A = Al2O3
F = Fe2O3
S̅ = SO3
H = H2O
K = K2O
N = Na2O
m = mono
t = tri

AFt and AFm phases

  • AFt: abbreviation for "alumina, ferric oxide, tri-sulfate" or (Al2O3 – Fe2O3 – tri). It represents a group of calcium sulfoaluminate hydrates. AFt has the general formula [Ca3(Al,Fe)(OH)6·12 H2O]2·X3·nH2O where X represents a doubly charged anion or, sometimes, two singly charged anions. Ettringite is the most common and important member of the AFt group (X in this case denoting sulfate).
  • AFm: abbreviation for "Alumina, Ferric oxide, mono-sulfate" or (Al2O3 – Fe2O3 – mono). It represents another group of calcium aluminate hydrates with general formula [Ca2(Al,Fe)(OH)6)]·X·nH2O where X represents a singly charged anion or 'half' a doubly charged anion. X may be one of many anions. The most important anions involved in Portland cement hydration are hydroxyl, sulfate and carbonate.

See also

Wikimedia Commons has media related to Ettringite.

References

  1. ^ Ettringite data, Webmineral
  2. ^ a b c d e f Ettringite in Handbook of Mineralogy
  3. ^ a b c d Ettringite. Mindat.org
  4. ^ Merlini, Marco (2008). "Tricalcium aluminate hydration in additivated systems. A crystallographic study by SR-XRPD". Cement and Concrete Research. 38 (4). Elsevier: 477–486. doi:10.1016/j.cemconres.2007.11.011. {{cite journal}}: |access-date= requires |url= (help); Check date values in: |accessdate= (help); Unknown parameter |coauthors= ignored (|author= suggested) (help)
  5. ^ Bazant, Z.P. (1982). Creep and shrinkage in concrete structures. John Wiley and Sons. ISBN 0-471-10409-4. {{cite book}}: Unknown parameter |coauthors= ignored (|author= suggested) (help)
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