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{{Short description|Aluminate Ferrite trisubstituted phases}}
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'''AFt Phases''' refer to the calcium Aluminate Ferrite trisubstituted, or calcium aluminate trisubstituted, phases present in hydrated (or hardened) cement paste (HCP) in [[Chemistry:Concrete|concrete]].<ref name="Taylor_1997" /><ref name="Lea_2019" />

== AFm and AFt phases in cement hydration products ==
Calcium aluminates can form complex salts in combination with different types of [[Physics:Ion|anions]]. Two series of calcium aluminates are known in [[Cement chemist notation|cement chemistry]]: [[Chemistry:AFm phases|AFm]] and AFt phases, being respectively mono- or tri-substituted with a given divalent anion X (''e.g.'' {{chem2|SO4(2–)}}, {{chem2|CO3(2–)}}, or hosting a divalent impurity such as {{chem2|SeO4(2–)}}<ref name="Baur2003" />...), or with two units of a monovalent anion, ''e.g.'' {{chem2|OH-}}, {{chem2|Cl-}}, or hosting a monovalent impurity such as {{chem2|I-}}, or {{chem2|B(OH)4-}}<ref name="Champenois2012" />...). 

Their general formulas are respectively: 

{|
|-
| {{space|4}} || AFm phases: || {{chem2|3CaO*Al2O3*CaX*nH2O}}, or {{chem2|C4AXH_{n}|}}  in [[Cement chemist notation|cement chemist notation]] (CCN)
|-
| {{space|4}} || AFt phases: || {{chem2|3CaO*Al2O3*3CaX*nH2O}}, or {{chem2|C6AX3H_{n}|}} in CCN
|}

in which n, the number of water molecules present in the hydrate, is in the range 10 to 12 for the AFm phases, and around 32 for the AFt phases.<ref name="Carlson_Berman_1960" />

== AFt phases ==
AFt phases are important [[Earth:Mineral hydration|hydration]] products of the cement clinker. They are [[Earth:Crystal|crystalline]] [[Chemistry:Hydrate|hydrate]]s with generic formula {{chem2|3CaO*(Al,Fe)2O3*3CaX*nH2O}} when also taking into account the possible substitution of the aluminium ion ({{chem2|Al(3+)}}) by the ferric ion ({{chem2|Fe(3+)}}). They are formed when [[Chemistry:Tricalcium aluminate|tricalcium aluminate]] ({{chem2|3CaO*Al2O3}}, also noted {{chem2|C3A}}) reacts with a dissolved calcium salt ({{chem2|CaX}}). {{chem2|CaX}} is most commonly {{chem2|link=calcium sulfate|CaSO4}}, but can also be {{chem2|link=calcium carbonate|CaCO3}} giving rise to sulfoaluminate, or carboaluminate, respectively.

=== Tri-sulfoaluminate ===
{{Main article|Chemistry:Ettringite}}
[[File:Ettringite-99753.jpg|thumb|260px|[[Chemistry:Ettringite|Ettringite]] is the main representative of AFt phases. It crystallizes under the form of characteristic acicular needles, often encountered as fibrous aggregates filling small cavities in concrete.]]
The main and most known AFt phase is [[Chemistry:Ettringite|ettringite]], also existing as a natural mineral which was first described in 1874 by {{nobreak|J. Lehmann}},<ref>Lehmann, J. (1874). Über den Ettringit, ein neues Mineral in Kalkeinschlüssen der Lava von Ettringen (Laacher Gebiet). N. Jb. Mineral. Geol. Paläont., 273–275.</ref> for an occurrence near the Ettringer Bellerberg Volcano, Ettringen, Rheinland-Pfalz, {{wipe|Germany}}.

Ettringite is also known as the 'Candlot's salt' in honor of the pioneering work of the French chemist {{ill|Édouard Candlot|fr}} (1858-1922) who studied cement hydration and discovered calcium sulfo-aluminates.<ref name="Candlot_1890" /><ref name="Thiery_2021" /> Henri Louis Le Chatelier also identified AFt phases when he investigated cement hydration products after the discovery of Candlot.<ref name="LeChatelier_1905" />

In the years 1930-1940, the system {{chem2|CaO\sAl2O3\sCaSO4\sK2O\sH2O}} at 25°C was studied in detail by Jones.<ref name="Jones_1938" /><ref name="Jones_1939" /><ref name="Jones_1944a" /><ref name="Jones_1944b" /><ref name="Jones_1945" />

In [[Cement chemist notation|concrete chemistry]], [[Chemistry:Ettringite|ettringite]] is an hexacalcium aluminate trisulfate [[Chemistry:Hydrate|hydrate]], of general formula {{chem2|6CaO*Al2O3*3SO3*32H2O}}, or {{chem2|3CaO*Al2O3*3CaSO4*32H2O}}, also abbreviated as C<sub>6</sub>A{{overline|S}}<sub>3</sub>H<sub>32</sub> in [[Cement chemist notation|cement chemist notation]].

Ettringite is formed in the hydrated Portland cement system as a result of the reaction of [[Chemistry:Tricalcium aluminate|tricalcium aluminate]] ({{chem|C|3|A}}) with [[Chemistry:Calcium sulfate|calcium sulfate]], both present in Portland cement.<ref name="Merlini_2008" />

:{{chem2|C3A + 3 CaSO4 + 32 H2O → ettringite}}

Ettringite, the most prominent representative of AFt phases or ({{chem2|Al2O3 \s Fe2O3 \s tri}}), can also be directly synthesized in [[Chemistry:Aqueous solution|aqueous solution]] by reacting stoichiometric amounts of [[Chemistry:Calcium oxide|calcium oxide]], [[Chemistry:Aluminium oxide|aluminium oxide]], and [[Chemistry:Calcium sulfate|sulfate]].

In the cement system, the presence of ettringite depends on the [[Ratio|ratio]] of calcium sulfate to tri-calcium aluminate ({{chem2|C3A}}); when this ratio is low, ettringite forms during early hydration and then converts to the corresponding calcium aluminate monosulfate ([[Chemistry:AFm phases|AFm phase]] or ({{chem2|Al2O3 \s Fe2O3 \s 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.

=== Tri-carboaluminate ===
Jones (1938) reported the existence and some optical characteristics of AFt and AFm calcium carboaluminate hydrate phases.<ref name="Jones_1938" /> Feldman ''et al.'' (1965) have shown that the hydration reaction of {{chem2|3CaO*Al2O3}} can be suppressed by {{chem2|CaCO3}} additions and that this is primarily due to the formation of calcium carboaluminate onto the surface of the {{chem2|C3A}} grains.<ref name="Feldman_1965" /> The mechanism is the same as with the sulfate ion released by the more soluble gypsum added to the cement clinker during its milling to prevent the flash setting of concrete.

According to Carlson and Berman (1960)<ref name="Carlson_Berman_1960" /> and Klieger (1990),<ref name="Klieger_1990" /> carbonate-AFm, monocarbonate and hemicarbonate, are more stable than carbonate-AFt, the tricarboaluminate. 

Lothenbach and Winnefeld (2006)<ref name="Lothenbach_2006" /> [[Physics:Thermodynamic equilibrium|thermodynamic]] calculations also indicate that in the presence of small amounts of [[Chemistry:Calcite|calcite]], calcium aluminate monocarbonates (AFm) are present amongst the main common hydration products of ordinary Portland cement, along with the other hydrates, [[Chemistry:Calcium silicate hydrate|C-S-H]], [[Chemistry:Portlandite|portlandite]], and [[Chemistry:Ettringite|ettringite]].<ref name="Lothenbach_2006" />

The tricarboaluminate, {{chem2|3CaO*Al2O3*3CaCO3*32H2O}} (C<sub>6</sub>A{{overline|C}}<sub>3</sub>H<sub>32</sub>), is the carbonate equivalent of ettringite, {{chem2|3CaO*Al2O3*3CaSO4*32H2O}} (C<sub>6</sub>A{{overline|S}}<sub>3</sub>H<sub>32</sub>). It has an [[Physics:Isomorphism (crystallography)|isomorph structure]] and the same number of water hydration molecules: 32 {{H2O}}. The corresponding monocarboaluminate {{chem2|3CaO*Al2O3*CaCO3*11H2O}} (C<sub>4</sub>A{{overline|C}}H<sub>11</sub>) is also less hydrated: 11 water molecules in place of 12 for the monosulfoaluminate.

== Reactivity of {{chem2|C3A}} during clinker hydration ==
{{Main article|Chemistry:Tricalcium aluminate}}
Amongst the four main phases of the cement clinker ([[Chemistry:Alite|alite]]: {{chem2|link=alite|C3S}}, [[Chemistry:Belite|belite]]: {{chem2|link=belite|C2S}}, {{chem2|link=tricalcium aluminate|C3A}}, and the tetracalcium alumino ferrite: {{chem2|link=|C4AF}}), the [[Chemistry:Tricalcium aluminate|tricalcium aluminate]] ({{chem2|C3A}}: {{chem2|3CaO*Al2O3}}), is the most reactive phase and its [[Chemistry:Hydration reaction|hydration reaction]] is also the most exothermic. If nothing is done to control and slow down the {{chem2|C3A}} hydration rate, [[Chemistry:Concrete|concrete]] can be easily subjected to flash setting, especially if the ambient temperature is elevated during the summer. 

This is why a small addition of {{nowrap|2 – 5 wt. %}} of [[Chemistry:Gypsum|gypsum]] ({{chem2|link=gypsum|CaSO4*2H2O}}: [[Chemistry:Solubility|solubility]] {{nowrap|~ 1 – 2 g/L water}}) is done to the clinker during the grinding process to manufacture cement. During the making of [[Chemistry:Concrete|concrete]], gypsum dissolves at the contact with water, freeing up {{chem2|Ca(2+)}} and {{chem2|SO4(2–)}} [[Physics:Ion|ion]]s in solution. These ions react with aluminate {{chem2|Al(OH)4-}} ions present at the surface of the hydrating {{chem2|C3A}} grains forming a thin [[Earth:Hydraulic conductivity|impervious]] coating of less soluble [[Chemistry:Ettringite|ettringite]] according to the following reaction:<ref name="Divet2000" /> 

:{{chem2|6 Ca(2+) + 2 Al(OH)4- + 4 OH- + 3 SO4(2-) + 26 H2O -> 3CaO*Al2O3*3CaSO4*32H2O}}

As a consequence, the surface of {{chem2|C3A}} particles undergoes some [[Engineering:Passivation|passivation]], becomes less accessible, and the  {{chem2|C3A}} hydration reaction slows down. A similar effect, although less pronounced, can also be obtained in the presence of the less soluble [[Chemistry:Calcium carbonate|calcium carbonate]] ({{chem2|link=calcite|CaCO3}}).<ref name="Feldman_1965" />

== Conversion of AFt-sulfate ⇌ AFm-sulfate ==
In the absence of an external source of sulfate ions, the transformation of [[Chemistry:Ettringite|ettringite]] (AFt) into [[Chemistry:AFm phases|AFm]] and ''vice versa'' depends both on [[Physics:Temperature|temperature]] and on [[Chemistry:PH|pH]] conditions (concentration in [[Chemistry:Hydroxide|{{chem2|OH-}}]] ions) in the concrete pore water.<ref name="Divet1998" /><ref name="Divet2000" /> Different mechanisms can co-exist and can explain these transformations. 

A first mechanism can directly depend on the respective [[Chemistry:Chemical stability|thermodynamic stability]] ([[Chemistry:Solubility|solubility]]: dissolution-[[Chemistry:Precipitation|precipitation]] reactions) of each phase, as a function of temperature and pH. 

Another mechanism can depend on the [[Physics:Sorption|sorption]] of sulfate anions onto the [[Chemistry:Calcium silicate hydrate|C-S-H]] phases. The sorption of {{chem2|SO4(2-)}} onto C-S-H increases with temperature and pH. At high T, or high pH, because of this sorption, the concrete pore water is depleted in sulfate anions and AFm preferentially forms with respect to AFt (ettringite). When T, or pH, decreases due to the cooling of concrete after setting and hardening, or because of the leaching of the concrete structure by water (immersed concrete component, such as a [[Engineering:Deep foundation|pile]] of a [[Engineering:Bridge|bridge]]), the sulfate ions physically [[Chemistry:Adsorption|adsorbed]] onto C-S-H are released ([[Physics:Desorption|desorption]] process) into the concrete pore water and become available for the slow [[Physics:Crystal growth|crystal growth]] of AFt (ettringite).<ref name="Divet1998" /> 

Other mechanisms have also been proposed in the literature, such as the slow and delayed release of sulfate ions by the clinker. Oxidation of [[Chemistry:Iron(II) sulfide|iron(II) sulfide]]s, such as [[Chemistry:Pyrite|pyrite]] ({{chem2|FeS2}}), or [[Chemistry:Pyrrhotite|pyrrhotite]] (Fe<sub>(1-x)</sub>S), sometimes present in [[Chemistry:Construction aggregate|construction aggregate]]s can also represent an additional internal source of sulfate into concrete. 

One mechanism does not necessarily exclude the other ones as all can co-exist. If the external sulfate attacks (ESA) are relatively well known, for internal sulfate attack (ISA) (delayed ettringite formation, DEF) there is no unanimity on the relative importance of the main mechanism at work inside concrete and the question is still debated.<ref name="Divet2000" /><ref name="Neville2004" />

=== Effect of temperature ===
[[File:Ettringite-99347.jpg|thumb|alt=Ettringite needles|[[Chemistry:Ettringite|Ettringite]] needles growing radially]]
At temperature lower than 65 °C, ettringite (AFt) is less soluble than AFm and therefore ettringite precipitates in a privileged way. Around 65 °C, the [[Chemistry:Solubility|solubilities]] of ettringite and AFm are similar (in fact, it also depends on the [[Chemistry:PH|pH]] value of the concrete pore water, as explained further in the next section). Above 65 °C, ettringite is more soluble than AFm and the less soluble AFm phase preferentially precipitates. If concrete is poured by hot weather in the summer, or that the concrete component or the structure is massive and that its internal temperature exceeds 65 °C, ettringite does not form, but only AFm. While concrete sets and hardens, it cools down back to ambient temperature. 

During the months, or the years, after its placing, concrete is subject to slow chemical reactions accompanied by mineral phases transformations and volumetric changes. Back to ambient temperature, AFm becomes more soluble that ettringite and slowly dissolves while ettringite slowly crystallizes. 

This slow conversion reaction is known under the name of ''Delayed Ettringite Formation'' (DEF)<ref name="Taylor_2001" /> and can be schematically expressed as: 

:{{chem2|AFm + 2 CaSO4 + 20 H2O -> AFt}} {{space|10}} (delayed ettringite formation: DEF reaction)

Ettringite occupies a larger volume than AFm phase and crystallizes under the form of acicular needles. This reaction is expansive and can cause a huge crystallization pressure in the small concrete pores once they are totally filled by the growing ettringite crystals.<ref name="Müllauer2013" /> As a consequence, the hardened cement paste (HCP) is submitted to an important tensile stress and starts to crack because of the internal expansion of the concrete matrix.

Contrary to the primary ettringite initially formed when concrete is still in the plastic state before hardening, the DEF reaction occurring in hardened concrete can be very harmful for concrete structures and components, potentially compromising their structural integrity and stability. Ultimately, DEF can cause the ruin of concrete structures.

=== Effect of pH ===
At high pH, in the presence of dissolved aluminates and calcium ions, ettringite is transformed into AFm-sulfate:<ref name="Divet2000" />

:{{chem2|3CaO*Al2O3*3CaSO4 * 32 H2O + 4 Al(OH)4- + 6 Ca(2+) + 8 OH- -> 3CaO*Al2O3*CaSO4 * 12 H2O + 8 H2O}}

The conversion of AFt into AFm at high pH can be schematically summarized as:

:{{chem2|AFt + n OH- -> AFm}}

The reverse reaction can also occur when concrete with a high alkali content (NaOH/KOH, expressed as {{chem2|Na2O_{eq}|}}) is leached by water: 

:{{chem2|AFm -> AFt + n OH-}}

AFm converts back into AFt or ettringite. The slow [[Physics:Crystal growth|crystal growth]] of small needles of ettringite into the concrete [[Earth:Porosity|pores]] can exert an important crystallization pressure inside the concrete matrix.<ref name="Müllauer2013" /> This reaction is expansive and can be very damaging for concrete structures and components.

To minimize the risk of DEF in massive concrete structures continuously immersed in water and subject to alkali leaching (bridge piles, [[Earth:Lock (water navigation)|locks]], [[Engineering:Sluice|sluice]]s, dams), a low {{chem2|Na2O_{eq}|}} content is therefore also a desirable characteristic for the selected sulfate resisting (SR) cement.

== Internal and external sulfate attacks of concrete ==
The formation of ettringite in the hardened cement paste is an internal expansive chemical reaction that can lead to severe degradation of concrete.<ref name="Understand_cement" /><ref name="Neville2004" />

The two main classical forms are the internal sulfate attack (ISA), also known as delayed ettringite formation (DEF), already described before, and the external sulfate attack (ESA) when concrete is exposed to an external source of sulfate, such as dissolved sulfate sometimes directly present in [[Chemistry:Soil|soil]]s or [[Earth:Aquifer|aquifer]]s, or produced by [[Chemistry:Pyrite|pyrite]] oxidation (see acid mine drainage).<ref name="Understand_cement" /><ref name="Neville2004" />

In ESA, or when pyrite oxidation is also sometimes involved in contaminated aggregates, beside ettringite [[Physics:Crystallization|crystallization]], a lot of [[Chemistry:Gypsum|gypsum]] ({{chem2|CaSO4*2H2O}}) can also be formed in the ultimate degradation stage.<ref name="Understand_cement" /> 

A less common, but very severe, form of ESA is the [[Chemistry:Thaumasite|thaumasitic]] form of sulfate attack (TSA) when concrete is exposed to an external source of sulfate in the concomitant presence of [[Chemistry:Carbonate|carbonate]], {{chem2|link=bicarbonate|HCO3-}} ions, or {{CO2}}.<ref name="Understand_cement" /> It preferentially occurs in clay formations exposed to air oxygen by excavation works and in which pyrite has been oxidized. The sulfuric acid ({{chem2|H2SO4}}) produced by pyrite oxidation also dissolves carbonates present in the surrounding clay, or directly in the concrete aggregates, freeing up the two main ingredients necessary for this very deleterious pathology. In contrast to conventional ESA, no expansive phase as ettringite needles forms, but [[Chemistry:Thaumasite|thaumasite]] ({{chem2|CaSiO3*CaCO3*CaSO4*15H2O}}), which consumes the [[Chemistry:Calcium silicate hydrate|calcium silicate hydrate]]s (C-S-H, the "glue" of the hardened cement paste), ultimately leading to the decohesion of the cement paste. In the most severe cases, concrete suffering TSA can be dug with a simple shovel, or even by hand.

Thaumasite forms a continuous [[Physics:Solid solution|solid-solution]] series with ettringite (AFt). Indeed, as more easily observable in another, but equivalent, expression of its chemical composition, {{chem2|Ca[Si(OH)6]*CaCO3*CaSO4*12H2O}}, its [[Physics:Crystal lattice|crystal lattice]] is [[Physics:Isostructural|isostructural]] with that of ettringite and an unusually hexacoordinated silicate anion {{chem2|[Si(OH)6](2-)}} can take the place of an aluminate anions {{chem2|[Al(OH)6](3-)}} in octahedral position, as long as another ion compensates for the difference in electrical charge. Although, thaumasite can develop alone at low temperature in the absence of ettringite (AFt), thus even in sulfate-resisting cement (SR0 cement without {{chem2|C3A}}), the presence of ettringite (AFt) acts as a scaffold (template, chaperone) for thaumasite crystallization and therefore favors its formation by hetero-[[Physics:Epitaxy|epitaxy]].

== Prevention of sulfate attacks ==
To minimize, and ideally to avoid, delayed ettringite formation (DEF; synonym: internal sulfate attack, ISA), several precautions can be taken:<ref name="Divet2000" /><ref name="GodartDivet2013">{{Cite book| publisher = ICE Publishing| isbn = 978-0-7277-5822-4| pages = 387–400| editor = John Carpenter| last1 = Godart| first1 = Bruno| last2 = Divet| first2 = Loïc| date = 2013| title = Forensic Engineering: Informing the Future with Lessons from the Past: Proceedings of the Fifth International Conference on Forensic Engineering organised by the Institution of Civil Engineers and held in London, UK, 16-17 April 2013| chapter = Lessons learned from structures damaged by delayed ettringite formation and the French prevention strategy| series = Conference Proceedings| doi = 10.1680/feng.58224| chapter-url = https://www.icevirtuallibrary.com/doi/abs/10.1680/feng.58224.389}}</ref>
* Maintaining the maximal temperature inside the concrete to a value lower than 65 °C, but as this critical threshold temperature also depends on the [[Chemistry:PH|pH]] of the concrete pore water, it is advised not to exceed 60 °C. Low-heat Portland cements with a coarse granulometry size, or better, the choice of an appropriate metallurgic cement with a high content in [[Chemistry:Ground granulated blast-furnace slag|blast furnace slags]] (BFS), and therefore a low content in Portland clinker, can be a way to keep temperature sufficiently low. Metallurgic cements are latent hydraulic binders and slow setting cements. They have the double advantage of producing less heat and also spreading their heat production over a longer time period. If the ambient temperature is too high in the summer, no concrete casting is allowed, or special precautions need to be taken such as making concrete with ice and cold aggregates in desertic conditions. 
* Selecting a cement with a low-alkali content ({{chem2|Na2O_{eq}|}} < 0.60 wt. % according to the European cement norm EN 197). 
* Choosing a sulfate-resisting (SR) cement with a low {{chem2|C3A}} content < 3 wt. % according to the European cement norm EN 197), or with the lowest possible {{chem2|C3A}} content (ideally 0 wt. %).

For massive concrete structures whose temperature at core will likely exceed 65 °C during the cement setting and hardening and moreover will be immersed under water or exposed to alkali leaching, the only effective solution to avoid, or to minimize, delayed ettringite formation is to eliminate the [[Chemistry:Tricalcium aluminate|tricalcium aluminate]] {{chem2|C3A}} phase in the cement clinker, or to drastically reduce its content. Concomitantly, it will also make it possible to limit the quantity of [[Chemistry:Gypsum|gypsum]] added to clinker during its grinding to avoid the risk of cement flash setting due to the very exothermic hydration reaction of {{chem2|C3A}}. 

Eliminating the [[Root cause analysis|root cause]] of DEF by removing {{chem2|C3A}}, the main culprit phase present in the cement, is the only way to completely get rid of DEF (ISA). 

The same precaution also applies to the prevention of the conventional external sulfate attack (ESA) when concrete is exposed to an external source of sulfate in the presence of water. 

However, this precaution is insufficient to completely eliminate the risk of formation of thaumasite (TSA) because this latter can still develop, although more difficultly, in concrete made with sulfate-resistant cement.

Finally, as a last resort, but challenging for immersed concrete structures, when feasible to prevent the development of expansive internal reactions harmful for concrete, it is always advisable to minimize the contact of concrete with water.

== See also ==
* {{annotated link|Chemistry:AFm phases}}
* {{annotated link|Chemistry:Aluminate}}
* {{annotated link|Chemistry:Calcium aluminates}}
* {{annotated link|Chemistry:Tricalcium aluminate}}
* {{annotated link|Chemistry:Dodecacalcium hepta-aluminate}}
* {{annotated link|Chemistry:Concrete degradation}}

== References ==
<!-- Please, in order to avoid to clutter the wikicode of the page, directly insert the references hereunder in the reflist template and use the citation tag <ref name="First_author_year" /> to cite the corresponding reference in the body text at the appropriate place -->
{{Reflist|refs=
<ref name="Candlot_1890">{{Cite journal| last1 = Candlot| first1 = E.| date = 1890| title = Properties of cements and hydraulic binders| journal = Bulletin de la Société d'encouragement pour l'industrie nationale| volume = 5| issue = 4| pages = 682–716}}</ref>

<ref name="LeChatelier_1905">{{Cite book| last1 = Le Chatelier| first1 = Henri| date = 1905| title = Experimental researches on the constitution of hydraulic mortars| publisher = McGraw Publishing Company}}</ref>

<ref name="Merlini_2008">{{cite journal|last1=Merlini|first1=Marco|last2=Artioli|first2=Gilberto|last3=Cerulli|first3=Tiziano|last4=Cella|first4=Fiorenza|last5=Bravo|first5=Anna|year=2008|title=Tricalcium aluminate hydration in additivated systems. A crystallographic study by SR-XRPD|journal=Cement and Concrete Research|publisher=Elsevier|volume=38|issue=4|pages=477–486|doi=10.1016/j.cemconres.2007.11.011}}</ref>

<ref name="Baur2003">{{cite journal | last1 = Baur | first1 = Isabel | last2 = Johnson | first2 = C. Annette | title = The solubility of selenate-AFt (3CaO·Al<sub>2</sub>O<sub>3</sub>·3CaSeO<sub>4</sub>·37.5H<sub>2</sub>O) and selenate-AFm (3CaO·Al<sub>2</sub>O<sub>3</sub>·CaSeO<sub>4</sub>·xH<sub>2</sub>O) | journal = Cement and Concrete Research | date = November 2003 | volume = 33 | issue = 11 | pages = 1741–1748 | issn = 0008-8846 | doi = 10.1016/S0008-8846(03)00151-0 | pmid = | url = }}</ref>

<ref name="Champenois2012">{{cite journal | last1 = Champenois | first1 = Jean-Baptiste | last2 = Mesbah | first2 = Adel | last3 = Cau Dit Coumes | first3 = Céline | last4 = Renaudin | first4 = Guillaume | last5 = Leroux | first5 = Fabrice | last6 = Mercier | first6 = Cyrille | last7 = Revel | first7 = Bertrand | last8 = Damidot | first8 = Denis | title = Crystal structures of Boro-AFm and sBoro-AFt phases | journal = Cement and Concrete Research | date = October 2012 | volume = 42 | issue = 10 | pages = 1362–1370 | issn = 0008-8846 | doi = 10.1016/j.cemconres.2012.06.003 | pmid = | url = }}</ref>

<ref name="Divet1998">{{Cite journal| last1 = Divet| first1 = L.| last2 = Randriambololona| first2 = R.| date = 1998| title = Delayed ettringite formation: the effect of temperature and basicity on the interaction of sulphate and C-S-H phase| journal = Cement and Concrete Research| volume = 28| issue = 3| pages = 357–363| doi = 10.1016/S0008-8846(98)00006-4| issn = 0008-8846| url = https://www.sciencedirect.com/science/article/pii/S0008884698000064}}</ref>

<ref name="Divet2000">{{cite journal |last1=Divet |first1=Loïc |date=2000 |title=Etat des connaissances sur les causes possibles des réactions sulfatiques internes au béton |journal=Bulletin de Liaison des Laboratoires des Ponts et Chaussées |volume=227 |pages=71–84 |url=https://www.ifsttar.fr/collections/BLPCpdfs/blpc_227_71-84.pdf}}</ref>

<ref name="Klieger_1990">{{cite book | author = Paul Klieger | date = 1990 | title = Carbonate additions to cement | publisher = ASTM International | pages = 60– | isbn = 978-0-8031-1454-8 | url = https://books.google.com/books?id=UY0Xbnya1-YC&pg=PA60}}</ref>

<ref name="Jones_1938">{{Cite conference| last = Jones| first = F. E.| date = 1938| title = The calcium aluminate complex salts| book-title = Proceedings of the Symposium on the Chemistry of Cements (Stockholm, 1938)| volume = 232}}</ref>

<ref name="Jones_1939">{{Cite journal| doi = 10.1039/TF9393501484| issn = 0014-7672| volume = 35| pages = 1484–1510| last = Jones| first = F. E.| date = 1939| title = The quaternary system CaO–Al<sub>2</sub>O<sub>3</sub>–CaSO<sub>4</sub>–H<sub>2</sub>O at 25°C| journal = Transactions of the Faraday Society| accessdate = 2023-04-06| url = https://pubs.rsc.org/en/content/articlelanding/1939/tf/tf9393501484}}</ref>

<ref name="Jones_1944a">{{Cite journal| last = Jones| first = F. E.| date = 1944| title = The quaternary system CaO–Al<sub>2</sub>O<sub>3</sub>–CaSO<sub>4</sub>–H<sub>2</sub>O at 25°C. Equilibria with crystalline Al<sub>2</sub>O<sub>3</sub>–3H<sub>2</sub>O, alumina gel, and solid solution.| journal = ACS Publications| volume = 48| issue = 6| pages = 311–356| doi = 10.1021/j150438a001| accessdate = 2023-04-06| url = https://pubs.acs.org/doi/pdf/10.1021/j150438a001}}</ref>

<ref name="Jones_1944b">{{Cite journal| last = Jones| first = F. E.| date = 1944| title = The quinary system CaO–Al<sub>2</sub>O<sub>3</sub>–CaSO<sub>4</sub>–K<sub>2</sub>O–H<sub>2</sub>O (1 per cent KOH) at 25°C| journal = ACS Publications| volume = 48| issue = 6| pages = 356–378| doi = 10.1021/j150438a002| accessdate = 2023-04-06| url = https://pubs.acs.org/doi/pdf/10.1021/j150438a002}}</ref>

<ref name="Jones_1945">{{Cite journal| last = Jones| first = F. E.| date = 1945| title = The formation of the sulfoaluminates and sulfoferrites of calcium in the Portland cement–water system| journal = ACS Publications| volume = 49| issue = 4| pages = 344–357| doi = 10.1021/j150442a007| accessdate = 2023-04-06| url = https://pubs.acs.org/doi/pdf/10.1021/j150442a007}}</ref>

<ref name="Carlson_Berman_1960">{{cite journal | last1 = Carlson | first1 = Elmer T. | last2 = Berman | first2 = Horace A. | title = Some observations on the calcium aluminate carbonate hydrates | journal = Journal of Research of the National Bureau of Standards Section A | date = 1960 | volume = 64A | issue = 4 | pages = 333–341 | issn = 0022-4332 | doi = 10.6028/jres.064A.032 | pmid = 32196171 | pmc = 5287087 | url = }}</ref>

<ref name="Feldman_1965">{{cite journal | last1 = Feldman | first1 = R. F. | last2 = Ramachandran | first2 = V. S. | last3 = Sereda | first3 = P. J. | title = Influence of CaCO<sub>3</sub> on the hydration of 3CaO·Al<sub>2</sub>O<sub>3</sub> | journal = Journal of the American Ceramic Society | date = 1965 | volume = 48 | issue = 1 | pages = 25–30 | issn = 0002-7820 | eissn = 1551-2916 | doi = 10.1111/j.1151-2916.1965.tb11787.x | pmid = | url = }}</ref>

<ref name="Lothenbach_2006">{{cite journal | last1 = Lothenbach | first1 = Barbara | last2 = Winnefeld | first2 = Frank | title = Thermodynamic modelling of the hydration of Portland cement | journal = Cement and Concrete Research | date = February 2006 | volume = 36 | issue = 2 | pages = 209–226 | issn = 0008-8846 | doi = 10.1016/j.cemconres.2005.03.001 | pmid = | url = }}</ref>

<ref name="Müllauer2013">{{cite journal | last1 = Müllauer | first1 = Wolfram | last2 = Beddoe | first2 = Robin E. | last3 = Heinz | first3 = Detlef | date = 2013 | title = Sulfate attack expansion mechanisms | journal = Cement and Concrete Research | volume = 52 | pages = 208–215 | issn = 0008-8846 | doi = 10.1016/j.cemconres.2013.07.005 | pmid = | url = https://www.sciencedirect.com/science/article/abs/pii/S000888461300166X}}</ref>

<ref name="Neville2004">{{cite journal | last1 = Neville | first1 = Adam | date = 2004 | title = The confused world of sulfate attack on concrete | journal = Cement and Concrete Research | volume = 34 | issue = 8 | pages = 1275–1296 | issn = 0008-8846 | doi = 10.1016/j.cemconres.2004.04.004 | pmid = | url = }}</ref>

<ref name="Thiery_2021">{{Cite journal| last1 = Thiery| first1 = Vincent| last2 = Rica| first2 = Brunilda| date = 2021| title = Minerals explained 59: Ettringite| journal = Geology Today| volume = 37| issue = 2| pages = 70–76| doi = 10.1111/gto.12346| s2cid = 233817487| issn = 1365-2451| url = https://onlinelibrary.wiley.com/doi/abs/10.1111/gto.12346| accessdate = 2023-04-06}}</ref>

<ref name="Taylor_1997">{{cite book | last1 = Taylor | first1 = Harry F. W.  |  date = 1997 | title = Cement Chemistry | publisher = Thomas Telford | pages = | isbn = 978-0-7277-2592-9 | url = https://books.google.com/books?id=1BOETtwi7mMC}}</ref>

<ref name="Taylor_2001">{{cite journal | last1 = Taylor | first1 = H.F.W | last2 = Famy | first2 = C | last3 = Scrivener | first3 = K.L | date = 2001 | title = Delayed ettringite formation | journal = Cement and Concrete Research | volume = 31 | issue = 5 | pages = 683–693 | issn = 0008-8846 | doi = 10.1016/S0008-8846(01)00466-5 | pmid = | url = https://www.sciencedirect.com/science/article/abs/pii/S0008884601004665}}</ref>

<ref name="Lea_2019">{{cite book | author1 = Peter Hewlett | author2 = Martin Liska | date = 2019 | title = Lea's Chemistry of Cement and Concrete | publisher = Butterworth-Heinemann | pages = | isbn = 978-0-08-100795-2 | url = https://books.google.com/books?id=0cxPCgAAQBAJ&pg=PP1}}</ref>

<ref name="Understand_cement">{{cite web|url=http://www.understanding-cement.com/sulfate.html |title=Sulfate attack in concrete |publisher=Understanding-cement.com |date=2022 |accessdate=2023-01-17}}</ref>
}}

== Further reading ==
{{Refbegin}}
* {{Cite book | last1 = Taylor | first1 = Harry F. W.  |  date = 1997 | title = Cement Chemistry | publisher = Thomas Telford | pages = | isbn = 978-0-7277-2592-9 | url = https://books.google.com/books?id=1BOETtwi7mMC}}

* {{cite book | author1 = Peter Hewlett | author2 = Martin Liska | date = 2019 | title = Lea's Chemistry of Cement and Concrete | publisher = Butterworth-Heinemann | pages = | isbn = 978-0-08-100795-2 | url = https://books.google.com/books?id=0cxPCgAAQBAJ&pg=PP1}}

* Brown, P.W.; Taylor, H.F.W. (1999). The role of ettringite in external sulfate attack. Sulfate Attack Mechanisms, Materials Science of Concrete. Amer. Ceramic Society, Ohio, 73–97.

* {{Cite journal| last1 = Feng| first1 = Pan| last2 = Miao| first2 = Changwen| last3 = Bullard| first3 = Jeffrey W.| others = R. Riman (ed.)| date = 2016| title = Factors influencing the stability of AFm and AFt in the Ca – Al – S – O – H System at 25 °C| journal = Journal of the American Ceramic Society| volume = 99| issue = 3| pages = 1031–1041| doi = 10.1111/jace.13971| issn = 1551-2916| pmid = 27335503| pmc = 4911640}}

* {{citation | first1 = Svetlana | last1 = Samchenko | first2 = Evgeny | last2 = Makarov | title = SP-326: Durability and Sustainability of Concrete Structures (DSCS-2018) | chapter = The influence of the different factors on the stability of the AFt and AFm Phases | date = 2018 | publisher = American Concrete Institute | doi = 10.14359/51711066 | isbn = 9781641950220 | s2cid = 146657140 | chapter-url = https://www.concrete.org/publications/internationalconcreteabstractsportal/m/details/id/51711066}}
{{Refend}}

== External links ==
* {{cite web|url=http://www.understanding-cement.com/sulfate.html |title=Sulfate attack in concrete |publisher=Understanding-cement.com |date=2022 |accessdate=2023-01-17}}


{{DEFAULTSORT:AFt Phases}}
[[Category:Aluminium compounds]]
[[Category:Hydrates]]
[[Category:Iron compounds]]
[[Category:Iron(III) compounds]]
[[Category:Silicates]]
[[Category:Sulfate minerals]]
[[Category:Sulfates]]

{{Sourceattribution|AFt phases}}