Friedel's salt

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Friedel's salt
IUPAC name
Calcium chloroaluminate
Other names
Friedel's salt

Calcium aluminium chlorohydrate
Calcium aluminium chlorohydroxide

Calcium aluminium oxychloride
Ca2Al(OH)6(Cl, OH) · 2 H2O
Appearance White solid
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Infobox references

Friedel's salt is an anion exchanger mineral belonging to the family of the layered double hydroxides (LDHs). It has affinity for anions as chloride and iodide and is capable to retain them to a certain extent in its crystallographical structure.


Friedel's salt general formula is:

Ca2Al(OH)6(Cl, OH) · 2 H2O.

In the cement chemist notation, considering that

2 OH ↔ O2− + H2O,

and doubling all the stoichiometry, it can also be written as follows:

3CaO·Al2O3·CaCl2 · 10 H2O

Friedel's salt can also be considered as an AFm phase in which chloride ions have replaced sulfate ions and is formed in cements initially rich in tri-calcium aluminate (C3A).

2 Cl + 3CaO·Al2O3·CaSO4 · 10 H2O   →   3CaO·Al2O3·CaCl2 · 10 H2O + SO42−

It plays a main role in the retention of chloride anions in cement and concrete. However, Friedel's salt remains a poorly understood phase in the CaO-Al2O3-CaCl2-H2O system, and is critical for the stability of salt-saturated Portland cement-based grouts.


Friedel's salt discovery is relatively difficult to trace back from the recent literature, simply because it is an ancient finding of a poorly known and non-natural product. It has been synthesised and identified in 1897 by Georges Friedel, mineralogist and crystallographer, son of the famous French chemist Charles Friedel.[1] Georges Friedel also synthesised Calcium aluminate (1903) in the framework of his work on the Macles theory (twin crystals). This point requires further verification.[citation needed][2]


Role in cement[edit]

  • Importance for the reactive transport of chloride in cement in relation with corrosion of steel reinforcement.

Anion getter[edit]

  • Trap toxic anions in cement such as, e.g., 129I, SeO32−, SeO42−

See also[edit]


  1. ^ Friedel, Georges (1897). "Sur un chloro-aluminate de calcium hydrate´ se maclant par compression". Bulletin de la Société française de minéralogie et de cristallographie. 19: 122&ndash, 136.
  2. ^ Biography of Georges Friedel by F. Greandjean on, in French.
  • Bai, J.; S. Wild; B. B. Sabir (2003). "Chloride ingress and strength loss in concrete with different PC–PFA–MK binder compositions exposed to synthetic seawater". Cement and Concrete Research. 33 (3): 353–362. doi:10.1016/S0008-8846(02)00961-4.
  • Barberon, F.; V. Baroghel-Bouny; H. Zanni; B. Bresson; J. B. d'Espinose de la Caillerie; L. Malosse; Z. Gan (2005). "Interactions between chloride and cement-paste materials". Magnetic Resonance Imaging. 23 (2): 267–272. doi:10.1016/j.mri.2004.11.021. PMID 15833625.
  • Birnin-Yauri, U. A.; F. P. Glasser (1998). "Friedel's salt, Ca2 Al(OH)6 (Cl, OH) · 2H2O: its solid solutions and their role in chloride binding". Cement and Concrete Research. 28 (12): 1713–1723. doi:10.1016/S0008-8846(98)00162-8.
  • Brown, P. W.; S. Badger (2000). "The distributions of bound sulfates and chlorides in concrete subjected to mixed NaCl, MgSO4, Na2SO4 attack". Cement and Concrete Research. 30 (10): 1535–1542. doi:10.1016/S0008-8846(00)00386-0.
  • Brown, P. W.; A. Doerr (2000). "Chemical changes in concrete due to the ingress of aggressive species". Cement and Concrete Research. 30 (3): 411–418. doi:10.1016/S0008-8846(99)00266-5.
  • Chatterji, S. (1995). "On the applicability of Fick's second law to chloride ion migration through portland cement concrete". Cement and Concrete Research. 25 (2): 299–303. doi:10.1016/0008-8846(95)00013-5.
  • Csizmadia, J.; G. Balázs; F. D. Tamás (2001). "Chloride ion binding capacity of aluminoferrites". Cement and Concrete Research. 31 (4): 577–588. doi:10.1016/S0008-8846(01)00458-6.
  • Mohammed, T. U.; H. Hamada (2003). "Relationship between free chloride and total chloride contents in concrete". Cement and Concrete Research. 33 (9): 1487–1490. doi:10.1016/S0008-8846(03)00065-6.
  • Nakamura, A.; E. Sakai; K. Nishizawa; Y. Ohba; M. Daimon (1999). "Sorption of chloride-ion, sulfate-ion and phosphate-ion in calcium silicate hydrates". Journal of the Chemical Society: 415–420.
  • Nielsen, E. P.; M. R. Geiker (2003). "Chloride diffusion in partially saturated cementitious material". Cement and Concrete Research. 33 (1): 133–138. doi:10.1016/S0008-8846(02)00939-0.
  • Pitt, J. M.; M. C. Schluter; D. Y. Lee; W. Dubberke (1987). Sulfate impurities from deicing salt and durability of Portland cement mortar. Transportation Research Board.
  • Reddy, B.; G. K. Glass; P. J. Lim; N. R. Buenfeld (2002). "On the corrosion risk presented by chloride bound in concrete". Cement and Concrete Composites. 24 (1): 1–5. doi:10.1016/S0958-9465(01)00021-X.
  • Suryavanshi, AK; RN Swamy (1998). "Influence of penetrating chlorides on the pore structure of structural concrete". Cement, concrete and aggregates. 20 (1): 169–179. doi:10.1520/CCA10451J.
  • Suryavanshi, A. K.; J. D. Scantlebury; S. B. Lyon (1996). "Mechanism of Friedel's salt formation in cements rich in tri-calcium aluminate". Cement and Concrete Research. 26 (5): 717–727. doi:10.1016/S0008-8846(96)85009-5.
  • Dousti, A; M. Shekarchi; R. Alizadeh; A. Taheri-motlagh (2011). "Binding of externally supplied chlorides in micro silica concrete under field exposure conditions". Cement and Concrete Composite. 33 (-): 1071–1079. doi:10.1016/j.cemconcomp.2011.08.002.

External links[edit]