On the correct chemical nomenclature of C3S, tricalcium oxy silicate

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C3S, the main constituent in Portland cement, incorrectly has been denominated as tricalcium silicate at times when analytical instrumentation did not allow to uncover its actual chemical constitution. Today, we know that it is composed of three building blocks, namely Ca2+, SiO4 4 tetrahedra and interspersed oxide anions, O2 . Consequently, its scientifically correct designation is tricalcium oxy silicate, and its formula needs to be written as Ca3O(SiO4) when indicating its chemical constitution, while Ca3SiO5 only represents an empirical or sum formula. The presence of separate O2 anions in its structure is responsible for its different hydration behavior and higher basicity (release of Portlandite), as compared to C2S. Consequently, it is proposed to henceforth exclusively use the scientifically correct designation tricalcium oxy silicate and the formula Ca3O(SiO4). Moreover, it is suggested to abandon the oxide-based abbreviations 3CaO·SiO2, 2CaO·SiO2 and 3CaO·Al2O3 for the clinker phases as they grossly misrepresent their actual chemical constitution.

Original languageEnglish
Article number105957
JournalCement and Concrete Research
StatePublished - Apr 2020


  • Alite
  • CS
  • Cement (D)
  • Silicate


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