Discussion of the paper “Understanding expansion in calcium sulfoaluminate–belite cements” by I.A. Chen et al., Cem. Concr. Res. 42 (2012) 51–60

The interpretation of the expansive behavior of calcium sulfoaluminate belite cements given by Chen et al. (2012) is discussed with reference to the influence of image content, gypsum addition and water/cement ratio. In particular, the role assigned by the authors to the porosity of hydrated cement is criticized with the support of literature data and still unpublished experimental results. It is concluded that the explanation of the expansive phenomena associated with ettringite formation has to be traced back to the common basis of the major schools of thought about the origin of expansion: the “crystal growth” and “swelling” theories.