ABSTRACT
It is important to stress that XRD must not be used as a 'black box' to characterize cementitious materials. Ordinary Portland cement (OPC) is not made from pure minerals but from quarries that generally contain substantial amounts of impurities. Thus, the alite component of Portland cement is not pure C^S but is generally a solid solution containing Mg, Al and Si. These impurities can, and mostly do, have a substantial effect on the XRD patterns and should be always considered before interpreting XRD patterns of cements.
