Real time study of cement and clinker phases hydration

Abstract

Real time studies of hydration of a Portland cement and of calcium silicate extracted clinker were made. X-Ray diffraction measurements were made using either an INEL powder diffractometer (Zr-filtered Mo-Kα radiation, CPS120 position sensitive detector) or a MAR diffractometer (synchrotron X-radiation, wavelength 0.90371 Å). The dry samples were mounted in glass capillaries and hydrated in-situ by the application of internal nitrogen gas pressure of up to about 150 kPa which pressed the water into contact with the dry sample. This allowed the study of early phase transitions in the reaction mixture. The experiments were conducted over the temperature range 25–100 °C. The laboratory based X-ray experimentation provided similar results to those obtained using the synchrotron radiation, although the counting statistics in the synchrotron data were far superior. The use of constant wavelength synchrotron radiation gave well-resolved lines of powder diffraction data over the angular range investigated. This is in contrast to the less well-resolved reflections previously observed in the energy dispersive diffraction mode. The hydration of the Portland cement showed the immediate formation of ettringite (3CaO·Al₂O₃·3CaSO₄·32H₂O) upon the addition of water. Two silicate extracted clinker residues were considered: one being predominantly cubic C₃A and the other comprising a mixture of orthorhombic C₃A and brownmillerite (Ca₄Al₂Fe₂O₁₀, C₄AF). The reaction paths of these two residues were different. The hydration of cubic C₃A proceeded via C₄AH₁₉ to the end product, C₃AH₆, Ca₃Al₂(OH)₁₂. The reaction of orthorhombic C₃A, C₄AF and water proceeded via C₂AH₈ to the end product C₃AH₆.