The first 24 hours of Portland cement hydration

The research in this article is focused on the first 24 hours of hydration of five commercially available Portland cements. Particular interest has been given to the so called induction or dormant period. The different cements have been analysed using isothermal calorimetry, quasi-elastic neutron scattering (QENS), nuclear resonance reaction analysis (NRRA), pore solution analysis, and in-situ synchrotron x-ray diffraction. The results clearly show that the cements do not react identically. It is concluded that C3S amount shows potential of reaction, but specific surface area is the parameter to control rate of reaction. Results by QENS measurements indicate that this product layer is not directly attached to the cement grain, but is separated by a small layer of solution. From the NRRA measurements it is concluded that the shell product layer is not fixed but seems to change over time, which classifies it as metastable or intermediate. The complexity of sulphate related phases is established. It is concluded that calcium seems to control the start of the induction period and that a necessary level of silicon or silicon based nuclei controls the end of the induction period.

Author: M.R. De Rooij, S. Scher

Section: Science and production

Keywords: portland cement, hydration, induction period