Microstructure and Flow Behavior of Fresh Cement Paste

A rheological technique (creep/recovery) was used, in combination with scanning electron microscopy, to study the effects of hydration on both the microstructure and flow properties of fresh cement paste during the induction period, which is the first few hours after cement and water are mixed. The principal hydration product was calcium silicate hydrate (C-S-H), which was first observed in the neck areas between cement particles. At the same time, yield stress increased progressively, which reflected a strengthening of bonds between particles attributed to the C-S-H. Failure strain also increased, which reflected a fundamental change in the nature of that bond. Based on rheological measurements, the activation energy of the hydration process during this time period was estimated to be 5.2 kcal/mol (˜22 kJ/mol).