Understanding the mechanisms behind the time-dependent viscoelasticity of fresh C3A-gypsum paste

This paper monitored the viscoelasticity development of fresh C(3)A-gypsum paste in situ by small amplitude oscillation shear (SAOS) within 5 h. The development of viscoelasticity of paste with time can be characterized by two different stages. Isothermal microcalorimetry, X-ray diffraction (XRD), scanning electronic microscopy (SEM) and low field H-1 nuclear magnetic resonance (NMR) measurements were used to investigate the underlying mechanisms behind these two stages. It was found that the first stage is governed by the increase of solid volume fraction while the second stage is controlled by the rigidification of ettringite networks. The growth of loss modulus is restricted since the formation of ettringite linkages between particles. Moreover, the considerable elasticity development of fresh C(3)A-gypsum paste is stemmed directly from the increasing ettringite precipitation.