Mechanical evolution of concrete during setting

This paper deals with the rheological behaviour of fresh concrete during setting. An experimental non-destructive device based on the propagation of acoustic waves (compression and shear waves) at low frequency (20Hz-800Hz) is used to continuously characterise the setting and hardening of hydraulic concrete. The results are presented for various concrete formulations involving various initial temperatures and water/cement ratios. The characteristics of wave propagation (velocities, damping coefficients,...) enable to monitor material setting and hardening phases. By means of an inverse analysis, the evolution of rheological parameters is presented from the fluid to the solid state. It is shown that the mechanical evolution of fresh concrete exhibits a characteristic time (tau). The wave velocity presented as a function of normalized time (t/tau) follows a master curve which depends only slightly on the formulations tested.