Monitoring early age concrete hydration through time-dependent wave dispersion

This paper explores into the intricate realm of wave dispersion behavior within the early stages of fresh concrete, with a specific focus on the dynamic interplay between micro-structure evolution and rheological properties in the quasi-solid state. Based on the characteristic of wave dispersion is factored by impulse frequency, the range used for the experiment is from 40 kHz to 100 kHz, where the wavelength is enough to be influenced by the medium. The time-dependent analytical solution and FE simulation show more linear changes in phase velocity at different times during the quasi-solid state. On the other hand, experimental data exhibits more dispersion behavior, likely due to the effect of viscoplasticity. To simulate the viscoplasticity effect, the FE simulation is compared between cases with applied viscoplasticity and without viscoplasticity. The phase velocity in the viscoplasticity case decreases by approximately 30% compared to the non-viscoplasticity case. This demonstrates that the effect of viscoplasticity cannot be overlooked in the quasi-solid state of concrete. The wave dispersion behavior in the early stages is predominantly influenced by particles and viscoplasticity, causing changes in phase velocity over time and impulse frequency. The highest phase velocity is observed between 50 kHz to 60 kHz. As the concrete undergoes hydration and hardening, both group velocity and phase velocity generally increase with the same frequency impulse. This study aims to unravel the complexities inherent in these phenomena, shedding light on the fundamental mechanisms governing wave dispersion in quasi-solid materials.