Early Age Properties of Portland Cement Pastes Investigated with Ultrasonic Shear Waves and Numerical Simulation

In this paper, the correlation of reflection loss measured by an ultrasonic shear wave reflection method and the microstructure in cement-based material is investigated. Three cement pastes (Portland cement type I) with different water-cement ratios (0.35, 0.50 and 0.60) cured at 25 °C were examined. The ultrasonic shear wave reflection factor (WRF) was measured by the wave reflection technique. Reflection loss was calculated based on WRF measurement. Initial and final setting time were obtained by Vicat Needle tests. Thermogravimetric tests were conducted to observe the hydration process of cement pastes. To obtain the evolution of the microstructure in cement pastes, a numerical cement hydration model, HYMOSTRUC3D, was applied. Correlations between the microstructural evolution (e.g. growing of solid phases, percolation threshold of solid phases, and capillary porosity) calculated by HYMOSTRUC3D model and the reflection loss have been established. From this study, it was found that the WRF behavior is closely related to the microstructural evolution, such as, the total solid phase volume, the connectivity of solid phase and the pore structure. The study shows that, the wave reflection technique, as a non-destructive testing method, can be used to monitor the microstructural evolution of cementitious materials at early ages.