| Popis: |
The mechanical properties of cementitious materials (strength, stiffness, durability) strongly depend on the mix design and the early age curing. During that stage several processes occur like segregation, air bubbles formation, water and air bubbles migration, formation of hydration products, as well as shrinkage cracking. An ideal means to examine the ongoing processes are the elastic waves due to their non-invasive nature. The constituents of the mix (usually air bubbles, sand and cement grains) impose scattering dispersion and attenuation to the propagating waves, and their thorough investigation reveals the quality of the mix much earlier than the standard compression test performed at the age of 28 days. In this study, single sized populations of spherical glass beads are embedded in a cement paste matrix to have better control on the microstructure relatively to sand grains of random shapes and wide size distributions. The sizes of the spherical glass beads as well as the applied ultrasonic frequencies are systematically varied revealing the phase velocity vs. frequency curves. The obtained experimental results of the early age behavior are used to theoretically model the material through multiple scattering and enhanced elastic theories. The characteristics of the initial ultrasonic data are correlated with the final mechanical properties of the specimens and the possibility of predicting the final properties after hardening, based on the ultrasonic behavior of the fresh material is examined. |
