Estimation of concrete’s durability based on innovative early age ultrasonic measurements

The mechanical properties of cementitious materials (strength, stiffness, durability) strongly depend on the mix design and the early age curing. Thus, the succesfull characterization of the mix and the reliable monitoring of it are the key points for prolonging the life time of the material and at the same time for reducing the repair and maintenance costs. The elastic waves, due to their non-invasive nature, are the perfect candidate for achieving the aforementioned goals. In this study, the traditional use of the Ultrasonic Pulse Velocity (UPV) technique is replaced by advanced ultrasonic measurements which take into account the wave propagation through the cementitious material. The constituents of the mix (usually air bubbles, sand and cement grains in concrete elements) impose scattering dispersion and attenuation to the propagating waves, and their thorough investigation reveals the quality of the mix much earlier than the standard tests. Herein, 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 size and content of the spherical glass beads as well as the applied ultrasonic frequencies are systematically varied revealing the phase velocity and attenuation vs. frequency curves. The characteristics of the initial ultrasonic data are compared with the final ones in an attempt to assess the suitability of the mix as early as possible, while the final aim is to use the obtained experimental results of the early age behavior to theoretically model and characterize the material through multiple scattering and enhanced elastic theories.