Abstract
The relationship between Rayleigh wave velocity at ultrasonic frequencies and capillary porosity is investigated in dry and water saturated cement paste. Capillary porosity is varied by changing the water/cement (w/c) ratio. Water saturation is set at four levels – 100, 70, 30 and 0% – by drying the fully saturated specimen. Rayleigh wave (RW) wavefront and phase velocities are measured using air-coupled ultrasonic transducers as transmitter and receiver. The measurement accuracy is evaluated using a reference specimen made up of a non-dispersive material. As expected, a linear decrease of RW velocity vs. porosity is observed for the intermediate saturation states, but not for the fully and dry states, possibly due to micro-cracks induced during the drying phase and to the presence of bubbles in the specimens with low w/c ratio. The comparison of phase velocity in specimens with low and high w/c ratio shows an inversion of the porosity gradient perpendicular to the surface of measurements, which is due to segregation of cement at high w/c ratio. Finally, the correlation between RW velocity and capillary porosity is analyzed and compared with results obtained in mortar.
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