Monitoring cementitious materials during setting and hardening with an ultrasonic shear wave reflection method

The setting and hardening process of concrete can be considered as the most critical time period during the life of a concrete structure. This paper presents a new method to monitor the hydration process of cementitious materials at early ages. The technique is based on the measurement of the reflection coefficient (or reflection loss) of high frequency shear waves at an interface between a steel plate and concrete. Several experimental studies that examine the ability of the wave reflection method to qualitatively and quantitatively describe the setting and hardening process of cement paste, mortar and concrete are presented. The results show that parameters such as compressive strength and elastic moduli can reliably be monitored with the wave reflection method. Furthermore, it is shown how the results obtained with the wave reflection method compare with measurements of other nondestructive techniques such as the pulse velocity method and the maturity method. Results of a first field trial emphasize the potential of the wave reflection method to practical application on the construction site.