Jerome Carette

Monitoring of the ultrasonic P-wave velocity in early-age concrete with embedded piezoelectric transducers

This note deals with the use of embedded piezoelectric transducers to monitor the ultrasonic P-wave velocity evolution during the setting and hardening phases of concrete subsequent to casting time. The main advantage of the technique is the possibility of overcoming the limitations of traditional methods which prevent the application of specific mechanical boundary conditions during the measurement. The embedded transducers are based on the ‘smart aggregates’ concept previously developed at the University of Houston, Texas. Two piezoelectric transducers are embedded in a prismatic mold and the evolution of the P-wave velocity is recorded for the first 24 h in concrete after the casting time. The results are very promising and show a good agreement with classical ultrasonic tests using external transducers. (Some figures may appear in colour only in the online journal)

Applicability of ultrasonic measurement on the monitoring of the setting of cement pastes: effect of water content and mineral additions

Until now, standardized methods developed for the detection of initial and final setting time of cement paste were destructive and non-continuous. The well-established ultrasonic pulse transmission velocity (UPV) method can be correlated to the setting process of cement-based materials by the measurement of P-waves. However, S-waves seem to be better indicators of the setting of cement-based materials, because they are more sensitive to the solid matrix connectivity and less dependent to the air content. A new methodology, based on the combined monitoring of P-waves and S-waves, has already been developed to determine the setting times of mortar and concrete. The purpose of this study is to extend this methodology to cement pastes. Ordinary portland cement pastes with three water/cement ratio between 0.3 and 0.5 have been investigated. In addition, a portland cement, blast-furnace slag and limestone filler blended cement paste with a 0.4 water/cement ratio is studied in order to validate all observations. This study shows that the dynamic elastic properties can be linked to the initial and final setting times of cement paste. The early age evolution of the elastic properties depends on the air content and the binder nature. The combined monitoring of P-waves and S-waves provide accurate indicators of the setting process.