Characterization of Early Stage Concrete by Ultrasonic Method

Seismic methods are useful tools to non-destructively assess the integrity of concrete. It has also been applied to characterize the behaviors of curing concrete to provide information for construction decision. This paper shows that freezing of concrete significantly affects the seismic properties of concrete. Attention needs to be paid when applying seismic method to concrete curing in cold weather. In the experimental program ultrasonic tests were conducted on curing concrete subjected to different freezing process. The results indicate while there exists linear correlation between small strain seismic wave velocity and concrete strength under normal curing conditions, such relationships do not hold if the concrete is subjected to freezing process. A correction accounting for the effects of ice on the bulk strength needs to be applied. This correction was found to have linear relationship with water content (or ice content if concrete is completely frozen). Procedures to correct the effects of freezing are proposed, which include the use of Time Domain Reflectometry to measure the water content. Fianally the strength of concrete in frozen status can be estimated. This information could be incorporated to determine the magnitude of Winter Load Increase in cold regions.