Characterising the segregation of self‑consolidating concrete using ultrasonic pulse velocity

Segregation is the unintentional separation of the fresh components of concrete or mortar, which can have negative impacts on the mechanical, transport and durability properties of the cured product. The problem is acute in self-consolidating concrete (SCC), because of its high fluidity level. To help evaluate segregation, this paper investigates the potential of using ultrasonic pulse velocity (UPV) as a means to identify and characterise segregation in traditional and SCC mixes. Fourteen different concrete mixes were tested using standard techniques (sieve and column) in comparison with the UPV-based test proposed herein. Six of the 14 concrete mixtures were stable, as indicated by having sieve segregation indices lower than 15% and segregation resistances (f) higher than 95%. These six stable samples displayed UPV segregation index values (f_u) approaching 100%. The remaining samples were found to be unstable concretes with sieve segregation index values higher than 15% and resistance index values lower than 65%. These concretes could also be clearly identified as unstable by a UPV segregation index lower than 80%. The UPV method provides a clean, quick and easy nondestructive alternative for testing segregation of both fresh and hardened concrete.