Set time measurements of self-compacting pastes and concretes using ultrasonic wave reflection

The ultrasonic shear-wave reflection coefficient at the interface between a hydrating material and a buffer material was monitored immediately after mixing as a function of time to study setting behavior of self-compacting pastes and concretes. High-impact polystyrene was used as the buffer material because it is very sensitive to early changes. Self-compacting pastes were produced using fly ash and superplasticizer. Initial and final set times were measured and compared with those obtained from the standard penetration resistance test. Both methods showed reproducible results with self-compacting pastes and were able to distinguish fairly small changes in composition. A good correlation was found between set times obtained from the two methods. The self-compacting pastes were seen to have a substantially delayed set as compared with plain pastes. In addition, self-compacting concretes were made and their set times were measured using ultrasonic wave reflection. The method was seen to be quite reproducible for concrete, and concrete set times matched those of the corresponding pastes reasonably well.