ULTRASONIC TESTING FOR FRESH MIXES

The equipment described was designed and developed in a site environment to give an early indication of the properties of the large volumes of high quality concrete needed to be poured quickly in the building of a North Sea offshore platform. It was important to know how long the mix remained workable, and to be sure no premature setting took place. The method described does not permit absolute measurements to be made, the results must be interpreted empirically. It was found experimentally that the end of workability was defined by the area where the ultrasonic pulse velocity increased from 1 km/sec to 1.5 km/sec. Experiments were carried out to determine the effect on hardening of the water/cement ratio, different cement types and environmental temperature. The influence of plasticisers, accelerators and retarders on the hardening was also investigated. The system has good reproducibility and has proved to be reliable. The technique can give valuable on-site information on the behaviour of different cement types and classes and also the effect of additives. /TRRL/