The early age non-destructive testing of concrete made with recycled concrete aggregate

The increasing demand for concrete in construction places pressure on its constituent materials including aggregate. Attention has previously been turned to alternative aggregates, such as recycled concrete aggregate (RCA), to reduce the impact of quarrying. It is the aim here to investigate the very early age behaviour and properties of RCA concrete in relation to normal concrete using non-destructive testing. Ultrasonic pulse velocity (UPV) and surface hardness tests have been carried out on concretes made with different mix proportions. A system was set up which enabled the continuous measurement of UPV throughout the fresh and hardening stages. RCA concrete produced lower strength and UPV values than normal concrete. However, higher surface hardness was obtained for RCA concrete.Relationships have been established between strength and UPV, covering the period from immediately after mixing and up to 1 day or 28 days. This would enable more accurate assessments of important early age concrete strengths from UPV measurements. It has also been established that UPV measurements can be used to determine concrete setting.

► Established a continuous ultrasonic pulse acquisition system for fresh concrete. ► Investigations applied to concretes with recycled concrete and normal aggregates. ► Obtained expressions allowing early strength estimation from non-destructive tests. ► The setting of concrete is determined using rate of change in ultrasonic pulse. ► The type of aggregate has a direct effect on the heat the concrete generates.