The Effect of Reinforcement on the Ultrasonic Longitudinal Waves Propagation Velocity in Concrete by Modeling the Concrete Structure Research of the Reinforced Concrete Hollow Core Slabs

In practice, it is often required to evaluate the technical condition and the load carrying capacity of the hollow core slabs made of the precast reinforced concrete. Quality of the slabs is also characterized by the structural properties of the concrete. However, it is problematic to drill out the full value concrete specimens from such constructions for carrying out the research with the help of the material destructive control methods. The physiccal and mechanical properties of concrete are known to be best characterized by its density, porosity and strength, as well as its integrity indexes, which can be determined by using the material nondestructive control methods – by applying the ultrasonic pulse velocity measuring devices. However, at the same time, it is also known that there are several factors that influence the ultrasonic pulse propagation velocity in the concrete and the reinforced concrete structures. The earlier performed investigations have established that the reinforcement increased concentration in the upper layers of the tested unit increases the ultrasonic pulse propagation velocity. Explanations to different standards indicate to the effect of reinforcement as well. Still, when widely applying the concrete structure sounding with the help of the ultrasonic longitudinal waves (by using the ultrasonic tester "УК-1401" for this purpose) at a number of different building objects and determining the longitudinal waves propagation velocity in case of the single-sided (i.e. surface) sounding, doubts have arose with regards to essentiality of the effect of reinforcement. To further investigate it, 5 model specimens were manufactured – the reinforced concrete specimens different from each other, where the reinforcement diameters were in conformity with the work reinforcement of the typical reinforced concrete hollow core slabs. When performing measurements in the zones exactly over the rebars and in the rebar-free zones, there were no significant differences in the ultrasonic longitudinal waves propagation velocity established. A conclusion can be drawn that for the uncracked precast hollow core slabs and other construction elements made of the reinforced concrete, which maximal rebars diameter does not exceed 22 mm, the concrete integrity measurements with the help of the "УК-1401" tester can be performed sufficiently correctly even, when the rebars are quite close to the sounded surface