Precision of rebound hammer tests and ultrasonic measurement
Table of contents
Project data
| Titel | Title Vergleichsuntersuchungen zur Einordnung der Präzision zerstörungsfreier Prüfmethoden (Rückprallhammer und Ultraschallmessung) | Comparative studies to classify the precision of non-destructive testing methods (rebound hammer and ultrasonic measurement) Förderer | Funding Institut für Massivbau, TU Dresden Zeitraum | Period 05/2021 – 12/2021 Leiter | Project manager Prof. Dr.-Ing. Steffen Marx Bearbeiter | Contributors Daniel Gebauer, M. Sc., Raúl Enríque Beltrán Gutierrez, M. Sc |
Report in the year book 2021
Hitting and Hearing – How accurate can it be?
Cube specimen with test pattern
The rebound hammer and ultrasonic transit time measurement are two common methods of non-destructive testing of reinforced and prestressed concrete structures. Contrary to popular belief, the rebound hammer measures only the elastic surface behavior of the concrete under investigation by determining either the rebound distance or the difference between the impact and rebound velocities. The corresponding values are translated into rebound values (so-called R or Q values). They are assumed to be related to hardness, which in turn is related to strength. The ultrasonic transit time, on the other hand, measures the duration required for a wave to travel a defined distance through the concrete. Depending on the concrete properties, a signal emitted by a transmitter takes a certain time to reach the receiving sensor of the measuring system. From the measured ultrasonic wave velocity and from known density, the dynamic modulus of elasticity can be calculated. Both of them should be correlated to concrete strength.
With both methods, qualitative statements can be made about the homogeneity of the concrete. However, an unerring determination of the concrete compressive strength as a decisive parameter for the assessment of structures is currently not possible with non-destructive testing methods. To get closer to this goal, six national laboratories have joined forces and examined concrete specimens in two test series.
The first test series consisted of concrete from an existing structure with the associated scatter, whereas the second test series consisted of concrete cubes manufactured specifically for the investigation. Together, independent test series were used to create a data basis on which to derive statements on both repeatability and comparative precision. This information is important in order to be able to use non-destructive measuring methods in the future for the reliable determination of compressive strengths within the framework of recalculation. In this way, the currently necessary invasive interventions in the as-built structure can be reduced.