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Materials and Structures

, 51:138 | Cite as

Testing of concrete by rebound method: Leeb versus Schmidt hammers

  • Konstantin Kovler
  • Fengzhe Wang
  • Boris Muravin
Original Article
  • 188 Downloads

Abstract

Hardness is considered as an important property of concrete; it can be used to estimate compressive strength of concrete in situ. The classic Schmidt rebound hammer is the most popular nondestructive method to measure concrete surface hardness, while the Leeb rebound hammer has been extensively studied in geological and metallographic fields over decades, and its use for testing concrete is almost not known. The national and international standards for the measurement of hardness are reviewed. Concrete made different w/c ratios (0.33, 0.4 and 0.5) were tested by both methods. The simple linear correlation between rebound numbers (both Schmidt and Leeb) and concrete compressive strength are proposed. Schmidt rebound number was differently correlated with compressive strength for concretes with different w/c ratios, while the Leeb rebound numbers were more consistent and could be applied in predicting concrete compressive strength within 10% error for all w/c ratios. It was also concluded that Schmidt test can be considered as a semi-destructive method, because of significant strength reduction (in average by 10.5 MPa) that was observed after application of Schmidt hammer impact on specimens, while the Leeb rebound test procedure did not result in any damage of concrete. This difference can be explained by the dramatic difference in impact energy of the two hammers (2207 and 11 N·mm - for Schmidt rebound hammers of N-type and Leeb hammers of D-type, respectively). Moreover, the classic Schmidt rebound hammer is not recommended to be used on the concrete specimens, which are aimed for compressive tests at early age (less than 3 days) or when expected compressive strength is less than 7 MPa. These constraints do not apply to lower impact Leeb rebound devices, which can be considered as perfectly invasive (non-destructive). At the same time, as expected, Leeb rebound test is sensitive to the surface conditions, such as carbonation and surface moisture.

Keywords

Concrete Nondestructive tests Schmidt rebound hammer Leeb rebound hammer Compressive strength Hardness 

Notes

Acknowledgements

The authors thank to Mr. Boris Gershengoren and Mr. Elhanan Itzhak for their valuable assistance in conducting the experiments.

Compliance with ethical standards

Conflict of interest

The authors declare that they have no conflict of interest.

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Copyright information

© RILEM 2018

Authors and Affiliations

  1. 1.Faculty of Civil and Environmental EngineeringTechnion - Israel Institute of TechnologyHaifaIsrael
  2. 2.Integrity Diagnostics Ltd.NetanyaIsrael

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