Abstract
Surface hardness testing of materials can be considered as the oldest method to get information about strength related material properties. In recent decades the rebound hammer has been the most popular surface hardness testing device for concrete uniting the advantages of its predecessors. In the technical literature numerous proposals are available for simple, two-parameter regression analyses of rebound surface hardness vs. compressive strength relationship of concrete. The remarkable diversity of the proposed curves implies the need of the more than two-parameter regression techniques to reveal the most pronounced parameters governing hardness behaviour. The objectives of present experimental studies were to carry out dynamic and static hardness tests, Young’s modulus and compressive strength tests on concrete specimens. From the development of the tested properties with time it can be concluded that the rebound hammers provide a hardness value for high strength concretes connected to the Young’s modulus rather than the compressive strength. Present paper includes a parametric simulation and a parameter fitting of the verified phenomenological constitutive model of the authors which recognizes the w/c ratio as the main driver of the interrelated material properties and gives a realistic formulation for the time dependent behaviour of the rebound surface hardness of concrete.
Highlights
Surface hardness testing of materials is a long established idea for the estimation of mechanical properties
Aim of rebound hammer tests is usually to find a relationship between surface hardness and compressive strength with an acceptable error
The results demonstrate that the impact energy of the Schmidt rebound hammers can result considerable plastic deformations in the case of high w/c ratio
Summary
Surface hardness testing of materials is a long established idea for the estimation of mechanical properties. For the insitu testing of structural concrete the first surface hardness testing device was developed by Kurt Gaede in the form of a spring hammer (Gaede 1934). Aim of rebound hammer tests is usually to find a relationship between surface hardness and compressive strength with an acceptable error. It can be found in some publications that the method is suitable only for assessing the uniformity of concrete. In the technical literature numerous proposals are available for simple, two-parameter regression analyses of rebound surface hardness and compressive strength of concrete, regardless of the theoretical restrictions of mathematical statistics. Results clearly demonstrate that the validity of a proposal should be restricted to the testing conditions and the extension of the validity to different types of concretes or testing circumstances is impossible
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