Static indentation hardness testing of concrete: a long established method revived

摘要

Hardness (even in-situ) testing of materials offers the potential of strength estimation by means of a much simpler test than the direct compressive or tensile strength testing. Nevertheless, the theoretical approaches of contact mechanics and hence that of hardness has several gaps. In the technical literature limited number of experimental studies is available on cement mortars and concretes by static ball indentation hardness testing devices. It can be found that a power function can suitably characterize the relationship between the Brinell hardness and the compressive strength of concrete in those cases where one load level is applied for testing. A much detailed analysis can be provided if several load levels are used. Power functions between the indenter load (F) and the residual impression diameter (d) can be formulated for different concrete strengths, F ∝ a×d^sup n^ , of those empirical parameters a and n are material properties as it was demonstrated for metals by Meyer in 1908. Objective of present experimental study was to thoroughly investigate normal weight hardened concrete specimens by a static ball indentation hardness testing laboratory device at several load levels on a wide range of compressive strength and age of concrete at testing. It was found that the power in the Meyer relationship is apparently a constant for concrete, independently of the water-cement ratio and the age at testing, while the multiplier in the Meyer relationship is very sensitive to both influencing factors. The results disproved the hypothesis of the power function relationship between the residual indentation diameter and the compressive strength of concrete with a power of -4.0 published in the technical literature. The results confirmed the existence of a linear general model for the relationship between the compressive strength and the Brinell hardness of concrete, as an average power of 1.128 was found. [PUBLICATION ABSTRACT]