New Method for Nondestructive Evaluation of Concrete Strength

This paper presents information on a newly developed test method of non-destructive type called "twist-off" test, which can be used for investigations in to in-situ concrete strength of structures built and used under different circumstances. The twist-off test is a near-to-surface method in which a circular steel disc is glued to the surface of the concrete with an epoxy or polyester resin. The force required to twist this disc off the surface, together with an attached layer of concrete, is measured. Ordinary torque-wrench is used for this purpose. In order to make the applicability of the use of this new method as wide as possible, eight different concrete mixtures with design compressive strengths of 10-75 MPa were exposed to six different curing regimes and the correlations between their twist-off and compressive strengths are discussed.