The surface at the test location is ground using a planing tool and a 18.4 mm hole is made perpendicular to the surface using a diamond coring bit. A recess (slot) is routed in the hole to a diameter of 25 mm and at a depth of 25 mm. A split ring is expanded in the recess and pulled out using a pull machine reacting against a 55 mm diameter counter pressure ring. The concrete in the strut between the expanded ring and the counter pressure ring is in compression. Hence, the ultimate pullout force F required to pullout the ring is related directly to compressive strength.
In-situ concrete strength.