Using modified core drilling method to estimate the damage of fire exposed concrete

In a fire scenario, the temperature gradient in concrete structural member leads to damage gradient. However, the traditional detection methods have issues in determining the damage gradient of concrete in post-fire assessment. The present study aims to propose a novel method to solve the problem. A special drilling machine was retrofitted to perform core drilling on damaged concrete under constant pressure. The rate of steel bit penetrating was adopted to reflect the damage variation induced by elevated temperatures. To validate the proposed method, a series of experiments were conducted on concrete specimens heated to different temperatures. The rate of penetration (ROP) was found significantly related with elevated temperatures. Comparative study was carried out on the obtained values of ROP, ultrasonic pulse velocity, compressive strength, tensile strength, loss of ignition (LOI) and hardness of concrete after thermal treatment. By comparison, ROP is demonstrated sensitive to the fire damage of concrete and has the possibility of revealing the fire damage gradient in concrete with satisfied accuracy for engineering practice.