Fracture analysis of the pullout test

Pullout tests are increasingly being used to determine the in situ strength of concrete. Several studies have shown that a close correlation exists between the maximum pullout load and compressive strength of concrete. However, the failure mechanism of the pullout test is yet not understood. Conflicting theories have been forwarded to analyze the pullout test. In this study, progressive internal microcracking was examined during the pullout testing. A commercially available equipment was modified to enable monitoring the pullout load vs. relative displacement relationship. Specimens were loaded and unloaded from predetermined fractions of the ultimate load. Acoustic activity was measured during testing. Unloaded specimens were sectioned and examined for microcracking. Results indicate a two-stage cracking process. An extensive stable cracking system dominates for loads up to than the peak load. A different cracking pattern develops near the peak load and governs the shape of the finally extracted core.