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Effectiveness of a Simplified Pullout Test Using a Post-Installable Break-Off Bolt

The pullout test is known to be more reliable for estimating the strength of concrete structures under construction than other nondestructive testing methods such as the Schmidt rebound hammer test, penetration resistance test, and ultrasonic pulse velocity method. However, existing pullout tests require several complex installation steps. Loading equipment that contains load cells is expensive. We propose a simplified pullout test using a post-installable break-off bolt, a standard bolt with a groove on the shaft, as an insert. The specific groove diameters of break-off bolts are designed to indicate concrete strength. However, the appropriate groove diameters for certain concrete strengths are not necessarily known. Regression models of groove diameter and the concrete strength were derived through a series of 188 experiments. The resulting equation showed 70.2% prediction accuracy for predicting concrete strength. The average difference between incorrect estimates and actual strengths was 0.13mm, a magnitude that can easily be overcome if appropriate safety factors are studied and added to the prediction equations.

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