The post-installed screw pull-out test: Development of a method for assessing in-situ concrete compressive strength

Abstract

In concrete structures, the current methodology for concrete strength estimation combines the use of in-situ test methods with destructive techniques (taking cores). In-situ tests are indirect approaches, and can be affected by several uncontrolled factors, thus inducing uncertainty in the strength estimate. Low cost in-situ methods are often deployed in practice, without taking due consideration of the low reliability. Thus, the reliability of the estimated concrete strength is always a questionable issue. In this context, this paper seeks to develop an in-situ test method as an alternative to the available techniques to assess in-situ compressive strength of concrete. The PSP test is proposed based on the modified pullout testing of post-installed screw. The test is a partially destructive technique that involves insertion of an oversized screw into a predrilled hole in the hardened concrete and subsequent pullout of the screw compelling the concrete to follow a specific failure pattern – a complete pullout failure. The peak load obtained in the process is then correlated to the concrete compressive strength. In determining an appropriate and robust configuration for the PSP test, commercially available screws of different sizes were investigated along with different sizes of drilled hole. High strength correlation of the PSP test in mortar with selected test configuration reveals the potential of the test to be used in the strength assessment. Further investigations are proposed to confirm the suitability of the test to be applied in concrete.