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The form and the perpendicularity of boreholes influence the ultimate behaviour of post-installed fasteners and are restricted with regard to the concrete surface to 5° in Europe and to 6° in the United States in various regulations (e.g., EAD 330232-00-0601 resp. ACI 355.2-19). It is assumed that the deviation of the borehole from the vertical axis has an effect on the load transfer behaviour of an anchorage. This article investigates on the perpendicularity of vertically downward drilled boreholes using different drilling tools considering hammer drilling, hollow drilling and diamond core drilling. It can be shown that the requirements of e.g., EAD 330232-00-0601 of a maximum deviation to the concrete surface of 5° can be fulfilled for approximately 95% of the determined values for different drilling methods. This is based on a considerable number of measurements (generated from drilled boreholes) in different concrete types. As a result, a detailed statistical evaluation is provided to describe the borehole perpendicularity by means of statistical methods.

Statistical Evaluation of the Perpendicularity of Boreholes in Concrete for Post-Installed Fasteners