An experimental study on interpretation of core test results for assessment of concrete in-situ strength

Abstract

In existing concrete structures, concrete cores may be extracted to assess the current condition of the structure. This is often done when there are concerns about the structural integrity or if the structure is undergoing renovations or modifications and to determine its ability to carry additional loads. This is generally done by taking cores at representative locations in the structure, to give a good overall indication of the strength. This helps ensure that the concrete meets the required strength and durability standards. Core testing is therefore introduced in most local and international codes such as British, European and ACI Codes. The core test results should be carefully interpreted taking into account a number influencing factors such as diameter, aspect ratio (l/d), moisture condition of the core specimen, direction of drilling, etc. The factors considered in different standards and interpretation of the core results and influence of above factors are different. In New Zealand, the technical standards NZS 3112:2 and NZS3109, have detailed how these tests should be carried out and the results analysed. In the New Zealand concrete construction standard NZS3109, the evaluation of core test results is determined by Technical Report No. 11 (TR11) from the UK Concrete Society. However, this document was withdrawn and replaced in the UK by Concrete Advice No. 68 (CA68), which is a summary of BS EN 13791. In this research, an experimental study was undertaken to examine different factors affecting the interpretation of core test results, in particular comparing the methods described in TR11 and CA68. The experimental program involves four concrete test blocks. In total 24 concrete cores were taken with different length/diameter ratios in vertical and horizontal directions. The compressive test results obtained from the cores are analysed and the influence of different factors are discussed. The results are evaluated in accordance with TR11 and CA68 codes, to compare and identify possible differences between the two methods in assessment of Concrete In-Situ Strength from core test results.