Vol.18, No.1, 2018, pp.61–69
UDC  624.012.45.046

Weakening of concrete is largely affected by the design of the structures, construction procedure and activities of the construction site, and the length of experiences the structure is exposed to during its service life. However, proper maintenance and timely inspection of existing building can minimize the possible structural failures. The concrete strength of an existing building plays a vital role in overall performance of the building. The estimation of strength properties of concrete can be performed by several methods: visual, destructive and non-destructive test methods. The core test (destructive) is considered as the most reliable test method since it provides the direct compressive strength of the concrete, but often it is difficult of extracting large diameter concrete core due to the presence and interference of reinforcement bars inside of concrete. Therefore, the core diameter varies significantly, even in the same building, in order to extract the cores without interfering the inside main reinforcements. In this study, six existing buildings are studied in the field to estimate the in-situ concrete strength using extracted core test. Different sizes of cores are collected and tested in the laboratory to investigate concrete strength. No consistent trend is found from the collected samples. In these type of cases, more core samples with a smaller diameter (51 mm) might be an option to estimate the existing concrete strength of a building with more consistent manner, and as well as safe for the building during the safety evaluation. To justify the effectiveness of smaller diameter cores, the concrete strength is calculated for different core diameters using finite element analysis in Abaqus environment. Variation in core diameter does not show any significant deviation in estimating concrete strength, which is a promising indication of using cores with 51 mm (2 in.) diameter to estimate existing concrete strength.

Keywords: existing structure, concrete strength, destructive test, core extraction, smaller diameter core, finite element analysis