Abstract—Non-destructive testing (NDT) is commonly implemented to determine the reliability of the concrete structure elements. In this study, we present a non-destructive diagnosis of structural members of an existing reinforced concrete building. Different types of in situ non-invasive tests such as Schmidt Hammer and ultrasonic pulse velocity together with invasive concrete coring were carried out to investigate the relation between rebound number/ultra sonic pulse velocity and concrete compressive strength by the following correlations: 1) Linear regression, 2) Exponential regression, and 3) Multiple nonlinear regression. Among these cases, the combined SonReb model yielded the most reliable estimates to predict the compressive strength, where a coefficient of determination (R2) of 0.81 was obtained. However, the use of rebound hammer test only found to be not adequate for the estimation of compressive strength. Due to the exposure of the RC building to the harsh environment for long period (more than 30 years), data from 18 extracted cores were further analyzed to study the effect of carbonation on steel reinforcement. The presence of significant carbonation depth (22 mm) and the large amounts of chloride lead to severe steel corrosion in several parts of the structure.