Non destructive testing of concrete

Assessment of in-situ concrete, a major building material in construction has been of considerable interest in Construction Industry, mainly for quality control as well as to find in-situ strength. The measurement of strength and other performance parameters is generally done by normal destructive tests. However load tests or core tests are not always possible or practicable. Since last decade, non-destructive testing (NOT) has been widely accepted throughout the world to assess the quality of in-situ concrete. The NOT technique includes Rebound hammer, Ultrasonic Pulse Velocity tests, Penetration tests, radiography tests etc. However none of these tests can be used independently to yield reliable quantitative results. Generally combination of a few Non-destructive tests yields results of acceptable levels. A number of Correlations between Rebound hammer test and Ultrasonic pulse velocity test results have been developed to obtain reliable results. Recently a combination of NOT techniques like Rebound hammer, Ultrasonic pulse velocity and Windsor probe has been used to evaluate the quality of few distressed structures in India, successfully to recommend their restoration. Supplementary core test results confirmed the reliability of the correlation between the different NOT techniques used. This thesis describes a study carried out to investigate the effects of some factors that have significant influence on Rebound Hammer and Ultrasonic Pulse Velocity results. Therefore, test cubes were cast and tested for different grades of concrete, curing conditions and age of testing in order to obtain correlations of concrete strength with Rebound Hammer and Ultrasonic Pulse Velocity test results. Use of more than one NOT method at a time is advantageous when the variation of properties of concrete affects the test results in opposite directions. Further, adopting the test results a combined method has been developed to predict concrete strength with a reasonable accuracy