Correlation between Non-Destructive Testing (NDT) and Destructive Testing (DT) of Concrete for Linear, Quadratic and Cubic Relation
Abstract
This work present a correlation and comparison between Non- Destructive test (Rebound Hammer) & Destructive test of testing the compressive strength of concrete cubes for Linear, Quadratic & Cubic Relation. Concrete cubes of 150mm×150mm×150mm were cast of M-20, M-25, M-30 and M-35 grades and each grade cured for 7days, 14days and 28days. A total 120 cubes were cast. When analyses were carried out, there are a relation between the results of rebound number obtained from rebound hammer and compressive strength obtained from compression machine. These results i.e. rebound number and compressive strength value of cubes M-20, M-25, M-30 and M-35 grades were correlate and compared with Linear, Quadratic & Cubic Equation and checked from which equations among these three gives a more accurate results with compressive strength. After analyses it was found that among three of them predicted strength of cube only the linear and quadratic equation gave more accurate relationships with compressive strength of concrete. And at the end it also gave statistical analysis of the results which shows that there were a significant difference between the rebound number and compressive strength.
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Introduction
Concrete is a composite material which is produced from the combination of fine aggregates, coarse aggregates and water with proper proportion. The strength of concrete is most important along with its durability. Therefore it is important to check or find out the compressive strength of concrete before used in structural purpose. Therefore, it is very important to check the compressive strength of concrete before subjecting it to its anticipated loads. Compressive strength of a hardened concrete can be determine using destructive & non- destructive test (NDT) methods. The (DT) is carried out by crushing the cast specimen to failure while the NDT method is carried out without destroying the cast specimen. The Rebound Hammer (Schmitz) is one of the most popular NDT methods used to test the strength of concrete. The aim of this project is to compare the concrete compressive strengths measured using destructive method and those measured using the NDT for Linear, Quadratic & Cubic Relation and to check from which equations among these three gives a more accurate results with compressive strength.
Conclusion
The correlation among the strength values obtained by destructive and NDT test methods on
Concrete cubes have been established. Schmidt Hammer test method is used as a non-destructive test. The following principal conclusions have been drawn:-
The use of rebound hammer test method on concrete cubes is not suitable to estimate its strength.
Direct use of rebound hammer demonstrates high variations, which makes engineering judgment quite difficult.
The Schmidt Hammer method could only be used as a reliable instrument to calculate the compressive strength.
This project gives a useful mathematical linear and non-linear relationship that help the engineer to predict confidently the crushing strength of standard concrete cubes, by measuring the rebound index by means of Schmidt hammer.
The linear and quadratic equations give perfect relationships with the compressive strength of concrete whereas there is a much difference in cubic equation results. It means only linear and quadratic mathematical expression is applicable for a wide range of concrete strengths.