Differences among Various Non-Destructive Methods

Estimation of concrete strength by non-destructive methods (I)

Abstract

From 1989, we have carried out experimental studies for estimating the compressive strength of concrete by non-destructive methods. In this paper, the non-destructive methods used to estimate the strength are as follows.
(a) Rebound method (rebound number by the Schmidt hammer N type);
(b) Penetration method (penetration depth using the Pin tester);
(c) Resonant frequency method (dynamic modulus of elasticity); and
(d) Pulse velocity method (ultrasonic pulse velocity).
The compressive strength estimated by these methods was compared with the measured compressive strength from cylindrical and beam specimens. As a lot of data on the strength has not been used and the concrete with a wide range of strength has not been made, it was difficult to estimate the reliable compressive strength by these non-destructive methods. Up to now, the results obtained are as follows.
(1) Among the non-destructive methods, the Pin tester method gave the closest estimation to the measured strength but this method took a great amount of time to measure the penetration depth and left small holes that needed to be repaired on the concrete surface.
(2) The estimation from the Schmidt hammer method disperses frequently because the surface hardness of concrete is greatly affected by the surface conditions such as moisture content or surface roughness.
(3) The pulse velocity method is promising to estimate the strength of concrete because unskillful people can use it easily.
(4) The most promising combination is the ultrasonic pulse method in conjunction with rebound method because this combination gives a higher correlation between the measured strength and that estimated and these method have no restriction with respect to the shape of specimens and structures.