Concrete is one of the most important materials in construction engineering. Evaluation of in-Situ concrete
strength has become of great concern in construction process as well as for quality control. There
are many destructive tests which can be conduct for the strength evaluation and for other performance
parameters as well. However, load tests or core tests are not always possible or practicable. Since last decade,
non-destructive testing has been widely accepted throughout the world in order to assess the quality
of in-situ concrete. Compressive strength is considered as the most common measurement used by engineerings
in design. The results of this test indicate if the concrete fulfills the requirements of the desired
structure or not.
In the present work, the laser-induced breakdown spectroscopy (LIBS) technique has been used as a
diagnostic tool for the elemental composition of concrete and determination of the compressive strength.
The ratio between the ionic calcium lines at 393.3 and 396.8 nm and the neutral line at 422.6 nm have
been utilized to measure their compressive strength. These lines are reversible lines, as they are greatly
self-absorbed. The self-absorption of calcium lines under investigation was corrected via comparison of
the electron densities. These densities have been measured from calcium lines to that computed from the
hydrogen Ha-line at 656.27 nm which are in the same spectra under the same state. A linear relationship
has been obtained between compressive strength and the ratio of the calcium ionic to atomic spectral
lines intensities (Ca II/Ca I). The results showed an acceptable with high accuracy linear relations.
A new relation has been developed for comparison between compressive strength and the plasma temperature.
The results reflect the importance of correcting the intensity of the emitted spectral line for the
self-absorption effect before utilizing the compressive strength measurement in LIBS experiments. Also,
it has been confirmed that the LIBS technique can be considered as a trustful semi nondestructive concrete
strength test. |
