Report on optimum set-up for a LIBS system for applicationon on site (Laser Induced Breakdown Spectroscopy) : Sustainable Bridges Background document SB 3.12

In this report, the principal applicability of LIBS (Laser Induced Breakdown Spectroscop) for the quantitative determination of Chloride contents in concrete has been shown by preliminary results obtained on reference samples and concrete cores originating from real, contaminated sites.The physical background, the necessary components for a LIBS experiment and the measurement procedure are described. A suitable Chlorine spectral line is found at 837,6 nm. Linear calibration curves are obtained for reference samples made of cement and cementmortar with Chloride concentrations ranging between 0 wt% Cl up to 2,34 wt% Cl related to the total mass of the sample. LIBS results of concrete cores are in good agreement with chemical analysis. Further spectral lines in the investigated wave length region allow advanced interpretation of the measured data. The ratio of the intensity of the Calcium spectral line at at 849,9 nm and the Oxygen spectral line at 844,6 nm (Ca/O-ratio) is used for assignment of spectra to cement paste or aggregate, respectively. Therefore, both, the Chlorine content related to cementand the Chlorine content related to concrete is available. The laser must provide enough energy, at least 200 mJ/pulse, to create a plasma on concrete. The other laser parameters are not so crucial, so that a usual NdYAG laser with about 10 ns pulse duration, 1064 nm wave length and about 10 Hz repetition frequency is sufficient. Additionally the laser should have a compact geometry and low weight, no need for external water circulation and capable of normal power supplies. It should be robust against dust and impacts. Lasers with these specifications are commercially available and the laser in the BAM laboratory is suitable for on-site application.EC Sixth Framework ProgramSustainable Bridges – Assessment for Future Traffic Demands and Longer LivesTIP3-CT-2003-001653