It has been demonstrated that a spectrochemical analysis of carbon using the laser plasma method can be successfully applied to inspect the carbonation of concrete by detecting carbon produced in aged concrete by a chemical reaction of Ca(OH)<sub>2</sub> with CO<sub>2</sub> gas in environmental air, turning into CaCO<sub>3</sub>, which induces degradation of the quality of building concrete. A comparative study has been made using a TEA CO<sub>2</sub> laser (500–1000 mJ) and a Q-switched Nd–YAG laser (50–200 mJ) to search for the optimum conditions for carbon analysis, proving the advantage of the TEA CO<sub>2</sub> laser for this purpose. Also, it was clarified that laser irradiation with suitable defocusing conditions is a crucial point for obtaining high sensitivity in the detection of carbon. Practical experiments on the inspection of carbonation were carried out using both a concrete sample that had been intentionally carbonated by exposure to high concentrations of CO<sub>2</sub> gas and a naturally carbonated concrete sample. As a result, good coincidence was observed between the laser method and the ordinary method, which uses the chemical indicator phenolphthalein, implying that this laser technique is applicable as an<i> in situ</i> quantitative method of inspection for carbonation of concrete.
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