Reproducibility of w/c ratio determination from fluorescent impregnated thin sections

The ease and reproducibility of preparing fluorescent epoxy impregnated thin sections for w/c determination of concrete has been studied. Five sets of thin sections were prepared from 6 concrete mixes having different compositions and w/c ratios (0.35 to 0.80). The thin sections were prepared by different technicians and produced over a period of nearly a year. The quality of the thin sections was checked and the w/c ratio determined by seven petrographers using fluorescent light microscopy as a Round Robin test.The investigation showed that, within a reasonable time, different technicians were able to produce a comparable quality of fluorescent epoxy impregnated thin sections, even though the thin sections were produced from concrete at different ages and using different equipment and chemicals. The petrographers were able to distinguish between the green shades of the fluorescent dye epoxy impregnated cement paste, with sufficient accuracy. The result of the w/c Round Robin test gave standard deviations between 0.02 and 0.03 (average 0.026).