Fluorescence Measurement Method for Evaluating Slurry Mixing Quality and Strength Development in Cement Improved Soil

Abstract In this study, the applicability of the fluorescence measurement method (FMM) to quality control of the deep mixing method (DMM), a ground improvement technique, was verified. The DMM has a history of approximately 60 years, but in recent years, the number of cases of poor solidification of the improved columns has increased. One of the main issues is that the cement-based binder and natural soil are not well mixed. In areas such as the Saga Lowland, it is difficult to visually assess the mixing quality because the color of the soft clay and the slurry are very similar. An integrated experimental approach was adopted to evaluate the effectiveness of the FMM compared with the conventional phenolphthalein solution spray method. The FMM uses water-soluble fluorescent dye and applies the principle of photoluminescence to accurately visualize the distribution of the slurry under ultraviolet light. Experiments in the laboratory demonstrated that the FMM can not only accurately identify the mixing quality but also quantitatively evaluate the uniformity of the mixing using the degree of luminous (DL). Regarding the strength development characteristics, it was confirmed that the addition of water-soluble fluorescent dye does not affect the unconfined compressive strength. In addition, a positive correlation was shown to exist between DL and strength development characteristics. This correlation was verified by the needle penetration test. This study highlights the advantages of the FMM over existing methods for visualizing and quantifying mixing quality, and its usefulness in evaluating strength development. The findings emphasize the potential of the FMM for improving quality control, reducing construction costs, and minimizing repair work.