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    Using Fluorescent Microscopy as a Tool in the Determination of Water to Cementitious Binder Ratios in Hardened Concrete Samples

    Published: 2019

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    The relationship between the water to cement (w/cm) ratio of a cement-based matrix and its capillary porosity is well documented. It is also well documented that this relationship extends to light intensity of the cement paste matrix using the fluorescence technique. It is also well reported that for 28-day-old portland cement–only (PC-only) concrete mixes hydrated under normal conditions, this relationship is reliable for w/cm ratio assessments between 0.35 and 0.70. This study confirmed that a similar linear relationship exists with concrete mixes containing various supplementary cementitious materials (SCMs) with differing w/cm ratios. It also showed, however, a consistently higher fluorescence developed at 28 days of age with these various SCM-containing mixes when compared with the equivalent PC-only references. The light intensity of the various SCM mixes appeared to relate more to the relative amounts of SCM material and to a lesser degree the material’s apparent translucency or coloration. Finally, this paper described the findings from a set of companion test samples produced at a greater age (18 months), which showed that the same linear relationship between w/cm ratio and fluorescent light intensity existed for all the mixes and showed that, in most cases, the differences between SCM-containing mixes and the equivalent PC-only mixes was reduced. The 18-month-old samples containing SCMs, however, still exhibited a greater fluorescent light intensity than the equivalent PC-only samples. This finding underscored the absolute requirement for appropriate reference samples when applying this technique to mixes containing SCMs.


    28-day, 18-month-old samples, water to cementitious ratio determination, fluorescence microscopy, supplementary cementitious materials

    Author Information:

    Sibbick, Richard G.
    R&D Department, GCP Applied Technologies, Cambridge, MA

    LaFleur, Callie
    R&D Department, GCP Applied Technologies, Cambridge, MA

    Garrity, Steven
    R&D Department, GCP Applied Technologies, Cambridge, MA

    Committee/Subcommittee: C01.23

    DOI: 10.1520/STP161320170235