Evaluation and Adaptation of the Dobrolubov and Romer Method of Microscopic Examination of Hardened Concrete

About the report:

The optical procedures used in Switzerland as a part of the program of quality control of concrete were investigated for usefulness in determining the microstructural parameters and potential durability of concrete. The Swiss procedure uses thin sections impregnated with a fluorescent dye. The investigations showed such sections to be more useful when polished to a thickness of 8 to 14 µm. Quantitative measurements of many parameters were made by a modified point count procedure. It was found possible to distinguish concretes of three different water/cement ratios. The cement content could not be investigated independently without reference to total paste content or to yield. Admixtures such as hydrated lime were found to be indistinguishable from normal hydration products at advanced ages. Siliceous admixtures such as fly ash could be easily detected at 28 days and 6 months. Type III cement appeared different from Type II at early ages. Four general ages of cement hydration were investigated and found to be distinguishable. The effect of aggregate type was investigated and is discussed. It was found that although at least one suite of specimens did not produce any correlation in voids percent volume as determined at high magnification in thin section with similar data obtained by linear traverse, the spacing factors obtained by the two methods were quite comparable. The sample preparation procedures are intricate and time-consuming when only one or two sections are produced at one time. The use of fluorescent ultrathin sections can be recommended only for the collection of data which cannot be obtained by other means. Whenever it is required that hardened portland cement concrete be examined for the cement type used, the relative age of placement, the presence or absence of siliceous admixtures, the shape and effects of aggregate surfaces or that the relative water/cement ratio be ascertained, then the methods that are described will not only be useful but will be among the best and most complete methods of gathering such data. Whenever questionable effects occur in localized small areas of concrete such as surfaces, research into the microstructural nature of these effects can well include optical examination at high magnification of fluorescent impregnated ultrathin sections.

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