Quantitative Determination of the Content of Ground Calcium Carbonate in Hardened Concrete

Abstract

ASTM recently adopted Standard C1797, Specification for Ground Calcium Carbonate and Aggregate Mineral Fillers for Use in Hydraulic Cement Concrete, which outlines the compositional requirements of mineral fillers for use in concrete. Ground calcium carbonate (GCC) currently is used in self-consolidating concrete and concrete masonry units, among other applications, and the demand for and use of calcium carbonate mineral filler is only expected to increase. Currently, however, there is no reliable and cost-effective way to quantitatively determine the concentration of GCC in hardened concrete, which will become an important issue in quality control of concrete as the use of these materials increases. This paper is focused on the development of such a method using petrographic techniques. GCC can be accurately identified in hardened cement paste based on the unique optical properties, and the content of GCC can be determined via point count on thin sections under a petrographic microscope. By performing point count on thin sections of laboratory-prepared mortar and concrete samples with known GCC contents, empirical equations are developed that allow petrographers to estimate the GCC content relatively accurately and efficiently. Experimental details, including the implementation of the point count method and statistical analysis of the data, are discussed. The significance of the method and representative case studies of concrete with different compositions and mix proportions are presented.