Quantifying a Particulate-Based Admixture in Hardened Concrete

Micron-size, polymeric, hollow, spherical particles, generically referred to as microspheres, currently are used to improve freeze-thaw durability in niche concrete applications in Europe and North America. As more applications are developed for this emerging technology, there is increasing demand for methods to quantify the microsphere content in hardened concrete. A key feature for methods is the use of standard equipment available in testing laboratories. Initial evaluation within one laboratory indicated the potential use of a modified version of ASTM C457, Standard Test Method for Microscopical Determination of Parameters of the Air-Void System in Hardened Concrete, to quantify microspheres in hardened concrete. An exploratory round robin with three additional laboratories was conducted for further evaluation of the potential of the modified ASTM C457 method for quantifying microspheres in hardened concrete. Sample preparation and method modifications are described. Results of the exploratory round robin are presented and discussed. Challenges with microsphere identification as well as potential solutions are presented.