Characteristics of the Narrow Fractions of Fly Ash Microspheres as the Basis of Light-Weight High-Strength Materials

The narrow fractions of microspheres with a size of −0.4 + 0.2 mm with a low bulk density in the range of 0.34–0.64 g/cm3 were separated from cenosphere concentrates of fly ashes and fly ash from local selection obtained from pulverized coal combustion. The main components of the chemical composition in obtained narrow fractions are SiO2 – 55–66 and Al2O3 – 21–40 wt. %. The part of amorphous glass phase are 63–93, the mullite phase are 1–34, the quartz phase are 2–8 and the calcite phase are 0–1 wt. %. It is found that microspheres, characterized by maximum values of bulk density 0.64 g/cm3 and apparent thickness of the shell 20 μm, has the best strength properties. The successive twofold compressive loading the particles by increased strength were selected, for which the values of bulk density and apparent shell thickness increased to 0.86 g/cm3 and 29 μm, respectively. It is shown that the spheres with the single-ring structure are primarily subjected to destruction; the particles with network and solid structure provide improved strength characteristics of narrow fractions of microspheres