Study of the Composition and Structure of High-Strength Material Based on a Fine High-Calcium Fly Ash Using the SEM-EDS Method

This study examines the microspherical high-calcium fly ash (HCFA) and the high-strength binder material based on it by method of scanning electron microscopy and energy-dispersive X-ray spectroscopy (SEM-EDS). The composition of 568 individual microspheres of the initial HCFA was determined and presented as ternary diagrams CaO–Al2O3–SiO2 and CaO–FeO–SiO2. The binder specimens have a compressive strength of 24–90 MPa at a curing time of 3–300 days. Their strength is close to that of CEM I 42.5N cement specimens with a curing time of up to 28 days, but exceeds it with a curing time of up to 300 days. The SEM-EDS method showed that the predominant composition of hydration products is concentrated in the high-calcium region of the CaO–Al2O3–SiO2 diagram with a CaO content of 60–80%. The SiO2 content in them is 15-30%, and their composition includes 1–15% Al2O3 and 5–14% FeO. The SEM-EDS method allowed us to understand the transformation of calcium silicate glass microspheres into C-S-H gel, which is the main component of the strengthening matrix. The results contribute to the data for development of models for predicting the effect of HCFA on the properties of composite binders.