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 24–82 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. It follows that the predominant products that provide the strength of the binder are calcium silicate hydrates with a CaO/SiO2 ratio of 1.7 to 4.2. The results contribute to the data for development of models for predicting the effect of HCFA on the properties of composite binders.