Abstract: A method of estimating the hydration reactivity of coal ash with high precision and determining the amount of milling water for obtaining a milling product in funicular form at the stage of milling; and a molding method being free from the problem of adhesion to a pressurization board at the stage of molding after the milling. When any collected coal ash exhibits a corrected basicity ((CaO+Fe2O3+MgO)/SiO2 (weight ratio)) of 0.1 or higher and a reactivity index (corrected basicity/(R2O/Al2O3) (weight ratio)) of 10 or higher, the coal ash as a raw ash is transferred to raw ash silo (2). Otherwise, the coal ash is transferred to waste ash silo (3). The raw ash within the raw ash silo (2) is poured in mill (8), and lime and gypsum are added and further milling water is charged thereto and milled.

Abstract: To enable high-added-value low-specific-gravity hollow particles to be efficiently mass-produced by using, as a raw material, coal ash discharged when coal is combusted; enriching low-specific-gravity hollow particles contained in the raw material coal ash by classification to reduce the weight of the coal ash to be subjected to wet specific gravity separation; subjecting the raw material coal ash which have been reduced in weight to wet specific gravity separation to obtain low-specific-gravity components; and dehydrating and drying the low-specific-gravity components.