Physicochemical Engineering of Hybrid Fiber-Reinforced Geopolymer Composites Based on Coal Ash

Energy-efficient and environmentally friendly processing of industrial coal ash waste is an important physicochemical, technological, and environmental problem. The aim of this paper is to propose a method for the physicochemical development of hybrid fibrous (steel and/or polypropylene) geopolymer composites based on coal ash. The method is based on the experimental and theoretical control of the physicomechanical properties (compressive and flexural strength at different curing times) in accordance with the influence of the chemical composition and microstructure of the new composites on their properties. For fiber-reinforced geopolymers, quantitative structure–activity relationship (QSAR) approaches have been adapted to macro-level structural parameters. instead of molecular descriptors, the following are used: activator composition (SiO2/Na2O modulus, alkali concentration); coal ash proportion and type; fiber type, volumetric content, length, elastic modulus, and orientation; The water-to-alkali ratio serves as "descriptors", while workability (slump, slump flow), and compressive and flexural strength (7 and 28 days) serve as "activity." It was found that the physical workability characteristics of these geopolymers (slump and flow) depend on the inclusion of different types of fiber. Compressive and flexural strength (to a greater extent) increase throughout the curing period, with the most significant increase in strength observed with the use of hybrid fiber (54% and 37% higher than that of the control sample at 7 and 28 days, respectively). The chemical composition of the geopolymer matrix of the new composites, including mainly silicon, aluminum, and calcium oxides due to the use of coal ash, was determined experimentally and theoretically, which is confirmed by the creation of a durable geopolymer matrix. © The Minerals, Metals & Materials Society 2025.