Study of the Effect of Fly Ash Replacement Ratio of Cement on Microstructure Evolution, Stress–Strain Behavior, and Chloride Ion Penetration Resistance in Self-Compacting Concrete

The development of sustainable high-performance concrete requires the incorporation of supplementary cementitious materials (SCMs) to enhance mechanical properties, improve durability, and reduce the environmental impacts associated with cement production. Fly ash, as a reactive pozzolanic material, can significantly improve concrete performance by promoting secondary hydration reactions, reducing pore volume, and refining the microstructure of the interfacial transition zone (ITZ) between aggregates and cement paste. In this study, the effects of partially replacing cement with fly ash at replacement levels of ۱۰%, ۲۰%, and ۳۰% on the mechanical properties, stress–strain behavior, chloride ion penetration resistance, and microstructure of self-compacting concrete (SCC) with different cement contents (۲۵۰, ۳۰۰, and ۳۵۰ kg/m³) were investigated. The performance of the concrete mixtures was evaluated through compressive strength tests conducted at curing ages of ۷, ۲۸, and ۹۰ days, the Rapid Chloride Migration Test (RCMT), and stress–strain curve analysis. The results demonstrated that incorporating fly ash at replacement levels of up to ۲۰% improved the densification of the concrete matrix, reduced permeability, and enhanced resistance to aggressive environmental conditions. The SCC mixture containing ۳۵۰ kg/m³ of cement with a ۲۰% fly ash replacement exhibited the best overall performance in terms of reduced chloride ion penetration and improved mechanical properties. Although a ۳۰% fly ash replacement resulted in lower early-age compressive strength, improvements in durability and microstructural refinement were observed at later curing ages due to the continued pozzolanic reaction. Furthermore, the stress–strain analysis revealed that the incorporation of ۲۰% fly ash increased the ultimate strain capacity, enhanced ductility, and provided more effective control of crack propagation. Based on these findings, a ۲۰% replacement of cement with fly ash can be considered an effective strategy for producing sustainable, low-carbon, and durable self-compacting concrete with superior resistance to chloride-rich environments.

کلیدواژه ها:

Self-compacting concrete (SCC) ، Fly ash ، Supplementary cementitious materials (SCMs) ، Chloride ion migration ، Stress–strain behavior