The increasing emphasis on sustainable development in the construction industry necessitates the exploration of alternative cementitious materials. Fly ash, a by-product of thermal power plants, presents significant potential for enhancing concrete properties while minimizing environmental impact. However, traditional usage of fly ash in concrete is often limited by delayed early-age strength development. This study investigates the mechanical, durability, and microstructural performance of concrete incorporating raw fly ash (RFA), pulverized (ultrafine) fly ash (UFFA), and zinc sulphate (ZnS) as a chemical retarder to address these limitations. Pulverization of fly ash significantly enhances its surface area and reactivity, promoting pozzolanic activity and improving the filler effect within the concrete matrix. Experimental work includes compressive strength, split tensile strength, flexural strength assessments, and durability evaluations such as rapid chloride penetration tests. Additionally, microstructural analyses through SEM, XRD, and FTIR techniques provide insights into the hydration behavior and crystalline structure formation. Results reveal that optimized incorporation of ZnS enhances setting times without compromising strength, while UFFA contributes to improved mechanical and durability properties. The UFFA-ZnS blended concrete exhibited superior performance compared to conventional blends. This research offers a novel perspective on fly ash utilization, providing significant techno-economic and environmental benefits for sustainable construction practices. The findings contribute to the growing body of knowledge promoting the use of industrial by-products for high-performance and eco-friendly construction materials.