The rapid expansion of infrastructure has intensified the need for high-performance and sustainable concrete. This study presents an experimental investigation into the mechanical properties of high-strength concrete incorporating fly ash as a partial cement replacement (0% and 40% by weight) and polypropylene (PP) fibers as reinforcement (0% and 1% by volume fraction). Concrete grades M20 to M60 were designed, cast, and tested at 28-day and 56-day curing ages for compressive strength (cube specimens, 150×150×150 mm) and split tensile strength (cylinder specimens, 150×300 mm). Minitab statistical software was used to develop regression models, perform ANOVA, and generate Main Effects and Contour plots for all four response variables: 28-day compressive strength (Comp28), 56-day compressive strength (Comp56), 28-day split tensile strength (Tensile28), and 56-day split tensile strength (Tensile56). Results indicate that concrete grade is the dominant factor for compressive strength, fly ash significantly enhances later-age (56-day) compressive strength through secondary pozzolanic reactions, and PP fiber content exerts the strongest influence on split tensile strength, particularly at 56 days. The regression models achieved R² values exceeding 97%, validating excellent predictive accuracy. The optimized mix M60 grade with 40% fly ash and 1% PP fiber achieved a 56-day compressive strength of 74.8 MPa and demonstrated significantly improved crack resistance and sustainability.

Keywords— Fly Ash Concrete; Polypropylene Fibers; Compressive Strength; Split Tensile Strength; Minitab Optimization; ANOVA; Regression Analysis; Sustainable Concrete