In this study, a comprehensive and comparative analysis was conducted on nine types of silica-rich agricultural waste ashes including rice husk ash, peanut shell ash, sugarcane bagasse ash, date palm fiber ash, corn stalk ash, wheat straw ash, cotton stalk ash, soybean husk ash, and pine fiber ash as pozzolanic replacements in Ultra-High-Performance Concrete (UHPC). Fresh properties were evaluated through slump flow, J-ring, L-box, U-box, and V-funnel tests, while hardened properties were assessed via compressive strength, tensile strength, modulus of elasticity, freeze–thaw durability, permeability, chloride and sulfate resistance, and thermal conductivity tests. Response Surface Methodology (RSM) was employed to model the synergistic effects of variables and predict compressive strength at 28 and 90 days. Results indicated that replacing 30% of cement with rice husk ash improved compressive strength, tensile strength, and modulus of elasticity by 15%, 46%, and 27%, respectively, while reducing permeability and thermal conductivity by 48% and 27%. RSM analysis demonstrated high predictive accuracy (R² = 0.99). This study provides an integrated framework for designing sustainable and advanced concrete by optimizing the incorporation of waste materials while achieving superior mechanical and thermal performance.

Ultra-High-Performance Concrete, natural ash, cement, compressive strength