###### Abstract  
High-performance concrete (HPC) is commonly used in the main structures of bridges. HPC is widely applied in the main structures of bridges, yet some skepticism remains with integrating fly ash and mineral powder as admixtures into prestressed HPC bridges. To address this, this study conducted scaled-model experiments to analyze the flexural fatigue behavior of prestressed HPC bridges with double-mineral fine powder admixtures (PB-DA). This study derives the similarity criteria for a simply supported beam bridge under a concentrated load based on similarity theory. Subsequently, in following these criteria, a 30 m long actual bridge is scaled down to a 6 m PB-DA at a 1:5 scale. For this scaled PB-DA, the concentrated load is reduced to 1/25 of the actual bridge, while the strain remains the same as in the actual bridge. The double-mineral fine powder admixture (D-A) was produced and used to fabricate PB-DA by mixing fly ash and mineral powder. Five PB-DAs were constructed, with C50 and C80 concrete strength grades, and admixture ranges from 10% to 32%. Sinusoidal half-wave constant stress amplitude loading at 5 Hz frequency was applied, with 2 million fatigue loading cycles. After fatigue loading, a continuously increasing static load was applied until the PB-DA failed. The experimental results show that the upper part of the PB-DA is compressed, and the lower part is in tension. The PB-DA strain distribution from top to bottom generally conforms to the plane section assumption. During 2 million fatigue loading cycles, 200,000 cycles mark the beam strain and stiffness evolution boundary. Below 200,000 cycles, the PB-DA strain rapidly increases, and flexural stiffness quickly decreases. Beyond 200,000 cycles, the rate of increase in strain and the rate of decrease in flexural stiffness significantly slow down. After fatigue loading, the PB-DA displacement increases exponentially under a continuously increasing static load. The crack distribution is uniform across all PB-DA, with the cracks being sparsest at a 30% admixture. A comprehensive analysis shows that all PB-DAs demonstrate good flexural fatigue behavior. Notably, when D-A content reaches 30%, strain increases, but reductions in flexural stiffness and damage in PB-DA significantly decrease. This paper's conclusions provide a reference for applying D-A at PB-DA. p 2024 14 7511 11  
concrete and mineral admixtures, there have been concerns in early engineering projects regarding the use of mineral admixtures in large proportions [6]. Exploring the application of D-A in high-performance concrete, especially high-strength concrete, holds significant engineering value. As railway and highway bridges are inevitably subjected to natural environments and cycle loads during the operational period, concrete faces challenges with durability. In 1994, 6137 railway bridges in China showed signs of deterioration, accounting for 18.8% of the total number of railway bridges that year. Incorporating mineral additives into the concrete to enhance bridges' mechanical and durability properties has become vital to ensuring the service life of bridges [7; 8; 9]. Mineral additives are widely used in designing high-performance electrically conductive cementitious composites, which are applied in traffic detection, structural health monitoring (SHM), and pavement deicing [10; 11; 12; 13; 14]. Research on incorporating mineral additives into concrete has evolved from micro to macro aspects. Microscopically, the focus has been on the role of mineral additives in concrete, which includes the following [15; 16; 17]: (1) the morphology of mineral additives can alter the rheological properties, initial structure, and multiple functions of the mixture, especially acting as a lubricant during concrete pumping; (2) mineral additives can chemically react with alkaline substances in humid environments to form cementitious materials, thereby enhancing the concrete's corrosion resistance; and (3) the tiny beads and fragments in mineral additives can improve the concrete's strength.