The mechanical properties of High-Performance Self-Compacting Concrete (HPSCC) are strongly influenced by its pore structure, but the impact of varying water–binder ratios (W/C) on this relationship remains unclear. To address this, the present study investigates HPSCC with W/C ratios ranging from 0.19 to 0.23, aiming to elucidate the connection between pore structure, fractal characteristics, and mechanical performance. Through a combination of compressive strength testing, low-temperature nitrogen adsorption, and Scanning Electron Microscopy (SEM) observations, this study reveals key insights. First, compressive strength initially increases with a decreasing W/C ratio but plateaus beyond W/C = 0.21, identifying an optimal range for balancing strength and workability. Second, the pore structure of HPSCC is characterized by cylindrical, ink-bottle, and planar interstitial pores, with significant fractal characteristics. Notably, the fractal dimension decreases as the W/C ratio increases, indicating reduced pore complexity and improved homogeneity. Finally, a strong linear correlation (R² > 0.9) between the W/C ratio, fractal dimension, and compressive strength provides a predictive tool for assessing HPSCC performance. This study concludes that the internal pore structure is a critical determinant of HPSCC strength, and the identified optimal W/C ratio range offers guidance for mixture designs. Additionally, fractal dimension analysis emerges as a novel method to evaluate HPSCC’s microstructural quality, enabling predictions of long-term performance and durability. These findings contribute to the scientific basis for designing high-performance concrete materials with improved mechanical properties and durability.

The dosage of mineral powder has a complex influence on the compressive strength of self-compacting concrete, among which the pore structure is a key determining factor. This study investigated the effects of different dosages of mineral powder (0%, 5%, 10%, 20%, and 30%) on the workability, mechanical properties, and pore distribution in C80 self-compacting concrete. The research results show that an appropriate dosage of mineral powder (0–20%) can significantly improve the spreadability and fluidity of C80 self-compacting concrete. This phenomenon is mainly attributed to the shape effect and micro-aggregate effect of mineral powder, which improve the fluidity of concrete, reduce the viscosity of the paste, and thereby increase the spreadability and gap-passing rate. By testing the BSD-PS1/2 series fully automatic specific surface area and pore size analyzer, we found that there are columnar pores and ink bottle-shaped pores in C80 self-compacting concrete, as well as a small amount of plate-like slit structures. Our observations with an SEM scanning electron microscope revealed that the width of micro-cracks and micro-holes is between 1 and 5 μm and the diameter is between 3 and 10 μm. These microstructures may have an impact on the mechanical properties of the structure. By applying fractal theory and low-temperature liquid nitrogen adsorption tests, this study revealed the relationship between the fractal characteristics of internal pores in C80 self-compacting concrete and the dosage of mineral powder. The results show that with the increase in mineral powder dosage, the fractal dimension first decreases and then increases, reflecting the change rule of the complexity of pore structure first decreasing and then increasing. When the dosage of mineral powder is about 20%, the compressive strength of SCC reaches the maximum value, and this dosage range should be considered in engineering design.