To investigate the influence of the fly ash (FA) content on the performance of high-performance concrete (HPC), seven groups of tests were conducted, aiming to evaluate both the macroscopic properties (workability and compressive strength) and microscopic pore structure. Low-field nuclear magnetic resonance (NMR) technology and SEM images were employed to analyze the changes in the internal pore structure of the concrete. The results showed that the workability of HPC initially increased and then decreased with the increase in the FA content. When the FA content was 15%, the slump of HPC reached a maximum of 264 mm, and the 28-day compressive strength exhibited a 23.2% increase compared to the 7-day compressive strength. The pore size distribution of the concrete varied with different fly ash content. At 15% FA content, secondary hydration of the FA was sufficient, refining the pores to between 0 and 0.1 µm. Excessive FA substitution deteriorated the internal structure of the HPC matrix and reduced the workability and mechanical properties of the HPC. When the content of FA was 35%, the slump of HPC decreased to 176 mm, while the macropores within the matrix significantly increased, resulting in porosity of 6.81%.

In this paper, the damage constitutive model of reactive powder concrete (RPC) in uniaxial tension is investigated. The relationship between the uniaxial tensile strength of RPC and the steel fiber admixture was analyzed by preparing RPC specimens with different steel fiber volume admixtures for uniaxial tensile tests, and the stress–strain curves were recorded. The test results show that the uniaxial tensile strength of RPC is significantly enhanced with an increase in steel fiber doping, especially after the doping amount is greater than 2%, showing a linear increase. Based on the classical damage mechanics and Weibull distribution, the damage evolution equation and the constitutive model of RPC uniaxial tension were established. The validation shows that the model can effectively describe the damage process of RPC in uniaxial tension, which provides a theoretical basis for the application of RPC in engineering practice.