The Effect of Different Particle Sizes of Fly Ash on the Properties of Mortar

Fly ash is a commonly used mineral addition in construction engineering. Research on its different particle size distributions can help optimize material performance, promote resource utilization, and support environmental protection. In this study, the particle size of fly ash was used as a variable; fly ash with a single particle size was prepared by means of sieving, and the particle size was precisely controlled as a variable, thus avoiding the errors caused by the addition of multiple different particle sizes. Replacing 10% of the cement with fly ash to prepare cement mortar, the influence of fly ash particle size on the performance of cement mortar was investigated. The results show that the mortar incorporating fly ash with a particle size range of 10-20 μm achieves a 28-day compressive strength of 58.25 MPa and a flexural strength of 10.29 MPa. The hydration heat release rate of fly ash in the 10-20 μm range reaches a maximum of 1.84 mW/g, and the total hydration heat release peaks at 211.17 J/g at 70 h. The influence of fly ash particle size on the total hydration heat release is relatively small in the early stages but increases rapidly with prolonged hydration time. When the fly ash particle size is in the 10-20 μm range, the cement mortar exhibits the lowest total porosity at 12.88%, with the smallest average pore size of 27.1 nm and the smallest most probable pore size of 21.2 nm. This reduces harmful pores, increases the number of harmless pores, makes the cement mortar structure denser, and improves the durability of the mortar. The types of hydration products of different particle sizes of fly ash did not change. The smaller the particle size of fly ash, the more complete the volcanic ash reaction, promoting the hydration of mortar.