In the field of cement production, improving the activity of flyash has always been a key issue in reducing dependence on clinker. A building materials research and design institute successfully converted the original flyash (specific surface area 290 m²/kg, activity index 72.3%) into highly active ultrafine flyash with a specific surface area ≥500 m²/kg. This was achieved through the mechanochemical activation technology of a Φ4.2m×13m tube mill. As a result, its 28-day activity index increased to 91.1%.
Laser particle size analysis revealed the following changes: the average particle size (D50) dropped sharply from 28.45 μm to 11.14 μm. The proportion of fine particles smaller than 3 μm increased from 6.43% to 16.39%. The characteristic particle size (X’) was reduced by 26 μm. These changes significantly improved the hydration reaction efficiency of active SiO₂ and Ca(OH)₂. The amount of C-S-H gel generated increased by more than 30%, and the density of the cement paste microstructure increased by 25%.
Three major effects reconstruct material properties
Micro-aggregate filling effect
The particle size distribution of ultrafine flyash (93.3% of particles <45μm) forms a gradient mix with cement. This fills the gaps between cement particles. As a result, the bulk density of the binder material increases by 18%.
When 20% ultrafine flyash is added to P·O42.5 cement, the standard consistency water demand increases by only 1.8%. The 3-day compressive strength remains at 23.4 MPa. The 28-day strength reaches 48.2 MPa, which is close to the performance of pure clinker cement.
Volcanic Ash Activity Effect
During grinding, glass microspheres break and expose more active sites. This increases the secondary reaction rate with cement hydration products by 40%.
Tests show that concrete with 20% ultrafine flyash achieves a 28-day compressive strength of 50.3 MPa. This is 13.6% higher than concrete with raw fly ash. The chloride ion penetration resistance improves by two levels, and the rebar protection ability is significantly enhanced.
Particle Morphology Bearing Effect
Scanning electron microscopy shows that spherical SiO₂ microspheres in ultrafine fly ash increased from 45% to 78%. In concrete, they create a “ball bearing” effect. The initial slump is 210 mm, with only a 30 mm loss after 60 minutes. This improves by 50% compared to raw fly ash, significantly enhancing workability.
Cost reduction and efficiency improvement in industrial applications
In a cement company’s Φ4.2m tube mill production line, optimizing with a 0.7‰ grinding aid increased output. The grinding system capacity rose from 70 t/h to 100 t/h. The unit power consumption was controlled under 35 kWh/t.
A performance revolution in concrete applications
In the C30 concrete mix, when ultrafine flyash replaces 30% of cement, the 28d compressive strength reaches 29.9 MPa, 13.7% higher than the original flyash group. The strength loss after 50 freeze-thaw cycles is only 5.2%, compared to 8.9% for the original flyash group. In marine engineering concrete, the microfilling effect of ultrafine flyash reduces chloride ion diffusion coefficient by 42%, extending the rebar corrosion period to over 20 years. Notably, it shows excellent compatibility with polycarboxylate superplasticizers, with a 60-minute slump retention value of 180 mm, meeting the long-distance transportation needs of ready-mixed concrete.
conclusion
The material revolution spurred by grinding technology fundamentally aims to unlock the latent value of industrial solid waste via particle micronization. Flyash is evolving from a “passive additive” in composite materials to an “active optimizing” functional mineral admixture. This shift meets not only the practical demands of cost reduction and efficiency enhancement in the cement industry but also embodies the future vision of green building materials. With the ongoing iteration of grinding processes and standard systems, high-activity ultrafine fly ash is poised to redefine the performance frontiers of concrete materials. It offers critical technological support for the circular economy under the “dual-carbon” objectives.
Epic Powder
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