High-performance concrete emerged from changes in particle size distribution due to grinding technology. In modern society, it is a powerful tool for construction development. It is not only an essential building material but also a cement paste. This paste’s density varies based on particle size and cement properties. Consequently, we can alter cement’s characteristics, such as its particle size, which is key to changing its performance. However, the packing density of cement particles links directly to modern grinding technology development. This connection led to experiments on cement particle size. We now study different particle characteristics to make cement more suitable for our construction needs. This effort represents our drive for improvement and progress.
01 Analyzing Cement Particle Size Distribution
We selected four new cement grinding processes as research subjects:
Roller press + V-type separator + open-circuit шаровая мельница
Roller press + V-type separator + closed-circuit ball mill
Vertical mill as final grinding process
Vertical mill + closed-circuit ball mill
We measured fineness through sieve analysis and used the Rosin-Rammler-Bennett expression to calculate uniformity coefficient and characteristic particle size. This helped us analyze the particle size distribution. We also used a laser particle size analyzer for further measurement.
The research results show:
(1) The particle distribution of cement from these four processes is more uniform than from traditional open-circuit ball mills. The roller press + V-type separator + open-circuit ball mill process can control uniformity through collaboration between components. Further tests show that uniform particle distribution helps control cement’s viscosity and durability. Therefore, it allows better control over cement usage and effectiveness.
(2) These four processes improve the efficient utilization rate of cement. The mechanical grinding alters cement’s properties, giving these processes good usability and development prospects.
(3) Adding a pre-grinding system (roller press + V-type separator) to traditional ball mill grinding reduces the difference in particle size distribution between open and closed-circuit systems. It clarifies the cement’s characteristics and combines old and new formulas for more pronounced effects. This enhances service life and creates strong development prospects.
(4) The product from a vertical mill as the final grinding process has a particle size distribution similar to systems combining a roller press or vertical mill with a ball mill.
02 Research Findings
When using mixed grinding, fly ash (which grinds easily) tends to concentrate in finer particles, while slag (which is harder to grind) concentrates in coarser particles. This results in lower dry powder packing density. Separate grinding produces cement with lower coarse and slightly insufficient fine particle content. Increasing the specific surface area of mixed materials significantly affects particle distribution and increases dry powder packing density.
A good correlation exists between particle size distribution and packing density in cement paste. As the particle uniformity coefficient increases, the packing density in the paste decreases linearly. For mixed grinding systems, paste with fly ash has higher packing density, while paste with slag has lower packing density. In separate grinding, increasing the specific surface area of mixed materials significantly improves paste density.
When the mixed material content is fixed, higher packing density in the paste leads to higher strength. Comparing the two grinding methods:
For cement with fly ash ground separately at 400 m²/kg specific surface area, the strength is lower than mixed grinding with the same content.
For cement with slag, separate grinding produces better strength than mixed grinding.
Furthermore, cement with fly ash has worse compatibility with admixtures than cement with slag. As mixed material content increases, the water demand for standard consistency rises, setting time extends significantly, and chemically bound water at different ages decreases. Overall, separately ground cement has better mechanical properties, and cement with slag performs better than cement with fly ash.
03 Application of Ground Cement in Daily Life
Cement is a vital construction material, but its production consumes significant energy. Today, with energy conservation and emission reduction priorities, minimizing energy use while obtaining high-performance products is crucial.
Cement particle size distribution is a key factor affecting its performance. Optimizing this distribution allows cement to perform better and meets the demand for low-energy cement production. Two important aspects are the distribution across different particle size ranges and the overall particle packing.
This study explored both aspects. Based on this, we optimized cement particle size distribution and proposed a new model for initial tight packing of cement particles. Research on strength development across different particle sizes reveals that strength comes from the intergrowth, connection, and hydration of cement particles and their products, creating resistance to external forces.
Cement particle size directly links to hydration speed and degree. Different sizes hydrate at vastly different rates. Among all particles, those between 3-32 μm dominate strength development. The distribution within this range should be continuous, with total content not below 65%. Further research shows that particles between 16-24 μm are particularly important – the more, the better.
Particles smaller than 3 μm hydrate very quickly, some even during mixing, so they only benefit early strength. Particles between 32-60 μm have a low hydration degree, while particles larger than 60 μm have minimal activity and act mostly as filler. Thus, more content above 32 μm means lower clinker utilization and worse cement performance.
Studying strength development reveals:
Particles in the (0, 3) μm range develop strength quickly but do not achieve the highest 3-day strength. Their strength can even shrink after 28 days. Content should be limited, ideally below 10%.
Particles in the (3, 16) μm range provide the highest 3-day strength.
Particles in the (16, 32) μm range provide the highest 28-day strength.
Overall, particles in the (3, 32) μm range are crucial for strength development – the more, the better. Particles in the (32, 64) μm range contribute little to early strength, but their long-term strength (after 180 days) catches up or even surpasses that of the (3, 32) μm range. For long-term strength development, this range is essential, ideally no less than 10%.
Particles larger than 64 μm develop strength very slowly. Their content should be restricted, ideally below 5%. Theoretical analysis and experimental results confirm that fractal dimension is a feasible characteristic parameter for particle size distribution. It correlates well with other parameters.
Under the given experimental conditions:
With uniformity index n=1, as characteristic particle size X increased from 16μm to 32μm, fractal dimension D decreased from 2.50 to 2.27.
With characteristic particle size X=29μm, as uniformity index n increased from 0.6 to 2.2, fractal dimension D decreased from 2.73 to 0.21.
With uniformity index n=1, as specific surface area S increased from 324 m²/kg to 405 m²/kg, fractal dimension D increased from 2.28 to 2.36.
The Fuller curve, describing optimal packing, cannot meet the distribution requirements for different particle size ranges. It leads to excessive fine powder. We can replace fine particles below 16μm and coarse particles above 45μm with active additives like fly ash or slag powder. This increases the content of the key (16, 45) μm range that contributes most to strength, optimizing the particle size distribution and saving cement clinker.
We propose a new model for initial tight packing of cement particles: the LH model. Its maximum particle size is 60μm, and the minimum is 0.6μm. Particles smaller than 3μm should not exceed 5%, and particles in the (3, 32) μm range should exceed 70%. Computer simulation shows the LH model has a void ratio of 27.9%. It meets performance requirements while maintaining low porosity.
04 Summary
With advances in grinding technology, cement quality has progressively improved. Different cement particle sizes determine its application. The expanded particle size range allows varied utilization based on density, pushing cement development into a new trend. This creates more opportunities for advancement, promotes urbanization, and accelerates progress. Consequently, the development of cement grinding technology continues to be widely adopted and utilized.
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