Rapid Laboratory Particle Size Analysis of Cements Using Laser Diffraction bak

Abstract: The laser diffraction method for measuring particle size was first invented in 1974, and the first industries to adopt the technique were coal, ceramics, chocolate, and cement. The particle size distribution or fineness of cement has been measured by laser diffraction in laboratories since 1975. But why was the cement industry such an early adopter of this technology? The reason lies in the fact that the particle size distribution of cement directly affects the hardening rate, strength, and fluidity of the final set concrete—the major application of cement. Accurate and repeatable measurement of cement particle size is therefore essential, not only to ensure product quality but also to reduce the high costs associated with cement production. The Bettersizer 2600 Plus laser diffraction analyzer can be used in the cement sector to provide QC and laboratory managers with the information they need to maintain specification while optimizing production efficiency. In addition, as shown in Figure 1, the Bettersizer 2600 Plus can measure both the size and shape of cement particles, which opens up new research areas on both optimal particle size and particle shape.



Keywords: Cement particle size distribution, Laser diffraction, Cement fineness, Quality control (QC), Dry dispersion, Particle shape analysis, Fly ash, Bettersizer 2600 Plus

 

Product	Bettersizer 2600 Plus
Industry	Building Materials
Sample	Ordinary Portland Cement (OPC)
Measurement Type	Particle Size & Shape
Measurement Technology	Laser Diffraction, Dynamic Image Analysis

 

 

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 Introduction 

 

The most common cement is Ordinary Portland Cement (OPC) which is a gray powder, but there are other types produced for different applications. Broadly speaking, cement is produced through a three-stage process. 

 

The first stage involves raw milling of limestone using a primary crusher, where the rocks are reduced to approximately the size of baseballs. This is followed by a secondary crushing stage, which further reduces the particle size to around 2 centimeters. The second stage (clinkering) involves the mixing of this ground material, silica, Iron ore, fly ash, and sometimes alumina shale being treated in a preheater where the temperature increases from 80 to 800 °C. At this temperature, the mix is calcined, thus removing the CO₂. The feed is sent to a roller mill where the dry Raw Meal is created and transported to the Rotary kiln. All the ingredients are heated up to 1450-1550 °C, a temperature at which a chemical reaction can take place, driving off certain elements in gaseous form. The remaining elements form a gray material called the clinker. A balance has to be maintained between insufficient heat, which results in under-burnt clinker containing unconverted lime, and excessive heat, which shortens the lifetime of the refractory bricks in the kiln.

 

Finally, the clinker is ground after cooling to produce a cement fineness of less than 45 microns. Gypsum is blended with the ground clinker to control the cement hydration rate such that its setting time is appropriate for the application. Significant amounts of electrical energy are required for milling, and the total power demand depends on the fineness of the grind, the distribution of particle size, and the efficiency of separation of the finely ground particles. The finer the grind, the more reactive the finished cement is, and in turn the faster its setting time. Rapid-setting cements will thus have a smaller particle size than the less reactive, low heat of hydration cements. As a general rule, reducing the particle size increases the rate of hydration and strength.

 

 Experimental 

 

Many historical techniques have been used to measure the particle size/fineness of the cement. The first was 45-micron sieves, which only provide the second largest dimension, Blaine air permeability, which predicted the compressive strength by a single number, and the Wagner turbidimeter. These techniques took a minimum of 5 minutes of measurement time and were limited to only providing a single number. Laser diffraction, however, became the instrument of choice in the 1990s because the technique is easy and reproducible, and in addition, is much faster than older methods. In addition, it calculates many more relevant parameters with which to optimize the cement particle size distribution.

There are a number of cement types, but we will focus on grades 32.5, 42.5 and 52.5, which are named after the expected strength derived from each of their optimized particle size distribution/fineness. The Bettersizer 2600 Plus can measure the fineness of cement in its natural dry state or as a wet dispersion using an industrial alcohol such as Propanol or Ethanol. As can be seen in Figure 2, both wet and dry dispersion methods yield the same result, but due to lower running costs, better statistical representation, and easier usage, the dry method is preferred. 

 

Figure 2. Particle size results of 32.5 cement by wet and dry dispersion

 

Table 1. Typical values of 32.5 cement by wet and dry dispersion

Sample Name	D10 (µm)	D50 (µm)	D90 (µm)
32.5 Cement - Wet	1.912	11.41	32.56
32.5 Cement - Dry	1.525	11.57	33.85

 

When making a wet analysis of cement, up to 5 different parameters need to be taken into account, including the solvent used, pump speed, need of ultrasound, ultrasonic dispersion time, and strength of ultrasound. When using the dry analysis method, there is only one requirement, and that is to make a pressure titration curve. This involves measuring the cement at 4 different pressures, typically from 1-4 bar.

 

For many applications in other industries, results can change at different pressures, but as we can see in Figure 3, the variation between results at 4 different pressures is minimal.

 

Figure 3. Particle size results of 32.5 cement at 4 different pressures from 1-4 bar

 

Table 2. Typical values of 32.5 cement at 4 different pressures from 1-4 bar

Sample Name	D06 (µm)	D10 (µm)	D16 (µm)	D26 (µm)	D50 (µm)	D75 (µm)	D84 (µm)	D90 (µm)	D97 (µm)
32.5 Cement – 1 bar	1.065	1.692	2.803	4.706	12.47	23.45	29.60	35.78	51.63
32.5 Cement – 2 bar	1.002	1.579	2.624	4.509	12.18	22.78	28.58	34.54	50.06
32.5 Cement – 3 bar	0.950	1.465	2.410	4.107	11.17	21.80	27.51	33.25	46.92
32.5 Cement – 4 bar	0.935	1.438	2.368	4.089	11.13	21.24	26.88	32.50	46.00

 

Typically, a pressure of 3 bar is recommended for dispersion in conjunction with a vacuum to suck away the dispersed particles after they have exited the measuring area.

 

Figure 4. Cement is added to the sample tray of the dry sample feeder.

In order to make a measurement, a sample of cement is placed on the dry sample feeder, as can be seen in Figure 4. An icon on the computer screen is activated by the mouse, which performs a fully automated measurement and analysis of any number of repeat results; in this case, 5 repeat analyses were attained in less than 90 seconds (Figure 5). In addition to the measurement of cement, it is also possible to measure additives such as fly ash (Figure 6). Comparison graphs of measurements from 3 grades of cement (32.5, 42.5 and 52.5) and the fly ash can be made (Figure 7).

 

Figure 5. Particle size distribution and repeatability of 32.5 cement

 

Table 3. Typical values of 32.5 cement

Sample Name	D06 (µm)	D10 (µm)	D16 (µm)	D25 (µm)	D50 (µm)	D75 (µm)	D84 (µm)	D90 (µm)	D97 (µm)
32.5 Cement – 3 bar - 1	0.958	1.488	2.450	4.180	11.29	21.60	27.33	33.13	46.91
32.5 Cement – 3 bar - 2	0.942	1.450	2.402	4.123	11.34	21.80	27.55	33.32	46.82
32.5 Cement – 3 bar - 3	0.946	1.461	2.400	4.090	11.05	21.40	27.08	32.76	46.42
32.5 Cement – 3 bar - 4	0.950	1.465	2.410	4.107	11.17	21.80	27.51	33.25	46.92
32.5 Cement – 3 bar - 5	0.955	1.482	2.451	4.179	11.44	22.11	27.74	33.42	46.65
Repeatability	0.68%	1.06%	1.06%	1.01%	1.35%	1.22%	0.91%	0.77%	0.45%

 

Figure 6. Particle size distribution and repeatability of fly ash

 

Table 4. Typical values of fly ash

Sample Name	D06 (μm)	D10 (μm)	D16 (μm)	D25 (μm)	D50 (μm)	D75 (μm)	D84 (μm)	D90 (μm)	D97 (μm)
Fly Ash – 3 bar - 6	2.077	2.976	4.293	6.439	15.18	39.24	62.89	86.20	132.0
Fly Ash – 3 bar - 7	2.132	3.026	4.340	6.480	15.33	38.82	61.78	83.78	128.3
Fly Ash – 3 bar - 8	2.135	3.041	4.371	6.510	15.06	38.57	62.05	82.63	127.6
Fly Ash – 3 bar - 9	2.098	2.992	4.285	6.385	15.29	39.95	64.77	87.97	132.3
Fly Ash – 3 bar - 10	2.123	3.017	4.317	6.414	15.04	38.17	60.57	83.10	132.0
Repeatability	1.18%	0.87%	0.81%	0.78%	0.86%	1.75%	2.50%	2.44%	1.76%

 

Figure 7. Comparison measurements from 3 grades of cement (32.5, 42.5 and 52.5) and the fly ash

 

Table 5. Typical values of cement (32.5, 42.5 and 52.5) and the fly ash

Sample Name	D06 (μm)	D10 (μm)	D16 (μm)	D25 (μm)	D50 (μm)	D75 (μm)	D84 (μm)	D90 (μm)	D97 (μm)
32.5 Cement – 3 bar - 4	0.950	1.465	2.410	4.107	11.17	21.80	27.51	33.25	46.92
42.5 Cement – 3 bar - 23	0.948	1.454	2.356	3.955	10.57	20.60	26.03	31.28	44.44
52.5 Cement – 3 bar - 29	1.006	1.543	2.429	3.941	10.29	19.98	25.23	30.45	43.14
Fly Ash – 3 bar - 10	2.123	3.017	4.317	6.414	15.04	38.17	60.57	83.10	132.0

 

The results from all these experiments can be displayed in tabular, graphical, percentage, or Tromp (Efficiency of separation) curve form, but the most important value within the cement industry is the percentage of ground cement that is between 3 and 32 microns.

Theoretically, this percentage should approach 70% in order to have the optimal strength properties. The rationale for this percentage is that particles larger than 45 microns aren’t fully hydrated, and an excess of particles smaller than 3 microns causes faster exothermal setting in the final
product due to the increased heat of hydration. Increased amounts of gypsum can be added to inhibit this increased heat of hydration and thus control the setting time when water is added to the cement. The addition of gypsum can be an unnecessary cost, especially if the grinding process is optimized. In such cases, the cement will have 70% of its particles by volume between 3 and 32 microns. 

 

From a research perspective, you can measure alternative additives and check the effect on the overall size distribution and determine how much to add to reach the optimal strength. The Bettersizer 2600 Plus is a fast and easy-to-use particle size analyzer that serves both quality control and research purposes. Its capability to measure both particle size and shape in a single analysis provides significant advantages when working with new additives or raw materials, offering deeper insight into material properties and supporting more informed decision-making in laboratory and production settings.

We have already seen that the cement particle size is now seen as critical for the determination of the quality of the cement. Finer particle sizes have a greater surface area, affecting the cement’s compressive strength and setting rate.

However, the cement particle’s shape also has an influence, as spherical particles will have a lower surface area than cement that is irregular in shape if both populations have nominally the same size. The required amount of water in a cement mix will reduce for spherically shaped cement and increase as the particles become more irregular in shape.

 

 Conclusion

 

The large power demands of finish milling mean that improved monitoring of the grinding efficiency and optimization of the classifier speed yield an in-specification product with significant energy efficiency improvements and ultimately cost savings. This is best achieved by having a laser diffraction, which is quick and easy to use, with consistent repeatable results being attained, no matter which operator is using the system.

In addition, by having control standard results for each cement grade maintained inside the computer database, all newly produced cement for all grades can be compared in seconds to the ideal product's fineness parameters. With the added software benefit of being able to put upper and lower set point limits on each key parameter, the operator will know when the latest grind meets the specifications for that grade of cement.

The Bettersizer 2600 Plus combines comprehensive software functionality with rapid laboratory fineness analysis, ensuring that cement meets specifications and is fit for purpose. With new feed materials and additives being introduced continuously—often with different morphologies and from various sources—the Bettersizer 2600 Plus is also an integrated laser diffraction and dynamic image analysis system. By measuring both particle size and shape, it provides added versatility and adaptability to meet these challenges, meeting the growing industrial demand for control over both shape and size to improve product performance and economics.

 

About the Authors

Zhibin Guo Application Research Lab, Bettersize Instruments Ltd.

 

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