Production practice has shown that there is little difference in the grinding effect of the same type of grinding aid on the same type of cement; The grinding effect of the same type of grinding aid on different types of cement and different grinding aids on the same type of cement varies greatly. The effectiveness of grinding aids depends on factors such as the variety, quality, and mix ratio of the grinding aid and cement, and there is a problem of the adaptability of grinding aids to cement. Composite grinding aids have a better grinding effect on various types of cement because they follow the matching rule of "applicability is the best". This article conducted experimental research on the grinding efficiency of various types of cement using different grinding aids, in order to seek relevant usage rules and provide practical theoretical basis for the correct use of grinding aids, improving the grinding efficiency of mills, and enhancing the economic benefits of enterprises.

1 Experiment 

1.1 Experimental Materials and Instruments 

The experimental raw materials for the shaft kiln clinker were obtained from FSFJ factory, while the rotary kiln clinker was sourced from MZTP factory. The chemical composition, rate values and mineral composition of the cement clinker used in the experiment are shown in Table 1. The SO3 content of the dihydrate gypsum was 36.07%. The grinding aids used were: S agent containing triethanolamine, Y agent containing ethylene glycol, M agent containing lignosulfonate, and DB agent composed of sodium polyphosphate (D) and propylene glycol (B) in a ratio of 2:1. In addition, there were granulated blast furnace slag and zeolite admixtures. The experimental equipment included: a φ500mm×500mm small mill, Cilasl064L laser particle size analyzer, DBT-127 Blaine specific surface area tester, and SXY150-13 negative pressure sieve analyzer (80μm sieve analysis). 

1.2 Experimental Procedure 

The cement clinker was crushed to a particle size of less than 5mm using a PCX30 high-efficiency fine crusher. Then, the clinker was mixed with slag and zeolite in the proportions of ordinary Portland cement, slag cement and pozzolanic cement respectively. The proportions of the three types of cement are shown in Table 2. 5kg of each sample prepared according to the above proportions was ground together with a grinding aid of 30% concentration for 20 minutes. The blank sample and the sample with 0.03% grinding aid were compared. After grinding, the 80μm sieve residue, specific surface area and particle size distribution of each cement sample were measured to determine the effect of different grinding aids on grinding efficiency. 

2. Test results and analysis The particle composition of the three types of cement after adding different grinding aids was measured. 

2.1 Experimental Analysis 

1) After adding different grinding aids, the sieve residue of 80um for the three types of cement all decreased to varying degrees, but the extent of reduction was quite different. The reduction range for ordinary Portland cement was 4.8% to 24.2%, for pozzolanic cement was 9.7% to 29.0%, and for slag cement was 4.9% to 12.8%. The DB and S grinding aids had the best grinding effect; the M grinding aid was second; and the Y grinding aid had the poorest effect. 

2) Changes in specific surface area After adding different grinding aids, the specific surface area of the three types of cement increased to varying degrees. The increase rates for ordinary Portland cement, slag cement, and pozzolanic cement were 5.7% - 16.3%, 4.4% - 13.6%, and 5.8% - 14.5%, respectively. Generally speaking, when S agent was added, the relative increase in specific surface area of the three types of cement was the largest, with the order being S agent > DB agent > M agent > Y agent.

3) Changes in particle size distribution As shown in Table 3, the increase in the content of particles < 32 μm in the three types of cement varied significantly with different grinding aids. The increase was the largest when S agent and DB agent were added, approximately 10%; followed by M agent; and the increase was relatively small when Y agent was added. The increase in the content of particles < 3 μm in pozzolanic cement was the smallest, but the increase in the content of particles 12 - 32 μm was still relatively large, indicating that due to the sharp increase in the specific surface area of fine particles, the grinding aid at this dosage could not meet the needs of particles < 3 μm, and the dosage of grinding aid needed to be increased. Through the above analysis, it can be seen that the overall grinding aid effect of S agent was the best, followed by DB agent, and the grinding aid effect of M agent was significantly inferior to that of S agent and DB agent. The effect of Y agent on the grinding efficiency of the three types of cement was not obvious. At the same time, since DB agent is composed of relatively inexpensive sodium polyphosphate and propylene glycol, DB agent has better practical application value. When the admixtures are the same, the grinding aid effect of grinding aid on rotary kiln cement is greater than that on shaft kiln cement. 

2.2 The Effectiveness of Grinding Aids 

The test results show that the effect of grinding aids on the three types of cement varies significantly. The increase in grinding efficiency of ordinary Portland cement with a low slag content is greater than that of slag cement with a high slag content, while the increase in grinding efficiency of pozzolanic cement with added zeolite is the greatest. This indicates that grinding aids have certain adaptability or compatibility with cements of different admixture contents. Compared with the isotropic glassy structure of slag, the anisotropic crystal structure of cement clinker and zeolite has stress concentration at the interface between relatively weak minerals. Slag has a high content of glassy phase and poor grindability, and it is difficult to produce new surfaces under the same conditions, so the disaggregation and dispersion effects of grinding aids cannot be fully demonstrated, and the increase in grinding efficiency is relatively small. Compared with cement clinker, zeolite has better grindability due to its mineral structure, and more fine particles are produced under the same grinding conditions, resulting in stronger mutual adhesion. The addition of grinding aids effectively weakens this effect, presenting a more superior grinding aid effect. The different clinker burning process conditions of shaft kilns and rotary kilns result in significant differences in the degree of mineral crystal development, microstructure and density of the clinker, and thus their grindability varies greatly. Compared with shaft kiln clinker, rotary kiln clinker has less C2S content and less flux minerals (C3A + C4AF), and should be easier to grind. Therefore, the grinding aid effect of grinding aids on rotary kiln clinker is better than that on shaft kiln clinker. Research by the School of Materials Science and Engineering of Southwest University of Science and Technology shows that when grinding 32.5 grade pozzolanic cement with grinding aids, the output can be increased by 10% to 25%, and when grinding 42.5 grade ordinary Portland cement, the output can be increased by 15% to 40%. Under the same energy consumption, the specific surface area can be increased by 20 to 80 m2/kg. The effects of five grinding aids on the specific surface area and early strength of slag cement are shown in Table 4. 

3 Conclusions: 

1) The grinding aids S, DB, M and Y all have good grinding aid effects on ordinary cement, slag cement and pozzolanic cement. Among them, the grinding aid DB, which is composed of D and B, has a good grinding aid effect and a relatively low price, thus having excellent practical value. The grinding aid effect of S and DB is better than that of M and Y. 

2) The grinding efficiency of ordinary cement and pozzolanic cement can be significantly improved by adding different or the same grinding aids, but the grinding aid effect on slag cement is not obvious.

3) When the type and dosage of admixtures are the same, the grinding aid effect on rotary kiln cement is better than that on shaft kiln cement. 

4) For the same grinding aid, as the dosage increases, the specific surface area and early strength of the slag cement also increase continuously. The effects of different grinding aids and dosages on the physical properties of slag cement vary greatly. In production practice, single or composite grinding aids can be applied, and the rule of "test first and then select, and the most suitable is the best" should be followed.