The application of ultra-fine fly ash in cement production

The blending method of ultrafine powder

For cement plants, the "grinding before mixing" post blending method can be adopted, which means that ultra-fine powder does not need to be ground and is directly added at a determined amount during the grinding of the mixed material, saving electricity and ball consumption. Specific method: After determining the specific dosage of ultra-fine fly ash powder through cement mortar strength test, for those without homogenization equipment, the mixture can be added proportionally at the tail grinding elevator and fed into the powder selection machine along with the abrasive. Ultra fine powder, due to its much lower specific surface area than other components of cement, can be directly and uniformly selected by the powder selection machine, effectively ensuring the uniformity of cement.

Cement mixtures and their classification

The artificial or natural mineral materials added to improve the workability of cement, adjust the strength grade of cement, and increase cement production during cement grinding are called cement mixtures. At present, the mixed materials used by cement enterprises are mainly industrial waste residue. According to their different performance, they are usually divided into two categories: active and non active mixtures, with the former having a larger dosage.

The physical activation principle of ultrafine powder

Physical activation, also known as mechanical activation, has a good treatment effect on fly ash, slag, coal gangue, etc. Ultrafine grinding can reduce the particle size of fly ash, increase the specific surface area, and effectively fill the pores of cement hardened slurry, playing a role in density enhancement. At the same time, there are dislocations, point defects, and structural defects on the surface of ultrafine particles, which increase the surface free energy and enhance the activity. During the cement hydration process, ultra-fine fly ash will undergo a secondary hydration reaction with the calcium hydroxide generated during the initial hydration of cement. This not only helps to improve the later strength of cement, but also reduces the alkalinity of the system and improves durability.

The particle size of ultrafine powder is much smaller than that of cement, and its dense filling effect replaces the water in the cement voids, offsetting the increased wetting water due to the high specific surface area. Therefore, adding ultrafine powder will not increase but reduce the water demand of cement. The darker color of ultrafine powder can improve the color of cement and enhance the adaptability of cement and water reducing agents.