Concrete Mineral Admixtures

What are the mineral admixtures used in concrete

Used to improve the performance of concrete, industrial waste or mineral fine powder with a certain degree of fineness added in the concrete mixing process, it is an auxiliary cementing material that replaces part of the cement consumption.

Classification of mineral admixtures

  • According to the categories involved in the hydration reaction: active mineral admixtures, inert mineral admixtures.
  • Divided by composition: single-variety mineral admixtures and composite mineral admixtures.

What is active admixture

The active admixture itself does not harden or hardens very slowly, but it can react with Ca(OH)₂ generated by cement hydration to form hydration products with gelling ability, such as fly ash, blast furnace slag powder, and steel slag powder , Silica fume, zeolite powder, volcanic ash, etc.

What is an inert admixture (inactive)

Inactive mineral admixtures basically do not react with cement components, such as ground limestone powder, ground quartz powder, etc.

What kind of materials can be used as mineral admixtures

Materials that can be used as active mineral admixtures

All inorganic non-metallic solid materials that have undergone a high-temperature process and do not contain a large amount of components that are harmful to the durability of concrete and the environment. Such as blast furnace granulated slag, fly ash, steel slag, natural siliceous materials, waste red bricks, metakaolin, natural zeolite, waste slag after calcination of sewage sludge, etc.

Materials that can be used for inert mineral admixtures

In the natural state, inorganic non-metallic solid materials that do not contain components that are harmful to the durability of concrete and the environment, and do not participate in cement hydration or rarely participate in cement hydration. Such as limestone, sandstone, iron tailings, etc.

Types of concrete mineral admixtures

Fly ash, finely ground blast furnace slag powder, steel slag powder, pozzolan, desulfurized gypsum powder, phosphogypsum powder, tuff powder, basalt powder, glass ceramic powder, sintered brick powder, limestone powder, granite powder, quartz powder, etc.

Especially fly ash, granulated blast furnace slag powder, silica fume (micro silica fume), fine limestone powder, etc. are widely used and have good effects.

How to produce mineral admixtures

Separate grinding or mixed grinding?

When making mineral admixtures, various materials should be ground separately, because the grindability coefficients of various materials are different. Therefore, it needs to be separately ground into fine powder and then mixed in proportion.

Fine or coarse?

For active admixtures, it is recommended to grind as fine as possible on the premise of meeting economic requirements. (For example, slag is ground to an average particle size of 5μm, fly ash is ground to an average particle size of 2μm, and metakaolin is ground to an average particle size of 10μm).

For inert admixtures, it is recommended not to grind too fine, increase the output as much as possible to reduce energy consumption (for the grinding process, use cyclones as much as possible when selecting powder to promote powder particle impact, which can improve the particle shape).

Read Also: How to Process Concrete Admixtures

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