Concrete admixtures are divided into four categories according to their main functions:

1. An admixture to improve the rheological properties of concrete mixtures. Including various water reducers, air-entraining agents and pumping agents.

2. The admixture that adjusts the setting time and hardening performance of concrete. Including retarder, early strength agent and accelerator, etc.

3.Additives to improve the durability of concrete. Including air-entraining agents, waterproofing agents and rust inhibitors.

4. Additives to improve other properties of concrete. Including air entraining agent, expansion agent, coloring agent, antifreeze agent, waterproof agent and pumping agent.

Performance effect

The initial use of admixtures was just to save cement. With the development of construction technology, admixtures have become the main measure to improve the performance of concrete.

Thanks to the superplasticizer, high-fluidity concrete, self-compacting concrete, and high-strength concrete are used; thanks to the thickener, the performance of underwater concrete is improved: thanks to the retarder, the setting time of cement is prolonged , It is possible to reduce the slump loss and extend the construction operation time: because of the antifreeze, the freezing point of the solution can be lowered, or the ice crystal structure will not cause frost damage, and then it is possible to carry out construction at negative temperature.

In general, admixtures have the following effects in improving the performance of concrete:

(1) The water consumption of concrete can be reduced. Or the fluidity of concrete can be increased without increasing the water consumption.

(2) The setting time of concrete can be adjusted.

(3) Reduce bleeding and segregation, improve workability and resistance to washing with water.

(4) It can reduce the slump loss and increase the pumpability of pumping concrete.

(5) Shrinkage can be reduced, and expansion agent can be added to compensate for shrinkage.

(6) Delay the initial hydration heat of concrete, reduce the temperature rise rate of mass concrete, and reduce the occurrence of cracks.

(7) Improve the early strength of concrete and prevent freezing under negative temperature.

(8) Improve strength, increase frost resistance, impermeability, abrasion resistance and corrosion resistance.

(9) Control the alkali-aggregate reaction, prevent the corrosion of steel bars, and reduce the diffusion of chloride ions.

(10) Make concrete with other special properties.

(11) Reduce the viscosity coefficient of concrete, etc.