Concrete admixture refers to the material added to improve and regulate the performance of concrete. The application of concrete admixtures in engineering is getting more and more attention. The addition of additives plays a certain role in improving the performance of concrete, but the selection, adding methods and adaptability of additives will seriously affect its development.
The concrete admixtures are divided into four categories according to their main functions:
1. admixtures to improve the rheological properties of concrete mixture. It includes water reducing agent, air entraining agent and pumping agent.
2. admixtures for regulating the setting time and hardening performance of concrete. It includes retarder, early strength agent and accelerator.
3. admixtures to improve the durability of concrete. It includes air entraining agent, waterproofing agent and rust inhibitor.
4. admixtures to improve the other properties of concrete. It includes aeration agent, expansive agent, coloring agent, antifreeze agent, waterproof agent and pumping agent.
Concrete admixtures properties:
(1) the water consumption of concrete can be reduced or the flow degree of concrete can be increased without the increase of water consumption.
(2) the setting time of concrete can be adjusted.
(3) reduce bleeding and segregation. Improve the workability and resistance of water washing.
(4) the slump loss can be reduced and the pumping capacity of the pump concrete can be increased.
(5) the shrinkage can be reduced. The expansion agent can also compensate for the contraction.
(6) postpone the initial hydration heat of concrete, reduce the temperature rise speed of mass concrete and reduce the occurrence of cracks.
(7) improve the early strength of concrete to prevent freezing at negative temperature.
(8) increase the strength and increase the frost resistance, permeability, abrasion resistance and corrosion resistance.
(9) control the reaction of alkali aggregate, prevent corrosion of steel bar and reduce the diffusion of chloride ion.
(10) made of other special properties concrete.
(11) reduce the viscosity coefficient of concrete and so on.