Concrete admixtures refer to substances added to improve and adjust the properties of concrete. The application of concrete admixtures in engineering has attracted more and more attention. The addition of admixtures plays a certain role in improving the performance of concrete, but the selection, addition method and adaptability of admixtures will seriously affect its development.
Anti-segregation agents are used to improve the water retention and cohesion of concrete
Classification
Concrete admixtures are divided into four categories according to their main functions:
1 Admixtures that improve the rheological properties of concrete mixtures. Including various water reducing agents, air entraining agents and pumping agents, etc.
2 Admixtures that adjust the setting time and hardening properties of concrete. Including retarder, early strength agent and quick-setting agent.
3 Admixtures to improve the durability of concrete. Including air-entraining agents, waterproofing agents and rust inhibitors.
4 Admixtures that improve other properties of concrete. Including air-entraining agents, expansion agents, colorants, antifreeze agents, waterproofing agents and pumping agents, etc.
Admixtures were initially used just to save cement. With the development of construction technology, admixtures were added It has become the main measure to improve the performance of concrete.
Due to the efficient water reducing agent, large flow concrete, dense concrete, and high -strength concrete are applied; due to the thickened agent, the performance of underwater concrete can be improved: due Only when the condensation time is extended can it be possible to reduce slump loss and extend the construction operation time: due to the antifreeze, the freezing point of the solution can be lowered, or the ice crystal structure will not deform to cause freezing damage. Only then can construction be carried out at negative temperatures.
Generally speaking, admixtures have the following effects in improving the properties of concrete:
(1) They can reduce the water consumption of concrete. Or they can increase the fluidity of concrete without increasing the water consumption.
(2) The setting time of concrete can be adjusted.
(3) Reduce bleeding and segregation. Improve workability and water elution resistance.
(4) It can reduce slump loss and increase the pumpability of pumped concrete.
(5) It can reduce shrinkage. Adding expansion agent can also compensate for shrinkage.
(6) Delay the initial hydration heat of concrete. Reduce the temperature rise rate of large-volume concrete and reduce the occurrence of cracks.
(7) Improve the early strength of concrete and prevent freezing at negative temperatures.
(8) Improve strength, increase frost resistance, impermeability, wear resistance and corrosion resistance.
(9) Control the alkali-aggregate reaction. Prevent the corrosion of steel bars and reduce the diffusion of chloride ions.
(10) Made into concrete with other special properties.
(11) Reduce the viscosity coefficient of concrete, etc.
After adding admixtures to concrete, the effects will be different due to different types. Most of them are physical effects, such as adsorbing on the surface of cement particles to form an adsorption film, changing the potential, and producing different effects. Suction or repulsion; some will destroy the flocculation structure, improve the stability of the cement diffusion system, and improve the conditions for cement hydration: some can form macromolecular structures and change the adsorption state on the surface of cement particles; some will reduce the surface tension of water. And surface energy, etc.: There are also a few that directly participate in chemical reactions and form new compounds with cement.
Because admixtures can effectively improve the properties of concrete and have good economic benefits, they have been widely used in many countries and have become an indispensable material in concrete. Especially with the use of high-efficiency reducing agents, the cement particles can be fully dispersed, the water consumption is greatly reduced, and the cement potential is fully utilized. As a result, the cement stone is denser, the pore structure and the microstructure of the interface zone are well improved, thus making the concrete The physical and mechanical properties of concrete have been greatly improved. Whether it is impermeability, chloride ion diffusion, carbonization, resistance to sulfate erosion, impact resistance, wear resistance and other aspects, it is better than concrete without additives. Not only Increased strength, improved workability. It can also improve the durability of concrete. Only by adding high-efficiency water-reducing admixtures, it is possible to prepare high-performance concrete with high workability, high strength and high durability.
3.1 Water-reducing admixture
Ordinary water-reducing admixture
An admixture that can reduce the amount of mixing water when the slump of concrete is basically the same. Commonly used water reducing agents are anionic surfactants.
High-efficiency water-reducing admixture
An admixture that can significantly reduce mixing water consumption under the condition that the slump of concrete is basically the same.
Retarded water-reducing admixture
Admixture with both retarding and water-reducing functions.
Early-strength and water-reducing admixture
Admixture with both early-strength and water-reducing functions.
Air-entraining and water-reducing admixture
An admixture with both air-entraining and water-reducing functions.
3.2 Early strength agent
Early strength agent
An admixture that improves the early strength of concrete and has no significant impact on the later strength.
3.3 Retarder
Retarder
An admixture that prolongs the setting time of concrete.
3.4 Air-entraining agent
Air-entraining agent
An admixture that can introduce a large number of evenly distributed, stable and closed micro-bubbles during the mixing of concrete.
微信扫一扫打赏
