The dosage of concrete admixtures is generally not more than 5% of the cement mass.
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.
Introduction
1.1 This standard applies to the classification and naming of cement concrete admixtures , and define each named admixture. Every product that meets the definition of concrete admixtures in Chapters 2 and 3 of this standard shall belong to a certain category of this standard and be given a name.
This standard also applies to cement paste or mortar admixtures.
1.2 Each admixture is defined according to one or more functions it has and named according to its main function. Compound admixtures have more than one main function and are named according to more than one function.
1.3 Concrete admixtures are substances added during the concrete mixing process to improve the properties of concrete. The dosage shall not exceed 5% of the cement mass (except in special circumstances).
1.4 This standard adopts the draft international standard ISO/DIS 7690.
Classification
Concrete admixtures are divided into four categories according to their main functions:
2.1 Admixtures that improve the flow properties of concrete mixtures. Including various water reducing agents, air entraining agents and pumping agents, etc.
2.2 Admixtures that adjust the setting time and hardening properties of concrete. Including retarder, early strength agent and quick-setting agent.
2.3 Admixtures that improve the durability of concrete. Including air-entraining agents, waterproofing agents and rust inhibitors.
2.4 Admixtures that improve other properties of concrete. Including air entraining agents, expansion agents, colorants, antifreeze agents, waterproofing agents and pumping agents, etc.
Performance effect
Admixtures were initially used just to save cement. With the development of technology, the addition of admixtures has become the main measure to improve the performance of concrete.
Due to the high-efficiency water-reducing agent, high-fluidity concrete, self-compacting concrete, and high-strength concrete have been applied; due to the thickener, underwater concrete Improved performance: Due to the retardant, the setting time of cement can be extended, which makes it possible to reduce slump loss and extend the construction operation time: due to the antifreeze, the freezing point of the solution can be reduced, or the deformation of the ice crystal structure will not cause freezing damage. , it is possible to carry out construction under negative temperatures.
Generally speaking, admixtures have the following effects in improving the performance of concrete:
(1) It can reduce the water consumption of concrete. Or it can increase the fluidity of concrete without increasing 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) can reduce shrinkage, and 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 corrosion of steel bars, and reduce the diffusion of chloride ions.
(10) Concrete with other special properties.
(11) Reduce the viscosity coefficient of concrete, etc.
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