Due to the use of superplasticizer, high fluidity concrete, self-compacting concrete and high strength concrete have been applied; due to the use of thickener, the performance of underwater concrete has been improved: due to the presence of retarder, the setting time of cement can be prolonged, it is possible to reduce slump loss and prolong construction operation time: With antifreeze, the freezing point of the solution can be reduced or the ice crystal structure can be deformed without causing freezing damage. Only under negative temperature can construction be carried out.
Generally speaking, admixtures play the following roles in improving the performance of concrete:
(1) Water consumption of concrete can be reduced. Or the fluidity of concrete can be increased without increasing water consumption.
(2) The setting time of concrete can be adjusted.
(3) Reduce bleeding and segregation. Improve workability and washability.
(4) Slump loss can be reduced. Increase pumpability of pumping concrete.
(5) Contraction can be reduced. Expansion agent can also 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) Increase the early strength of concrete. Prevent freezing at negative temperature.
(8) Increase strength, frost resistance, impermeability, wear resistance and corrosion resistance.
(9) Control of alkali-aggregate reaction. Prevent steel corrosion and reduce chloride ion diffusion.
(10) Making concrete with other special properties.
(11) Reducing the viscosity coefficient of concrete, etc.
When admixtures are added to concrete, the effects are different due to different kinds of admixtures. Most of them have physical effects, such as adsorbing on the surface of cement particles to form an adsorbing film, changing the potential and generating different suction or repulsion; some of them will destroy flocculation structure, improve the stability of cement diffusion system and improve cement quality. Hydration conditions: some can form macromolecule structure, change the adsorption state of cement particle surface; some can reduce the surface tension and surface energy of water; and a few directly participate in chemical reactions to form new compounds with cement.
Because the admixture can effectively improve the performance of concrete, and has good economic benefits. It has been widely used in many countries and has become an indispensable material in concrete. Especially the use of highly effective reducing agents. Cement particles can be fully dispersed, water consumption is greatly reduced, and cement potential can be fully developed. As a result, cement paste is denser, pore structure and interfacial micro-structure are well improved, which greatly improves the physical and mechanical properties of concrete, whether it is impermeable, chloride ion diffusion, carbonization, sulfate resistance. As well as the impact resistance, wear resistance and other aspects are superior to concrete without admixture, not only improve the strength, improve and ease. It can also improve the durability of concrete. Only by mixing high-performance water reducing agent can it be possible to prepare high-performance concrete with high construction, high strength and high durability.
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