Performance effects of concrete admixtures

The initial use of concrete admixtures was just to save cement. With the development of construction technology, the use 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 thickening agent, 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. . Only then can construction etc. be carried out under negative temperatures.

Generally speaking, concrete admixtures have the following effects in improving the performance of concrete:

(1) It can reduce the water consumption of concrete. Or increase the fluidity of concrete without increasing water consumption.

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

(3) Reduce bleeding and segregation. Improves workability and resistance to water elution.

(4) It can reduce slump loss. Increase the pumpability of pumped concrete.

(5) It can reduce shrinkage. Adding expansion agents can also compensate for shrinkage.

(6) Delay the initial heat of hydration of concrete. Reduce the temperature rise rate of large-volume concrete and reduce the occurrence of cracks.

(7) Improve the early strength of concrete. Prevent freezing in negative temperatures.

(8) Improve strength, 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) Concrete with other special properties.

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

After adding admixtures to concrete, the effects produced are different due to different types. Most of them are physical effects, such as adsorption on the surface of cement particles. The adsorption film changes the potential and produces different suction or repulsion forces; 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 on the surface of cement particles. state; some will reduce the surface tension and surface energy of water, etc.; and a few will directly participate in chemical reactions and form new compounds with cement.

Because concrete admixtures can effectively improve the properties of concrete and have good economic benefits. It has been widely used in many countries and has become an indispensable material in concrete. Especially the use of high-efficiency reducers. Cement particles can be fully dispersed, water consumption is greatly reduced, and the potential of cement can be fully utilized. The cement stone is made denser, and the pore structure and interface zone microstructure are well improved, thereby greatly improving the physical and mechanical properties of concrete, whether it is impermeability, chloride ion diffusion, carbonization, and resistance to sulfate erosion. . In terms of impact resistance and wear resistance, it is superior to concrete without admixtures, which not only increases strength but also improves 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. </p