The performance role of concrete admixtures

Initially the use of admixtures, only to save cement, with the development of construction technology, admixtures have become the main measures to improve the performance of concrete.

As a result of efficient water reducing agent, large flow concrete, self-compacting concrete, high-strength concrete is used; as a result of thickening agent, the performance of underwater concrete can be improved: as a result of the retarder, the cement setting time can be extended, it is possible to reduce slump loss, extend the construction operation time: as a result of antifreeze, the solution freezing point can be reduced, or ice crystal structure deformation does not cause frost damage. It is only possible to carry out construction at negative temperatures, etc.

Overall, the admixture has the following roles in improving the performance of concrete:

(1) It can reduce the amount of water used in concrete. Or the flow of concrete can be increased without increasing the amount of water used.

(2) It can adjust the setting time of concrete.

(3)Reduce water secretion and segregation. Improves the compatibility and water washing resistance.

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

(5) It can reduce shrinkage. The addition of expansion agents can also compensate for shrinkage.

(6) Retard the initial heat of hydration of concrete. Reduce the rate of temperature rise of bulk concrete and reduce the occurrence of cracks.

(7) Increase the early strength of concrete. Prevent freezing at negative temperature.

(8) Improve strength and increase frost resistance, impermeability, abrasion resistance and corrosion resistance.

(9)Control alkali-aggregate reaction. Stops rusting of steel bars and reduces the diffusion of chloride ions.

(10) Make other special properties of concrete.

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

After the addition of admixtures in concrete, due to the different varieties, the role of different, most of them are physical effects, such as adsorption on the surface of cement particles to form adsorption film, changing the potential, resulting in different suction or repulsion; some will destroy the flocculation structure, improve the stability of the cement diffusion system, improve the conditions of cement hydration: some can form a macromolecular structure, changing the adsorption state on the surface of cement particles. Some will reduce the surface tension and surface energy of water, etc.: there are a few directly involved in chemical reactions, and cement to generate new compounds.

As admixtures can effectively improve the performance of concrete, and has good economic benefits. In many countries are widely used, becoming an indispensable material in concrete. Especially the use of high performance reducing agents. Cement particles can be fully dispersed, water consumption is greatly reduced, the cement potential to give full play. To make the cement stone more dense, pore structure and interface area microstructure is well improved, thus making the physical and mechanical properties of concrete has been greatly improved, whether impermeable, or chloride ion diffusion, carbonation, resistance to sulfate attack. As well as impact resistance, wear resistance and other aspects are better than the concrete without admixtures, not only to increase the strength, improve the compatibility. Can also improve the durability of concrete. Only mixed with high efficiency water reducing agent, formulated with high constructability, high strength, high durability of high-performance concrete is possible to achieve.