Why is retardant added to concrete for construction projects?

Retarding water-reducing admixtures mainly affect the properties of fresh concrete and hard-base concrete.

The hazards to the properties of freshly mixed soil are roughly as follows:

(1 ) Increase the initial and final setting time. The harm caused by the retardant to the initial setting time of concrete is specifically manifested before the final setting, and the harm after the final setting is very small. This is related to the type, dosage, and mixing method of the retarder, as well as the type of concrete, concrete mix ratio, application season, and decoration method. The impact on the retarder time is different.

(2) Improve the workability of concrete, reduce slump damage, and reduce water demand.

(3) Adsorption hypothesis. Because the surface of concrete particles has extremely strong adsorption energy, the surface of concrete particles absorbs retarder, forming a retarder film layer of concrete, which blocks the hydration process of concrete.

(4) Nucleation transforms into inhibition hypothesis.

The main influence on the properties of hard-base concrete is the defaulting party:

(1 ) intensity. After adding retarder and retarding admixture, the morning strength of concrete is lower than that without adding retarder, especially when adding retarder.

(2) Shrink. The shrinkage of concrete mixed with retarder and retarder admixture is larger than that without retarder, but it increases with the increase of the dosage. However, when retarding admixtures are added to reduce water and concrete dosage, the shrinkage value will further decrease.

(3) Usage performance. The performance of concrete mixed with retarder is basically the same as that of concrete without retarder. However, due to the reduction in water-cement ratio, the joint distribution of final hydration products and the improvement in strength of concrete mixed with retarder admixtures, It will be beneficial to improve waterproof concrete and freeze-thaw resistance.

Concrete retarder can delay the hydration reaction of concrete, thereby increasing the initial setting time of concrete, allowing fresh concrete to maintain ductility for a period of time It is a water-reducing agent that facilitates pouring, improves the speed of decoration projects, and at the same time will not have a negative impact on various properties of concrete in the final stage. It is used in concrete summer decoration projects and underwater concrete construction sites. According to the different ingredients, concrete retarder for concrete is divided into two types: organic concrete retarder and inorganic concrete retarder. At present, lignocellulose sulfur salt is a widely used retarder with large production and sales volume. In addition, molasses, hydroxycarboxylic acids and many carbonate retarders are also widely used. Therefore, the different types of retarder are combined to explain the retarding function principle of the retarder.

</p