What effect do retarder have on concrete? Can be known

What impact does retarder have on concrete? It mainly affects the properties of fresh concrete and hardened concrete.

There are roughly four aspects that affect the performance of fresh concrete:

(1) Extend the initial and final setting time. The influence of retarder on the setting time of concrete is mainly before the final setting, and has little effect after the final setting. This is related to the type, dosage, and mixing method of the retarder, as well as the cement type, concrete mix ratio, season of use, and construction methods. The impact on the retarder time is different.

(2) Improve the workability of concrete, reduce slump loss, and reduce water consumption.

(3) Adsorption hypothesis. Since the surface of the cement particles has strong adsorption energy, the surface of the cement particles absorbs the retarder, forming a cement retarder film layer, which hinders the hydration process of the cement.

(4) Nucleation inhibition hypothesis.

The main influences on the properties of hardened concrete are:

(1) Strength. After adding retarder and retarding water-reducing admixture, the early strength of concrete is lower than that without adding retarder, especially when retarder is added.

(2) Shrinkage. The shrinkage of concrete mixed with retardant and retarded water-reducing agent is larger than that without mixing, but it increases with the increase of the amount. However, when retarded water-reducing admixture is added to reduce water and cement content, the shrinkage value will be reduced.

(3) Durability. The durability of concrete mixed with a retardant is basically the same as that without a retardant. However, due to the reduction in the water-cement ratio, the uniform distribution of hydration products and the improvement of the strength of the concrete mixed with a retardant water-reducing agent. It will help improve the impermeability and freeze-thaw resistance.

Retarder mainly delays the initial setting and final setting time of concrete without affecting the later strength of concrete. It can be used alone or in combination with water-reducing agents to have a certain water-reducing effect. Generally, it does not affect the quality of concrete. When used together with water-reducing agent, it can increase the water-reducing rate. After over-admixing, the concrete will not solidify for a long time, thus destroying the quality of concrete. Attention should be paid during the construction process.

The impact of retarder on the performance of cement concrete

1. Retarder is a commonly used admixture used to extend the setting time of concrete. During summer construction, add an appropriate amount Retarder can make fresh concrete maintain good plasticity for a long time.

2. Retarder is a surfactant that only plays a physical adsorption and dispersion role in concrete, and does not directly participate in the cement hydration reaction to generate new substances. Therefore, it is suitable for use within a certain dosage range. It has no direct impact on the final strength of concrete, but because it delays the setting time of concrete, it affects the early strength of concrete to a certain extent. However, the later strength can generally catch up with or exceed that of concrete without retarder.

Today, with the rapid development of commercial concrete, retarder plays a very important role. As people’s understanding of retarder continues to deepen, the application of retarder will become more and more extensive, especially when producing large-volume concrete that needs to reduce the instantaneous hydration heat of cement and delay the peak hydration of cement. Agents are indispensable.

The effect of retarder on the shrinkage properties of hardened concrete

The speed of concrete setting and hardening depends on the speed of hydration reaction. Adding a retardant will slow down the cement hydration reaction, lengthen the concrete setting time, and the related concrete properties will also change accordingly. When the retarder dosage is too large, the cement reaction time is too long, resulting in unreacted cement core, which directly leads to the reduction or even loss of concrete-related properties. When the dosage is too small, the retarder does not play a corresponding role and the concrete retardation fails. When retarder is used together with other admixtures, certain properties of concrete will be strengthened and better adapted to engineering applications. </p