Can retarder solve concrete slump loss? Is it the only way?

After the concrete is mixed with water, the slump will gradually decrease as time goes by. This is a normal condition that occurs during the use of commercial concrete. However, if the slump is lost rapidly in a short period of time, the concrete will fail. French cast-in-place concrete construction project construction. In order to deal with the slump loss of concrete, retarder is usually added when formulating admixtures. This makes construction workers mistakenly believe that the only way to solve the slump loss of concrete is to increase the required amount of retarder.

Various factors lead to concrete slump loss. The biggest loss factor may be the accelerated solidification of concrete, but the damage caused by repeated absorption of concrete cannot be ignored. In addition to the fineness of the cement, the moisture content of tricalcium aluminate in the concrete and the construction temperature of the concrete all affect the solidification rate of the concrete. Adding a retarder may be able to inhibit the solidification of concrete, but due to different types of concrete, the alkalizing components in concrete vary greatly. Not all retarders can inhibit the solidification of this alkalizing component. For example, for some sulfur-deficient and alkali-deficient concrete, adding a retardant will speed up the solidification of the concrete and increase the slump loss. Adding sulfate early strength agent to fill up the insufficient sulfur trioxide in concrete can suppress the setting rate and reduce slump loss. Glycogen retarder used in concrete with high C3A water content does not have the expected effect of retarder to prevent slump. Used in high-alkali concrete, it will also accelerate the solidification of concrete and even cause rapid setting of concrete.

After adding water-reducing agent to concrete, due to the adsorption and dispersion effect of the water-reducing agent, the concrete molecules are dispersed, improving the fluidity of the concrete, and the concrete has a large slump. Due to factors such as non-specific concrete molecules, the concrete molecules will absorb together again after a certain period of time and encapsulate a large amount of free water, causing the concrete slump loss to increase. . When mixed with a small amount of air-entraining agent, the fine bubbles can effectively protect the concrete blocks so that they cannot absorb each other, which can reduce slump damage. Even if available retarder is used, the required amount is not suitable for unlimited expansion. The excessive use of retarder not only increases the direct cost of construction, but also damages the early strength of concrete and affects the progress of the project. Too much retarder is added, and the concrete is often in a state of plastic deformation. The plastic deformation shrinks and expands as the sand and gravel move downwards, and a large amount of water in the concrete evaporates. Before the concrete solidifies, too little water and too much water will cause the concrete to form layers, which is resistant to Pressure strength decreases. It can be seen that to deal with the problem of slump loss of concrete goods, we must first find the key damage factors of slump damage. Adopt appropriate preventive measures to prevent collapse, rather than randomly increasing the amount of retarder required to completely solve the problem.

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