Selection and application of concrete defoamer

On construction sites, you may have seen this scene: dense bubbles rising from the surface of freshly mixed concrete, like boiling porridge. These bubbles may seem harmless, but they can actually significantly reduce the concrete's strength. This is where a seemingly inconspicuous yet crucial material comes into play: a defoamer specifically for cement concrete.

Why does concrete need a defoamer?

During the mixing and pouring process, air is inevitably entrained into the concrete, forming bubbles. If these bubbles remain in the hardened concrete, they create pores, reducing the concrete's density and strength. Bubbles can also affect the concrete's surface aesthetics, especially in decorative concrete that requires a smooth surface. Defoamers destabilize these bubbles, causing them to burst or escape quickly, thereby improving the concrete's overall performance.

Classification and Characteristics of Defoamers

There are many types of defoamers, but they can be broadly divided into the following categories based on their mechanism of action and chemical composition:
-Silicone defoamers: These defoamers are characterized by high efficiency and excellent stability, making them suitable for most concrete formulations. They can quickly break down the bubble film, but may affect the concrete's fluidity.
-Polyether defoamers: These defoamers have minimal impact on concrete fluidity and are suitable for concrete requiring high fluidity, such as self-leveling concrete.
-Mineral oil defoamers: These are relatively inexpensive, but their effectiveness may not be as significant as the previous two types, making them suitable for cost-sensitive projects.

How to Choose the Right Defoamer?

When selecting a defoamer, consider the following:
-Concrete Type: Ordinary concrete, high-strength concrete, and self-leveling concrete have different requirements for defoamers. For example, high-strength concrete requires a more effective defoamer to reduce porosity.
-Construction Environment: High or low temperatures may affect the performance of the defoamer, so choose a product with strong adaptability.
-Cost Budget: The prices of different defoamers vary significantly, so a balance must be struck between effectiveness and cost.

How to Use a Defoamer

Proper use of a defoamer is key to achieving its full effectiveness. Here are a few key points to note:
-Timing of Addition: It is usually added in the middle or late stages of concrete mixing. Adding too early may affect the defoaming effect.
-Dosage: Excessive use may cause surface defects in the concrete, while too little may be ineffective. It is recommended to refer to the product instructions or conduct a pilot test to determine the recommended dosage.
-Uniform Mixing: The defoamer must be thoroughly dispersed in the concrete to be effective, so sufficient mixing time is required.

Common Problems and Solutions

-Unsatisfactory Defoaming Effect: This may be due to improper defoamer selection or insufficient addition. Try changing the type or adjusting the dosage.
-Oil Spots on the Concrete Surface: Some defoamers may react with other ingredients in the concrete, so compatibility should be checked.
-Decreased Flowability: If the defoamer affects the flowability of the concrete, try reducing the dosage or switching to a type that has less of an impact on flowability.