Defoamer

Why are defoamers needed in water reducers?

Due to the molecular structure of PCE, it tends to introduce an excessive number of unevenly sized bubbles during mixing. If left uncontrolled, these bubbles can lead to two major problems: first, they compromise the surface appearance of the concrete, and more importantly, they reduce the concrete's long-term strength and durability.

Main types and characteristics of defoamers

The defoamers commonly used in PCE-based water reducers fall into the following categories:

Silicone-based defoamers: These offer extremely fast defoaming action and are widely applicable. They are also one of the most extensively researched and applied types.

Polyether-based defoamers: Modified polyether defoamers provide longer foam-suppression duration and generally exhibit better compatibility with PCE than traditional silicone-based options.

Mineral oil-based defoamers: This is a more traditional type, but it is less commonly used today, as its effectiveness and stability are generally inferior to the previous two categories.

Application:

Precise dosage: More is not necessarily better. Research indicates that increasing the defoamer dosage from 0.01%–0.02% to 0.04% of the total mass shifts its dominant role from an air-entraining agent to a defoaming agent, causing a sharp drop in air content. The recommended starting dosage is generally 0.05%–0.2% of the total mass. Overdosing can lead to bleeding and poor workability of the concrete.

"Defoam first, then entrain" process: This is a widely recognized and effective method. The defoamer is added first to eliminate the uneven large bubbles introduced during mixing, followed by the addition of an air-entraining agent to introduce uniform and stable micro-bubbles. This approach ensures both good concrete fluidity (workability) and improved strength through optimized pore structure.

Mixing and storage considerations: Due to compatibility issues, the defoamer may float to the surface during storage of the compounded water reducer. It is recommended to stir continuously or mix thoroughly before use. Additionally, it is best to operate at a pH below 10, as excessively high alkalinity can adversely affect performance.

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