The entrainment of uncontrolled air into cement based building

materials leads inevitably to a loss of quality of high-performance concretes. Undesired air voids can weaken the system resulting in lower mechanical strength and abrasion resistance. A highly porous structure on the surface allows the penetration of harmful substances and can lead to surface defects.

Defoamers are preferably used for the prevention and removal of large air inclusions at the concrete’s surface and for rapid foam collapse in aqueous formulations. If, on the other hand, it is necessary to remove finely distributed air from a system, deaerators are the preferred alternative. However, practice has shown that a clear differentiation between defoamers and deaerators is usually not possible. Most defoamers also have a deaerating effect to some extent and vice versa. 

How defoamers work can be best explained in the images below. Defoamers and deaerators are active at the air/water interface; they cause the stabilized structure of air voids to rupture in a liquid medium, thus allowing air to escape. 

DEFOAMERS ARE CHARACTERIZED BY:

1.a low surface tension

2.insolubility in the formulation to be defoamed

3.a positive spreading coefficient

4.a positive penetration coefficient

Amber Zhang Ms.

Foreign trade 

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