Adding defoaming agent in concrete can prevent bubbles from forming in concrete mixture or reduce the original bubbles. To join in the test of antifoaming agent is a kind of surface active agent, can reduce the surface tension of the liquid phase, wetting Angle decreases to a certain extent, the bubbles out of solid surface adsorption and escape or burst, so join defoaming agent can eliminate the bubbles in concrete to a certain extent, prevent or eliminate honeycomb, pits on the surface of the concrete, the concrete surface has high smoothness and gloss, can improve the surface performance and so on.The meaning of defoaming mainly has two aspects, one is "bursting", that is, the elimination of foam; Second, "bubble suppression", that is, to prevent the regeneration of foam. The defoaming agent with excellent performance usually has excellent ability to break and restrain bubbles at the same time.Although defoaming agents have been used for a long time, different types of defoaming agents are needed for different defoaming systems. There are three widely accepted defoaming agent mechanisms:(1) by adding the defoamer to the foaming system, the defoamer molecules will approach the foam.First, the defoaming agent attached to the foam began to invade and gradually expand on the bubble film, causing the local thickness of the bubble film to decrease sharply, and finally leading to the bubble merger or burst.(2) the defoaming mechanism of hydrophobic solids is bubbly liquid after adding hydrophobic solids, hydrophobic particles would immediately the hydrophilic end of bubbles in the liquid surfactant adsorption, made of hydrophobic particles into the outermost layers of the surfactants hydrophilic side, is hydrophilic, into the water phase, hydrophobic solids of foaming system of surfactant adsorption, making bubbles in the liquid surfactant concentration, the bubble burst. This defoaming mechanism can not explain the mechanism of other defoaming agents, too one-sided.(3) defoaming mechanism of polyether modified silicone oil for the explanation of the defoaming process of polyether modified silicone oil as a defoaming agent, the most complete defoaming mechanism is: "bridging - stretching" mechanism, "bridging - drainage" mechanism."Bridging - tensile mechanism: the antifoaming agent is much lower than the surface tension of the liquid membrane, the surface tension of the defoamer droplet to continue to spread out in the liquid film surface and in-depth, local liquid film bubble continue thinning, eventually forming oil in water even in the middle of the bridge, oil phase and water phase is far, the surface tension of the oil phase in the surrounding water phase constant traction, stretched thin, deformation over a certain range, liquid membrane was damaged and lead to the bubble burst."Bridge - platoon is wet" mechanism, to join in blister fluid solid hydrophobic particles after defoaming agent, defoaming agent immediately fanned out in the foam system, fixed in the foam liquid membrane surface hydrophobic particles, when the solid particles and liquid membrane with sufficient hydrophobic Angle between solid particles and the surrounding liquid membrane has the opposite interface, becomes a bridge between the liquid film around even, will eventually wear out foam liquid membrane, enter into the bubble.Based on the characteristic of low surface tension and easy spreading of silicone oil, the mechanism of "bridging and stretching" points out that defoamer droplets can produce different degree of deformation, but this mechanism is difficult to explain the difference between silicone paste and pure silicone oil. Based on the lipophilic property of silicone oil, the mechanism of "bridging and wetting" can explain the principle of low viscosity polyether modified silicone oil.Therefore, polyether modified silicone oil defoaming agent has three characteristics of defoaming: first, it is basically insoluble in foaming liquid (most of the dissolved silicone oil helps foam); Secondly, the surface tension should be lower than the foaming liquid; Finally, it can be quickly dispersed in the foaming liquid. Only the substances with small solubility and large dispersion can become the defoaming agents with good bubble breaking and bubble suppressing ability, so as to maximize their dispersion and achieve the purpose of double strength of bubble suppressing and bubble breaking.Ross once explicitly said: no one defoaming mechanism can cover all the defoaming phenomenon, various, numerous defoaming agent, can correspond to a variety of defoaming mechanism.