Application of Defoamer in Mortar


Release time:

2021-08-11

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Defoamer

Application of Defoamer in Mortar

With the rapid development of new building materials, special mortar has been widely used in the construction field, and more and more construction chemical additives are used in mortar products. In cement-based or gypsum-based products, in order to meet some special needs in the construction field, it is necessary to modify the existing mortar products, such as redispersible rubber powder, cellulose ether and other chemical additives used in mortar products. In the process of mixing mortar with water, mixing mortar, air is brought into the fresh mortar, air is wrapped by wet mortar to form bubbles, and chemical additives such as redispersible rubber powder and cellulose ether have hydrophilic groups, which can reduce the surface tension of the liquid and also cause foam aggregation. Instantaneous generation of hydrophobic groups towards the bubble, hydrophilic groups towards the liquid phase of the adsorption film. Under normal circumstances, under the condition of low viscosity of the solution, the bubbles formed rise due to buoyancy and rush to the surface of the solution. The bubbles escape from the surface to the external air, and the liquid film moving to the surface produces a pressure difference due to gravity. The thickness of the film becomes thinner with time, and finally the bubbles burst. However, due to the high viscosity of fresh mortar, on the one hand, the increase of viscosity will slow down the average speed of liquid exudation in the liquid film, so that the liquid film is not easy to thin; on the other hand, the increase of viscosity of fresh mortar will slow down the diffusion speed of surfactant molecules, which is beneficial to the stability of foam. This causes a large amount of air bubbles introduced in the mortar to stay in the mortar. Uniform and stable small bubbles are helpful to mortar performance, such as improving the workability of mortar, enhancing the frost resistance and durability of mortar. Theoretically, the increase of air bubbles will affect the physical properties of the mortar itself, increase the porosity of the mortar, and reduce the strength of the mortar itself. Especially for mortar products with waterproof requirements, it is inevitable to suppress and defoam the mortar.

The defoaming agent can inhibit the formation of foam and destroy the formed foam in the mortar. Its mechanism is: the defoamer into the liquid film, reducing the viscosity of the liquid, the formation of a new low surface viscosity interface, so that the liquid film loss of elasticity, accelerate the liquid exudation process, and finally make the liquid film thin and rupture. At present, the defoamers used in mortar products are compounds composed of one or more additives on the basis of the main agent. The chemical composition of defoamers provided by different suppliers is different, and the compatibility of different types of defoamers and mortar systems is different. The effect of defoamer on the performance of mortar is briefly introduced below.

Key words:

Defoamer