How to play the role of redispersible latex powder in mortar

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Redispersible latex powder

How to play the role of redispersible latex powder in mortar

The redispersible emulsion powder is physically mixed with other inorganic binders (such as cement, hydrated lime, gypsum, etc.) and various aggregates, fillers and other additives (such as methyl hydroxypropyl cellulose ether, starch ether, lignocellulose, water repellent, etc.) to make dry-mixed mortar. When the dry-mixed mortar is added to the water and stirred, the latex powder particles are dispersed in the water under the action of the hydrophilic protective colloid and mechanical shear. The time required for the dispersion of normal redispersible latex powder is very short, and the time index of redispersion is also an important parameter to examine its quality. For example. In dry shotcrete repair mortar, the dry mortar added with redispersible latex powder and water are only mixed at the end of the nozzle for about 0.1 seconds before spraying on the construction surface, but this is enough to make the redispersible latex powder fully dispersed and film-formed. In the early mixing stage, the latex powder has begun to have an impact on the rheology and workability of the mortar.

Due to the characteristics of each subdivided latex powder itself and the different modification, this effect is also different, some help flow, and some have increased thixotropy. The mechanism of its influence comes from many aspects, including the influence of the affinity of latex powder to water during dispersion, the influence of different viscosity after dispersion of latex powder, the influence of protective colloid, the influence of cement and water, the influence of increasing air content and bubble distribution of mortar, and the influence of self-additive and interaction with other additives. Therefore, the choice of customization and subdivision of redispersible latex powder is an important means to affect product quality. One of the more common point of view is that re-dispersible latex powder will usually increase the air content of mortar, thus playing a lubricating role in the construction of mortar, and latex powder, especially when the protective colloid is dispersed, the increase of affinity and viscosity to water will help to improve the cohesion of construction mortar, thus improving the workability of mortar. Subsequently, the wet mortar containing latex powder dispersion is constructed on the working surface. With the reduction of water on three levels-the absorption of the base layer, the consumption of cement hydration reaction, and the volatilization of water on the surface layer into the air, the resin particles gradually approach, the interface gradually fuses with each other, and finally becomes a continuous polymer film. This process mainly occurs in the pores of the mortar and the surface of the solid.

It should be emphasized that in order to make this process irreversible, that is, when the polymer film is once again exposed to water without secondary dispersion, the protective colloid of the redispersible latex powder must be separated from the system of the polymer film. This is not a problem in the alkaline cement mortar system, because it will be saponified by the alkali generated by the hydration of cement. At the same time, the adsorption of quartz materials will gradually separate it from the system. Without the hydrophilic protective colloid, the film which is insoluble in water and is formed by the redispersible latex powder once dispersed can not only be used under dry conditions, can also play a role in the long-term immersion conditions. In non-alkaline systems, such as gypsum systems or filler-only systems, the protective colloid still partially exists in the final polymer film for some reason, affecting the water resistance of the film, but because these systems are not used in long-term water immersion, and the polymer still has its unique mechanical properties, it does not affect the application of redispersible latex powder in these systems.

Key words:

Latex powder