Application of redispersible emulsion powder in mortar system

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The redispersible latex powder is physically mixed with other meta-machine adhesives (such as cement, hydrated lime, gypsum, etc.) and various aggregates, fillers and other additives (such as methyl short propyl cellulose vinegar, starch tunnel, 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 into the water under the action of the hydrophilic protective colloid and mechanical shear. The time required for normal redispersible latex powder dispersion is very short. 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 s to spray onto the construction surface, which is enough to fully disperse and film the redispersible latex powder. 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 the 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 when it is dispersed, the influence of different teaching degrees after the dispersion of latex powder, the influence of protective colloid, the influence of cement and water, the influence of the increase of air content of mortar and the distribution of bubbles, as well as the influence of self-additives and interaction with other additives, etc. o The more common view is that redispersible latex powder usually increases the air content of mortar, thus lubricating the construction of mortar, and the increase of affinity for water and teaching consistency of latex powder, especially when protective colloid is dispersed, helps 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 moisture on three levels, the absorption of a base layer, the consumption of cement hydration reaction, and the volatilization of surface moisture 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.

In order to make this process irreversible, that is, when the polymer film meets water again, it will not be dispersed twice, and the protective colloid of the redispersible latex powder-polyvinyl alcohol must be separated from the polymer film system. This is not a problem in the alkaline cement mortar system, because polyvinyl alcohol will be saponified by the alkali generated by the hydration of cement, and the adsorption of quartz materials makes polyvinyl alcohol gradually separated from the system. Without the hydrophilic protective colloid, the film formed by the redispersible latex powder, which is insoluble in water and is dispersed once, 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, some polyvinyl alcohol still 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:

Redispersible latex powder