Redispersible latex powder is a commonly used organic gelling material obtained by spray-drying a polymer emulsion with polyvinyl alcohol as a protective colloid. It can be re-dispersed evenly in water to form an emulsion when it meets water. Adding redispersible latex powder can improve the performance of freshly mixed cement mortar.
As soon as the cement-based material added with latex powder contacts water, the hydration reaction begins, and the calcium hydroxide solution quickly reaches saturation and crystals are precipitated, and at the same time, ettringite crystals and calcium silicate hydrate gels are formed. The solid particles are deposited on the gel and unhydrated cement particles. As the hydration reaction proceeds, the hydration products increase, and the polymer particles gradually gather in the capillary pores, forming a densely packed layer on the surface of the gel and on the unhydrated cement particles. The aggregated polymer particles gradually fill the pores, but not completely to the inner surface of the pores. As water is further reduced by hydration or drying, the closely packed polymer particles on the gel and in the pores coalesce into a continuous film, forming an interpenetrating mixture with the hydrated cement paste and improving hydration Bonding of products and aggregates.
Because the hydration products with polymers form a covering layer at the interface, it may affect the growth of ettringite and coarse calcium hydroxide crystals; and because the polymers condense into films in the pores of the interface transition zone, the polymer cement-based materials The transition zone is denser. The active groups in some polymer molecules will also produce cross-linking reactions with Ca2+ and A13+ in cement hydration products to form special bridge bonds, improve the physical structure of hardened cement-based materials, relieve internal stress, and reduce generation of microcracks.
As the cement gel structure develops, the water is consumed and the polymer particles are gradually confined in the pores. As the cement is further hydrated, the moisture in the capillary pores decreases, and the polymer particles aggregate on the surface of the cement hydration product gel/unhydrated cement particle mixture and the aggregate, thereby forming a continuous close-packed layer with large pores Filled with sticky or self-adhesive polymer particles.
The dispersed emulsion of the redispersible latex powder can form a water-insoluble continuous film (polymer network body) after drying, and this low elastic modulus polymer network body can improve the performance of cement; at the same time, in the polymer molecule Certain polar groups in the cement react chemically with the cement hydration products to form special bridges, improve the physical structure of the cement hydration products, and alleviate and reduce the generation of cracks. After the redispersible latex powder is added, the initial hydration rate of the cement slows down, and the polymer film can partially or completely wrap the cement particles, so that the cement can be fully hydrated and its various properties can be improved.