Views: 0 Author: Site Editor Publish Time: 2020-10-21 Origin: Site
PTMATECH Additive RDP Redispersible Polymer Powder in Dry-Mixed Mortar III
The main function of the RDP redispersible polymer / latex powder thickener is to improve the water retention and stability of the mortar. Although it can prevent the mortar from cracking to a certain extent (slow down the rate of water evaporation), it is generally not used to improve the toughness, crack resistance and waterproof of the mortar. Sexual means.
The practice of adding polymers to improve the impermeability, toughness, crack resistance and impact resistance of mortar and concrete has been recognized. Commonly used polymer emulsions used to modify cement mortar and cement concrete are: neoprene latex, styrene butadiene rubber latex, polyacrylate latex, polyvinyl chloride, vinylidene rubber latex, polyvinyl acetate, etc. With the development of scientific research, not only the modification effects of various polymers have been studied in depth, but also the modification mechanism and the interaction mechanism between polymers and cement and cement hydration products have also been theoretically studied. More in-depth analysis and research, and a large number of scientific research results have appeared.
Polymer emulsion can be used in the production of ready-mixed mortar, but it is obviously impossible to directly use it in the production of dry mortar, so redispersible latex powder was born. At present, the redispersible latex powder used in dry mortar mainly includes: ①vinyl acetate-ethylene copolymer (VAC/E); ②vinyl acetate-tertiary carbonate copolymer (VAC/VeoVa; ③acrylate homopolymer ( Acrylate); ④Vinyl acetate homopolymer (VAC); 4) Styrene-acrylate copolymer (SA), etc. Among them, the use ratio of vinyl acetate-ethylene copolymer is the largest.
Practice has proved that the redispersible latex powder has stable performance and has unparalleled effects on improving the bonding strength of the mortar, improving its toughness, deformability, crack resistance and impermeability. The addition of hydrophobic latex powder copolymerized with polyvinyl acetate and vinyl chloride, ethylene, vinyl laurate, etc. can also greatly reduce the water absorption of the mortar (because of its hydrophobicity), make the mortar breathable and impermeable, and enhance Its weather resistance and durability are improved.
Compared with improving the mortar's flexural strength, bonding strength, and reducing its brittleness, redispersible latex powder can improve the water retention of mortar and enhance its cohesiveness is limited. Since the addition of redispersible latex powder can play a dispersing effect, and will cause a large amount of air entrainment in the mortar mixture, its water reducing effect is very obvious. Of course, due to the poor structure of the introduced bubbles, this water-reducing effect does not improve the strength. On the contrary, the strength of the mortar will gradually decrease as the amount of redispersible latex powder increases. Therefore, in the development of some mortars that need to consider compressive and flexural strength, defoamers are often added at the same time in order to reduce the negative impact of latex powder on the mortar's compressive strength and flexural strength.