Views: 3 Author: Site Editor Publish Time: 2020-10-21 Origin: Site
PTMATECH Additive Construction Admixture Thickener in Dry-Mixed Mortar II
Thickeners, water-retaining agents and stabilizers are ordinary mortars prepared from cement, inert or active mineral admixtures, and fine aggregates. The main disadvantages are poor cohesion, poor stability, easy bleeding, segregation, and sedimentation. It is not easy to construct. After construction, the bonding strength is low, easy to crack, water resistance is weak, and durability is poor. It must be modified with suitable additives. In terms of improving the cohesiveness, water retention and stability of the mortar, the additives that can be selected are cellulose ether, modified starch ether, polyvinyl alcohol, polyacrylamide and thickening powder.
1. Cellulose ether methyl cellulose (MC), hydroxypropyl methyl cellulose (HPMC) and hydroxyethyl methyl cellulose (HEMC) are all made of natural polymer materials (such as cotton, etc.). A series of non-ionic cellulose ethers produced by chemical treatment. They have the characteristics of cold water solubility, water retention, thickening, adhesion, film-forming, lubricity, non-ionic and pH stability. The cold water solubility of these products is greatly improved, and the water retention capacity is enhanced, the thickening is obvious, the diameter of the bubbles introduced is relatively small, and the effect of improving the bonding strength of the mortar is greatly enhanced.
Cellulose ethers are not only diverse in varieties, but also in a wide range of average molecular weights, with a viscosity ranging from 5 mPa. s to 200,000 mPa. s. The effect on the performance of the mortar at the fresh mixing stage and after hardening is also different. A lot of tests should be carried out when selecting the mortar, and the cellulose varieties with suitable viscosity and molecular weight range, small content, and no air-entraining properties can be selected in this way. Ideal technical performance and good economy.
2. Starch ether Starch ether is an ether produced by the reaction between the hydroxyl groups on the starch glucose molecule and chemical reagents, and is called starch ether or etherified starch. The main varieties of modified starch ethers are: sodium carboxymethyl starch (CMS), hydrocarbon alkyl starch (HES), hydrocarbon propyl ethyl starch (HPS), cyanoethyl starch, etc. They all have excellent functions such as water solubility, bonding, expansion, flow, covering, desizing, sizing, dispersing and stabilization, and are widely used in medicine, food, textile, paper, daily chemical and petroleum industries.
At present, the prospect of starch ether used in dry mortar is also very promising. The main reasons are: ①The price of starch ether is relatively cheap, only 1/3 to 1/4 of cellulose ether; ②The mixing of starch ether in mortar will also improve The viscosity, water retention, stability and bonding strength of the mortar; ③ Starch ether can be compounded with cellulose ether in any ratio, so as to improve the anti-sagging effect of the mortar. Some mortar products, such as ceramic wall and floor tile adhesives, interface treatment agents, caulking agents and ordinary commercial mortars, use starch ether as the main thickening, water-retaining agent and stabilizer. However, looking at my country's starch ether manufacturers, many only stay on the supply of primary products, and only a few manufacturers produce and supply modified starch ethers to meet part of the needs of mortar manufacturers.
3. Thickening powder mortar Thickening powder is a new product developed to adapt to the production of ordinary dry powder (ready-mixed) mortar. It is mainly composed of inorganic minerals and organic polymer materials, and does not contain lime and air-entraining components. Minute. Its mixing amount is about 5%-20% of the cement weight. At present, in the production of ordinary commercial mortar in Shanghai, thickening powder is generally used as a thickening, water-retaining and stabilizing component, and the effect is remarkable.
Polyvinyl alcohol and polyacrylamide also have a wide range of viscosity, but sometimes the amount of air entraining is large, or the water demand of the mortar increases too much after being mixed, and it should be selected through a large number of experiments.