The main function of additives in dry mixed mortar


Release time:

2020-03-23

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Because the traditional mortar has the shortcomings of single variety and low performance, it has become increasingly unable to meet the needs of actual engineering. Dry-mixed mortar is gradually being promoted and applied, and the development of dry-mixed mortar admixtures is the technical key to promote dry-mixed mortar.

The main function of dry mixed mortar commonly used additives

Because the traditional mortar has the shortcomings of single variety and low performance, it has become increasingly unable to meet the needs of actual engineering. Dry-mixed mortar is gradually being promoted and applied, and the development of dry-mixed mortar admixtures is the technical key to promote dry-mixed mortar. With the continuous improvement of people's requirements for environmental protection and building quality, there have been many high-efficiency admixtures with excellent technical performance, superior product quality, wide range of use, strong adaptability and obvious economic benefits. Dry-mixed mortar admixture can not only improve the reduction of mortar and ease, water retention, strength and other properties, but also to save building gelding materials, process costs, reduce energy consumption, ensure the quality of the project is of great significance.

redispersible latex powder
Re dispersible powder in thin layer plastering mortar, tile adhesive, exterior insulation system, self leveling floor materials and other materials have good application effect. Redispersible rubber powder is used as the second binder in mortar to complement each other with inorganic binder cement, so that the bonding performance of mortar is improved. After adding redispersible latex powder into dry-mixed mortar, the workability of mortar is well improved. After adding redispersible latex powder, the folding-compression ratio and tensile-compression ratio of mortar are greatly improved. Emulsion powder increases the dry apparent density of mortar with the increase of emulsion powder content, modified mortar has certain wear resistance and impermeability.

Cellulose
The hardening of cement and gypsum is due to their hydration, but the thin layer of mortar is smeared, and water quickly seeps into the matrix or evaporates. Cellulose ether has good water retention capacity due to intermolecular forces (van der Waals forces). It can also ensure the uniformity and completeness of hydration of inorganic binder, because it has roughly the same evaporation heat and capillary diffusion with water. Mortar is a non-homogeneous system, in which water and aqueous solution are continuous phases. When water is first added, friction and movement resistance are greatly increased, so that the mortar is difficult to apply, especially in thin layers. The addition of cellulose ether plastic agent can lubricate the slip of mortar and change the workability of mortar at the same time, which can prevent the danger of thick layer smearing and cracking. In addition, cellulose dissolved in the liquid phase of the mortar slurry volume expansion and due to the bridge effect will increase the viscosity of the slurry, to hinder the fine aggregate in the cement paste and cement particles in the water dispersion of the sinking (I. e. layering), improve the workability and uniformity of the mortar, improve the bond strength between the mortar and the matrix material, reduce shrinkage and so on has a very important significance.

water reducing agent
Water reducing agent has a good plasticizing effect, the basic function of water reducing agent is to reduce the water demand of mortar, in the case of obtaining the same ease of performance significantly reduce the water demand, the extent of its reduction increases with the increase of the amount of water reducing agent. Due to the dispersion effect of water reducing agent and certain air-entraining effect, the water retention of mortar is also improved. Water reducer is often used in the need to have a good self-leveling good mortar, such as self-leveling cushion, surface mortar or leveling mortar. There are three main types of dry mortar: casein, melamine formaldehyde condensate, polycarboxylic acid. Casein is an excellent superplasticizer, especially for thin layer mortar, but because it is a natural product, the quality and price often fluctuate. Melamine formaldehyde condensate is a superplasticizer with good performance, but it has limited effect on thin layer mortar and has formaldehyde release. Polycarboxylic acid is a newly developed technology with high efficiency and no formaldehyde emission.

water repellent
Organosilane compounds and their modified compounds have active reactive groups. In the highly alkaline environment after cement hydration, the hydrophilic organic functional groups in the silane are hydrolyzed to form silanol groups with high reactivity, and the silanol groups continue to react irreversibly with the hydroxyl groups in the cement hydration products to form chemical bonds, so that the silanes connected together by cross-linking are firmly fixed on the surface of the pore wall in the cement mortar. Due to the hydrophobic organic functional groups towards the outside of the pore wall, the surface of the pore obtains hydrophobicity, thus bringing the overall hydrophobic effect to the mortar.

Defoamer
Since the addition of a finely divided organic polymer increases the porosity of the mortar, a defoamer must be introduced at the same time to eliminate air bubbles. Powdered defoamers are based on different chemical groups, such as hydrocarbons, stearic acid and its esters, tributyl phosphate, polyethylene glycol or polysiloxanes adsorbed on inorganic carriers. At present, the powder defoamers used in dry mixed mortar are mainly polyols and polysiloxanes. In addition to adjusting the bubble content, the application of defoaming agent can also reduce shrinkage. A good defoaming agent must have good chemical stability, lower than the surface tension of the defoaming medium and insoluble in the defoaming medium. The defoaming effect may occur in another system. Therefore, the most effective defoamer or composite defoamer should be selected for different systems.














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