Admixtures play a key role in improving the performance of building dry-mixed mortar. The following analyzes and compares the basic properties of latex powder and cellulose, and analyzes the performance of dry-mixed mortar products using admixtures.

Redispersible latex powder

Redispersible latex powder is processed by spray drying of special polymer emulsion. The dried latex powder is some spherical particles of 80~100mm gathered together. These particles are soluble in water and form a stable dispersion slightly larger than the original emulsion particles, which form a film after dehydration and drying.

Different modification measures make the redispersible latex powder have different properties such as water resistance, alkali resistance, weather resistance and flexibility. latex powder used in mortar can improve the impact resistance, durability, wear resistance, ease of construction, bonding strength and cohesion, weather resistance, freeze-thaw resistance, water repellency, bending strength and flexural strength of the mortar .

Cellulose ether

Cellulose ether is a general term for a series of products produced by the reaction of alkali cellulose and etherifying agent under certain conditions. Alkali cellulose is replaced by different etherifying agents to obtain different cellulose ethers. According to the ionization properties of substituents, cellulose ethers can be divided into two categories: ionic (such as carboxymethyl cellulose) and non-ionic (such as methyl cellulose). According to the type of substituent, cellulose ether can be divided into monoether (such as methyl cellulose) and mixed ether (such as hydroxypropyl methyl cellulose). According to different solubility, it can be divided into water-soluble (such as hydroxyethyl cellulose) and organic solvent-soluble (such as ethyl cellulose), etc. Dry-mixed mortar is mainly water-soluble cellulose, and water-soluble cellulose is divided into instant type and surface treated delayed dissolution type.

The mechanism of action of cellulose ether in mortar is as follows:

(1) After the cellulose ether in the mortar is dissolved in water, the effective and uniform distribution of the cementitious material in the system is ensured due to the surface activity, and the cellulose ether, as a protective colloid, “wraps” the solid particles and A layer of lubricating film is formed on its outer surface, which makes the mortar system more stable, and also improves the fluidity of the mortar during the mixing process and the smoothness of construction.

(2) Due to its own molecular structure, the cellulose ether solution makes the water in the mortar not easy to lose, and gradually releases it over a long period of time, endowing the mortar with good water retention and workability.

wood fiber

Wood fiber is made of plants as the main raw material and processed by a series of technologies, and its performance is different from that of cellulose ether. The main properties are:

(1) Insoluble in water and solvents, and also insoluble in weak acid and weak base solutions

(2) Applied in mortar, it will overlap into a three-dimensional structure in a static state, increase the thixotropy and sag resistance of the mortar, and improve the constructability.

(3) Due to the three-dimensional structure of wood fiber, it has the property of “water-locking” in the mixed mortar, and the water in the mortar will not be easily absorbed or removed. But it does not have the high water retention of cellulose ether.

(4) The good capillary effect of wood fiber has the function of “water conduction” in the mortar, which makes the surface and internal moisture content of the mortar tend to be consistent, thereby reducing cracks caused by uneven shrinkage.

(5) Wood fiber can reduce the deformation stress of the hardened mortar and reduce the shrinkage and cracking of the mortar.