Cellulose ether in cement mortar

The improvement of mortar performance also has different effects. At present, many masonry and plastering mortars have poor water retention performance, and water slurry separation will occur after a few minutes of standing. So it is very important to add cellulose ether in cement mortar.

Here is a detailed look at cellulose ether in cement mortar which hard ability.

Cellulose ether - water retention

Water retention is an important performance of methyl cellulose ether, but also a lot of domestic dry mortar manufacturers, especially in the southern area of higher temperature manufacturers concerned about the performance.

In the production of building materials, especially dry mortar, cellulose ether plays an irreplaceable role, especially in the production of special mortar (modified mortar), is an indispensable part.

The viscosity, dosage, ambient temperature and molecular structure of cellulose ether have great influence on its water retention performance. Under the same conditions, the greater the viscosity of cellulose ether, the better water retention; The higher the dosage, the better the water retention, usually little dosage of cellulose ether can greatly improve the water retention rate of mortar, when the dosage reaches a certain degree, the increase trend of water retention rate becomes slow; With the increase of ambient temperature, the water retention of cellulose ether usually decreases, but some modified cellulose ether also has good water retention under high temperature conditions; Cellulose ether with lower degree of substitution has better water retention.

Cellulose ether molecule hydroxyl and ether bond on the oxygen atoms will synthesize hydrogen bond with water molecules, so that free water into combined water, so as to play a good role in water retention; The mutual diffusion between water molecules and cellulose ether molecular chain makes the water molecules can enter the cellulose ether macromolecular chain inside, and by strong binding force, thus forming free water, winding water, improve the water retention of cement slurry; Cellulose ether improves the rheological properties, porous network structure and osmotic pressure of new cement slurry or cellulose ether film formation performance hinders the diffusion of water.

Cellulose ether - thickening and thixotropy

Cellulose ether endows wet mortar with excellent viscosity, can significantly increase the bonding ability of wet mortar and base, improve the anti-sag performance of mortar, widely used in plastering mortar, surface brick bonding mortar and exterior insulation system. The thickening effect of cellulose ether can also increase the anti-dispersion ability and uniformity of new mixed materials, to prevent material stratification, segregation and bleeding, can be used in fiber concrete, underwater concrete and self-compacting concrete.

The thickening effect of cellulose ether on cement-based materials comes from the viscosity of cellulose ether solution. Under the same conditions, the higher the viscosity of cellulose ether, the better the viscosity of the modified cement-based material, but if the viscosity is too large, it will affect the fluidity and operability of the material (such as sticking plaster knife). Self-leveling mortar and self-compacting concrete, which require high fluidity, require a very low viscosity of cellulose ether. In addition, the thickening effect of cellulose ether will increase the water requirement of cement-based materials and increase the output of mortar.

Celulose ether aqueous solution with high viscosity has high thixotropy, which is one of the characteristics of cellulose ether. Aqueous solutions of methyl cellulose usually have pseudoplastic, non-thixotropic flow below their gel temperature, but newton-type flow properties at low shear rates. Pseudoplasticity increases with the increase of molecular weight or concentration of cellulose ether and is independent of substituent type and degree. Therefore, cellulose ethers of the same viscosity grade, whether MC, HPMC or HEMC, always show the same rheological properties as long as the concentration and temperature remain constant. When the temperature increases, structural gel is formed and high thixotropic flow occurs.

Cellulose ethers with high concentration and low viscosity exhibit thixotropy even below the gel temperature. This property is of great benefit to the construction of building mortar to adjust its flow and flow hanging property. It needs to be explained here that the higher the viscosity of cellulose ether, the better the water retention, but the higher the viscosity, the higher the relative molecular weight of cellulose ether, the corresponding reduction of its solubility, which has a negative impact on the mortar concentration and construction performance.

Cellulose ether - aeration

Cellulose ether has obvious air - entraining effect on fresh cement - based material. Cellulose ether at the same time with hydrophilic group (hydroxyl, ether group) and hydrophobic group (methyl, glucose ring), is a surfactant, with surface activity, so as to have the effect of engassing.

The air entraining effect of cellulose ether will produce "ball" effect, which can improve the working performance of new mixed materials, such as increasing the plasticity and smoothness of mortar in the process of operation, which is conducive to mortar paving; It can also increase the output of mortar and reduce the production cost of mortar. However, the porosity of hardened materials will be increased and the mechanical properties such as strength and elastic modulus will be reduced.

As a surfactant, cellulose ether also has wetting or lubrication effect on cement particles, which increases the fluidity of cement-based materials together with its air entraining effect, but its thickening effect will reduce the fluidity, cellulose ether on the fluidity of cement-based materials is plasticizing and thickening effect of the synthesis. Generally speaking, when the dosage of cellulose ether is very low, the main performance is plasticizing or reducing water; When the dosage is high, the thickening effect of cellulose ether increases rapidly, and its air entraining tends to saturation, so it is manifested as thickening effect or increased water demand.

Cellulose ether - retarding action

Cellulose ether will prolong the setting time of cement slurry or mortar, delay cement hydration dynamics, which is conducive to improve the operational time of new mixed materials, improve mortar consistency and concrete slump loss, but may also delay the construction progress.