Self-leveling mortar relies on its flowability and self-healing properties to form a smooth, flat, and durable base on the substrate, enabling the application or bonding of other materials while allowing for large-area, high-efficiency construction. High flowability is a highly notable characteristic of self-leveling mortar; additionally, it must possess adequate water retention and bonding strength, prevent bleeding and segregation, and exhibit thermal insulation properties with low temperature rise.
Cellulose ether is a primary additive in pre-mixed mortar, enhancing mortar performance such as consistency, workability, bonding strength, and water retention. It plays a significant role in the pre-mixed mortar industry.
Benefits of cellulose ether
1.Flowability
Cellulose ether significantly influences the water retention, consistency, and workability of self-leveling mortar. As a self-leveling mortar, flowability is one of the primary indicators for evaluating self-leveling performance. Under the premise of ensuring the normal composition of the mortar, the flowability can be adjusted by modifying the dosage of cellulose ether.
However, excessive addition can reduce the mortar’s flowability, so the cellulose ether content should be controlled within a reasonable range.
2.Water Retention
Mortar water retention is an important indicator of the internal stability of freshly mixed cement mortar. To allow gel materials to undergo hydration reactions fully, cellulose ether at appropriate concentrations can maintain moisture in the mortar for an extended period. Generally, the water retention rate of the mortar increases with the addition of cellulose ether.
The water retention effect of cellulose ether prevents the substrate from absorbing too much water too quickly and inhibits water evaporation, thereby ensuring that the mortar environment provides sufficient water for cement hydration.
Additionally, the viscosity of cellulose ether significantly affects the water retention of mortar. Higher viscosity results in better water retention. Cellulose ethers with a viscosity of 400 mPa·s are commonly used in self-leveling mortars to enhance flowability and improve the density of the mortar.
3.Setting time
Cellulose ether has a certain retarding effect on mortar. As the dosage of cellulose ether increases, the setting time of the mortar is prolonged.
The retarding effect of cellulose ether on cement paste primarily depends on the degree of alkyl substitution, with little relation to molecular weight. The lower the alkyl substitution degree, the higher the hydroxyl content, and the more pronounced the retarding effect.
Additionally, higher cellulose ether content results in a more pronounced delay in the early hydration of cement due to the complex membrane layer, thereby enhancing the retarding effect.
4.Flexural and compressive strength
Strength is one of the key evaluation criteria for the curing effect of cement-based binding materials on mixtures. Within a reasonable addition range, increasing cellulose ether content improves the compressive strength and flexural strength of mortar.
5.Bond strength
Cellulose ether has a significant impact on the bonding performance of mortar. In the liquid phase system, cellulose ether forms a polymer film with a sealing effect between cement hydration particles, promoting the retention of moisture within the polymer film surrounding the cement particles. This facilitates complete cement hydration, thereby enhancing the bond strength of the hardened mortar.
Additionally, an appropriate amount of cellulose ether enhances the plasticity and flexibility of mortar, reducing the rigidity of the transition zone between the mortar and the substrate interface. This decreases the slip resistance between interfaces, thereby enhancing the bonding effect between mortar and the substrate to a certain extent.