Self-leveling mortar can rely on its own weight to form a flat, smooth and strong foundation on the substrate for laying or bonding other materials. At the same time, it can carry out large-scale and efficient construction. Therefore, high fluidity is a very significant aspect of self-leveling mortar In addition, it must have certain water retention and bonding strength, no water segregation phenomenon, and have the characteristics of heat insulation and low temperature rise.
Generally, self-leveling mortar requires good fluidity, but the fluidity of actual cement paste is usually only 10-12cm; among cellulose ethers, hydroxypropyl methylcellulose (HPMC) is a main additive of ready-mixed mortar , although the addition amount is very low, it can significantly improve the performance of the mortar, it can improve the consistency, work performance, bonding performance and water retention performance of the mortar. It plays a very important role in the field of ready-mixed mortar.
1. Mobility
Hydroxypropyl methylcellulose (HPMC) has an important influence on the water retention, consistency and construction performance of self-leveling mortar. Especially as a self-leveling mortar, fluidity is one of the main indicators for evaluating self-leveling performance. Under the premise of ensuring the normal composition of the mortar, the fluidity of the mortar can be adjusted by changing the amount of HPMC. However, if the dosage is too high, the fluidity of the mortar will be reduced, so the dosage of HPMC should be controlled within a reasonable range.
2. Water retention
The water retention of mortar is an important index to measure the stability of the internal components of freshly mixed cement mortar. In order to fully carry out the hydration reaction of the gel material, a reasonable amount of HPMC can maintain the moisture in the mortar for a long time. Generally speaking, the water retention rate of slurry increases with the increase of HPMC content. The water retention function of HPMC can prevent the substrate from absorbing too much water too quickly, and hinder the evaporation of water, so as to ensure that the slurry environment provides sufficient water for cement hydration. In addition, the viscosity of hydroxypropyl methylcellulose also has a great influence on the water retention of mortar. The higher the viscosity, the better the water retention. Generally, products with a viscosity of about 400mpa.s are mostly used for self-leveling mortar, which can improve the leveling performance of the mortar and increase the compactness of the mortar.
3. Setting time
HPMC has a certain retarding effect on mortar. With the increase of the dosage, the setting time of the mortar is prolonged. The retarding effect of HPMC on cement paste mainly depends on the degree of substitution of alkyl groups, and has little relationship with its molecular weight. The smaller the degree of alkyl substitution, the larger the hydroxyl content, and the more obvious the retarding effect. And the higher the HPMC content, the more obvious the effect of the complex film layer on the early hydration retardation of cement, so the retarding effect is also more obvious.
4. Flexural strength and compressive strength
Usually, strength is one of the important evaluation indexes for the curing effect of cement-based cementitious materials on the mixture. The compressive strength and flexural strength of mortar will decrease with the increase of HPMC content.
5. Bond strength
HPMC has a great influence on the bonding performance of mortar. HPMC forms a polymer film with a sealing effect between the liquid phase system and the cement hydration particles, which promotes more water in the polymer film outside the cement particles, which is conducive to the complete hydration of the cement, thus improving the slurry quality. Hardened bond strength. At the same time, adding an appropriate amount of HPMC enhances the plasticity and flexibility of the mortar, reduces the rigidity of the transition zone between the mortar and the substrate interface, and reduces the sliding ability between the interfaces. To a certain extent, the bonding effect between the mortar and the substrate is enhanced. In addition, due to the existence of HPMC in the cement paste, a special interface transition zone and interface layer are formed between the mortar particles and the hydration product. This interface layer makes the interface transition zone more flexible and less rigid. Therefore, the Mortar has strong bonding strength.
Post time: Apr-25-2024