Self leveling mortar can rely on its own weight to form a flat, smooth and firm foundation on the substrate, which can be used for laying or bonding other materials, and can also be used for large-scale and efficient construction. Therefore, high fluidity is a very important aspect of self-leveling mortar. In addition, it must also have a certain water retention and bonding strength, regardless of water, and have the characteristics of heat insulation and low temperature rise.
Generally, self-leveling mortar requires good fluidity, but the fluidity of actual cement slurry is usually only 10-12cm; Among cellulose ethers, hydroxypropyl methylcellulose (HPMC) is the main additive of ready-mixed mortar, although the amount added is very small. few. rare. Low, but it can significantly improve the performance of mortar, improve the consistency, workability, bonding performance and retention performance of waterproof mortar. It occupies a very important position in the field of ready-mixed mortar.
- 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, excessive use will reduce the fluidity of the mortar, so the use of HPMC should be controlled within a reasonable range. - 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, an appropriate amount of HPMC can keep the moisture in the mortar for a long time. In general, the water retention 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. - Set the time
HPMC has a certain retarding effect on mortar. With the increase of dosage, the setting time of 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 retarding effect of the composite film layer on the early hydration of cement, and the more obvious the retarding effect. - Flexural strength and compressive strength
Usually, strength is one of the important evaluation indexes for the curing effect of cement-based cementitious material mixture. The compressive strength and flexural strength of mortar will decrease with the increase of HPMC content. - 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, thereby improving the quality of the cement Cement grouting. Hardened bond strength. At the same time, adding an appropriate amount of HPMC enhances the plasticity and flexibility of the mortar, reduces the stiffness 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 cement paste, a special interfacial transition zone and interfacial layer are formed between mortar particles and hydration products. This interface layer makes the interfacial transition zone more flexible and less rigid. Therefore, the mortar has a strong bond strength.