Effect of HPMC on the properties of self-leveling mortar

Self-leveling mortar can form a smooth, smooth and strong foundation on the substrate by its own weight, so as to lay or bond other materials, and can carry out large-area and efficient construction. Therefore, high fluidity is a very significant one of self-leveling mortar. Features; in addition, it must have a certain water retention and bonding strength, no water segregation phenomenon, and has the characteristics of thermal insulation and low temperature rise.
Generally, self-leveling mortar is required to have good fluidity, but the actual fluidity of cement paste is usually only 10-12cm; in cellulose ether, 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, working performance, adhesion 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 to evaluate the self-leveling performance. Under the premise of ensuring the normal composition of mortar, the fluidity of mortar can be adjusted by changing the amount of HPMC. However, if the amount is too high, the fluidity of the mortar will be reduced, so the amount of HPMC should be controlled within a reasonable range.
2. Water retention
The water retention of mortar is an important indicator to measure the stability of the internal components of freshly mixed cement mortar. In order to make the gel material fully hydrated, a reasonable amount of HPMC can maintain the moisture in the mortar for a long time. Generally speaking, the water retention rate of the slurry increases with the increase of HPMC content. The water-retaining effect of HPMC can prevent the substrate from absorbing too much water too quickly and hinder the evaporation of water, thus ensuring that the slurry environment provides sufficient water for cement hydration. In addition, the viscosity of hydroxypropyl methylcellulose also has a greater impact 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 in self-leveling mortar, which can improve the leveling performance of the mortar and improve the density of the mortar.
3. Setting time
HPMC has a certain retarding effect on mortar. With the increase of the amount, the setting time of the mortar will be extended. The retardation 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 and the larger the hydroxyl content, the more obvious the retarding effect. And the high content of HPMC, the more obvious the effect of the complex film layer on the early hydration delay of cement, therefore, the more obvious the retardation effect.
4. Flexural strength and compressive strength
In general, strength is one of the important evaluation indexes of the curing effect of cement-based cementitious materials on the mixture. As the amount of HPMC added increases, the compressive strength and flexural strength of the mortar will decrease.
5. Bonding strength
HPMC has a great influence on the adhesion properties of mortar. HPMC forms a polymer film with a sealing effect between the liquid phase system and the cement hydration particles, which promotes the polymer film outside the cement particles to have more moisture, which is conducive to the complete hydration of the cement, thus improving the slurry Bond strength after hardening. At the same time, adding an appropriate amount of HPMC enhances the plasticity and flexibility of the mortar, which reduces the rigidity of the transition zone of the interface between the mortar and the substrate, and reduces the slipping ability between the interfaces. To a certain extent, the bonding effect between the mortar and the substrate is enhanced. In addition, due to the presence 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, Mortar has a strong bonding strength.