Effect of hydroxypropyl methyl cellulose on performance of self-leveling mortar

Self-leveling mortar can form a flat, smooth and firm foundation on the base material by relying on its own weight, so as to lay or bond other materials. Meanwhile, it can carry out large-area and high-efficiency construction. Therefore, high fluidity is a significant feature of self-leveling mortar.In addition, there must be a certain water retention and bonding strength, do not produce qinshui segregation phenomenon, and have adiabatic and low temperature rise characteristics.

Generally, self-leveling mortar requires good fluidity, but the actual fluidity of cement slurry is usually only 10-12cm.In cellulose ether, hydroxypropyl methyl cellulose (HPMC) is a major additive of ready-mixed mortar. Although the addition amount is very low, it can significantly improve the performance of mortar, which can improve the consistency, working performance, bonding performance and water retention performance of mortar.It plays a very important role in the field of ready-mixed mortar.

1. The fluidity

Hydroxypropyl methyl cellulose (HPMC) has an important influence on the water retention, consistency and construction performance of self-leveling mortar.Especially as self-leveling mortar, fluidity is one of the main indexes to evaluate the self-leveling performance.On the premise of ensuring the normal composition of mortar, the fluidity of mortar can be adjusted by changing the mixing amount of HPMC.However, excessive mixing amount will reduce the flow of mortar, so the amount of HPMC should be controlled within a reasonable range.

2. Water retention

Water retention of mortar is an important index to measure the internal component stability of fresh cement mortar.In order to fully hydrate the gel material, reasonable amount of HPMC can maintain the moisture in the mortar for quite 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 base material from absorbing too much water too quickly, and prevent the evaporation of water, so the slurry environment can provide enough water for cement hydration.In addition, the viscosity of hydroxypropyl methyl cellulose has a greater impact on the water retention of mortar, the higher the viscosity, the better the water retention.Products with a general viscosity of about 400mpa. S are mostly used for self-leveling mortar, which can improve the leveling performance of mortar and improve the compactness of mortar.

3. Setting time

HPMC cellulose ether 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 slurry mainly depends on the substitution degree of alkyl group, but has little relationship with its molecular weight.The smaller the substitution degree of alkyl group, the larger the content of hydroxyl group and the more obvious the retarding effect.Moreover, the HPMC content is high, and the more obvious the hydrating delay effect of the complex film layer on the early hydration of cement is, the more obvious the retarding effect is.

4. Flexural strength and compressive strength

Generally, strength is one of the important evaluation indexes of cement-based cementitious materials for curing the mixture.With the increase of HPMC content, the compressive strength and flexural strength of mortar will decrease.

5. Bond strength

HPMC has a great influence on the bonding property of mortar.In the liquid phase system, HPMC forms a polymer film with sealing effect between cement hydration particles, which promotes the polymer film outside cement particles to have more water inside, which is conducive to the complete hydration of cement, so as to improve the bonding strength of slurry after hardening.At the same time, the addition of appropriate amount of HPMC enhances the plasticity and flexibility of mortar, reduces the rigidity of the interface transition zone between mortar and substrate, and reduces the slip ability between interfaces.To some extent, the bonding effect between mortar and substrate is enhanced.In addition, due to the presence of HPMC in cement slurry, a special interface transition zone and interface layer are formed between mortar particles and hydration products. This interface layer makes the interface transition zone more flexible and less rigid, so mortar has a strong bonding strength.