Thickening effect of hydroxypropyl methylcellulose in mortar system

Hydroxypropyl methylcellulose endows mortar with excellent viscosity, which can significantly increase the bonding ability of wet mortar and base layer, and improve the anti-sagging performance of mortar. . The thickening effect of cellulose ether can also increase the homogeneity and anti-dispersion ability of fresh cement-based materials, preventing delamination, segregation and bleeding of mortar and concrete
Hydroxypropyl methylcellulose increases the viscosity of cement-based materials from the viscosity of cellulose ether solution. The index "viscosity" is usually used to evaluate the viscosity of cellulose ether solution. The viscosity of cellulose ether generally refers to a certain concentration (such as 2%) of cellulose ether solution at a specified temperature (such as 20°C) and shearing. The viscosity value measured by a specified measuring instrument (such as a rotational viscometer) under the condition of a speed (or rotation rate, such as 20 rpm).
Viscosity is an important parameter to evaluate the performance of cellulose ether. The higher the viscosity of hydroxypropyl methylcellulose solution, the better the viscosity of the cement-based material, the better the adhesion to the substrate, the better the anti-sagging and anti-dispersing ability. Strong, but if its viscosity is too high, it will affect the fluidity and workability of cement-based materials. Therefore, the viscosity of cellulose ether used in dry-mixed mortar is usually 15,000~60,000 mPa. S-1, self-leveling mortar and self-compacting concrete that require higher fluidity require lower viscosity of cellulose ether.
In addition, the thickening effect of hydroxypropyl methylcellulose increases the water demand of the cement-based material, thereby increasing the yield of the mortar.
Cellulose ether solutions are usually pseudoplastics with shear thinning properties. The higher the shear rate, the lower the viscosity.
Therefore, the cohesion of the mortar will be reduced due to the action of external force, which is beneficial to the scraping construction of the mortar, so that the mortar can have good workability and cohesion at the same time. However, when the concentration of cellulose ether solution is very low and the viscosity is very small, it will show the characteristics of Newtonian fluid. When the concentration increases, the solution will gradually show the characteristics of pseudoplastic fluid, and the higher the concentration, the more obvious the pseudoplasticity.