The role of cellulose ether in cement mortar (1)
Cellulose ether – thickening and thixotropy
Cellulose ether gives wet mortar excellent viscosity. Can significantly increase the bonding ability of wet mortar and base. Improve the anti-sag performance of mortar. It is widely used in plastering mortar, brick bonding mortar and external wall insulation system.
The thickening effect of cellulose ether can also increase the anti-dispersion ability and homogeneity of the freshly mixed material, and prevent the material from delamination, segregation and bleeding. It can be used in fiber-reinforced concrete, underwater concrete and self-compacting concrete.
The thickening effect of cellulose ether on cement-based materials comes from the viscosity of cellulose ether solution. Under the same conditions, the higher the viscosity of cellulose ether, the better the viscosity of the modified cement-based material. However, if the viscosity is too high, it will affect the fluidity and workability of the material (such as sticking plastering knives).
Self-leveling mortar and self-compacting concrete, which require high fluidity, require low viscosity of cellulose ether. In addition, the thickening effect of cellulose ether will increase the water demand of cement-based materials and increase the yield of mortar.
High-viscosity cellulose ether aqueous solution has high thixotropy, which is also a major characteristic of cellulose ether. Aqueous solutions of methylcellulose usually have pseudoplastic, non-thixotropic fluidity below its gel temperature. However, it exhibits Newtonian flow properties at low shear rates. Pseudoplasticity increases with the molecular weight or concentration of cellulose ether, regardless of the type of substituent and the degree of substitution.
Therefore, cellulose ethers of the same viscosity grade, no matter MC, HPMC, HEMC. As long as the concentration and temperature are kept constant, they always exhibit the same rheological properties. Structural gels are formed when the temperature is raised, and highly thixotropic flows occur.
High concentration and low viscosity cellulose ethers show thixotropy even below the gel temperature. This property is of great benefit to the adjustment of leveling and sagging in the construction of building mortar. It needs to be explained here that the higher the viscosity of cellulose ether, the better the water retention. However, the higher the viscosity, the higher the relative molecular weight of cellulose ether, and the corresponding decrease in its solubility. This negatively affects mortar consistency and workability.
The role of cellulose ether in cement mortar (3)
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