Cement paste consistency and cellulose ether content

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There is also a good linear relationship between the consistency of cement paste and the dosage of cellulose ether, cellulose ether can greatly increase the viscosity of mortar, the greater the dosage, the more obvious the effect. High viscosity aqueous cellulose ether solution has high thixotropy, which is also a major characteristic of cellulose ether. Aqueous solutions of cellulosic polymers generally have pseudoplastic, non-thixotropic flow properties below their gel temperature, but exhibit Newtonian flow properties at low shear rates. Pseudoplasticity increases with the increase of 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, whether cellulose, HP cellulose or HE cellulose, always exhibit the same rheological properties as long as the concentration and temperature are kept constant. When the temperature is increased, a structured gel is formed and high thixotropic flow occurs. High concentrations of low viscosity cellulose ethers exhibit thixotropy even below the gel temperature. This property is of great benefit to the construction of building mortar to adjust its leveling and sagging. It should be noted here that the higher the viscosity of cellulose ether, the better the water retention, but the higher the viscosity, the higher the relative molecular weight of cellulose ether, the corresponding reduction in solubility, which has a negative impact on mortar concentration and construction performance. The higher the viscosity, the more obvious the thickening effect of mortar, but not completely proportional relationship. Some low viscosity, but the modified cellulose ether has more excellent performance in improving the structural strength of wet mortar. With the increase of viscosity, the water retention of cellulose ether is improved.

Retardation of cellulose ether: the third role of cellulose ether is to delay the hydration process of cement. Cellulose ether gives mortar various beneficial properties, but also reduces the early hydration heat of cement and delays the hydration process of cement. This is detrimental to the use of mortar in cold areas. This retarding effect is caused by the adsorption of cellulose ether molecules on C- S-H and Ca (OH)2 and other hydration products. Due to the increase of the viscosity of the pore solution, cellulose ether reduces the activity of ions in the solution, thus delaying the hydration process. The higher the concentration of cellulose ether in the mineral gel material, the more obvious the effect of hydration delay. Cellulose ethers not only delay setting, but also delay the hardening process of cement mortar systems. The retarding effect of cellulose ether depends not only on its concentration in the mineral gel system, but also on the chemical structure. The higher the degree of methylation of HE cellulose, the better the retarding effect of cellulose ether, and the hydrophilic substitution is stronger than the retarding effect of water-increasing substitution. However, the viscosity of cellulose ether has little effect on the hydration kinetics of cement.

With the increase of cellulose ether content, the setting time of mortar increases significantly. The initial setting time of mortar has a good nonlinear correlation with the amount of cellulose ether, and the final setting time has a good linear correlation with the amount of cellulose ether. We can control the operable time of mortar by changing the dosage of cellulose ether.

Key words:

Mortar additive