As an additive for cement mortar, the cellulose ether usually has an addition amount not more than 2% of cement mass. For the study on cellulose ether, there has been a long history of research abroad. For example, DOW had successfully developed and marketed as early as 1938.
First, the higher viscosity the cellulose ether has, the lower the mass concentration required for the solution to achieve the same viscosity will be. For example, in order to make an aqueous solution with viscosity of 10,000mPa·s, the cellulose ether with the viscosity of 20,000mPa·s can be used and the addition amount can only be about 1.6%; when the viscosity is 12,000mPa·s, the dosage is about 1.8%; while the viscosity is 400mPa·s, dosage required is about 5%. That is, in order to achieve the same final viscosity, the use of high-viscosity cellulose ether required less amount than that of low-viscosity cellulose ether. However, if the viscosity does not increase much, then the dosage will not decrease much. For example, when the viscosity is increased from 12,000mPa·s to 20,000mPa·s, increasing by 80%, in order to achieve the viscosity of 10,000mPa·s, the dosage will be reduced from 1.8% to 1.6%, only reducing by 0.2%.
On the other hand, the larger the viscosity (or the molecular weight) of cellulose ether is, due to its slower dissolution, the longer time the solution will take to reach the final viscosity.Thus, if the mortar is prepared from the cellulose ether with a larger viscosity, the time required to achieve the final viscosity will be longer, that is, the mortar, after mixing well, requires a longer standing (or curing) time.
With the development of dry-mix mortar, the cellulose ether has become an important admixture for cement mortar. However, since there are many varieties and specifications for cellulose ether, there are still fluctuations in quality between batches. When using, pay attention to the following two things.
(1). The operational characteristics of modified mortar is closely related to the viscosity development of the cellulose ether. Although for the product with large nominal viscosity, the final viscosity is relatively large, due to slow dissolution, it will require a longer time to obtain the final viscosity. In addition, the cellulose ether in coarse particles will also require a longer time to obtain the final viscosity. Therefore, not all the products with the greater viscosity will be able to get the better operating characteristics.
(2). Due to the limitations on the degree of polymerization of the cellulose ether materials, the maximum viscosity of the cellulose ether is also limited.
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