Mechanism of Cellulose in Mortar


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2016-11-16

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Mechanism of Cellulose in Mortar

Cellulose ethers are mainly used as water retention agents and thickeners in cement-based materials. Its water retention function can prevent the substrate from absorbing water too quickly and hinder the evaporation of water, so as to ensure that the cement has enough water when it is hydrated. Taking plastering operation as an example, when ordinary cement slurry is plastered on the surface of the substrate, because the dry and empty substrate will quickly absorb a large amount of water from the slurry, the cement slurry layer close to the substrate will easily lose the water required for hydration, so not only cannot cement gel with adhesive strength be formed on the surface of the substrate, but also warping and water seepage are easy to cause, making the surface cement slurry layer easily fall off. When the cement paste is thin, it is also easy to form cracks in the whole slurry. Therefore, in the past, the substrate is usually wetted with water first, but this operation is not only time-consuming, but also difficult to control the quality of the operation.
 
Generally speaking, the water retention of the cement slurry increases with the increase of the content of cellulose ether, and the greater the viscosity of the added cellulose ether, the better the water retention. In addition to bonding and thickening, cellulose ethers also have an impact on other properties of cement mortars, such as retarding, air entraining, and increasing bond strength. Cellulose ether is the cement setting hardening process slows down, thereby prolonging the operational time, therefore, sometimes also used as a coagulant.
 
With the development of dry-mixed mortar, cellulose ether has become an important admixture for cement mortar. However, there are many varieties and specifications of cellulose ether, and the quality between batches still fluctuates. Attention should also be paid when using:
1. The working characteristics of modified mortar are closely related to the development of cellulose ether viscosity. Although the product with large nominal viscosity has a large final viscosity, it takes a long time to obtain the final viscosity due to slow dissolution. In addition, the cellulose ether with coarser particles takes a long time to obtain the final viscosity, so the product with higher viscosity is not sure to obtain better working characteristics.
2. Due to the limitation of the degree of polymerization of the cellulose ether raw material, the maximum viscosity of the cellulose ether is also limited.
3. It is necessary to check the purchase, production process and factory inspection to avoid quality fluctuations.

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