Post Date:11,Dec,2023
Celluloses are increasingly used in cement-based materials, especially in dry mortars, due to their excellent water retention and thickening effects. Therefore, the properties and formation mechanism of cellulose ether modified cement-based materials and the interaction between cellulose ether and cement slurry have gradually become the focus of attention in the fields of building materials and engineering in recent years. Many research results have been achieved. Combining research progress at home and abroad, there are still the following problems in the research and application of cellulose ether modified cement-based materials:
1.There are many types of celluloses. Even celluloses used in cement-based materials are divided into many types such as HEC, HEMC and HPMC due to their degree of substitution. The same type of celluloses have many differences in molecular structure, molecular weight, degree of substitution or substituent content. At present, most research at home and abroad focuses on one or several celluloses. The choice of cellulose ether is limited to their respective fields of application. The molecular structure characteristics of celluloses are not indicated, and their representativeness is not representative. The conclusion is the inevitable result of "partial substitution", and there are contradictions and disputes among the test results. Therefore, it is necessary to systematically study the classification and structural properties and mechanisms of different species of cellulose ether modified gelling materials.
2.Existing literature has studied the impact of celluloses on various properties of cementitious materials, and conducted a certain analysis of its formation mechanism, but failed to determine the relationship between the molecular structure of celluloses and the properties of modified cement slurry. regularity, and there are obvious differences in their mechanisms. Among cellulose ether-modified cement-based materials, there are few studies on materials with different molecular structures, which cannot essentially explain the formation mechanism of various properties of cellulose ether-modified cement-based materials. . Although some literature found that celluloses with different molecular structures have different effects on the hydration of cement, the underlying reasons have not yet been further elucidated.
3.The mechanism of the influence of cellulose ether on cement hydration kinetics remains to be further studied. At present, regarding the delayed hydration mechanism of cellulose ether, although adsorption is considered to be the real cause of delayed hydration of cellulose ether, it is found that the stronger the adsorption capacity between hydration products and cellulose ether, the more delayed hydration of cement. The adsorption mechanism between celluloses and cement hydration products, as well as the reasons for the different adsorption capacities of different celluloses and cement hydration products, have not been further studied.
4.Existing literature shows that celluloses can significantly affect the pore structure of cement-based materials. Celluloses are also believed to be surface-active and have an air-entraining effect on fresh cement slurries, thereby increasing the porosity of hardened cement slurries. However, the influence of celluloses on the regularity and formation mechanism of cement slurry pore size distribution is rarely discussed.
5. Rheological properties are an important aspect of the application of celluloses in cement-based materials. Unfortunately, there are few studies on the rheological properties of cellulose ether modified cement slurry at home and abroad.
Post time: Dec-11-2023