The Structural Characteristics of Cellulose Ether and Its Influence on Mortar Properties

27 May.,2022

Cellulose ether is the main additive in ready-mixed mortar. The types and structural characteristics of cellulose ether are introduced. Hydroxypropyl methylcellulose ether (HPMC) is selected as the additive to systematically study the effects on various properties of mortar. Studies have shown that HPMC can improve the water retention of mortar, and has the effect of reducing water.

 

Semonova Cellulose ether is the main additive in ready-mixed mortar. The types and structural characteristics of cellulose ether are introduced. Hydroxypropyl methylcellulose ether (HPMC) is selected as the additive to systematically study the effects on various properties of mortar. Studies have shown that HPMC can improve the water retention of mortar, and has the effect of reducing water. At the same time, it can also reduce the density of mortar mixture, prolong the setting time of mortar, and reduce the flexural and compressive strength of mortar.

 

Mortar is one of the most widely used materials in the construction industry. With the development of material science and the improvement of people's requirements for building quality, mortar, like the promotion and development of ready-mixed concrete, has gradually developed towards commercialization. Compared with the mortar prepared by the traditional process, the commercialized mortar has many advantages:

1. High product quality; 2. High product efficiency; 3. Less environmental pollution, which is convenient for civilized construction. At present, there are Guangzhou, Shanghai, Beijing, etc. in China. Many cities have promoted ready-mixed mortar, and relevant industry standards and national standards have been introduced or are about to be introduced.

 

A big difference between ready-mixed mortar and traditional mortar is the incorporation of chemical admixtures, among which cellulose ethers are commonly used chemical admixtures. Cellulose ether is usually used as a water-retaining agent, and its purpose is to improve the operability of ready-mixed mortar. The content of cellulose ether is small, and it is a main additive that affects the construction performance of mortar. Therefore, a further understanding of the influence of the types and structural characteristics of cellulose ethers on the performance of cement mortar is helpful for the correct selection and use of cellulose ethers to ensure stable performance of the mortar.

 

1. Types and structural characteristics of cellulose ethers


Cellulose ether is a water-soluble polymer material, which is processed from natural cellulose through alkali dissolution, grafting reaction (etherification), washing, drying, grinding and other processes. Cellulose ether is divided into ionic and non-ionic, ionic cellulose has carboxymethyl cellulose salt, non-ionic cellulose has hydroxyethyl cellulose ether, hydroxypropyl methyl cellulose ether, methyl cellulose ether etc. Since ionic cellulose ether (carboxymethyl cellulose salt) is unstable in the presence of calcium ions, it is rarely used in dry powder products made of cement, slaked lime and other cementing materials. The cellulose ethers used in dry powder mortar are mainly Hydroxyethyl methyl cellulose ether (HEMC) and hydroxypropyl methyl cellulose ether (HPMC), which have a market share of over 90%


2. The effect of cellulose ether on the properties of cement mortar

 

① Raw materials for testing

Cellulose ether: produced by Semonova, Henan, viscosity: 75 000; cement: 32.5 grade composite cement; sand: medium sand; fly ash: II grade. 

 

② Test results

1. Water reducing effect of cellulose ether

It shows the relationship between the consistency of mortar and the content of cellulose ether under the same mixing ratio. It can be seen from the figure that with the increase of the content of cellulose ether, the consistency of the mortar increases gradually. When the mixing amount is 0.3‰, the consistency of the mortar is increased by about 50% compared with that without mixing, which shows that cellulose ether can improve the workability of the mortar. The amount of water increases, the water consumption can be gradually reduced, it can be considered that cellulose ether has a certain water-reducing effect.

 

2. Water retention

Water retention of mortar refers to the ability of mortar to retain water, and it is also a performance index to measure the stability of internal components of fresh cement mortar during transportation and parking. Water retention can be measured by two indicators: stratification and water retention. However, due to the incorporation of water-retaining agent, the water retention of ready-mixed mortar is improved. The sensitivity of the stratification index is not enough, and it may not be able to reflect the difference. The water retention rate test is to calculate the water retention rate by measuring the change in the quality of the filter paper before and after the filter paper is in contact with a specified area of ​​mortar within a certain period of time.

 

Due to the good water absorption of the filter paper, even if the water retention of the mortar is high, the filter paper can still absorb the water in the mortar. Therefore, the water retention rate can accurately reflect the water retention of the mortar. The higher the water retention rate, the better the water retention. Semonova group produces high viscosity HPMC, HEMC, RDP, CMC and so on.