Improvement Effect of Hydroxypropyl Methyl Cellulose Mortar Concrete


Release time:

2021-05-21

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Improvement Effect of Hydroxypropyl Methyl Cellulose Mortar Concrete
 
In recent years, with the continuous development of exterior insulation technology, the continuous progress of cellulose production technology, and the excellent characteristics of HP cellulose itself, HP cellulose has been widely used in the construction industry. In order to understand the mechanism of HP cellulose and cement-based materials, this paper introducesThe improvement effect of the element on the cohesive properties of cement-based materials.
 
setting time
 
The setting time of concrete is mainly related to the setting time of cement, and the effect of aggregate is not large, so the setting time of mortar can be used instead of studying the effect of HP cellulose on the setting time of underwater non-dispersible concrete mixture. Because the setting time of mortar is affected by water cement ratio and mortar sand ratio, in order to evaluateThe effect of HP cellulose on the setting time of mortar, the water-cement ratio and mortar ratio of mortar need to be fixed.
 
In the experimental reaction, the addition of HP cellulose has obvious retarding effect on the mortar mixture, and with the increase of HP cellulose content, the setting time of the mortar is prolonged one after another, and under the same HP cellulose content, the underwater molding mortar is longer than the setting time in the air. When measured in water, doped.The setting time of HP cellulose mortar is 6~18 h delayed in initial setting and 6~22 h delayed in final setting. Therefore, HP cellulose should be used together with early strength agent.
 
HP cellulose is a high molecular polymer with a linear structure of macromolecules with hydroxyl groups on the functional groups, which can form hydrogen bonds with mixing water molecules and increase the viscosity of mixing water. The long molecular chains of HP cellulose attract each other, making HP cellulose molecules entangled with each other to form a network structure, wrapping cement and mixing water.Come on. Because HP cellulose forms a network structure similar to a film and has a wrapping effect on cement, it can effectively prevent the volatilization of water in the mortar and hinder or slow down the hydration rate of cement.
 
Bleeding
 
Mortar and concrete bleeding phenomenon is similar, will make the serious settlement of aggregate, resulting in the top slurry water cement ratio increases, so that the top slurry in the early plastic shrinkage, even cracking, and the strength of the surface of the slurry is relatively weak.
 
When the dosage is above 0.5%, there is no bleeding phenomenon. This is due to the fact that when HP cellulose is incorporated into mortar, HP cellulose has a film-forming and reticular structure, as well as the adsorption of hydroxyl groups on the long chain of macromolecules, so that cement and mixing water in the mortar form flocculation, ensuring the stable structure of the mortar body. AgainAfter HP cellulose is added to the mortar, many independent tiny bubbles will be formed. These bubbles will be evenly distributed in the mortar and hinder the deposition of aggregate. This technical performance of HP cellulose has a great influence on cement-based materials and is often used to formulate new cement-based composite materials such as dry powder mortar and polymer mortar, Make it have good water retention and plasticity.
 
Water demand of mortar
 
In the case of HP cellulose content is very small, it has a great influence on the water demand of mortar. Under the condition that the expansion degree of fresh mortar is basically the same, the amount of HP cellulose and the water demand of mortar change linearly in a certain period of time, and the water demand of mortar decreases first and then increases obviously. HP cellulose in dosage
 
When it is less than 0.025%, with the increase of the dosage, the water demand of mortar decreases under the condition of the same expansion degree, which shows that HP cellulose has a water reducing effect on mortar when the dosage is small, and HP cellulose has an air-entraining effect, so that there are a large number of tiny independent bubbles in mortar, which play a lubricating role and make mortar flow.The movement is improved. When the dosage is more than 0.025%, the water demand of mortar increases with the increase of the dosage, which is due to the further integrity of the network structure of HP cellulose, the shortening of the flocculation gap on the molecular long chain, with attraction and cohesion, reducing the fluidity of the mortar body. So the degree of expansion is basically the same. In this case, the slurry shows an increase in water demand.
 

Key words:

HPMC