The Improvement Effect of Hydroxypropyl Methylcellulose on Cement-based Materials

25 May.,2022

In recent years, with the continuous development of external wall insulation technology, the continuous progress of hydroxypropyl methyl cellulose production technology, and the excellent characteristics of hydroxypropyl methyl cellulose HPMC itself, hydroxypropyl methyl cellulose HPMC is widely used in the construction industry.

 

In recent years, with the continuous development of external wall insulation technology, the continuous progress of hydroxypropyl methyl cellulose production technology, and the excellent characteristics of hydroxypropyl methyl cellulose HPMC itself, hydroxypropyl methyl cellulose HPMC is widely used in the construction industry. In order to deeply explore the interaction mechanism between hydroxypropyl methylcellulose HPMC and cement-based materials, this paper focuses on the improvement effect of HPMC on the cohesive properties of cement-based materials.

 

The coagulation time

 

The setting time of concrete is mainly related to the setting time of cement, and the effect of aggregate is not large. Therefore, the setting time of mortar can be used to study the effect of HPMC on the setting time of underwater non-dispersed concrete mixtures. Since the setting time of mortar is affected by water Therefore, in order to evaluate the influence of HPMC on the setting time of mortar, it is necessary to fix the water-cement ratio and mortar ratio of mortar.

 

The experimental reaction shows that the addition of HPMC has a retarding effect on the mortar mixture, and the setting time of the mortar is successively prolonged with the increase of the content of HPMC and cellulose ether. Under the same content of HPMC, the mortar formed under water is better than air molding takes longer to set. When measured in water, the setting time of the mortar mixed with HPMC was 6-18 h delayed at the initial setting and 6-22 hour at the final setting compared with the blank specimen. Therefore, HPMC should be used in combination with early strength agent.

 

HPMC is a macromolecular polymer with a macromolecular linear structure with hydroxyl groups on the functional groups, which can form hydrogen bonds with the mixing water molecules and increase the viscosity of the mixing water. The long molecular chains of HPMC will attract each other, so that the HPMC molecules are entangled with each other to form a network structure, which wraps the cement and mixing water. Because HPMC forms a film-like network structure and wraps the cement, it can effectively prevent the volatilization of water in the mortar and hinder or slow down the hydration speed of the cement.

 

The Bleeding

 

The bleeding phenomenon of mortar and concrete is similar to that of concrete, which will cause serious aggregate settlement, resulting in an increase in the water-cement ratio of the top slurry, which will cause the top slurry to undergo a large plastic shrinkage in the early stage, or even crack, and the strength of the surface of the slurry. relatively weak.

 

When the dosage is above 0.5%, there is basically no bleeding phenomenon. This is because when HPMC is mixed into the mortar, HPMC has a film-forming and network structure, as well as the adsorption of hydroxyl groups on the long chain of macromolecules, so that the cement and mixing water in the mortar form a flocculation shape, which ensures the stable structure of the mortar body. After adding HPMC to the mortar, many independent tiny bubbles will be formed. These air bubbles will be evenly distributed in the mortar and hinder the deposition of aggregates. This technical performance of HPMC 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, so that it has good water retention and plasticity retention.

 

The water requirement for mortar

 

When the content of HPMC is small, it has a great influence on the water demand of the mortar. Under the condition that the expansion degree of fresh mortar is kept basically the same, the content of HPMC and the water demand of the mortar change linearly in a certain period of time, and the water demand of the mortar first decreases and then increases. When the content of HPMC is less than 0.025%, with the increase of the content, the water demand of the mortar decreases under the condition of the same expansion degree. There are a large number of tiny independent air bubbles in the mortar, which play a lubricating role and improve the fluidity of the mortar. When the dosage is greater than 0.025%, the water demand of the mortar increases with the increase of the dosage.

 

This is because the network structure of HPMC is further completed, and the flocculation gap on the long molecular chain is shortened, which has the effect of attraction and cohesion, reducing the the fluidity of the mortar. So in the case of basically the same degree of expansion, the slurry shows an increase in water demand. Semonova group, your profeesional cellulose ether expert, we will serve you the best products.