Improvement effect of hydroxypropyl methyl cellulose on cement-based materials

In recent years, with the continuous development of external insulation technology, hydroxypropyl methyl cellulose production technology progress, as well as hydroxypropyl methyl cellulose HPMC itself has excellent characteristics, hydroxypropyl methyl cellulose HPMC in the construction industry has been widely used. In order to investigate the interaction mechanism between HPMC and cement-based materials, this paper focuses on the improvement effect of HPMC on the cohesion of cement-based materials.

Setting time

 The setting time of concrete is mainly related to the setting time of cement, and the aggregate has little influence, so the setting time of mortar can be used instead to study the influence of HPMC on the setting time of underwater non-dispersed concrete mix. Because the setting time of mortar is affected by the water-cement ratio and the cement-sand ratio, in order to evaluate the influence of HPMC on the setting time of mortar, The water-cement ratio and cementity-sand ratio of the mortar should be fixed.

Experimental reaction, HPMC addition to mortar mix has retarding effect, and with the increase of cellulose ether HPMC content of mortar setting time has been extended, the same HPMC content, underwater forming mortar than in the air forming setting time longer. When measured in water, the setting time of HPMC mixed mortar is compared with the blank specimen, the initial setting delay is 6~18 h, and the final setting delay is 6~22 h. Therefore, HPMC and early strength agents should be used together.

HPMC is a polymer, linear structure of large molecules, functional groups with hydroxyl, can form hydrogen bonds with mixing water molecules, so that mixing water viscosity increase. HPMC long molecular chains will attract each other, so that HPMC molecules intertwine with each other to form a network structure, the cement, mixing water wrapped up. Due to the formation of a similar film network structure and the coating effect of HPMC on cement, will effectively prevent the volatilization of water in mortar, hinder or slow down the hydration rate of cement.

hydrocele

The bleeding phenomenon of mortar and concrete is similar, both of which will cause serious settlement of aggregate, leading to the increase of water-cement ratio of the top slurry, resulting in great plastic shrinkage and even cracking of the top slurry in the early stage, and the strength of the surface layer of slurry is relatively weak.

When the dosage is above 0.5%, there is no longer bleeding phenomenon. This is because when HPMC is mixed into mortar, HPMC has film forming and network structure, as well as the adsorption of hydroxyl group on the long chain of macromolecules, so that cement in mortar and mixing water form flocculation, to ensure the stable structure of mortar. After adding HPMC to mortar, many independent tiny bubbles will be formed. These bubbles will be evenly distributed throughout the mortar, impeding the deposition of aggregate. HPMC This technical performance has a great impact on cement-based materials, often used to prepare such as dry mortar, polymer mortar and other new cement-based composite materials, so that it has good water retention, plastic retention.

Water requirement of mortar

When the content of HPMC is very small, it has great influence on the water requirement of mortar. Under the condition that the expansion degree of newly mixed mortar is basically the same, the HPMC content changes linearly with the water requirement of mortar in a certain period of time, and the water requirement of mortar first decreases and then increases. When the content of HPMC is less than 0.025%, with the increase of the content, the water requirement of mortar decreases under the condition of the same degree of expansion, which indicates that the content of HPMC is small, the mortar has the effect of water reduction, HPMC has the air entraining effect, so that there are a lot of small independent bubbles in the mortar, these bubbles play a lubricating role, so that the mortar fluidity can be improved. When the dosage is greater than 0.025%, the water requirement of mortar increases with the increase of the dosage. This is because the HPMC network structure is further complete, the flocculation gap on the long chain of molecules is shortened, which has the effect of attraction and cohesion, and reduces the fluidity of mortar. So when the degree of expansion is basically the same, the slurry appears to need more water.