Improvement effect of hydroxypropyl methyl cellulose (HPMC) on cement-based data
In recent years, with the continuous development of external wall insulation skills, the continuous progress of cellulose production skills, as well as the excellent characteristics of HPMC itself, HPMC has been widely used in the construction industry.
In order to further explore the effect mechanism of
HPMC cellulose ether and cement-based data, the main points of this paper are to study the improvement effect of HPMC on the cohesion function of cement-based data.
Condensed moment
The coagulation time of concrete and cement coagulation time, the influence of aggregate, mortar condensed moment so you can use to replace discussion HPMC for underwater not mar the influence of concrete mixture condensed moment, because the condensed moment by the water-cement ratio of mortar, cement sand ratio effect, so in order to comment on HPMC influence on mortar condensed moment, need fixed water-cement ratio of mortar and mortar.
Response to the test, the participation of HPMC has a significant retarding effect on mortar mixture, and with the addition of HPMC mixing amount of mortar coagulation moment extends successively, under the same HPMC mixing amount, the underwater molding mortar is longer than the air molding coagulation moment.When measuring punctuality in water, the coagulation time of mortar mixed with HPMC was compared with that of blank specimen, the initial setting was delayed by 6~18 h, and the final setting was delayed by 6~22 h.Therefore, HPMC should be used in combination with early strength agent.
HPMC is a high molecular polymer with linear structure of macromolecule and hydroxyl group on the functional group. It can form hydrogen bond with the stirred water molecule, so that the viscosity of stirred water can be added.HPMC long molecular chains will attract each other, making the HPMC molecules wrap each other into a network structure, cement, mixing water wrapped up.Because HPMC forms the network structure of similar film and the coating effect on cement, it can be useful to avoid the evaporation of water in mortar and prevent or slow down the hydration rate of cement.
Secrete water
Similar to the bleeding phenomenon of mortar and concrete, both make the aggregate settlement severe, leading to the increase of water-cement ratio of the top layer of slurry, so that the top layer of slurry in the early onset of great plastic shortening, or even cracking, and the strength of the slurry surface is relatively thin.
When the dosage is above 0.5%, there is no longer any bleeding phenomenon.This is because when HPMC is mixed into mortar, HPMC has film formation and network structure, as well as the adsorption effect of hydroxyl group on the long chain of macromolecules, which makes cement and mixing water form flocculation in mortar, ensuring the stable structure of mortar.Again in the mortar after HPMC, will form many independent small bubbles.These bubbles are distributed evenly throughout the mortar, preventing aggregate from building up.This function of HPMC has a great impact on cement-based data, which is often used to make new cement-based composite data, such as dry mortar, polymer mortar, so that it has excellent water and plastic retention.
Water requirement of mortar
When HPMC content is 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 mixing amount of HPMC changes linearly with the water demand of mortar within a guarding time interval, and the water demand of mortar decreases first and then increases significantly.When the mixing amount of HPMC is less than 0.025%, the water demand of mortar decreases with the increase of the mixing amount and the same extension degree, which indicates that when the mixing amount of HPMC is small, mortar has the effect of reducing water, and HPMC has the effect of air-entraining, so that there are many small independent bubbles in mortar, and these bubbles have a smooth effect, so that the flow of mortar can be improved.When the mixing amount is more than 0.025%, the water demand of mortar increases with the increase of the mixing amount. This is because the network structure of HPMC is further intact, and the voidage of flocculation group on the molecular long chain is shortened, which has the attraction and cohesion effect and reduces the fluidity of mortar.Therefore, when the expansion degree is basically the same, the slurry shows an increase in water demand.
