Experimental effect of hydroxypropyl methylcellulose in mortar

With the progress of science and technology, the continuous development of external wall insulation technology, the continuous progress of HPMC production technology, and the excellent characteristics of HPMC, HPMC has been widely used in the construction industry. In order to further explore the mechanism of HPMC and cement-based materials, Shandong chuangyao Biotechnology Co., Ltd. focuses on the improvement effect of HPMC on the cohesiveness of cement-based materials.

setting time 

The setting time of concrete is mainly related to the setting time of cement, and the influence of aggregate is not obvious. Therefore, the setting time of mortar can be used to study the influence of HPMC on the setting time of underwater non dispersible concrete mixture. Since the setting time of mortar is affected by water cement ratio and cement sand ratio, so in order to evaluate the influence of HPMC on the setting time of mortar, it is necessary to strengthen Determine the water cement ratio and mortar ratio of mortar.

The experimental results show that HPMC has obvious retarding effect on mortar mixture, and the setting time of mortar increases with the increase of HPMC content. The setting time of mortar formed under water is longer than that in air with the same HPMC content. Compared with blank specimens, the setting time of HPMC mortar is delayed by 6 ~ 18 h in water and 6 ~ 22 h in final setting. Therefore, HPMC should be combined with early strength agent.

HPMC is a high molecular polymer with linear macromolecular structure and hydroxyl groups. It can form hydrogen bond with mixing water molecules and increase the viscosity of mixing water. The long molecular chains of HPMC will attract each other, which makes HPMC molecules entangle with each other and form a network structure to wrap cement and mixing water. HPMC can effectively prevent the evaporation of water in mortar and retard or slow down the hydration rate of cement due to the formation of network structure similar to film and the wrapping effect on cement.

Bleeding 

Similar to the bleeding phenomenon of concrete and mortar, the aggregate settlement will be serious, resulting in the increase of water cement ratio of the top slurry, which makes the top slurry have a great plastic shrinkage and even cracking in the early stage, and the strength of the slurry surface is relatively weak. When the content is more than 0.5%, there is no bleeding phenomenon. This is because when HPMC is added into mortar, HPMC has film-forming and network structure, and the adsorption of hydroxyl groups on macromolecular long chain, which makes cement and mixing water in mortar form flocculation, which ensures the stable structure of mortar body. When HPMC is added into 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 property of HPMC has a great influence on cement-based materials. It is often used to prepare new cement-based composite materials such as dry powder mortar and polymer mortar, so that it has good water retention and plastic retention.

Water requirement of mortar

When the content of HPMC is very small, it has a great influence on the water demand of mortar. Under the condition of keeping the expansion degree of fresh mortar basically the same, the content of HPMC changes linearly with the water demand of mortar in a certain period of time, and the water demand of mortar first decreases and then increases obviously. When the content of HPMC is less than 0.025%, with the increase of HPMC content, the water demand of mortar decreases under the same expansion degree, which indicates that the water reducing effect of HPMC is small, and the air entraining effect of HPMC makes mortar have a large number of small independent bubbles, which play a lubricating role and make the mortar flow

Mobility was improved. When the content of HPMC is more than 0.025%, the water demand of mortar increases with the increase of the content. This is because the network structure of HPMC is more complete, the flocculation group gap on the molecular long chain is shortened, and the fluidity of mortar is reduced.

Therefore, when the expansion degree is basically the same, the water demand of slurry increases.

Anti dispersion test:

Anti dispersion is an important technical index to measure the quality of anti dispersant. HPMC is a water-soluble polymer, also known as water-soluble resin or water-soluble polymer. It increases the consistency of the mixture by increasing the viscosity of the mixing water. It is a hydrophilic polymer material, which can be dissolved in water to form a solution or dispersion.

It can be seen from the experiment that when the content of naphthalene superplasticizer increases, the addition of superplasticizer will reduce the anti dispersion of fresh cement mortar. This is because naphthalene superplasticizer belongs to surfactant. When water reducer is added to mortar, the water reducer will make directional arrangement on the surface of cement particles, so that the surface of cement particles will have the same charge. This electric repulsion force makes the flocculation structure formed by cement particles be disassembled, and the water wrapped in the structure will be released, which will cause the loss of some cement. At the same time, it is found that with the increase of HPMC content, the anti dispersion of fresh cement mortar becomes better and better.

Strength characteristics of concrete:

HPMC underwater non dispersible concrete admixture with HPMC was applied in a pilot foundation project, and the design strength grade was C25. According to the basic test, the optimum content of HPMC is 0.6% of cement, water cement ratio is 0.42, sand ratio is 40%, naphthalene superplasticizer is 8% of cement dosage, the average 28d strength of concrete in air is 42.6mpa, and the average 28d strength of underwater concrete with falling height of 60mm in water is 36.4mpa The strength ratio of molding in soil and air is 84.8%

By.

The experimental results showed that: 1

(1) The addition of HPMC has obvious retarding effect on mortar mixture. With the increase of HPMC content, the setting time of mortar is prolonged. Under the same HPMC content, the setting time of underwater molding mortar is longer than that in air. This feature is beneficial to underwater concrete pumping.

(2) The fresh cement mortar mixed with HPMC has good cohesiveness and almost no bleeding phenomenon.

(3) The content of HPMC and water requirement of mortar decreased at first and then increased obviously.

(4) The addition of water reducing agent can improve the water requirement of mortar, but it must be controlled reasonably, otherwise the underwater anti dispersion property of fresh cement mortar will be reduced.

(5) There is no significant difference in the structure between the cement paste specimens mixed with HPMC and the blank specimens, and there is no significant difference in the structure and compactness of cement paste specimens poured in water and in air. The specimens formed under water for 28 days are slightly loose. The main reason is that the addition of HPMC greatly reduces the loss and dispersion of cement, but also reduces the compactness of cement paste. In the project, the amount of HPMC should be reduced as much as possible under the condition that the underwater dispersion effect is guaranteed.

(6) The results show that the strength ratio of concrete in water and in air is 84.8%, and the effect is remarkable.

For more information on the role of HPMC in mortar, please pay attention to Shandong chuangyao Biotechnology Co., Ltd.