Hydroxypropyl methylcellulose can improve the dispersion resistance of cement mortar.

Hydroxypropyl methylcellulose is a water-soluble polymer compound. It generally increases the consistency of the mixture by increasing the viscosity of the mixing water. It can be dissolved in water to form a viscous aqueous solution. It is a hydrophilic polymer-materials. Through experiments, we can find that when the amount of naphthalene-based high-efficiency superplasticizer in cement mortar increases, the incorporation of superplasticizer will reduce the dispersion resistance of freshly mixed cement mortar. Why would such phenomenon happen? This is because the naphthalene-based high-efficiency water reducer is a surfactant. When the water reducer is used in cement mortar, it will be oriented on the surface of the cement particles to make the surface of the cement particles have the same charge. This electric repulsion makes the cement particles form the flocculation structure of the cement is dismantled, and the water wrapped in the structure is released, which will cause a part of the loss of cement. At the same time, it was found that with the increase of the content of hydroxypropyl methylcellulose, the dispersion resistance of the freshly mixed cement mortar became better and better.

Strength characteristics of concrete:

In general expressway bridge foundation engineering, the design strength level is C25. According to the basic test, the amount of cement is 400kg, the compounded silica fume is 25kg/m3, the optimal amount of hydroxypropyl methylcellulose is 0.6% of the cement amount, the water-cement ratio is 0.42, the sand ratio is 40%, and the naphthalene series The output of high-efficiency water reducer is 8% of the amount of cement. The concrete specimen in the air has an average strength of 42.6MPa for 28 days, and the underwater concrete with a drop height of 60mm for 28 days has an average strength of 36.4MPa. The strength ratio of forming in air is 84.8%, and the effect is quite remarkable.

1. The addition of hydroxypropyl methylcellulose has an obvious retarding effect on the mortar. With the increase of the content of hydroxypropyl methyl fiber, the setting time of the mortar is extended successively. In the case of the same cellulose ether content, Mortars formed underwater will take longer to set than those formed in air. This feature is beneficial for underwater concrete pumping.

2. The content of hydroxypropyl methyl fiber and the water demand of mortar decreased first and then increased obviously.

3. The fresh cement mortar mixed with HPMC has good cohesive properties and almost no bleeding.

4. Adding hydroxypropyl methylcellulose underwater non-dispersible concrete admixture, controlling the dosage is beneficial to the strength. The pilot project shows that the strength ratio of water-formed concrete and air-formed concrete is 84.8%, and the effect is relatively significant.

5. The incorporation of water reducing agent improves the problem of increased water demand of mortar, but its dosage must be controlled reasonably, otherwise the underwater dispersion resistance of freshly mixed cement mortar will sometimes be reduced.

6. There is little difference in the structure between the cement paste specimen mixed with hydroxypropyl methylcellulose and the blank specimen, and the structure and compactness of the cement paste specimen poured in water and poured in air are not much different. The specimen formed under water for 28 days is slightly crisp. The main reason is that the addition of cellulose ether greatly reduces the loss and dispersion of cement when pouring in water, but it also reduces the compactness of cement stone. In the project, under the condition of ensuring the effect of non-dispersion under water, the dosage of cellulose ether should be reduced as much as possible.