Dispersion resistance is an important technical index to measure the quality of anti – dispersant. Hydroxypropyl methyl cellulose is a water-soluble polymer compound, 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 kind of hydrophilic polymer material, which can be dissolved in water and form a solution or dispersible liquid. Experiments show that when the amount of naphthalene system superplasticizer increases, the addition of superplasticizer will reduce the dispersion resistance of fresh cement mortar. This is because the naphthalene series high efficient water reducing agent belongs to the surface active agent, when the water reducing agent added to the mortar, the water reducing agent in cement particle surface oriented surface of cement particles with the same charge, the electric repulsion flocculation structure of cement particles formed by dividing, wrap in the structure of water release, will cause the loss of part of the cement. At the same time, it is found that with the increase of HPMC content, the anti dispersion of fresh cement mortar is better and better.

Strength characteristics of concrete:

HPMC underwater non-dispersive concrete admixture was applied in the bridge foundation engineering of the expressway, and the design strength grade was C25. After the basic test, cement dosage is 400kg, compound mixed silica fume 25kg/m3, HPMC optimum dosage is 0.6% of cement dosage, water cement ratio is 0.42, sand rate is 40%, naphthalene high efficiency water reducing agent yield is 8% of cement dosage, the concrete specimen in air 28d, the average strength is 42.6MPa, The average strength of the underwater poured concrete with a falling height of 60mm in water is 36.4mpa for 28 days, and the strength ratio of the concrete formed in water and the concrete formed in air is 84.8%, showing a significant effect.

1. The addition of HPMC has an obvious retarding effect on mortar mixture. With the increase of HPMC dosage, the setting time of mortar is prolonged successively. Under the same condition of HPMC dosage, the setting time of underwater mortar is longer than that of air. This feature is beneficial for underwater concrete pumping.

2, mixed with hydroxypropyl methyl cellulose of fresh cement mortar has good cohesion, almost no bleeding phenomenon.

3, HPMC dosage and mortar water demand first decreased and then increased significantly.

4. The incorporation of water reducer improves the problem of increasing water demand for mortar, but it must be reasonably controlled, otherwise it will sometimes reduce the underwater dispersion resistance of fresh cement mortar.

5. There is little difference in structure between HPMC mixed cement net slurry specimens and blank specimens, and there is little difference in structure and compactness between water poured cement specimens and air poured cement net slurry specimens. The 28d underwater molding specimen is slightly loose. The main reason is that the addition of HPMC greatly reduces the loss and dispersion of cement during water pouring, but also reduces the degree of cement compaction. In the project, under the condition of ensuring the underwater non-dispersion effect, the mixing amount of HPMC is reduced as far as possible.

6, add HPMC underwater does not disperse concrete admixture, control the amount of good strength, the pilot project shows that the strength ratio of forming concrete in water and forming in air is 84.8%, the effect is more significant.