Hydroxypropyl methylcellulose is a water-soluble polymer compound, also known as water-soluble resin or water-soluble polymer. It thickens the mixture by increasing the viscosity of the mixing water. It is a hydrophilic polymer material. It can be dissolved in water to form a solution or dispersion. Experiments show that when the amount of naphthalene-based superplasticizer increases, the incorporation of superplasticizer will reduce the dispersion resistance of freshly mixed cement mortar. This is because the naphthalene superplasticizer is a surfactant. When the water reducing agent is added to the mortar, the water reducing agent is arranged on the surface of the cement particles, so that the surface of the cement particles has the same charge. This electric repulsion disintegrates the flocculation structure formed by cement particles, and the water wrapped in the structure is released, resulting in the loss of part of the cement. At the same time, it was found that with the increase of HPMC content, the dispersion resistance of fresh cement mortar became better and better.
Strength properties of concrete:
HPMC underwater non-dispersible concrete admixture is used in highway bridge foundation engineering, and the design strength level is C25. According to the basic test, the amount of cement is 400kg, the amount of microsilica is 25kg/m3, the optimal amount of HPMC is 0.6% of the cement amount, the water-cement ratio is 0.42, the sand ratio is 40%, and the output of naphthyl superplasticizer is 8% of the cement amount. , The concrete specimens in the air for 28 days have an average strength of 42.6MPa, and the concrete poured underwater for 28 days with a water drop of 60mm has an average strength of 36.4 MPa.
1. The addition of HPMC has obvious retarding effect on the mortar mixture. With the increase of HPMC content, the setting time of mortar gradually prolongs. Under the same HPMC content, the mortar formed underwater is better than the mortar formed in air. The solidification time of molding is longer. This feature facilitates underwater concrete pumping.
2. Fresh cement mortar mixed with hydroxypropyl methylcellulose has good bonding performance and hardly bleeds.
3. The content of HPMC and the water demand of mortar decreased firstly and then increased significantly.
4. The incorporation of water reducing agent improves the problem of increased water demand for mortar, but it must be controlled reasonably, otherwise it will sometimes reduce the underwater dispersion resistance of freshly mixed cement mortar.
5. There is little difference in the structure of the cement paste specimen mixed with HPMC and the blank specimen, and there is little difference in the structure and density of the cement paste specimen in pouring water and air. The sample formed after 28 days underwater is slightly loose. The main reason is that the addition of HPMC greatly reduces the loss and dispersion of cement during pouring in water, but also reduces the compactness of cement stone. In the project, the amount of HPMC should be reduced as much as possible while ensuring the effect of non-dispersion under water.
6. The combination of HPMC underwater non-dispersible concrete admixture, the control of the amount is conducive to the improvement of strength. Pilot projects have shown that the concrete formed in water has a strength ratio of 84.8% of that formed in air, and the effect is even more significant.
Post time: Jun-16-2023