Anti-dispersion is an important technical index to measure the quality of anti-dispersion agent. Hydroxypropyl methylcellulose 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 hydrophilic polymer material. It can be dissolved in water to form a solution or dispersion. Experiments show that when the amount of naphthalene-based high-efficiency superplasticizer increases, the addition of superplasticizer will reduce the dispersion resistance of freshly mixed cement mortar. This is because the naphthalene-based high-efficiency water reducer is a surfactant. When the water reducer is added to the mortar, the water reducer 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 the loss of part of the cement. At the same time, it is found that with the increase of HPMC content, the dispersion resistance of fresh cement mortar is getting better and better.
01. The addition of HPMC has an obvious retarding effect on the mortar mixture. With the increase of HPMC content, the setting time of mortar is extended successively. Under the same HPMC content, the mortar formed under water is faster than that in air Molding takes longer to set. This feature is beneficial for underwater concrete pumping.
02. The addition of water reducing agent improves the problem of increased water demand for mortar, but its dosage must be controlled reasonably, otherwise the underwater dispersion resistance of freshly mixed cement mortar will sometimes be reduced.
03. There is little difference in the structure between 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 poured in water and in air. The specimen formed under water for 28 days is slightly crisp. The main reason is that the addition of HPMC greatly reduces the loss and dispersion of cement when pouring in water, but 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 HPMC should be reduced as much as possible
The HPMC underwater non-dispersible concrete admixture is used in the bridge foundation engineering of the expressway, and 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 HPMC is 0.6% of the cement amount, the water-cement ratio is 0.42, the sand rate is 40%, and the output of naphthalene-based high-efficiency water reducer is The amount of cement is 8%, the concrete specimen in the air for 28 days, the average strength is 42.6MPa, the underwater concrete with a drop height of 60mm for 28 days, the average strength is 36.4MPa, the strength ratio of the water-formed concrete and the air-formed concrete 84.8%, the effect is more significant.
Post time: Apr-24-2023