Hydroxypropyl methylcellulose can improve the dispersion resistance of cement!
Anti dispersion is an important technical index to measure the quality of anti dispersant. Hydroxypropyl methylcellulose is a water-soluble polymer compound, also known as water-soluble resin or water-soluble polymer. It adds the consistency of the mixture by adding the viscosity of the stirring water. It is a hydrophilic polymer material that can be dissolved in water to form a solution or lax solution. The test shows that when the content of naphthalene superplasticizer increases, the addition of superplasticizer will reduce the anti laxity of fresh cement mortar. This is because naphthalene superplasticizer belongs to exterior active agent. When the superplasticizer is added to the mortar, the superplasticizer is placed directionally on the surface of the cement particles, so that the surface of the cement particles has the same charge. This electric repulsion makes the flocculation structure composed of cement particles be disassembled, releasing the water wrapped in the structure, which will form the loss of some cement. It is found that with the addition of HPMC, the anti laxity of fresh cement mortar is getting better and better.
Strength characteristics of concrete:
HPMC underwater non lax concrete admixture is applied in the bridge foundation engineering of expressway, and the design strength grade is C25. Through the foundation test, the cement dosage is 400kg, the compound mixing of silica fume is 25kg / m3, the optimal mixing amount of HPMC is 0.6% of the cement dosage, the water cement ratio is 0.42, the sand rate is 40%, the output of naphthalene superplasticizer is 8% of the cement dosage, the concrete specimen in the air is 28d, the average strength is 42.6mpa, the underwater concrete with a falling height of 60mm in the water is 28d, and the average strength is 36.4mpa, The strength ratio of concrete formed in water and air is 84.8%, which has a significant effect.
The participation of HPMC has obvious retarding effect on the mortar mixture. With the addition of HPMC content, the coagulation time of mortar is extended successively. Under the condition of the same HPMC content, the coagulation time of mortar formed underwater is longer than that formed in air. This feature is favorable for underwater concrete pumping.
The fresh cement mortar mixed with hydroxypropyl methylcellulose has good cohesion function and almost no bleeding phenomenon.
HPMC content and mortar water demand are first reduced and then significantly increased.
The addition of water reducing agent improves the problem of increasing water demand of mortar, but its dosage must be controlled reasonably, otherwise the underwater anti laxity of fresh cement mortar will be reduced sometimes.
There is little difference in the structure between the cement paste specimen mixed with HPMC and the blank specimen, and there is little distance between the structure and compactness of the cement paste specimen poured in water and in air. The specimens formed under water for 28 days are slightly crisp. The main reason is that the participation of HPMC has greatly reduced the loss and laxity of cement during pouring in water, but also reduced the compactness of cement stone. In the project, the amount of HPMC shall be reduced as far as possible under the condition of ensuring no lax action under water.
Adding HPMC underwater non dispersible concrete admixture is beneficial to the strength. The pilot project shows that the strength ratio of concrete formed in water to that formed in air is 84.8%, which has a significant effect.