Questions about You Should Know about HPMCMarch 23rd 2023
Cement dispersion resistance is improved by hydroxypropyl methylcellulose
Anti-dispersion is an important technical indicator 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 is added to the viscosity of the mixture by adding the viscosity of the stirring water. It is a hydrophilic polymer material. It can be dissolved in water to form a solution or dispersion. It can be seen from the test that when the content of naphthalene-based superplasticizer increases, the addition of superplasticizer will reduce the dispersion resistance of freshly mixed cement mortar. This is because the naphthalene-based superplasticizer belongs to the surface active agent. When the superplasticizer is added to the mortar, the superplasticizer is oriented on the surface of the cement particles so that the surface of the cement particles has the same electric charge. This electric repulsion makes the cement particles The formed flocculation structure is dismantled and the water wrapped in the structure is released, resulting in the loss of a part of the cement. At the same time, it was found that with the addition of HPMC content, the disintegration resistance of freshly mixed cement mortar became better and better.
Strength characteristics of concrete:
The HPMC underwater non-disintegrating concrete admixture is used in the bridge foundation engineering of the expressway, and the design strength grade is C25. After the basic test, the cement dosage is 400kg, the composite blending silica fume is 25kg/m3, the optimum dosage of HPMC is 0.6% of the cement dosage, the water-cement ratio is 0.42, the sand ratio is 40%, and the output of naphthalene series superplasticizer is 8% of the cement dosage, the concrete specimen in the air is 28d, the average strength is 42.6MPa, the underwater pouring concrete with a drop height of 60mm in the water is 28d, the average strength is 36.4MPa, and the strength ratio of the concrete formed in water to that formed in the air was 84.8%, and the effect was significant.
1. The addition of HPMC has an obvious retarding effect on the mortar mixture. With the addition of HPMC content, the coagulation time of the mortar is successively prolonged. Under the same HPMC content, the mortar formed under water is better than that formed in the air. The agglomeration time is longer. This feature is advantageous for underwater concrete pumping.
2. The freshly mixed cement mortar mixed with hydroxypropyl methylcellulose has good cohesion function, and there is almost no bleeding phenomenon.
3. The content of HPMC and the water demand of mortar are first decreased and then increased significantly.
4. The addition of water reducing agent improves the problem of increasing water demand of mortar, but its content must be controlled reasonably, otherwise the underwater dispersion resistance of freshly mixed cement mortar will sometimes decrease.
5. There is little difference in structure between the cement paste specimens mixed with HPMC and the blank specimens. The structure and compactness of the cement paste specimens poured in water and in the air are not much different. The specimens molded under water for 28d were slightly crispy. The main reason is the participation of HPMC, which greatly reduces the loss and dispersion of cement during pouring in water, but also reduces the compactness of cement stone. In the project, the dosage of HPMC should be reduced as much as possible under the condition of ensuring that the water does not disperse.
6. Adding HPMC underwater non-dispersible concrete admixture, controlling the dosage well 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.