Preparation method and application of composite magnesium oxide expanding agent

A magnesium oxide and composite technology, which is applied in the field of preparation of special functional materials for concrete, can solve problems such as low ability to compensate shrinkage, difficult-to-harden concrete, and failure strength, and achieve good expansion efficiency, increased long-term strength, and high safety.

Inactive Publication Date: 2019-07-19
TSINGHUA UNIV
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  • Abstract
  • Description
  • Claims
  • Application Information

AI Technical Summary

Problems solved by technology

However, in the existing technology of preparing magnesium oxide expansion agent by replacing part of magnesite with dolomite, there is also a large amount of calcium oxide in the product. The early hydration of calcium oxide is too rapid, it is difficult to produce effective expansion inside the hardened concrete, and it may damage the The problem of the slurry structure of the initial cementitious material with low strength
[0005] Xu Lingling et al. used dolomite and serpentine to prepare magnesia expansion agent. The calcination temperature was higher than 1200°C, and the calcination time was 2h. The magnesia content in the fired expansion agent was higher than 50%, but the activity was extremely low (using the current Measured by the standard method, the activity index is higher than 500s), and the expansion time at 40°C is 80 days later, and the ability to compensate for the shrinkage of ordinary concrete structures is very low

Method used

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  • Preparation method and application of composite magnesium oxide expanding agent
  • Preparation method and application of composite magnesium oxide expanding agent
  • Preparation method and application of composite magnesium oxide expanding agent

Examples

Experimental program
Comparison scheme
Effect test

Embodiment 1

[0023] Composite magnesium oxide expansion agent is prepared according to the following steps:

[0024] (1) Dolomite and serpentine are used as raw materials, wherein the MgO content in dolomite is not less than 15%; the MgO content in serpentine is not less than 30%, Al 2 o 3 +Fe 2 o 3 The content is not higher than 15%; grind dolomite and serpentine so that the mass fraction of the 80 μm sieve of the raw material powder after grinding is less than 3%; fully mix dolomite and serpentine powder so that Ca and Si in the mixed powder The molar ratio is (1.9-2.0):1.

[0025] (2) Put the mixed powder obtained in step (1) into a kiln for firing, the calcination temperature is 1050°C, and the calcination time is 1 hour; after the calcination is completed, it is quenched in the air and avoids contact with water vapor; finally ground, and made If the mass fraction of the 80 μm sieve of the powder is less than 10%, the high-activity composite magnesium oxide expansion agent is obtai...

Embodiment 2

[0028] The difference from Example 1 is that the calcination temperature is 1100° C., and a composite magnesium oxide expansion agent with medium activity is obtained.

[0029] When mixing concrete in a ready-mixed concrete factory, mix 15-20 parts of composite magnesium oxide expansion agent, 10-30 parts of fly ash, 5-20 parts of finely ground mineral powder, 5-10 parts of silicon powder, silicic acid 20-60 parts of salt cement is blended as a cementitious material, the water-to-cement ratio is 0.3-0.55, and coarse and fine aggregates are added according to the concrete mix ratio design specification JGJ55 to prepare concrete. Cured under the conditions of 40°C and RH greater than 90%, the expansion time of the medium-active composite magnesium oxide expansion agent is 42 days; the expansion rate can reach the standard of 0.02%-0.05% for the long-term stability of the plastic sand.

Embodiment 3

[0031] The difference from Example 1 is that the calcination temperature is 1150° C., and a composite magnesium oxide expansion agent with low activity is obtained.

[0032] When mixing concrete in a ready-mixed concrete factory, mix 15-20 parts of composite magnesium oxide expansion agent, 10-20 parts of fly ash, 5-30 parts of ground mineral powder, 5-10 parts of limestone powder, silicic acid 20-60 parts of salt cement is blended as a cementitious material, the water-to-cement ratio is 0.3-0.55, and coarse and fine aggregates are added according to the concrete mix ratio design specification JGJ55 to prepare concrete. Cured under the conditions of 40°C and RH greater than 90%, the expansion time of the low-activity composite magnesium oxide expander is 120 days. The expansion rate can reach the standard of 0.03%-0.07% of the long-term stability limit expansion rate of the mortar.

[0033]According to the standard test method of free linear expansion rate (the sum of expansi...

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Abstract

The invention discloses a preparation method and application of a composite magnesium oxide expanding agent, and belongs to the technical field of preparation of concrete special functional materials.The preparation method specifically comprises the following step: calcining a dolomite and serpentine mixture with a specific ratio at the temperature of 1050-1150 DEG C for 60 minutes to obtain thecomposite magnesium oxide expanding agent. The obtained composite magnesium oxide expanding agent has high volume expansion rate, the reaction activity of the composite magnesium oxide expanding agentis reduced along with increasing of the calcination temperature, and the composite magnesium oxide expanding agent is mainly used for compensating long-term shrinkage of mass concrete. The preparation method provided by the invention not only can greatly reduce the production cost of the magnesium oxide expanding agent, but also can treat industrial tailings and realize resource utilization.

Description

technical field [0001] The invention belongs to the technical field of preparation of concrete special functional materials, in particular to a preparation method and application of a composite magnesium oxide expansion agent. Background technique [0002] During the molding and hardening process of concrete, volume shrinkage will occur due to the hydration and drying loss of cementitious materials, temperature changes and other reasons. When the component is constrained, internal stress will be generated inside the concrete, and cracks will occur when the internal tensile stress is greater than the tensile strength of the concrete. Shrinkage cracking of mass concrete will reduce the physical and mechanical properties of concrete structures, which is a major concern in the field of concrete engineering. Add magnesium oxide expansion agent to the concrete. Magnesium oxide hydrates to form magnesium hydroxide crystals during the hydration and hardening process of concrete. Ma...

Claims

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Application Information

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Patent Type & Authority Applications(China)
IPC IPC(8): C04B22/08C04B28/04
CPCC04B28/04C04B40/0039C04B22/066C04B22/08C04B18/08C04B18/141C04B18/146C04B14/28
Inventor 阎培渝曹丰泽
Owner TSINGHUA UNIV
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