Method of Vacuum Pouring Concrete in Steel Tube

Abstract

The invention discloses a method for vacuum pouring concrete in steel pipes, which comprises the following steps: ① preparing steel pipe concrete: adding 0.8%-1.5% by weight water reducer and appropriate amount of expansion agent or anti-shrinkage agent to the concrete, and controlling the water reducer The amount of air-entrained air is less than 2.2% by volume, and fly ash is mixed with 10%-20% by weight; ②In the vacuum perfusion system, the vacuum pressure inside the steel pipe is under the vacuum negative pressure condition of -0.1MPa~-0.09MPa , Use a concrete pump to inject concrete into the steel pipe; ③ Continuously pour concrete into the steel pipe: When the steel pipe is filled with cement slurry and the concrete flows out of the slurry outlet, the construction of pouring concrete is completed. The steel pipe concrete prepared by the invention can effectively reduce the number of air bubbles attached to the pipe wall, improve the compactness of the concrete in the steel pipe, and is beneficial to exert the mechanical properties of the steel pipe concrete structure.

Description

technical field

[0001] The invention relates to a method for pouring concrete in steel pipes, in particular to a method for pouring concrete in steel pipes under vacuum conditions. Background technique

[0002] The CFST structure has the advantages of high bearing capacity, light weight, good plasticity, fatigue resistance, and good seismic performance, so it has been widely used in long-span structures. The tight combination between the steel pipe wall and the core concrete is the key to the synergistic load-bearing effect of the steel pipe concrete structure. In addition to the hollowing phenomenon between the core concrete and the steel pipe wall caused by various shrinkage factors, the core concrete It is also very easy to form a layer of air film between the steel pipe wall and the steel pipe wall, which seriously affects the bonding between the core concrete and the steel pipe wall, thereby affecting the performance of the steel pipe on the core concrete hoop. Conten...

Examples

Embodiment 1

[0033] Preparation of steel tube concrete: Add 0.8% water reducer and a certain amount of expansion agent to the concrete, and control the air-entraining amount of the water reducer below 15%, and mix in different contents of fly ash as shown in Table 1. The prepared concrete has a viscosity of For, fluidity, and yield stress parameters are shown in Table 1. The air content of the concrete is controlled at 2.0%, and the air film produced during the pumping and jacking construction is relatively thin. When the expansion rate of the concrete is above 2.5×10-4 The air film gap formed can then be compensated. The other steps of vacuum pouring the concrete in the steel pipe are the same as above.

[0034] Using cement and different amounts of fly ash (level II) as the cementitious material, the influence of the trial-produced fly ash content on the rheological properties of cement paste is shown in Table 1:

[0035] Table 1 Effect of fly ash on the rheological properties of cement...

Embodiment 2

[0039] Add 0.8% water reducer and a certain amount of expansion agent to the concrete, and the amount of fly ash is 15%. The air content of the concrete mixture has a great influence on the expansion rate of the concrete under the condition of the steel pipe. Therefore, in order to ensure the close combination of concrete and steel pipe wall, the air content of concrete must be limited within a certain range.

[0040] The expansion properties of concrete mixtures with different air contents in each group tested under the condition of closed steel pipes are shown in Table 2.

[0041] Table 2 The expansion rate of concrete under the condition of closed steel pipes (×10 -4 )

[0042]

[0043]The above test results show that when the gas content of steel pipe concrete is 2.3% to 3.0%, under the action of pumping pressure and concrete self-weight, about 0.05% to 0.1% of the concrete volume will be enriched in the inner wall of the steel pipe, which will cause A circular gap wi...

Embodiment 3

[0045] Select 4 groups of test pieces and pump them to the vacuum states of different negative pressures (0, -0.02MPa, -0.06MPa, -0.08MPa) respectively. Other conditions and steps are the same as in Example 1.

[0046] Then take out the cement slurry at the top of the steel pipe, and carry out the rheological properties (viscosity and yield stress) test of the cement slurry to study and analyze the influence of negative pressure on the rheological properties of the cement slurry.

[0047] Table 3 Test results of rheological properties of cement paste under different negative pressures

[0048]

[0049] It can be seen from Table 3 that after the cement slurry is treated with negative pressure, the viscosity and yield stress of the top slurry both decrease to a certain extent, indicating that the cement slurry prepared with this water reducing agent does not segregate and bleed under negative pressure. , will not cause deterioration of the workability of the cement slurry, no...

technical field

[0001] The invention relates to a method for pouring concrete in steel pipes, in particular to a method for pouring concrete in steel pipes under vacuum conditions. Background technique

[0002] The CFST structure has the advantages of high bearing capacity, light weight, good plasticity, fatigue resistance, and good seismic performance, so it has been widely used in long-span structures. The tight combination between the steel pipe wall and the core concrete is the key to the synergistic load-bearing effect of the steel pipe concrete structure. In addition to the hollowing phenomenon between the core concrete and the steel pipe wall caused by various shrinkage factors, the core concrete It is also very easy to form a layer of air film between the steel pipe wall and the steel pipe wall, which seriously affects the bonding between the core concrete and the steel pipe wall, thereby affecting the performance of the steel pipe on the core concrete hoop. Conten...

Examples

Embodiment 1

[0033] Preparation of steel tube concrete: Add 0.8% water reducer and a certain amount of expansion agent to the concrete, and control the air-entraining amount of the water reducer below 15%, and mix in different contents of fly ash as shown in Table 1. The prepared concrete has a viscosity of For, fluidity, and yield stress parameters are shown in Table 1. The air content of the concrete is controlled at 2.0%, and the air film produced during the pumping and jacking construction is relatively thin. When the expansion rate of the concrete is above 2.5×10-4 The air film gap formed can then be compensated. The other steps of vacuum pouring the concrete in the steel pipe are the same as above.

[0034] Using cement and different amounts of fly ash (level II) as the cementitious material, the influence of the trial-produced fly ash content on the rheological properties of cement paste is shown in Table 1:

[0035] Table 1 Effect of fly ash on the rheological properties of cement...

Embodiment 2

[0039] Add 0.8% water reducer and a certain amount of expansion agent to the concrete, and the amount of fly ash is 15%. The air content of the concrete mixture has a great influence on the expansion rate of the concrete under the condition of the steel pipe. Therefore, in order to ensure the close combination of concrete and steel pipe wall, the air content of concrete must be limited within a certain range.

[0040] The expansion properties of concrete mixtures with different air contents in each group tested under the condition of closed steel pipes are shown in Table 2.

[0041] Table 2 The expansion rate of concrete under the condition of closed steel pipes (×10 -4 )

[0042]

[0043]The above test results show that when the gas content of steel pipe concrete is 2.3% to 3.0%, under the action of pumping pressure and concrete self-weight, about 0.05% to 0.1% of the concrete volume will be enriched in the inner wall of the steel pipe, which will cause A circular gap wi...

Embodiment 3

[0045] Select 4 groups of test pieces and pump them to the vacuum states of different negative pressures (0, -0.02MPa, -0.06MPa, -0.08MPa) respectively. Other conditions and steps are the same as in Example 1.

[0046] Then take out the cement slurry at the top of the steel pipe, and carry out the rheological properties (viscosity and yield stress) test of the cement slurry to study and analyze the influence of negative pressure on the rheological properties of the cement slurry.

[0047] Table 3 Test results of rheological properties of cement paste under different negative pressures

[0048]

[0049] It can be seen from Table 3 that after the cement slurry is treated with negative pressure, the viscosity and yield stress of the top slurry both decrease to a certain extent, indicating that the cement slurry prepared with this water reducing agent does not segregate and bleed under negative pressure. , will not cause deterioration of the workability of the cement slurry, no...

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