The application of vacuum assisted grouting technology of bookmark0 in Nanjing in Sanqiao, Nanjing, China Sun Lijun (the fourth company of the China Harbour Engineering Co., Ltd., and the second anchorage project in Wuhu, Anhui Province) successfully applied this technology to grouting, and the grouting effect was good.
The vacuum assisted grouting process is currently the most popular prestressed steel squeezing process. In the "National Highway Planning" (1999-2020) of the Ministry of Communications, the "Five Vertical and Seven Horizontal" National Road trunk line from Shanghai to Chengdu (GZ55) National Road, Nanjing spans. The application of Yangtze River's Nanjing Yangtze River Third Bridge construction. The use of vacuum-assisted grouting technology in Nanjing Sanqiao is now being introduced for similar projects.
1 Vacuum assisted grouting process principle and characteristics Vacuum assisted grouting process is based on the traditional grouting, the metal bellows is modified into a PT-PLUSR plastic bellows, after sealing the hole system, one end with a vacuum pump to 80% The above air is pumped out, and the vacuum degree of the channel is ensured to be about 80%. At the same time, the cement slurry with the water-cement ratio of 0.29-0.35 is pressed into the slurry at the grouting end. When the cement slurry flows out from the vacuum end and the consistency is basically the same as the squeezing end, the specific The slurry (drainage and micro-plasma slurry) is maintained under pressure to ensure that the cement slurry in the tunnel is full. There may be no observation hole in the middle of the pipe, and a certain number of observation holes may also be provided as required. However, attention must be paid to ensure the sealing performance of the observation hole when vacuum is used to prevent the observation hole from leaking and leading to vacuum failure.
Vacuum assisted grouting principle as shown.
Vacuum assisted grouting process features: It can reduce or eliminate bubbles caused by ordinary grouting method. At the same time, the remaining water droplets in the channel are vaporized near the vacuum and are extracted together with the air to enhance the density of the slurry.
Auxiliary chief engineer of D1 standard project of the Third Bridge of Yangtze River Vacuum-assisted grouting principle After the squeezing slurry enters the hole, bubbles mixed in the slurry can easily escape to avoid the accumulation of harmful water in the vicinity of the prestressed tendon, resulting in excellent corrosion of the prestressed tendon. The slurry is designed so that there is little or no problem such as water evolution or hard shrinkage. In the vacuum state of the cell, the pressure difference formed by the slurry itself due to the high and low curvature of the cell channel is reduced, and the slurry is easy to fill the entire cell. The curved, U-shaped, and vertical prestressed tendon channels can better reflect its superiority. The application of the vacuum-assisted grouting process in Nanjing Sanqiao The Nanjing Sanqiao Approach Bridge D1 uses a height of 28m and a standard span of 50m. Box beams with YM 4 (flat bellows) and other types of anchors have a maximum beam length of 58.4m. Selection of prestressed materials The main prestressed materials that satisfy the vacuum assisted grouting process include plastic bellows and anchors with good airtightness. Wait. The main prestressed materials used in this project are shown in Table 1. The holes of the prestressed steel bundles used in this project are PT-PLuS15 plastic corrugated pipes (see VSL China) produced by Weisheng Engineering Co., Ltd. (see VSL China), and used with gold sheet 1 prestressed materials. Condition profile prestressed steel beam model bellows model anchorage model production 1YMP15-9 Hefei geological anchor factory 15-(bundle) PT-PLUS21mm Friction resistance is small, the friction coefficient value range is generally 0. 12~0.14 The pipe deviation coefficient k is in the range of 0.0008~0.001; good sealing, corrosion resistance, no rust, and conducive to the protection of steel strands; non-conductive, can protect the prestressed steel bars against stray current, and prevent steel strand PT -PLUS' plastic corrugated pipe diagram is inflamed; high strength, high stiffness, not easily vibrated by the vibrating rod; weldable connection, no need for additional fittings, low material loss, remaining stub tube can still be used.
The prestressed steel beam anchors used in this project are Hefei geological anchorage plants specially produced for this project and have good airtight properties. In order to achieve good airtightness, caps are added to the ends of the anchor seats (see ) An O-ring seal is installed between the anchor seat and the cap. The components of the various components such as vacuum-assisted grouting process, the important equipment for the vacuum pump and squeezing pump vacuum pumping capacity required to achieve -0.08 ~-0.lMPa grouting pump with a better airtight screw grouting pump, Its motor power is 3kw maximum pressure 25MPa grouting capacity 3m3/h, horizontal cement slurry transport distance 400m vertical cement slurry transport distance 90m screw type grouting pump can continuously press the slurry into the pipeline, so as to avoid the air into the people In order to improve the quality of the slurry, the cement slurry mixer must use a high-speed pulper at 1400r/min. 3 Design of cement slurry The design of the mix ratio of the cement slurry is the key to the vacuum assisted grouting. The vacuum-assisted grouting mortar should reduce the water-cement ratio. Reduce pores, bleeding, eliminate segregation, and reduce and compensate the shrinkage deformation of cement slurry in the process of condensation, prevent the production of cracks to make it have higher compressive strength and effective bond strength to achieve the above properties The HF type mortar special additive developed by VSL was selected. This additive has the effects of reducing water, retarding and micro-expansion (without aluminum powder), and improves the fullness of the grouting. At the same time, a good plasticizer in the admixture keeps the slurry in a sufficiently viscous liquid state, giving the slurry excellent anti-segregation, anti-hygrogenicity and anti-shrinkage properties. The body adopts a water-cement ratio of 0.33 and the admixture dosage is 4*~5%. The cement used in the cement produced by the Nanjing Conch Cement Plant is a bag of P.042.5 cement. The mud has the following features: 33 (“Highway bridge letter construction†Technical specifications (JTJ041-2000) stipulate that the water-cement ratio of ordinary grouting slurry generally takes 0. 18s; within 45min, the consistency of slurry should not change more than 2s bleeding rate: after 3h of cement slurry, it Bleeding rate is less than 2%; and bleeding should be completely absorbed by the slurry within 24h Retarding time: The initial setting time is not less than 3h, the final setting time should be greater than the compressive strength: under standard curing conditions, its 7d instar The strength should not be less than 25MPa. After 28d age, the compressive strength of the slurry is not less than 50MPa and the expansion rate is about 2% when it reaches 28d strength.
4Construction operation at the end, strict construction operations, in order to achieve good grouting effect. Preparation before construction: After the tensioning process is completed, cut the exposed strand to ensure that the exposed length of the strand does not exceed 30mm (shown by the manufacturers Anchors;) Clean the anchor plate; evenly apply a layer of glass glue in the seal groove, install "O*-shaped sealing ring and cap, the exhaust hole is placed vertically upwards when the cap is installed, the bolt is screwed into the gasket Screw hole and tighten.
Install grouting equipment and piping as shown (see). The pipe connecting the slurry hole and the vacuum pump must be made of transparent plastic steel pipe, so that it can meet the requirement that the pipe is not crushed under vacuum, and at the same time, the discharge condition of the cement slurry can be conveniently observed. The length of the pipe from the slot to the valve 1 (see) is generally not less than 5m, so that when the slurry is discharged, there is sufficient time to control the valve to prevent the slurry from entering the vacuum pump.
Close valve 3 valve 4, open valve 1 valve 2, start the vacuum pump to vacuum, when the vacuum reaches -0.08MPa, you can open the valve 4, start the grouting pump to start grouting if the vacuum degree can not meet the requirements, should stop vacuuming After inspecting each connecting part to make the airtightness meet the requirements, the vacuum pump shall be activated to keep the vacuum pump open. When it is observed that there is slurry passing through the transparent three-way pipe between valve 1 valve 2 valve 3, the vacuum pump is turned off immediately. Valve 2, and open the valve 3. Observe the situation leading to the slurry in the waste slurry barrel, when the consistency of the slurry and the press-in side, turn off the valve 3, still grouting, so that the pipeline has 0. 5 ~ 0.7 MPa pressure, hold pressure for 2min, then turn off the valve 4 to remove the parts except the valve 1 valve 4 and clean, and then received another set of holes grouting the hole vacuum grouting to be continuous, once completed if it can not be timely When removing the fault, immediately remove the grouting pipe and flush the hole with high-pressure water. When the fault is re-pressed and grouted, the slurry temperature of the cement slurry should not be too high, preferably below 35C. . During grouting, the consistency of the discharged cement slurry and the cement paste at the press-in end is checked through the initial setting of the cement slurry, and the slurry in the discharge tube and the grouting hole is very full. The actual amount of cement used and the theoretical amount are also very consistent. Photographs taken at the construction site are as shown.
The squeezing site photographs real shot 5 Destructive test Plastic bellows, both ends of the installation of seals in accordance with the actual construction method. Vacuum In order to verify the success of vacuum grouting in this project, a destructive vacuum grouting test was performed. First make a 6m long model. In the model installation 6 Conclusion Vacuum assisted grouting can make the cement slurry in the prestressed pipeline full and dense, so that the prestressed tendons are not rusted and the durability of the structure is enhanced = Vacuum assisted grouting as a high level Construction technology, its successful implementation is mainly controlled by the following factors: The vacuum condition is properly completed and created in the pipeline. This requires the installation of special anchorages and good plastic bellows. In addition, the slurry with no water design in the pipeline has good performance.
Configure special equipment such as vacuum pumps, grouting pumps, well-tight pipes and pipe connections. In addition, high-speed slurry mixers must be equipped with correct and strict construction procedures and rigorous and skilled operators and managers.
Satisfying all conditions, strictly controlling every step of construction, vacuum assisted grouting can be successful; applying only strict control at the same time to achieve the purpose of vacuum assisted grouting in order to truly reflect its superiority.
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