Application of vacuum grouting in Xiebian overpass
The core tips: 1 The necessity of vacuum grouting The purpose of grouting post-tensioned prestressed components: First, prevent the prestressed beam from being rusted, and the durability of the strong prestressed components; Second, fill the holes of the prestressed bundles to form the components as a whole. ,Transmitting prestressing and preventing the relaxation of prestressed tendons therefore requires that the grouting of the hole must be full, and the solidified water

1 The necessity of vacuum grouting The purpose of grouting the post-tensioned prestressed components is to prevent the prestressed strands from being rusted and the durability of the strong prestressed components. The second is to fill the prestressed bundle channels and form the components as a whole. Stress and prevention of relaxation of prestressed tendons therefore requires that the grouting of the channels must be full, and that the solidified cement paste be dense and shrink less (even not shrink), and has a certain strength. Practice has proved that the grouting quality using ordinary pressure grouting process is often Unsatisfactory, there is a large shrinkage of the slurry, the pipeline is not full, etc., mainly due to the instability of the quality of the cement slurry, resulting in leakage of pulp and other reasons caused by the need to ensure or improve the quality of ordinary pressure grouting, from the technical measures Must improve the performance of cement slurry, such as reducing the water-cement ratio, adding additives, etc.; from the technical measures as far as possible to do the sealing work of the pipeline, to eliminate the mixed air in the slurry, plus the slurry density of vacuum grouting is to solve The vacuum grouting that arises from the problems mentioned above is the first step of using a vacuum pump to draw out the air in the tunnel, requiring a negative pressure of about 0.1 MPa in the hole. This requires that the anchor must be tight. Vacuum grouting is vacuum edging while maintaining a negative pressure of about 0.1 MPa in the channel, which is beneficial to the discharge of mixed air in the slurry, which is conducive to denseness of the slurry, and is equivalent to applying a pulling force to the slurry. Reducing the load on the grouting press and reducing the difficulty of squeezing from another point of view means that the water-cement ratio of the cement slurry can be further reduced, the compactness and strength of the slurry can be increased, and the shrinkage of the slurry can be reduced. 2 Overview of Xiebian overpass The upper structures of the Xiebian overpass are all prestressed concrete continuous box girders with a span of 24-35m. Women's 4-span box-girder bridges have a complex change in the curvature of the plane line. The minimum radius is 50m with a 015.24 strand, and the prestressed pipeline is double-helixed. Galvanized corrugated pipe forming, 7-9cm internal diameter corrugated pipe longitudinal profile line complex, each with 3 - 4 vertical undulations, vertical minimum radius of 15m continuous box girder prestressed pipe grouting all use vacuum grouting 3 construction Process 3.1 Pipe Requirements Vacuum grouting requires that the bellows have sufficient rigidity, the installation is firm, the joints are tightly sealed, the wires are smooth, and the inlet and exhaust ports are smooth to facilitate the possibility of residue in the discharge pipe. The remaining air ensures that the pipeline is full of slurry, and an exhaust pipe is embedded in each peak of the pipeline.

The negative pressure of 1MPa requires that both ends of the pipe must be sealed. Xiebian overpass uses cement mortar to seal the anchor. After the strand is stretched, let the strand protrude only about 5cm from the anchorage. When the rest of the strands are cut off with a portable grinder, the cement paste is used to fill the gap between the clips and between the clip and the strand. , Then use cement mortar to wrap all clips and exposed strand ends. Cover thickness is greater than 2cm. Package after curing 24h and then grouting. 3.2 Machine preparation Vacuum grouting required equipment includes: 1 slurry machine, filter 1 sheet, 1 slurry tank, 1 mechanical piston press, 20m pressure tube, 1 ball valve, 1 high-strength transparent hose, 1 QSL-20 air filter, 1 pressure gauge, SZ- A type 2 vacuum pump is used, and the connection of several devices of the water pipe is shown as shown.

3.3 Test vacuum equipment connection Connect the machine tool as shown (not connected before the feed valve), close the feed valve, drain valve, open the exhaust valve, vacuum valve, open the circulating water outlet, start Vacuum pump, observe the pressure gauge reading, when the pressure gauge reaches -0l06~-0.1MPa stable reading, then grouting; otherwise, you should re-check the seal at each place, and then try vacuum pumping 3.4 cement paste preparation vacuum grouting process In the middle, the quality of cement paste is the key to the quality control of grouting. The main measure to require the shrinkage, compactness and strength of the paste after hardening is to reduce the water-cement ratio of the slurry as much as possible, and by adding a certain proportion The water-reducing agent adds the fluidity of the slurry, and the expansion agent is added to make up for the shrinkage produced when the slurry hardens. The mix ratio of cement paste is: 40S, the maximum bleeding rate is 25%, and the bleeding is completely absorbed by the slurry within 24 hours, the free expansion rate is 2%, the strength at 3d is 34MPa, and the strength at 28d is 50MPa. 3.5 squeezing The slurry is moistened with water. Put the remaining amount of water into the mixture before pouring the remaining water. Then start the mixer and stir. After the mixture is mixed (about 3-5 minutes), pass the filter to the cement. The storage capacity of the slurry slowly poured into the storage tank of the storage tank must be greater than the volume of the cement slurry needed for a pipeline to ensure continuous grouting. The slurry storage tank also has a stirring function. Before the cement slurry is not filled, the stirring and shutting-in of the slurry inlet valve, the discharge valve, the opening of the exhaust valve, the vacuum valve, the opening of the circulation water outlet, the start of the vacuum pump, and the pressure gauge reading After stabilization, open the inlet valve and start the squeezing machine. When the transparent hose in the vacuum end is out of the slurry, close the vacuum valve and the vacuum pump, open the discharge valve, and continue squeezing until the slurry is continuous. When it is sprayed and the consistency is equivalent to press-in, close the discharge valve and continue squeezing and pressurizing to about 0.7MPa, hold pressure for 2min, and close the feed valve.

The exhaust pipe of each peak discharges residual air and bleeding water to ensure that the slurry in the pipeline is full: at full 3.6 Cleaning After the grouting of each pipe is completed, the outlet pipe of the vacuum pump is folded and the water is reversed from the high-strength transparent hose. Out, rinse the filter and transparent hose. The inlet valve and exhaust valve of each pipe shall be removed at least 45 minutes after the grouting, and the grouting port shall be sealed after the grouting is completed on the day of the pregnancy. All the machines and components with the cement slurry shall be washed 4 Control Points (1) Strictly control the quality of cement paste. The key is to reduce the water-cement ratio as much as possible to reduce the shrinkage of the slurry, ensure that the pipeline is full, and make the slurry hardened and dense, and improve the strength of the slurry (2 good sealing measures such as poor sealing of the pipeline, no vacuum can be formed in the pipeline Is equivalent to the ordinary pressure grouting, because the consistency of the cement slurry, which in turn increases the difficulty of grouting, it is easy to plug the pipe; and then after the slurry is filled, the pipeline will not be full.

It is very necessary to bury the exhaust pipe at each peak of the corrugated pipe. During the holding process, the exhaust pipe can be opened one by one from low to high, and residual air at each pipe roof and water that is escaping from the slurry can be discharged to ensure the inside of the pipeline. The slurry is full.

After the grouting is completed, the grouting valve and the exhaust valve must be removed after the slurry has lost its fluidity (generally 45 to 60 minutes after grouting). After the grouting is completed, the opening is closed with a cork stopper.

Except for the above-mentioned 4 points, the rest are the same as ordinary pressure grouting technology. 5 Conclusion Vacuum grouting can easily reach the negative pressure of Q1MPa in the tunnel in the application of the Xiebian Overpass, and the cement slurry with the consistency of 35~40S can be achieved. Smoothly passes over 120m4 channels with a minimum curvature radius of 15m and a maximum vertical height difference of about 7m, and the slurry in the channel is full and dense. The strength of slurry specimens reaches the holding pressure during the process from low to high. The application of the technique is successful by opening one by one to the U above the corrugations. Net

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