Vacuum assisted grouting construction process

Vacuum-assisted grouting construction process Wang Haibang (China Railway Wuchang 2nd Corporation, Hengyang 421002, Hunan, China) Vacuum assisted grouting process. Introduce the vacuum assisted grouting construction process.

1 Rumors At the end of the 20th century, some domestic and foreign bridges that used post-tensioned prestressed technology, due to corrosion of prestressed tendons, resulted in the collapse or reconstruction or reinforcement of the bridge. With regard to the problems of anti-corrosion of prestressed tendons and the durability of structures, universal attention has been paid to the civil engineering community.

Vacuum assisted grouting is a grouting process introduced to solve the grouting quality problem of the channel. It overcomes the deficiencies of the traditional grouting process, improves the fullness and compactness of the grouting, and greatly improves the durability of the structure. The use of vacuum grouting technology is an effective measure to improve the safety and durability of post-tensioned prestressed concrete structures.

2 Project Overview Jincheng Bridge is located on Jincheng Road, an important trunk line in southeastern Wuxi. Jincheng Bridge adopts the form of double bridges. One span of the bridge spans the Beijing-Hangzhou Grand Canal. Two main piers are installed on the river bank side. The main span superstructure uses 63m+105m+63m prestressed concrete three-hole continuous box girders. All adopt 7-hole 22m simple-supported plate girders with a total length of 540m and a total bridge width of 40m. The prestressed concrete continuous box girder box of Jincheng Bridge adopts a three-way prestressed system. Vertical and horizontal prestressed steel strands are made of high-strength, low-relaxation steel strands of grade 15.24 with a standard strength of Rh = 1860 MPa. Longitudinal bundles of prestressed anchorage are VSLCN15-12 and VSLCN-9 high-quality group anchor systems, and horizontal bundles are BM-3. Flat anchor, prestressed pipe using plastic bellows. In order to ensure the compactness of the channel grouting and the effective adhesion between the prestressed tendons and the structural concrete to prevent corrosion of the prestressed tendons, vacuum and auxiliary grouting are used for the grouting of the longitudinal and transverse prestressed channels.

3 Basic Principles and Advantages 3.1 Basic Principles The vacuum assisted grouting process is to modify the original metal bellows into plastic bellows on the basis of traditional grouting, and to seal the borehole system; one end uses a vacuum machine to move the inside of the borehole by 80%. The above air is pumped out, and the vacuum degree of the tunnel is ensured to be about 80%. At the same time, the grouting end is pressed into a cement slurry with a water-cement ratio of 0.20-0.35; when the cement slurry is pumped from the true (7) density: not less than 2. The pipe connection must be tight and airtight. For the compressive strength of bgingfO under the standard curing conditions, the superiority of the 3.2-stage vacuum assisted grouting technology can eliminate the bubbles caused by the ordinary grouting method. At the same time, the residual water droplets in the pores are vaporized near the vacuum, along with The air is drawn together and the density of the slurry is stronger.

Eliminate air bubbles in the slurry. This avoids the possibility of harmful water accumulating in the vicinity of the prestressed tendons and prevents corrosion of the prestressed tendons.

The micro foam slurry and slurry in the slurry first flow into the negative pressure vessel under vacuum negative pressure. After the thick slurry flows out, the consistency of the slurry in the channel can be kept consistent, so that the density and strength of the slurry can be ensured.

Under the condition of vacuum, the channel reduces the pressure head difference formed by the slurry itself due to the high and low bending of the channel, and facilitates the filling of the entire channel by the slurry, especially some special key parts. For curved type, U type, vertical prestressing tendons More able to reflect the advantages of vacuum grouting.

Using the right process as a comprehensive technology is a prerequisite for using this technology. The use of pre-stressed anchorage assemblies and plastic corrugated tubes with good pore formation performance, the use of special equipment, special additives for in-vitro addition, standardized construction procedures, and professional construction personnel are all necessary conditions to ensure the correct implementation of the process.

4 grouting construction process 4.1 Assemble the prestressed channel to set the pipe positioning reinforcement. Before installing the plastic corrugated pipe in the pipe, it should be set according to the coordinates of the designed pipe and set the positioning reinforcement.

The spacing of the positioning bars should not be greater than 0.8m. The curved pipe should not be larger than 0.5m. Lay the bellows. The corrugated pipe is laid on the positioning steel bar, and its position is correctly placed according to the design requirements, and the corrugated pipe is fixed on the positioning rebar by iron wire. The deviation of the position of the longitudinal prestressed pipe shall not be greater than 1 cm, and the deviation of the position of the transverse prestressed pipe shall not be greater than 0.5cm, the horizontal direction shall not be greater than 1cm. Set the observation tube. Observe the hole at the long beam of the straight line 20, and set the observation hole at the inflection point of the curve beam. The observation hole may not be provided with a straight hole within 30 m of the observation hole.

Install the anchor seat. Before the anchor seat is installed, the grouted hole and connecting screw hole on the surface of the anchor seat should be filled with sponge, butter, etc. to prevent clogging of the poured concrete; the anchor seat should be erected with positioning steel bar according to its position and height. Accurate positioning requires that the grouting end be under the squeezing port and the suction port of the evacuated anchor seat is at the top; the bellows should be inserted into the bell mouth of the anchor seat and be wrapped with adhesive tape at the joint of the anchor seat, and the surface of the anchor seat should be used The sponge is covered to prevent concrete from entering the holes in the surface of the anchor seat.

Pouring concrete. After the formation of the prestressed hole, when concrete is poured, the concrete vibrating pump should be prevented from contacting the corrugated pipe to prevent the corrugated pipe from breaking and causing the concrete to leak into the pipe. At the same time, when pouring concrete, the construction personnel should avoid walking on the bellows to prevent deformation of the bellows.

Inspect the holed pipe. After the prestressed concrete is poured, the corrugated pipe shall be inspected immediately with a hole remover to check whether the pipe is clogged, and if it is blocked, measures shall be taken immediately for cleaning.

Wear bunches, install anchors, and tension steel beams. After the concrete strength reaches the requirements, the end surfaces of the anchor seats at both ends and the holes can be cleaned to ensure the smoothness of the pipeline. After cleaning, it can be worn. When wearing the beam, depending on the number of specific strands, it is decided whether to wear it by hand or by a winch. When wearing the beam, the wire and foreign matter on the strand should be removed to prevent affecting the quality of the grouting. After the strand is put on, it is tensioned.

Install caps and grouting iron pipes. When installing the cap, clean the squeezing port and screw hole on the surface of the anchor seat. When installing, apply sealant on the surface of the anchor seat and the cap O-ring groove and the joint face, and pay attention to the exhaust on the cap. Holes should be vertical upwards. The pre-assembled grouting iron pipe is screwed onto the anchor seats at both ends of the hole, and the entire pre-stressed hole is assembled.

4.2 Slurry configuration Slurry consists of cement, water, and vacuum-assisted grouting additives. The mixture should meet the following criteria.

~0.35, generally controlled at around 0.33.

Pulp bleeding rate: After the slurry is mixed for 3 hours, its bleeding rate should be less than 2%, and the bleeding should be completely absorbed by the slurry within 24 hours.

Slurry temperature: slurry temperature should be less than 35*C. ~18s when slurry is stirred and grouted; within 45min, consistency of slurry should not change more than 2s. Retarding time: its initial setting time should not be less than 3h. The final settling time should be greater than 17h. The strength should not be less than 25MPa, and the 28d instar strength should not be less than 4.3. The commonly used equipment VSLYJJ type grouting machine () is a cement slurry pressurizing equipment that combines stirring and grouting. For pre-stressed hole grouting systems, the cement slurry is pressed into plastic bellows and other areas. When the pipeline is longer, 2 rotating mixers will have better grouting effect.

VSLYJ type grouting machine VSLCZB type vacuum evacuating machine VSLCZB type vacuum evacuating machine () is used for vacuum evacuation and auxiliary grouting of prestressed anchoring system to make it dense and plump and improve project quality. The machine is compact, small in size, light in weight, high in pumping speed and high in vacuum. It can be used directly in prestressed construction sites for bridges, dams, power stations, and high-rise buildings.

Adjustable temperature with cross-section planing device. The welding is rapid and firm, simple to use, and easy to operate. It does not require any auxiliary materials such as solder, flux, and adhesives. The weld seam has the same strength and performance as the plastic pipe body. Supporting the supply of various diameter clamps.

4.4 Grout construction See the vacuum grouting construction process as follows: Pulping. According to the slurry configuration index obtained by the experiment, pulping should be performed on the spot after the slurry is prepared. The consistency, bleeding rate, and expansion rate should be tested.

Padding. After the slurry system is in good condition, the grouting pump should be turned on to allow the slurry to flow out of the grouting tube, thereby draining the air and water in the grouting tube. When the consistency of the discharged slurry is consistent with the consistency of the slurry in the mixing barrel, Stop the discharge.

The hole is vacuumed. After the slurry has been tested and determined to be qualified, close the orifice squeezing end valve, open the orifice vacuum end valve, open the vacuum pump, draw the air in the tunnel, and confirm that the vacuum in the tunnel reaches the required level.

Squeezing. When the vacuum degree of the channel reaches the requirement and is stable, the valve of the pressure-grouting end of the hole shall be opened immediately, and at the same time, the grouting pump shall be opened for grouting. The entire process should ensure that the grouting is carried out continuously and uniformly, without interruption, and that the cement slurry should be maintained in a continuous one-way flow.

Vacuum end discharge. When seeing the cement slurry flow out from the transparent tube at the vacuum end, the valve to the vacuum pump should be closed immediately and the valve leading to the waste tube should be opened. At this time, the vacuum pump can be shut down.

The slurry discharged from the waste discharge pipe must be free from bubbles and micro-foam, and its consistency must be the same as that in the mixing tank before shutting down the squeezing pump and closing the vacuum valve at the port.

Exhaust vents on the caps at both ends of the hole. First open the exhaust hole on the vacuum end cap, inching the grouting pump, and the slurry discharged from the exhaust hole must be free of bubbles and micro-foam, and the consistency of the slurry must be closed when the consistency is the same as that in the mixing barrel. The squeezing pump closes the exhaust hole; after closing the vacuum exhaust hole, the same operation is performed at the squeezing end.

Keep pressure. When the end of squeezing the end of the squeezing, the grouting pump should still be maintained at a pressure of 0.5~0.7 MPa, and the pressure holding time should be no less than 2min. After the pressure is maintained, the squeezing pump and the squeezing pipe valve should be closed immediately. The squeezing of the bundle of pipes.

5 Conclusion As the vacuum-assisted grouting construction process itself has a relatively high level of quality control, coupled with a reasonable proportion of the mixture, the use of vacuum-assisted grouting technology can guarantee the uniformity of the hole grouting, forming a dense, impermeable protective layer , And can eliminate the pores. Therefore, the vacuum-assisted grouting technique is a powerful means of ensuring high-quality grouting. It is a 4m VT plastic corrugation! Pipe WeldingPublishM high-tech exhibition direction.å²£://ww.Cki.net

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