32m post-tensioned beam vacuum grouting process on Qinghai-Tibet line

Vacuum grouting technology of Zhangliang Guo tunnel after 32m of Qinghai-Tibet railway construction Xu Zouguo\ Wen Jiangtao 2 (Beijing Iron City Supervision Company, Beijing 100085; 2 China Railway First Bureau Bridge Construction Company, Xi'an 710000) New requirements The original grouting process was gradually Vacuum grouting process replaced. The article takes the Qinghai-Tibet Line 2000 porous 32m post-tensioned prestressed concrete simply supported beam as an example to describe the vacuum grouting construction process of the post-tensioned beam tunnel.

2:1 Overview of beam body design 32m post-tensioned prestressed concrete simply supported beam is designed by the professional design institute of the Ministry of Railways, and the figure number is “Shihyou Bridge Shijiazhuang 07”. The main girder adopts split-type T-beams, and the center-to-center distance between the webs of two beams is 2.0m. The longitudinal prestressed bars adopt standard loose steel strands with a nominal diameter of 15.2 mm and a tensile strength standard value of 1860 MPa. The modulus of elasticity is 195 GPa. Pre-embedded +80 mm metal bellows in the beam body, positioned with rebar positioning nets to allow for the formation of channels, see layout of channels.

2 Principle of vacuum grouting 2.1 The difference between vacuum grouting and ordinary secondary grouting The secondary grouting is carried out twice, without the use of a vacuum pump, and the second time (by the end pressure) from the first time (by the end pressure) 0.4, the sealing requirement for the anchor head is low, especially the second grouting can press out the first time the pressure of the squeezing pulp after 30min.

The vacuum grouting hole outlet is vacuum-pumped by a vacuum pump. The slurry is grouted at a time with a water-cement ratio of >0 32. The sealing of the anchor head is required to be high, a hole is formed and a negative pressure is generated, so that the grouting is dense.

2.2 The principle of vacuum squeezing The raw negative pressure guides the thick liquid to fill the pores, making the pore slurry more compact, so as to facilitate the protection of the strand. Its working principle is as follows.

3 Vacuum grouting technical requirements and conditions 3.1 Technical requirements 5MPa; DZ-4 admixture formulated by the Institute of Iron and Steel; incorporation of rust inhibitors in cement slurry; use of potable water.

32, the fluidity of the cement slurry is controlled at 3050 3. The grouting condition is reserved, and the hf liability review series 1 is Bai Minhua) The final tension is controlled by double control (the control stress, the tensile elongation value and the theoretical elongation value deviation within *6%) And no slip wire, broken wire phenomenon.

The grouting was completed within 48 h after the completion of final drawing.

*Q requires thermal insulation of the beam body and slurry.

4 Materials and Tools 4.1 Raw Materials and Mixture Ratio Check the date of shipment of the O425R cement and admixture DZ-4. Expired and agglomerated materials must not be used.

The mixture ratio was cement: water: admixture: rust inhibitor = 1:0.32:0.1:0.0004, and the amount of cement used for each mixing was 300 kg. The admixture was weighed well before construction and piled separately from the cement. Rust inhibitors are weighed and bagged in advance using a balance.

4.2 The grouting equipment, instruments, and test equipment and equipment can be used for bamboo plug type and screw type grouting pump. The LGB3 type screw pump and ZKB120 type vacuum pump manufactured by Liuzhou OVM Company are used here.

Check whether the machine and instrument are normal. If the workload is large, cement mortar mixer and grouting pump should be equipped with more than 2 sets.

Check the accuracy of scales, balances, flowmeters, hydrometers, stopwatches, cups, etc. The grouting outlet should have sufficient three-way pipe, and the vacuum grouting process should be used to remove the accumulated water and other debris in the hole before the first drawing and pulling through the beam to check the concrete closure of the anchor head.

*C, set the material feeding net at the feeding port, mesh 510cm, mix with water, admixture, and then cement. Mixing time is about 15min. The mortar is sieved and placed in the lower storage tank. The top of the storage tank is also equipped with a mixer. , Perform secondary stirring, then measure the relative density (> 1.9) and fluidity (3050s) qualified before grouting, check the connection of the grouting hole of the grouting tube, vacuum tube and anchor plate, and the valve closure with each stirring Open the situation.

The grouting can be carried out from the bottom up: N1 outside *N1 *N2 outside the inlet is connected to the feed tube, the outlet is connected to the vacuum tube to vacuum, the vacuum is up to a 0.06MPa, the inlet valve opens, grouting begins, At this point into the pulp pressure of about 0.20.3MPa exports into the vacuum tube slurry into the A valve, transparent casing removed, will enter the vacuum tube of the waste slurry rinse, ready to pump the next hole. B valve open, so that the slurry continues to flow into the water tanks and other containers, measuring the relative density of the cup, and the valve is closed when consistent with the import. The squeezing of the slurry into the slurry is still carried out. At this time, the holding pressure, the holding pressure of 0.60.8 MPa, and the holding pressure and vacuum degree are not normal due to the following reasons: 1 The pressure is not normal: The hole head seal is not good; the grouting machine is faulty Pressure gauge failure; grouting pipe plugging. Special attention should be paid when the grouting pipe is > 30m, the holding pressure needs to be increased by 0.10.2MPa.2 The vacuum degree is not normal: the hole anchor seal is not good; the vacuum system of the machine leaks; the vacuum pipe leaks; the water temperature is too high, and the water quantity is insufficient.

6 Concluding remarks * C, maintenance 6d or slurry strength> 25MPa before removal of insulation facilities. The bridge was erected after 28 days of grouting. Hole grouting technology is of utmost importance. The more dense the slurry in the channel, the less the prestress loss of the strand, and thus the durability of the beam.

Snow Frost Ice Shield Car Covers

Ningbo Yejin Supply Chain Management Co.,Ltd , https://www.car-parts-accessories.com