First, the characteristics and advantages of post-tensioned prestressed construction technology
1. Concept and technical characteristics of post-tensioned prestressed construction technology. Post-tensioned construction technology mainly refers to the construction method of pouring cement concrete, and then stretching prestressed tendons to form corresponding prestressed concrete members after its design strength can reach 75%. Compared with the traditional component construction technology, the post-tensioned construction technology has many advantages, which can not only effectively reduce the problems and troubles caused by long-distance transportation, but also control the cracks and deflection, thus reducing the cross-section size of long-span concrete beams, not only reducing the weight of building structures, but also effectively saving some construction costs.
2. The application scope and requirements of post-tensioned prestressed construction technology. Post-tensioned prestressed construction technology is widely recognized and applied in more fields because of its excellent characteristics, such as bridge construction, municipal infrastructure construction, water supply and drainage construction, housing construction and underground facilities construction. However, in the actual construction process, the post-tensioned prestress construction technology has a very critical connection with the prestress value data of concrete structures. There are many factors that affect the determination and establishment of prestress value, such as the performance and mode of raw materials and the curing degree of concrete in the later stage. In order to effectively improve the advantages of post-tensioned prestress, the construction quality must be strictly controlled.
Second, the post-tensioned construction technology
1. Process control of reserved channel. At present, the common reserved channel technologies in China include steel tube core-pulling method, rubber tube core-pulling method and embedded tube method. First, the steel pipe core-pulling method, generally leaving the relevant straight channel, the length should be kept within 15 meters, and the tube must be kept straight with the channel when drawing; Second, rubber tube core-pulling method, rubber tube core-pulling method construction, must leave the corresponding curved channel, generally will be fixed steel grid, fixed position is generally in the mold. Keep the grid spacing, in which the steel pipe is 1 to 2m, the rubber hose is 500mm in straight section and 300-400mm in curved section. Thirdly, the embedded pipe method, which is mainly composed of galvanized thin steel strip pressed by corrugated pipe winding machine, has many advantages, such as inserting steel wire and stranded wire into corrugated pipe before hole forming, which has a shorter process, or inserting cross beam after hole forming. Mainly from the following steps. 1. 1 When the corrugated pipe is embedded, the relevant design must be done well. The curve coordinates of prestressed tendons should be elastic on the side formwork and marked well, so as to accurately calibrate the curve position from the bottom of the corrugated pipe. 1.2 In general, when selecting materials for corrugated pipe, metal spiral pipe will be selected, and its size and performance will be set in strict accordance with relevant codes and standards. When connecting, you must choose a larger pipe, generally 400 mm long, and screw in about 150 mm on each side. After docking, it must be sealed with tape to ensure no slurry leakage. 1.3 In order to ensure the tightness of corrugated pipe, the joint between corrugated pipe and fixed-end steel strand must be blocked with cotton silk, and in order to improve its tightness, tape can be used for secondary sealing. 1.4 When the corrugated pipe is embedded, it is necessary to carefully check its specific conditions, such as the civil work, curve shape and pipe wall of the corrugated pipe. From the appearance, the beam should be straight and smooth without bending, and the horizontal deviation should be controlled within 10 mm.
2. Concrete pouring. 2. 1 Before concrete pouring, the positions and specifications of various pipelines must be inspected and adjusted in strict accordance with relevant codes and standards, and the elevation, position and firmness should be inspected in detail. 2.2 When pouring concrete, you should first choose layered vibrating, and each layer should be positioned 30cm. In addition, some matters should be paid attention to when vibrating, for example, the vibrating rod can not directly contact the corrugated pipe, mainly because the collapse prevention will seriously affect the hole grouting. 2.3 The tension end and beam-column joints must be protected, and small-diameter vibrating rods should be used for vibrating during concrete pouring. Its main purpose is to avoid honeycomb, which will lead to accidents when stretched. 2.4 In order to maintain the quality of concrete, after the completion of pouring, it must be protected accordingly. At present, the common methods generally adopt measures such as covering sacks and sprinkling water. In addition, the concrete on the anchor pad should be cleaned in time, so as to effectively ensure the smooth installation of the anchor.
3. Prestressed tendon tensioning process control. 3. 1 Before prestressing, the following aspects should be paid attention to. A, prestressed reinforcement comes into play, must be in accordance with the relevant regulations and standards, strictly check the product certificate and the factory inspection report. In addition, in order to ensure the quality of products, they should also conduct sampling inspection and re-inspection of products entering the site. Secondly, the concrete in the anchor pad pipe must be cleaned and kept clean. Thirdly, in order to maintain the construction quality of post-tensioning method, the rust and soil on the steel strand should be removed in time. Fourthly, jacks and oil pumps should be accurately positioned and installed according to the actual situation on site, and relevant manufacturers should be required to issue corresponding qualifications and reports in accordance with relevant regulations and standards. 3.2 Elongation value of prestressed reinforcement. When tensioning, the elongation value must be controlled in strict accordance with relevant codes and standards. In general, the actual stretching value should be controlled within the range of+10% and -5% of the calculated stretching value. Once the control value is found to be beyond the corresponding range, the tensioning must be stopped immediately, and the corresponding reasons should be checked and solved. 3.3 During tensioning, records of the construction site must be made at any time, including elongation data, broken wires of prestressed tendons, local damage of concrete, etc.
4. Hole grouting process control. 4. 1 During grouting, it is necessary to check and inject clean water into the pipeline through the grouting machine. Its main purpose is to flush and wet the pipeline, and grouting can only be started after flushing the pipeline. 4.2 At present, the material used for hole grouting in China is generally cement slurry, which also needs to have the characteristics of large fluidity, small dryness and little bleeding. It is particularly important to note that the bleeding should be controlled at 2% within 3 hours after mixing. In addition, in order to enhance its quality and performance, portland cement or ordinary portland cement with water-cement ratio of 42.5 or above should be added, and it should be controlled between 0.4 and 0.5. In order to enhance the density and strength of grouting, a certain amount of expansion agent and water reducer can also be added.
Third, the quality control of post-tensioned construction
In order to effectively control the quality of post-tensioned construction, it is necessary to effectively combine the contract documents, design documents and relevant specifications and standards, and supervise the whole process in the post-tensioned construction process to control the construction progress. When selecting steel products such as prestressed tendons, it is necessary to communicate with the supervision engineer, and then submit the samples to be purchased, and the relevant departments will check the quality in detail. Before the materials enter the site, they must be inspected in strict accordance with the relevant regulations and standards. The manufacturer shall provide the corresponding factory certificate and quality guarantee, and finally submit the inspection and test data to the supervision engineer. It is necessary to supervise the quality control self-inspection system of the construction unit. In order to improve the quality of post-tensioned prestressed construction, site construction management should also be combined with site supervision. On the basis of self-inspection and mutual inspection, the handover inspection of the construction process should be done at the same time. We must do a good job of recording concealed works. When recording, it must strictly abide by the relevant regulations and standards for acceptance.
Discussion on construction technology of rotary bored pile in sandy pebble geology; Construction technology of concrete slope protection; Discussion on construction technology of double-sided formwork support for sloping roof structure; Discussion on construction technology of asphalt SMA pavement; Construction technology of drainage on the same floor of toilet lowering slab; Construction technology of backhoe dredger excavating hard rock short-term bridge; Research on construction technology of lime-soil base of municipal road; Construction technology of slipform climbing formwork for high pier of bridge; Construction technology of laminated plate semi-prefabricated assembled garage.
For more information about project/service/procurement bidding, and to improve the winning rate, please click on the bottom of official website Customer Service for free consultation:/#/? source=bdzd