Why doesn't the expressway use reinforced concrete as pavement?

I. Overview and Characteristics of Newly-built Reinforced Concrete Chimney 05g2 12 Cement Chimney Construction Project

This project is a power plant chimney project of XX Group Co., Ltd. The chimney of Jiangsu Jiu Hao High-rise Building Anticorrosion Co., Ltd. is 240 meters high, with an outlet diameter of 6 meters. The cushion is C 10, the foundation is C30, the cylinder is C30, and the lining is refractory brick and acid-resistant cement.

This project is a high-rise structure with high construction height, great difficulty and complicated construction technology. However, Jiangsu Jiu Hao High-rise Building Anticorrosion Co., Ltd. has a group of professional chimney construction teams with rich theoretical and practical experience, which can fight hard, and both management and construction technology can meet the needs of this project.

Second, the construction goal

1. construction period: the total calendar construction period is 120 days, and all projects are completed.

2. Quality objective: the qualified rate of sub-item acceptance 100%, the excellent and good rate ≥90%, and the engineering impression ≥85%.

3. Cost objective: ensure the quality and safety of the project, and plan to save the project cost 17% through effective management means.

4. Safety objective: adhere to the policy of "safety first, prevention first", ensure that the frequency of general accidents is less than 1.5‰, the mortality rate is zero, and put an end to major safety accidents.

5. Environmental protection goal of civilized construction: strengthen the scientific management of the construction site, meet environmental protection requirements, establish the image of humanistic engineering, and create a municipal civilized construction site.

6. Scientific and technological progress goal: this project is listed as a professional scientific and technological demonstration project of this enterprise, and the benefit rate of scientific and technological progress reaches 1.5‰.

7. Service objective: establish the owner to meet the construction process and track the project quality for three years.

Third, the construction deployment

1. Main construction technologies of Jiangsu Jiu Hao High-altitude Building Anticorrosion Co., Ltd.

1. 1 Adopt vertical shaft frame to replace integral formwork construction.

1.2 same frequency construction of concrete pouring with lining thermal insulation layer.

2, the construction process

Construction preparation → excavation → cushion construction → equipment assembly → concrete pouring of foundation slab → backfill soil → concrete pouring of pipe body → lining pouring (per minute 1.25m) → insulation layer masonry (per minute 1.25m) → concrete pouring of pipe shell (per minute 1.25m) → signal.

Four, the main construction technical scheme

1. Installation and construction of internal derrick, platform and lifting system

The whole construction process is shown in figure 1.

1. 1 Installation and construction of internal derrick

The internal vertical lifting frame is1.25m high, which is erected by steel pipe scaffolding. The horizontal step of the station pole is 1.5m, and the vertical step of the horizontal pole is 1. 15m. According to the proportion of the inner diameter of the chimney, the diameter of the inner frame is gradually reduced with the size of the lining (see Annex I for the inner frame checking calculation). When erecting the steel pipe frame, both ends of the steel pipe should be inserted into the brick-lined masonry and placed on the brick masonry (see the following figure: Detail A). In the height direction, every 10m support, four peripheral steel pipes must be extended to both ends and anchored in the concrete wall for 50mm, and reinforced with the concrete wall once to ensure the strength and stability of the parallel frame. During installation, cement isolation concrete should be wrapped at the end to prevent the steel pipe from being removed in the future (see the following figure: Detail B).

The vertical frame of chimney construction gradually increases with the construction of chimney wall, and the first installation height is 3 ~ 5m outside 0.000. The bottom of the derrick is supported on the concrete foundation slab, and the uneven surface of the foundation concrete must be leveled with steel plates. When installing the derrick, the hanging cage is placed in the designated shaft in advance. During erection, all personnel must wear safety belts and non-slip insulating shoes. When steel pipes are uploaded in the same direction, they must be hoisted with hemp rope.

1.2 operation platform construction

Operating platform * * * has two layers, the lower layer is used for bricklaying and reinforcement, and the upper layer is used for hoisting and lifting plates, supporting templates and pouring concrete. Spread a 50×300 wooden springboard on the operation platform. Wooden springboard and suspender steel pipe shall be firmly bound with brown strength or No.8 iron wire, and "jumping around" is not allowed. The boards should be sewn tightly, and the big gap between the wooden springboard and the steel pipe should be sealed with narrow slats or iron sheets. The operating table rises with the derrick, and three sets of boards are prepared for turnover.

A square hole of 0.9×0.9m is left in the center of the derrick for entering and leaving the barrel, and a small hole of 0.2×0.2m is left in the center for measuring the center line of the barrel during construction. Make a hole sealing plate of 1.2m× 1.2m, and use it to seal the hole after the bucket reaches the platform, so as to facilitate the placement of the trolley during unloading and ensure the safety of pedestrians at ordinary times.

There is no outer ring platform on the derrick, so people who buckle the wire fly only buckle at the outer ladder. When shuttering and hanging formwork, everyone should stand in the bound ring wall reinforcement, and construction is not allowed outside. If it is necessary to deal with the surface quality problems of concrete, the personnel shall handle them on the external ladder.

A 3.8-meter-high external ladder is set at the position corresponding to the external ladder of the chimney, so that relevant personnel can safely board the platform through the external ladder of the chimney and carry out relevant construction operations and quality inspection. As shown in the figure below.

Description:

1, field anti-skid reinforcement rod 2, 14mm steel wire rope 3, operation platform and protection platform.

4. Corner pulley 5, top pulley 6 and top sliding chamber rod

7. All kinds of distribution boxes and instruments are placed in the work shed, and the top is covered with asbestos tiles for rain and sun protection.

Set lightning rod, which is connected with the lightning protection system of steel pipe frame to prevent lightning strike.

Operating platform and external ladder diagram

1.3 construction of internal and external hoisting system

The vertical lifting equipment in the chimney adopts 5t hoist with φ 14 steel wire rope, which is loaded and unloaded by a bucket. The bucket is round and welded with 6mm thick steel plate, with a height of 700mm, an inner diameter of 650mm and an outer diameter of 750mm at the bottom. A pin shaft is fixed on the bottom plate and can rotate up and down to close the feeding or open the discharging. Regularly check the flatness of the bottom plate during the construction process, and put it down gently when installing steel bars, steel pipes and fasteners. , in order to avoid bottom deformation, slurry leakage.

Because there is a height difference between the existing ground and 0.000, it is necessary to build a small steel pipe gantry at 0.000. Gantry hoisting equipment adopts 3t hoist with diameter of φ 14 wire rope. The vertical lifting equipment of the external mast derrick adopts a 3t hoist, which is loaded and unloaded by hanging plates.

Steel bar, concrete, etc. It is transported to the hanging plate of the gantry by handcart or manually, lifted to the flue platform by the gantry, and then transported horizontally to the derrick in the chimney in the safe passage of the flue platform to complete the horizontal and vertical conversion. Lifting steel bars, bars, concrete, etc. Use the bucket in the derrick to hoist it to the upper construction platform, and use the platform sealing plate to seal the hole. Unload steel bars and steel pipes, and manually transport them to the parts that need to be bound. Unload the concrete onto the trolley and push it to the concrete pouring place for pouring.

The crown block used for lifting the inner derrick and portal frame is installed on the crown block fixed frame at the top of the derrick. 4-8 diagonal rods are fixed on the crown block, and at least 8 fasteners are used to bear the load. When the moving load of sliding bar is 2× 1.t=2.6t, the dynamic load on each fastener is 2.6t/8=0.325t(3.25KN), which can fully meet the bearing capacity. As shown below.

Vertical and plan views of the sky slider

Requirements for 5t winch: the hoisting speed is 30-440m/min (3-5min for one trip) or 60m/min (about 3min for one trip), the drum rope capacity is at least 120m, and the total rope length is at least 250m. Requirements for 3t hoist: the hoisting speed can be 30-440m/min (one round trip 1min).

The 3t hoist uses angle steel to bury anchor piles, and the 5t hoist uses 13mm steel wire rope to pull anchors on the beams, plates and columns of flue flat smelting, and the frame of the hoist is welded and anchored by removing the steel bars of the beams and plates.

1.4 construction of protective shed

On the derrick in the chimney, a 5m-high double-layer protective shed is set to prevent objects from falling off during the upper construction and ensure the safety of the construction workers below. The shaft frame bears the full load of the operating table and is used for vertical transportation. A safe passage is arranged on the flue platform, and a double-layer protective shed is arranged at the top of the passage. The top of the outer gantry is provided with a double-layer protective shed. The spacing between the two layers of the double-layer protective shed is 500mm. As shown in figure 1.

2. Reinforced concrete construction of chimney

24-hour shift work system is adopted, and 50 people, including steel workers, carpenters, welders, electricians, concrete workers and mechanics, participate in daily work to ensure the progress of the project.

Quality requirements for barrel construction: In the construction project, it must be ensured that the verticality deviation of barrel center is not more than 60mm, the thickness error of barrel wall is less than 20mm, and the radius error of any section of barrel is not more than 1% radius and not more than 30mm. The deviation of the center line of the flue is not more than 15mm, the deviation of the elevation in the flue is less than 20mm, the local unevenness inside and outside the pipe wall and the back is not more than 1% of the section and not more than 30mm, and the height and width of the flue are not more than 30mm and not less than-20 mm. ..

2. 1 displacement formwork construction

2. 1. 1 displacement template structure

The external mold of the barrel body is made of 2mm thick tinplate with a thickness of 1 1,000× 2,000 m, and each tinplate is divided in proportion when processing. Each set of templates has 1m edges on both sides. Divided into two points, each segment is 1.25m high. Using the iron sheet coated with oil as the external mold can make the external surface of the chimney smooth and beautiful, support the mold quickly, make the proportion of the cylinder consistent, and reduce the flat-fell seam between the templates.

The internal model adopts the combination of brick-lined wooden wedge and internal steel formwork: firstly, the chimney lining is laid, and the internal steel formwork is placed between the lining and the reinforcement; then, the undeformed Chinese fir is processed into wedge-shaped wooden strips with the same thickness as the air insulation layer, which are used as measuring materials and placed between the internal steel formwork and the brick masonry to form the air insulation layer. Complete the wedge-shaped wood strips on the woodworking planer with a 3 cm thick square. Because the air insulation layer is 100mm and 50mm, there are two kinds of wedges, one is 75mm and 25mm, and the other is 30mm and 20 mm. In construction, the bricklaying time is generally 6 ~ 3 hours, and there is still a certain preparation time for setting the internal mold. Therefore, the time interval between bricklaying and internal formwork erection is generally 4 ~ 7 hours, and the speed of concrete pouring is extremely slow, so the strength of mortar can bear the construction load of internal formwork erection and concrete pouring.

According to the practical experience of our company for many years, the external formwork is processed into four groups with 2mm-thick iron sheet according to the grid scale of the chimney external wall, and the grid formwork is set aside on both sides of each group, and the upper interval of each group of plates is 2m, that is, every other plate is welded with φ 14 steel bar hooks for lifting the formwork. First, drill holes in two pieces of iron sheets with an electric drill, then fix them with anchor screws, from inside to outside, so that the inner side is flush with the surface of the iron sheets, and connect them by electric welding and spot welding. On each piece of iron, 250mm away from the joint, two rows of joints passing through the steel wire rope are welded, so that the steel wire rope can be used to fasten the formwork, and the external mold can be fastened when pouring concrete. Install 18-28 elevator bracket and 18-28 elevator (1t) on the vertical steel bar and operation platform. After the concrete reaches the formwork removal strength of 1.2n/m㎡, the external formwork will be lifted evenly by the elevator section by section.

Internal and external templates are bound or welded with φ 12 steel bars on the wall reinforcement to ensure the clear distance between internal and external templates and the thickness of internal and external protective layers. The length of the reinforcement is the same as the thickness of the wall in the first part. The spacing along the circumferential direction is @250mm, and four layers are set in the height direction.

Weld φ25 steel bar into a tripod as shown in Figure 2, and tie it with three or four No.8 iron wires and vertical steel bar with annular steel bar. The load shared by each elevator is (considering the dynamic load factor 1.4):

1.4×(4 1× 1.35×0.00 127×7.85× 103+ 18×36× 18/ 100)28

= 1.4×638.03/28 = 3 1.9× 10-2KN

This force is quite small, and the 1t elevator and the lifting frame welded with φ25 steel bars can bear it completely.

2. 1.2 Installation of displacement formwork

Internal model installation: Before installing the internal model, the chimney lining brick masonry shall be built first, and the center line and radius shall be measured at the same time to control the internal model installation radius and fix the formwork. After placing the inner steel formwork, add a set of wooden wedges between the lining and the steel formwork (the thickness of a set of wooden wedges is the same as that of the air insulation layer), and support the inner steel formwork with wood. Wedges are arranged in the circumferential direction according to the spacing of 100mm, and wooden supports are arranged up and down according to the joint position of the iron sheet of the internal mold. After the concrete is poured, it will be removed.

Installation of external mold: After the installation and correction of external mold meet the specified size requirements, use temporary wood with designed wall thickness to control the clear distance between internal and external mold and the protective layer distance between external mold and main mold. A chock should be placed every other iron sheet, and the chock will be gradually removed when concrete is poured into the temporary chock. After the installation of external formwork, each formwork in the outer ring shall be fastened with 18 6.5mm steel wire rope and rope tightener. Outside the template should be tied up, the gap should be blocked tightly, to prevent Zhang Mo and slurry leakage. The inner formwork shall be firmly supported. Prevent deformation.

Template lifting color is 18 ~ 25 lifting frame, which is lifted by elevator.

The error rate difference between the center of the displacement formwork and the geometric center of the chimney is less than 5mm, and the lower edge of the formwork overlaps with the poured concrete by about100 mm. After each demolition, the formwork surface should be cleaned with mortar and coated with release agent.

Check the determination of the center position of the barrel. Laser centering instrument is mainly used. After leveling the instrument with the total station, turn on the laser transmitter and level the laser on the top grid plate. Then, check the radius with the laser point as the center. Check the verticality of the chimney with a 20kg vertical ball which is convenient for construction operation every 5m. The vertical ball is hung on the zigzag frame for centering, and the vertical ball is lifted by wheels.

2.2 Reinforcement construction

Vertical steel bar and ring steel bar are bound and lapped, the lap length is 45d, and iron wires are tied at the middle and both ends of the joint. Any horizontal annular steel bar with a diameter greater than 12 mm shall be laid out in advance according to the curvature of the cylinder in which it is located and processed into an arc for later use. Steel bars below φ 12mm only need to be hooked at both ends, and can be bent when binding. When binding reinforcement, the vertical reinforcement should be bound first, and then the ring reinforcement should be bound.

The ring reinforcement at the top of each barrel should be positioned first, based on the edge of the formwork that has been poured with concrete. According to the upward scale and considering the thickness of the protective layer used for positioning, the ring reinforcement should be tied and fixed with a wire hammer, and then the ring reinforcement below should be tied based on this ring reinforcement.

After measuring the radius with a steel ruler, the vertical reinforcement of the cylinder shall be evenly distributed from the center of the cylinder according to the drawing requirements. Vertical steel bars shall be staggered in each horizontal section according to the head, and the number shall not exceed 25% of the total number of steel bars, and the number of welded joints shall not exceed 50% of the total number of steel bars. When changing the diameter or quantity of longitudinal reinforcement, it should be evenly distributed on the whole circumference of the barrel wall. The circumferential reinforcement of the cylinder shall be arranged on the outer side of the longitudinal reinforcement, with the allowable deviation of 20 mm, and all steel bar intersections shall be bound with 22 # tie wire.

The protective layer of steel bar shall be controlled by wood, and the radius measured from the center line shall be bound by binding wire, and the length per meter around the formwork shall be at least 0.5. The thickness of concrete protective layer and circumferential steel bar on the tube wall shall be 30mm, and the deviation of tube protective layer shall not exceed+10mm and -5mm.

Longitudinal reinforcement higher than the formwork shall be temporarily fixed by binding two annular reinforcement. After each layer of concrete is poured, there must be at least one stirrup on it.

2.3 concrete construction

2.3. 1 concrete material

Using easy standard 42.5 ordinary portland cement, cement mixture ratio test must be done when entering the site, and there must be quality certification documents such as variety label, material origin and factory date. The coarse aggregate is Baoquan 5 ~ 5~3 1.5mm igneous gravel, and weathered ones cannot be used.

The particle size is less than 40mm, the silt content is less than 1%, the aggregate is sheepfold sand (fineness modulus MX= 1.2 1), and the silt content is less than 3%. Water is the tap water of the factory. The water-cement ratio of concrete is not greater than 0.5. In order to ensure the engineering quality, speed up the construction progress and ensure the construction safety, Shanfeng brand SF-2 high-efficiency early strength agent with 0.6% cement content is added to the concrete.

concrete pouring

Before pouring concrete, the template size must be rechecked, and the elevation, position and quantity of various embedded parts should be checked in detail, and concrete can be poured only after it is confirmed.

A 500L forced mixer is set on site to mix concrete, which is transported to the outer gantry by trolley, lifted to the flue platform, pushed to the derrick, and lifted from the inner derrick to the platform for pouring. Concrete should be poured evenly in two layers along the circumferential section from one point, poured reversely after the intersection of the two paths, and layered continuously, and each layer is vibrated and compacted with a 50-type vibrator. Concrete is poured in layers, and the height of each layer is about 250-300mm. When pouring concrete, the pouring direction should be changed symmetrically to prevent the formwork from tilting and twisting in one direction. When vibrating concrete, don't touch steel bars and templates. The depth of vibrator inserted into the previous layer of concrete should not exceed 50 mm When lifting the formwork, the concrete shall not be vibrated. For the treatment of construction joints, the loose stones should be removed and rinsed first, then a 20-30 mm thick 1: 2 cement mortar layer should be laid, and then the upper concrete should be poured. When concrete and steel bars are polluted by oil, they should be cleaned up.

A set of concrete pressure test blocks shall be made every 5m in barrel height, and the sampling date shall be marked, so as to test the concrete strength at the age of 28. When pouring for the first time, several groups of test blocks are made to test the strength for one day, two days and three days respectively for construction reference. The production, maintenance and inspection of concrete test blocks shall be carried out by special personnel. The concrete surface and all joints must be smooth, without honeycomb pits and obvious construction joints.

2.3.3 Maintenance and form removal

The removal of the formwork outside the barrel shall be carried out when the concrete strength reaches the capacity of bearing the upper load without deformation, and the concrete strength shall not be less than 0.8Mpa. The load-bearing formwork at the smoke crossing shall be removed only after the concrete strength reaches 70% of the design label. After the formwork is removed, the surface shall be repaired in time, watered and maintained, and kept moist frequently for not less than 7 days and nights. Tube wall concrete can also be cured with film curing agent. Maintenance water, because the water pressure is not high, it is necessary to install a pressurized water pump, and use φ50-60 water pipe to send the water to the top of the derrick and connect it with the derrick height. From the top of the pipeline, use a hose to introduce water downward into the φ 25mm rubber spray pipe around the external ladder, and spray holes are drilled on the spray pipe with an interval of 120- 150mm φ 3-5mm for water spray maintenance.

3. Structure of chimney accessories

Before pouring concrete, the ladder of reinforced concrete chimney and the embedded parts of signal platform should be fixed in the outer reinforcement by binding and welding. The allowable deviation of embedded position of ladder is 20mm, and that of embedded signal station is 10mm. The threads of embedded parts shall be properly protected and shall not be defiled, and the threads of embedded parts shall be buttered to prevent concrete slurry from entering. When installing metal parts, the exposed parts should be coated with antirust agent before installation, then connected to the outside after installation, and finally painted with antirust agent. The bolts of chimney accessories shall be tightened and shall not be missed. Ladders and fences should be aligned up and down, and the concrete strength should reach at least 1.2N/m㎡ when accessories are installed. All parts of the chimney arrester should be welded firmly, and its grounding electrode should be buried when the foundation pit is backfilled. After the lightning arrester is installed, check the grounding resistance, and its value should not be greater than 10 ohm required by the design.

4, lining masonry construction

The construction method of internal masonry and external sliding should be adopted to ensure the quality of lining masonry and the accuracy of insulation layer position. The upper surface of the annular cantilever supporting the lining shall be leveled with 1:2 cement mortar, and its horizontal deviation shall not be greater than 20mm. Layered masonry lining is not allowed to stay straight, and mortar in masonry must be full. Plumpness of horizontal mortar joint: ordinary clay brick should not be less than 80%; Clay refractory bricks and acid-resistant bricks shall not be less than 90%. Vertical mortar joint should be squeezed and grouted to make its mortar full.

Allowable added value of lining mortar joint thickness and mortar joint quantity

Project lining type and mortar joint thickness

Allowable value of mortar joint thickness (mm)

The allowable added value (mm) of 5 square meters of surface is 10.

Allow to increase the number of mortar joint (place)

1 Ordinary clay brick and diatomite brick 8 +47

2 Clay refractory bricks and acid-resistant bricks 4 +25

When the lining thickness is 1/2 bricks, it should be laid along the bricks and staggered by half a brick. When the lining thickness is 1 brick, it should be laid together with the top brick and staggered with 1/4 bricks. Brick joints on the lining surface shall be smooth, and the roughness of the lining surface in one circle shall not exceed 1% of the lining radius in the radial direction, and the maximum shall not exceed 50 mm. The thickness of the insulation layer between the liner and the cylinder is 100 mm and 50 mm respectively. In order to maintain the stability of the lining, two top bricks are selected from the lining in the direction of the cylinder wall per square meter, and a temperature seam of 10mm is left between the top bricks and the cylinder wall. At the same time, a circle of anti-settling belt with a longitudinal spacing of 2.0m is set on the outer surface of the inner lining, and a temperature seam of 10mm is left between the anti-settling belt and the cylinder wall. Pay attention to the dosage of mortar when laying to avoid mortar falling into the air insulation layer.

5, chimney decoration construction

The outer surface of concrete on the upper part of chimney 95m- 120m is coated with red and white marker rings, which are designed as durable coating or paint. The logo ring is 5m wide and the steel platform with the elevation of 1 15m is painted red. The decorative groove of the cylinder is painted white and will be hung on the external cantilever beam by professional construction personnel. When painting, the concrete surface should be dry, the water content within 20mm depth should not be greater than 6%, and the floating ash and oil stain on the surface should be removed. The preparation and construction of anticorrosive coatings should be carried out in accordance with the current relevant national standards.

6, the demolition of the shaft frame construction

There should be professional command, and the demolition should be carried out by skilled workers. Demolition should be carried out layer by layer from top to bottom, and construction should be carried out layer by layer in ascending order. First, transfer the upper platform to the lower platform, pave it, then remove the steel pipe rack above, reserve the overhead slide bar rack, and put down the removed pipe fittings in the bucket. When removing one part, other parts should be prevented from falling. The balustrade ladder shall be dismantled as a whole, and the load-bearing columns and cross bars shall not be dismantled first, and can only be dismantled after all the structures undertaken by it are dismantled. For the original pipe fittings anchored in concrete, if they cannot be removed, they have to be cut off, and then the steel pipe holes are blocked with fine stone concrete; If it can be extracted, plug the hole with C35 fine stone concrete after extraction. Remove the left brick hole and plug it with bricks and M7.5 mortar. No leakage is allowed.

7, settlement observation construction

The settlement observation point is buried at the elevation of 0.44m outside the pipe wall, and the four observation points are set on two mutually perpendicular straight lines. When the concrete strength reaches 1.2N/m㎡, the formwork shall be removed and settlement observation points shall be set. After installation, observation should be started and recorded in detail. After the completion of the project, it should be filed for inspection and continuous observation.

8, special climate construction

8. 1 rainy day construction

In order to ensure the construction progress of the project, the construction is still carried out under the condition that it is not very rainy. All personnel put on raincoats and insulated water shoes. Cover all electrical equipment with plastic sheets to prevent rain. On the construction platform, build temporary shelter from the rain. As shown in the previous figure 1.

8.2 Lightning weather

This area belongs to strong lightning, and the measures must be practical. The lightning rod is installed on the sliding bar frame at the top of the inner derrick to connect the down lead to the underground grounding outside the chimney. A lightning rod is arranged on the rain cover, and the lightning rod is connected with the lightning protection system of the inner derrick. In case of lightning weather, all construction personnel shall enter the shelter in time and come out for construction after the weather is stable.

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