1 construction preparation
1. 1 technical preparation
1. Prepare the construction plan and submit it to the supervisor for approval.
2. Make technical disclosure to relevant construction personnel.
1.2 material requirements
1. Reinforcement: Reinforcement shall have factory quality certificate and retest report, and the variety, grade and specification of reinforcement shall meet the design requirements. When steel bars enter the site, samples shall be taken for mechanical performance test, and the quality shall conform to current national standards, such as Hot Rolled Round Steel for Reinforced Concrete (GB 130 13) and Hot Rolled Ribbed Steel for Reinforced Concrete (GB 1499).
2. Cement: Cement shall have product certificate or ex-factory inspection report when entering the site. After entering the site, the necessary performance indexes such as strength and stability should be sampled for re-examination, and the quality must conform to the current national standard Portland Cement and Ordinary Portland Cement (GB 175).
When there is doubt about the quality of cement or the cement has been out of the factory for more than 3 months, it must be retested before use and used according to the retest results. Different kinds of cement shall not be mixed.
3. Sand: The variety and quality of sand shall meet the requirements of the current national standard Technical Specification for Construction of Highway Bridges and Culverts (JTJ04 1). After entering the site, samples should be taken and tested according to different conditions such as origin, category, processing method and specifications.
4. Stone: The variety, specification and quality of stone shall meet the requirements of the current national standard "Technical Specification for Construction of Highway Bridges and Culverts" (JTJ04 1), and samples shall be taken for re-inspection after entering the site.
5. Water for concrete mixing: drinking water should be used. When other water sources are used, the water quality shall conform to the provisions of Standard for Water for Concrete Mixing (JGJ63).
6. Admixtures: The quality and application technology of admixtures shall comply with the relevant provisions of the current national standards "Concrete Admixtures" (GB8076) and "Technical Specification for Application of Concrete Admixtures" (GB50 1 19).
Admixtures should have product specifications, factory inspection reports, certificates of approval and performance test reports, and should pass the second interview when entering the site. The test report of harmful substance content shall be issued by the testing department with corresponding qualification grade, and the adaptability of admixture and cement shall be tested.
7. Admixtures: Admixtures should have factory certificate or quality certificate and quality inspection report of legal inspection unit, and should be sampled and rechecked after entering the site. The quality of admixture should meet the current national standards, and its dosage should be determined through experiments.
1.3 machinery and equipment
1. Main equipment: concrete mixer, dump truck, concrete tank truck, concrete pump truck, crane, etc.
2. Machines and tools: vibrators, shovels, steel plates, rubber hammers, etc.
1.4 operating conditions
Bridge beam and slab construction is completed and accepted.
2 construction technology
2. 1 process flow
Measuring unreeling → rebar processing and binding → formwork processing and installation → concrete pouring → formwork removal and maintenance.
2.2 Operation process
2.2. 1 measuring unreeling
(1) The surveyors set out the inner and outer contour lines of the guardrail and the template detection line according to the bridge control points, and played them on the beam and slab with ink lines.
(2) Weld a steel bar on the embedded steel bar of the guardrail every 10m, measure the elevation line at the top of the guardrail, and mark it on the steel bar with red paint as the elevation control line when binding the steel bar.
2.2.2 steel processing and binding
(1) The steel bars are processed in the steel bar workshop on the construction site and transported to the bridge for binding.
(2) The varieties, models and specifications of steel bars shall meet the design requirements. The connection mode, joint position, joint number and percentage of steel bar joints in the same section shall comply with the Technical Specification for Construction of Highway Bridges and Culverts (JTJ04 1).
(3) Decorate the reserved reinforcement on the beam slab, and then tie the reinforcement according to the design drawings and measuring unreeling position. When binding, tie the vertical bar first, and then tie the horizontal bar after the position of the vertical bar is adjusted. If the guardrail is equipped with embedded steel plates, the embedded steel plates shall be installed after the steel bar binding is completed. Carefully check the position and elevation of the steel plate, and spot weld it on the guardrail steel bar after confirmation.
2.2.3 Template processing and installation
(1) generally, the external processing steel formwork is adopted for the anti-collision guardrail formwork. The thickness, length, transverse ribs and vertical ribs of steel formwork shall be determined according to the size and length of guardrail and the turnover times of formwork. In order to ensure that the formwork is not deformed, channel steel is usually used to strengthen the edge of the formwork and some horizontal and vertical ribs.
(2) In order to fix the formwork, through-wall bolt holes are reserved at the bottom of the formwork, and the height of the holes should be covered after the bridge deck pavement construction. On the formwork, channel steel is used as the reinforcing vertical rib, which is 100mm higher than the top surface of the formwork, and bolt holes are left in the higher part for wall bolts. The diameter and spacing of through-wall bolts are calculated and determined according to the guardrail size and template conditions.
(3) In the wet joint position near the guardrail, a row of short steel bars shall be embedded during construction as the support for supporting the formwork.
(4) The contact surface between the template and the concrete must be polished and polished with clean cotton silk until the brushed cotton silk is basically free of rust and pollution, and then evenly coated with release agent.
(5) according to the design drawings and measuring unreeling position for template. The beam surface at the bottom of the template should be leveled with cement mortar first. Adjacent templates are connected by bolts, opposite templates are fixed by through-wall bolts, and overlapping parts of templates are sealed with sponge double-sided tape. The inside of the guardrail is supported by the reserved short steel bars, and reinforced with scaffolding pipes, square timber and steel ropes.
(6) A short square timber is placed horizontally on the top surface of the formwork every 1m, and the square timber is tightened with thick iron wire and reserved steel bars in the beam slab to prevent the formwork from floating when pouring concrete.
(7) The true seam and false seam on the guardrail shall be set according to the design position when shuttering. If the position of the joint is not specified in the design, the true joint should be set at the middle of the span, the end of the plate and the bearing of the continuous beam. The fake joint position can be symmetrically affixed with the processed rubber strip on the template, and the real joint position should adopt the method of sandwich foam board between two layers of plywood, which is convenient for removal.
(8) guardrail in the bridge expansion joint position should be reserved according to the drawings expansion joint construction slot.
(9) After the template is accepted, the surveyors will release the elevation control line at the top of the guardrail on the channel steel at the top of the template and mark it with red paint.
Pouring concrete
(1) Determine the concrete production and transportation mode according to the site conditions. After the concrete arrives at the site, the slump should be detected first, and the construction can only start after it meets the requirements.
(2) Concrete shall be poured in layers, and materials shall not be concentrated in one place to prevent the formation of wavy interfaces. The pouring thickness of each layer shall not exceed 300mm. When pouring to the chamfer position of guardrail, stop pouring temporarily, and continue pouring after the vibrating within this range is completed. The interval of layered pouring shall not be greater than the initial setting time of concrete.
(3) The vibrating rod should be inserted into the lower layer 50 mm ~ 100 mm, and the vibrating rod should keep a distance of 50 mm ~ 100 mm from the side formwork. It is forbidden for the vibrating rod to directly contact the template. Each vibrating must be carried out until the concrete stops sinking, no more bubbles appear, and the vibrating rod can be put forward only when the surface is smooth and pulpy.
(4) After vibrating, put concrete on the top of the guardrail.
2.2.5 Curing and form removal
(1) After the concrete pouring is completed, the formwork can be removed only when the concrete strength can ensure that the surface and edges and corners are not damaged by formwork removal, and the guardrail surface and real joints are cleaned up and then sprinkled with water for health preservation.
(2) The special person shall be responsible for sprinkling water for health preservation, and the curing time shall not be less than 7d, which may be extended or shortened as appropriate according to the temperature, humidity, cement varieties and additives.
(3) After the guardrail is removed, the mortar belt under the formwork shall be removed and cleaned in time.
2.3 seasonal construction
2.3. 1 summer and rain period construction
(1) The pouring temperature of concrete for summer construction should be controlled below 32℃, and it should be carried out in a day when the temperature is low.
(2) Building materials (especially cement and steel bars) shall be stacked in a waterproof and moisture-proof manner.
(3) Open-air electrical equipment should have reliable measures to prevent electric shock and leakage.
2.3.2 Winter construction
(1) In general, winter construction of concrete guardrail should not be arranged.
(2) The welding of steel bars in winter should be carried out indoors. When it must be carried out outdoors, the minimum temperature shall not be lower than -20℃, and measures shall be taken to prevent snow and wind.
(3) The mix proportion of concrete in winter construction should be adopted, and an appropriate amount of antifreeze should be added. The temperature of sand, stone and water for mixing concrete should meet the temperature requirements of concrete mixture mixing, transportation and concrete molding.
(4) Appropriate thermal insulation measures should be taken for containers transporting concrete. Before concrete pouring, the snow, ice and dirt on the formwork and steel bars should be removed.
(5) Appropriate covering and heat preservation measures should be taken after concrete pouring, and concrete shall not be frozen before its compressive strength reaches 40% of the design strength.
3 quality standards
3. 1 quality requirements
1. The quality and specifications of cement, sand, stone, water and additives used must meet the requirements of relevant specifications and be constructed according to the specified mixture ratio.
2. There should be no exposure and emptiness.
3. The steel members on the crash barrier should be welded firmly, and the weld should meet the requirements of the design and relevant specifications, and be protected according to the design requirements.
3.2 Measurement items
3.3 Appearance appraisal
1. The crash barrier is straight and beautiful.
2. The concrete surface is smooth, and there should be no honeycomb and pits.
3. The pouring section of the crash barrier should be connected smoothly.
4 finished product protection
1. After the guardrail construction is completed, protective measures should be taken to prevent the concrete surface from bumping.
2. When the components installed on the guardrail need to be welded, attention should be paid to protecting the concrete on the surface of the guardrail from being damaged.
5 Quality problems that should be paid attention to
1. Because the section size of the crash barrier is basically large at the bottom and small at the top, embedded steel bars must be used to hold down the formwork during formwork reinforcement to prevent the formwork from floating when pouring concrete.
2. When pouring guardrail concrete, bubbles tend to gather on the side. When pouring, two layers should be poured at the corner to make the bubbles in the lower concrete disperse as far as possible. In the process of concrete vibrating, the beating on the inclined plane of formwork should be strengthened manually to minimize the phenomenon of more bubbles on the inclined plane of concrete.
3. The bridge on the horizontal curve should carefully check the position of the guardrail and its relative relationship with the beam and slab to prevent the embedded reinforcement of the guardrail from being buried in the wrong position.
4. The position and angle of true seam should be accurate, and the template should be completely disconnected. After the guardrail is removed, the real joints shall be cleaned in time, and no hard objects such as concrete and stones shall be left at the joints to prevent blind joints.
6. Environmental and occupational health and safety management measures
6. 1 Environmental management measures
1. When the construction site is close to residential areas, sound insulation measures should be taken to avoid construction at night and prevent noise from disturbing people.
2. When the formwork is coated with isolation agent, measures should be taken to prevent the steel bar and the surrounding environment from being polluted.
3. Dust reduction measures should be taken to prevent dust.
6.2 Occupational Health and Safety Management Measures
1. Before construction, scaffolding, working platform and safety net shall be erected on the outside of the bridge.
Workers working outside the bridge should wear safety belts.
3. It is forbidden to throw objects under the bridge during construction.
4. The concrete pouring construction vehicles shall be uniformly dispatched by special personnel, and the cranes and pump trucks must be commanded by bell men with work licenses.
5. Night construction must have sufficient lighting facilities.
Copyright statement: All the above contents are from Zhu Long Luqiao.
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