1. Preparation for winter construction
1.1 Starting date of winter construction When the average outdoor daily temperature is lower than 5℃ and the lowest temperature is lower than -3℃ for five consecutive days, winter construction will be started; When the outdoor daily average temperature is higher than 5℃ for 5 consecutive days, the winter construction will be terminated.
1.2 Technical preparation for winter construction
1.2.1 Ensure project quality.
1.2.2 during winter construction, ensure safety in production; The construction of the project should be carried out continuously.
1.2.3 winter construction plan (measures) should be made according to the time, place and project, which requires both technical reliability and economic rationality.
1.2.4 reliable sources of required heat sources and materials should be considered to reduce energy consumption.
1.2.5 strive for fewer construction points, faster construction speed and shorter construction period.
1.3 preparation for winter construction production
1.3.1 preparation for winter construction site
1.3.1.1 preparation for construction site: ① remove the accumulated water on site, make necessary repairs to the construction site, cut off the water flowing into the site, and take drainage measures to eliminate the freezing phenomenon of construction water on site. (2) to ensure the smooth construction access road.
1.3.1.2 Heat preservation of mixer shed
The entrance and exit of mixer shed front and back should be closed and the shed should be warmed. Set hot water filling and admixture storage containers. When cleaning the mixer, the sewage should be well drained, the sedimentation tank should be closed, frozen should be prevented, cleaned regularly, and the sewage management should be kept smooth.
1.3.1.3 approach and erection of raw material heating equipment and facilities, such as mixing water heating equipment and sand heating hot pits.
1.3.2 preparation of winter construction resources
1.3.2.1 stability of additive materials and additive varieties. According to the varieties of additives selected in the winter construction scheme, combined with the market supply situation, the formula, varieties and quantity of additives are finally put forward. (1) admixture dosage plan. According to the use of additives engineering parts, quantities, calculate the dosage plan, submitted to the material supply department. (2) the second interview of admixture. For additives sold in the market, re-examination should be done in advance to ensure that their performance meets the technical requirements. For single-component admixture, determine the content of its effective components.
1.3.2.2 Preparation of insulation materials Selection of insulation materials The insulation materials used in winter construction require good insulation performance, low price and local materials. Some require good fire resistance. Commonly used thermal insulation materials can be roughly divided into: ① thermal insulation of steel formwork: polystyrene foam board and rock wool with light weight, fire prevention and good thermal insulation performance are used. ② Thermal insulation of concrete surface: plastic film with good gas insulation performance, rock wool felt with good thermal insulation performance, straw curtain, etc. (Grass curtain is flammable and easy to disperse, so it should be packaged with glass fiber cloth before use.) ③ Thermal insulation of foundation trench and foundation pit: choose cheap thermal insulation materials such as grass curtain.
1.3.3 Prepare the instruments and meters for atmospheric temperature test in winter: wooden louvers, maximum and minimum thermometers.
2. Main construction methods and techniques of bridge and culvert engineering
2.1 After excavation of foundation pit engineering, heat preservation measures should be taken in time to prevent frozen soil from being produced; after passing the inspection, the next working procedure should be entered in time.
2.2 reinforcement engineering, in the reinforcement engineering welding construction, when the ambient temperature is lower than -5℃, butt welding or arc welding of reinforcement is carried out for negative temperature welding of reinforcement. Welders in production must hold the examination certificate of rebar welder. Safety technical measures should be formulated and implemented to strengthen the labor protection of welders and prevent accidents such as burns, electric shocks and fires. Before rebar welding, a trial welding must be carried out according to the construction conditions, and welding can only be carried out after it is qualified: the welder shall conduct self-inspection on the appearance quality of all joints after welding, and reject the unqualified ones. When welding at negative temperature, the welding process parameters should be adjusted to make the weld and heat affected zone cool slowly. Wind protection measures should be taken when the wind force exceeds level 4. Joints that are not cooled after welding should avoid touching snow and ice. When the ambient temperature is lower than -2℃, welding shall not be carried out.
According to the grade, diameter, joint type and welding position of steel bar, choose the appropriate covered electrode diameter and welding current. When welding, it is advisable to adopt multi-layer temperature control welding process to prevent the cooling rate after welding from being too fast and the joint from overheating. The welding process shall meet the requirements of the specification.
2.3 concrete engineering concrete is mixed in a mixing station and transported by a concrete tanker.
2.3.1 material requirements of concrete ① cement: portland cement or ordinary portland cement is selected. (2) Aggregate: It is required to be clean, well graded, hard and free of minerals that are easily damaged by freezing. ③ Mixing water: water that has passed the test. ④ Admixtures: Admixtures that have passed technical appraisal and meet quality standards are selected.
2.3.2 the concrete mixture ratio is prepared according to the concrete mixture ratio provided by the laboratory.
2.3.3 concrete mixing control The mixing time of concrete in winter should be 5% longer than that at normal temperature.
2.3.4 transportation of concrete After the concrete mixture is discharged from the machine, it should be transported to the pouring site in time. During the operation meeting, pay attention to prevent concrete heat loss, surface freezing, concrete thinning, cement mortar loss and slump change.
2.3.5 Concrete pouring
2.3.5.1 Generally, it is required to ensure the uniformity and compactness of concrete, the integrity of the structure, the accurate size, the location of steel bars and embedded parts, and the smooth and smooth surface of concrete after formwork removal.
before pouring, the snow, ice and dirt on the formwork and steel bars should be removed. When pouring, the mortar removed from the mixing board, hopper, funnel or various running tools is easy to freeze with the container. Therefore, windproof and freezing protection measures should be taken before pouring. Once the concrete is found to be frozen, it should be heated and stirred twice to make the mixture suitable for construction and workability before pouring.
the position of the construction joint should be in the position where the structural shear is small and convenient for construction. Column should be horizontal seam; Vertical joints shall be reserved for beams and plates. Columns should be left on the top surface of foundation.
when pouring concrete at the construction joint, the cement film and loose stones should be removed first, and then the temperature of the original concrete at the joint should be higher than 2℃, and then a layer of cement slurry or mortar with the same composition as the concrete mortar should be spread. When the strength of the concrete to be poured is higher than 1.2mpa, it is allowed to continue pouring.
2.3.5.2 concrete pouring concrete mixture must be vibrated to make its interior compact, and it can fully fill all corners of the formwork to make components that meet the design requirements. In winter, the vibrating concrete shall be vibrated mechanically, and it shall be vibrated quickly. Before pouring, necessary preparations shall be made, such as inspection of formwork, steel bars and embedded parts, removal of frozen ice and snow, inspection of scaffolding used for pouring, anti-skid measures, preparation of vibrating machinery and tools, etc.
2.3.6 concrete should be cured by heat storage method: one layer of plastic film and two layers of straw bag for heat preservation.
2.3.7 concrete form removal ① The time for concrete formwork removal should be determined according to the structural characteristics, natural temperature and the strength of concrete, and it is generally advisable to slowly remove it. (2) remove the template, concrete strength must also meet the requirements. (3) when dismantling the formwork in winter, the surface temperature of concrete and the natural temperature should not exceed 2℃. (4) in the process of dismantling the template, if the concrete is found to have frost damage, the dismantling should be suspended, and the dismantling can be continued only after being processed. ⑤ The concrete whose formwork has been removed shall be protected by thermal insulation materials. Structural concrete is not allowed to bear load until it reaches the specified strength. It shall not be overloaded during construction, and it is forbidden to pile up excessive building materials or machines on it.
2.3.8 determination of concrete temperature the measurement of air temperature, raw materials and concrete temperature shall be carried out as follows: (1) measurement of air temperature shall be carried out four times at 8, 12, 14 and 2 o'clock every day and night. (2) the mixing material and antifreeze temperature measurement, not less than 3 times per shift. (3) the temperature of the concrete mixture when leaving the mixer shall be measured at least once every 2 hours. (4) The temperature before pouring and after vibrating shall be measured at least once every 2h. ⑤ Measurement of concrete temperature during curing: Before final setting, it shall be measured every 2h for the first three days, and then the index shall be measured twice every day and night. ⑥ After the curing period is over, the concrete temperature can be sampled when the temperature changes greatly. ⑦ In order to measure the internal temperature of concrete, some closed temperature pipes should be embedded when pouring concrete, and covered immediately, so as not to be affected by the external temperature. The thermometer stays in the pipe exponentially for 5 minutes, then takes it out and writes down the temperature quickly. ⑧ The thermometer hole should be located in a representative place where the concrete temperature is low. Pet-name ruby all thermometer hole should be numbered, thermometer hole layout should be drawn. At the same time, the temperature measuring personnel should check the covering insulation, and know the pouring date and curing period of the structure, as well as the allowable minimum temperature of concrete. If problems are found, the relevant personnel shall be informed immediately, so that measures can be taken in time to strengthen heat preservation or local short-term heating.
2.3.9 concrete specimen and strength inspection ① There shall be no less than one group in each shift. (2) every casting 1m? No less than one set of concrete.
3. Training of construction personnel in winter
Training of construction personnel: organize relevant professionals to learn the theories, norms, regulations and construction techniques related to winter construction.
4. Safety management of winter construction
Winter construction shall comply with safety laws and regulations, and carry out safety management in combination with the following contents.
4.1 winter construction safety education
4.1.1 technical safety education must be given to all employees regularly. Make safety technical disclosure before winter construction in combination with engineering tasks. Equipped with safety protection articles.
4.1.2 workers must be educated on safety and operating procedures: those who change jobs or temporarily take part in productive labor should also be educated on safety and safety disclosure.
4.1.3 Special types of work (including electrical, shelving, lifting, welding, machinery, vehicles, etc.) can only be operated after professional training by relevant departments and examination and certification. A review is conducted once a year.
4.1.4 adopt new equipment and tools. The new process shall provide the operators with safety technical disclosure on mechanical properties and operation methods.
4.1.5 safety technical measures must be taken in the construction organization design and construction scheme of all projects. Blasting, pit, shuttering, shelf and other projects are all prepared with a single technical safety plan (also known as safety design) and detailed disclosure, otherwise construction is not allowed.
4.2 On-site safety management
4.2.1 All kinds of materials, concrete components, acetylene bottles, oxygen and other storage sites and acetylene centralized stations in the site should meet the safety requirements, and management should be strengthened.
4.2.2 In winter pit and groove construction, slope protection measures should be formulated according to soil conditions and engineering characteristics in the scheme: slope stability should be checked during construction and after thawing, and timely measures should be taken in case of cracks, loose soil or deformation of slope protection piles.
4.2.3 Strengthen seasonal labor protection. In winter, anti-skid, anti-freezing and gas poisoning prevention should be done well. Scaffolding shall be provided with anti-skid measures. Clean it in time after frost and snow. Check the scaffolding in time after the snowstorm to prevent falling accidents.
4.3 electrical safety management in winter
4.3.1 During the winter construction prevention and construction organization time, there must be a site electrical circuit and location plan. Electricians should be set up on site to be responsible for the installation, maintenance and management of electrical equipment. It is forbidden for non-electricians to dismantle and change at will.
4.3.2 bare wires are strictly prohibited in the construction site. The laying of electric wires shall be protected against smashing and rolling, so as to prevent the wires from freezing in the snow and ice. After the snowstorm, the power supply lines should be inspected to prevent electric shock accidents caused by broken lines.
4.3.3 electric heating equipment shall be adopted to improve the temperature of the construction environment, and special switch box shall be used as the electrical equipment. The plugs of strong power supply and weak power supply should be separated to prevent accidents caused by misoperation.
4.4 release the safety management after winter construction
with the temperature rising, winter construction can be released only if there is no negative temperature for seven consecutive days and nights. However, the following points should be noted: ① The stability of the soil slope should be observed at any time in the deep pit, and a special person should be responsible for the observation. When conditions permit, we should pay close attention to backfill soil. (2) Masonry built by freezing and thawing method shall be constructed according to masonry engineering during thawing. (3) the provisions of the construction acceptance specification to take necessary measures. (4) material yard, big template yard should be checked and sorted. Prevent piles and components from collapsing in soil freezing and thawing.
5. Conclusion
China has a vast territory, and the climate in different regions is quite different. In the construction of highway bridges and culverts, it is inevitable to carry out winter construction to ensure the progress of the project. How to effectively determine the quality of bridge engineering in winter construction has become a problem worthy of discussion.
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