What problems should be paid attention to in winter construction?

Winter construction scheme of building engineering

1 winter construction start date

According to the Code for Winter Construction of Building Engineering (JJ104-97), when the daily average outdoor temperature is lower than 5℃ for five consecutive days, winter construction will begin. When the daily average outdoor temperature is higher than 5℃ for five consecutive days, the winter construction will be terminated. The start and end dates of winter construction in Dalian are generally 165438+ 10/4 to April of the following year 1. The start and end dates can be determined by actual measurement or through negotiation between both parties.

2 Winter construction technical preparation work

2. 1 winter construction technology preparation principle:

1) to ensure the engineering quality.

2) During winter construction, ensure safety in production; The construction of the project should be carried out continuously.

3) The winter construction plan (measures) should be made according to the time, place and project, which requires both technical reliability and economic rationality.

4) Reliable sources of required heat sources and materials should be considered to reduce energy consumption.

5) Strive for fewer construction sites, faster construction speed and shorter construction period.

6) The winter construction scheme (measures) or unfinished projects of winter construction preparation shall not be forcibly implemented.

7) Effective winter construction management measures must be formulated.

2.2 Preparation of Winter Construction Scheme

2.2. 1 Preparation before preparation of winter construction scheme

1) When entering the winter construction, it is necessary to conduct a comprehensive investigation and master the necessary information: the building area of the winter construction building, the project and its workload, the winter construction site and its technical requirements.

2) In winter construction projects, the drawings shall be comprehensively reviewed. If the project (or part of the project) is not suitable for the winter construction requirements, it should be timely proposed to the construction unit and design unit to modify the design requirements.

3) According to the technical requirements of winter construction, master the resource supply situation.

4) For complex projects and projects with high technical requirements, it is necessary to comprehensively analyze the technical feasibility of winter construction (including economy, energy, project quality, construction period, etc.).

2.2.2 Main contents of winter construction scheme:

1) winter construction production task arrangement and construction deployment.

2) The physical quantity and workload of the project, the construction procedures, progress, construction methods and technical measures of sub-projects in different stages of winter construction.

3) Heat source equipment plan (including heat source and heat energy conversion equipment).

4) thermal insulation materials, admixture materials plan.

5) Technical training and labor force planning of construction personnel in winter.

6) Key points of engineering quality control.

7) Technical measures for safe production and fire prevention in winter.

3 Winter construction production preparation work

3. 1 Winter construction site preparation

3. 1. 1 Construction site preparation:

1) Eliminate the accumulated water in the site, make necessary repairs to the construction site, cut off the water flowing into the site, and take drainage measures to eliminate the icing phenomenon caused by water and steam in the site construction.

2) After the construction site is cleared of snow, it should not be placed near the stacking site of mechanical and electrical equipment and parts.

3) Ensure smooth fire control roads.

3. 1.2 mixer shed insulation

The entrances and exits before and after the mixer shed should be closed, and the shed should be heated. Set hot water filling and admixture storage containers. When cleaning the mixer, the sewage should be well drained, the sedimentation tank should be closed to prevent freezing, and it should be cleaned regularly to keep the sewage management smooth.

3. 1.3 boiler room setup

Before entering the winter construction, the boiler room must be erected and the pipeline buried. The buried depth of buried pipelines should exceed the freezing depth, and overhead pipelines should be well insulated.

3. 1.4 Water pipes, cut-off wells and fire hydrant wells shall be well insulated.

3. 1.5 mobilization and erection of raw material heating equipment and facilities, such as mixed water heating equipment and sand heating hot pit.

3.2 Preparation of winter construction resources

3.2. 1 Stability of quasi-additive varieties of additive materials. According to the varieties of additives selected in the winter construction scheme and the market supply situation, the formula, varieties and dosage of additives are finally put forward.

1) admixture dosage plan. According to the parts and quantities of additives used in the project, the dosage plan is calculated and submitted to the material supply department.

2) The second interview of admixture. For additives sold in the market, re-inspection should be carried out in advance to ensure that their performance meets the technical requirements. For one-component admixture, the content of its effective components is determined.

3.2.2 Preparation of thermal insulation materials

Selection of thermal insulation materials.

Thermal insulation materials used in winter construction require good thermal 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: Lightweight, fireproof and good thermal insulation polystyrene foam board and rock wool are used.

② Thermal insulation of concrete surface: plastic film with good gas thermal insulation performance, rock wool felt with good thermal insulation performance, straw curtain, etc. The straw curtain is flammable and easy to disperse, so it should be wrapped with glass fiber cloth before use. )

③ Thermal insulation of foundation trench and foundation pit: choose cheap thermal insulation materials such as straw curtain.

④ Pipeline insulation: perlite insulation tile and straw rope are selected.

⑤ Thermal insulation of trolley and mortar barrel: polystyrene foam board is selected.

⑥ Windproof and greenhouse insulation: reed and canvas awning are generally used.

⑦ Door and window openings are closed for thermal insulation: plastic sheets and curtains are selected.

2) quantity and plan of thermal insulation materials

According to the varieties, specifications, turnover times and quantity of thermal insulation materials selected by winter construction method, the annual planned consumption is calculated, and the plan and entry date are put forward to the material department.

3.2.3 Preparation of Fuel for Winter Construction

Winter construction fuel mainly considers domestic coal and heat source medium for engineering heating construction to ensure the needs of life and production, and should be prepared according to the requirements in the construction plan.

Preparation of heat source equipment

1) Installation, heat preservation and trial burning of boilers and pipelines.

2) Installation of heat source equipment: such as installing large formwork, exhaust pipe or steel string, electric heating wire, etc. Air heater, coal stove, chimney, etc.

3) Raw material heating facilities at the construction site, such as water heaters and hot water tank bunkers.

4) Install domestic coal stoves or heating pipes and radiators.

3.2.5 Preparation of construction instruments and meters in each stage

Atmospheric temperature test: wooden shutter box, maximum and minimum thermometers.

Admixture concentration measurement: stick thermometer, electronic induction instrument, etc.

Indoor temperature measurement: dry and wet thermometer.

Various temperature measurements: forms and stationery.

4 Main construction methods and techniques for winter construction

4. 1 excavation and backfilling of frozen soil

4. 1. 1 artificial excavation of frozen soil.

1) Excavation method: generally, 1 person planed with a sharp pick, or 3-4 people split the frozen soil with an iron wedge.

2) Construction tools: pick, shovel, 18-24 pound sledgehammer, iron wedge made of 450-60 round steel and small railway steel, with the tip flattened.

3) Key points of operation: 1 One person holds the iron wedge, and 2-3 people take turns to smash the sledgehammer to split the frozen soil according to the stubble. Generally, 2-3 iron wedges are enough. When the first wedge is not completely split, put the second iron wedge on the next crack until the frozen soil is peeled off.

4) Measures to ensure safety:

(1) Pay attention to remove the flying thorn on the iron wedge head to avoid injury.

(2) The iron wedge and the sledgehammer can't face each other, and they must form a 90-degree angle to avoid the sledgehammer turning around and hurting people.

(3) The iron wedge should be made of thick iron wire or steel handle to prevent broken hands and accidental injuries.

4. 1.2 Mechanical excavation of frozen soil

1) Method of mechanical excavation of frozen soil: When the thickness of frozen soil is less than 0.4m, different types of mechanical equipment can be selected for direct excavation; If the thickness of frozen soil exceeds 0.4- 1.2m, the frozen soil shall be crushed with a heavy hammer, and then loaded and transported out with a loader or backhoe loader.

2) According to the size and shape of the excavation area and the specific situation of the excavation depth, determine the working direction of excavators, loaders, shredders, etc. Should be reasonably arranged to ensure the smooth transportation road, and should have a reasonable access to the ring road, in order to give full play to the efficiency of all kinds of working machinery and equipment.

4. 1.3 Frozen soil backfill

After the foundation pit and foundation trench are laid, when the soil containing frozen soil blocks is allowed to be backfilled, the diameter of frozen soil particles shall not be greater than 5cm, and the content shall not exceed 15% of the total fill volume.

1) Frozen soil is not allowed to be backfilled inside the house.

2) When backfilling underground pipeline trench, frozen soil shall not be used for backfilling within 50cm of the pipe top thickness, and the frozen soil volume below 50cm shall not exceed 15%.

3) The frozen soil shall not be backfilled in the structures, paved roads and grooves in the subgrade.

4) In order to ensure the quality of backfilling in winter, some major projects can be used to backfill sand when necessary.

5) Ground beams and caps on frost heave soil may be lifted by frozen soil, and loose materials such as slag and slag should be backfilled.

6) All backfilled places must be drained of accumulated water and cleared of ice and other sundries. The paving thickness of each layer should be less than that in summer, generally not more than 20cm, compacted by rammer or roller, and dug into the lower part of the guide ditch, but not more than two-thirds of the thickness of frozen soil layer.

4. 1.4 Foundation pit protection

After foundation pit excavation, heat preservation measures should be taken in time to prevent frozen soil: after passing the inspection, the following procedures should be entered in time.

4.2 Negative temperature welding of reinforcement

When the ambient temperature is lower than -5℃ in the welding construction of steel bar engineering, the welder engaged in steel bar welding production must hold the Certificate of Steel Bar Welder Examination before negative temperature welding of steel bar can be carried out. Formulate and implement safety technical measures, strengthen the labor protection of welders, and prevent accidents such as burns, electric shocks and fires. Before welding steel bars, trial welding must be carried out according to the construction conditions, and welding can only be carried out after passing the test: after welding, the welder shall conduct self-inspection on the appearance quality of all joints, and the unqualified ones shall be rejected. 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 contact with ice and snow. When the ambient temperature is lower than -20℃, welding is not allowed.

4.2. 1 negative temperature electroslag pressure welding of steel bar

1) scope of application: when the diameter of steel bar is ≥22cm, lap welding should be adopted.

2) Quality acceptance

① Sampling: visually inspect 65,438+00% of joints in each batch, not less than 65,438+00. In the mechanical property test, 6 specimens (qualified by visual inspection), 3 tensile tests and 3 bending tests should be cut from each batch of finished products.

In the same category, 200 joints of the same type completed by the same welder according to the same welding parameters are regarded as a batch. When welding continuously within one week, it can be calculated cumulatively. If there are less than 200 joints in a week, it will be counted as a batch. Welding equal-length prestressed steel bars (including welded joints between threaded steel bars and steel bars), simulation specimens can be made according to production conditions.

② Appearance inspection

The visual inspection results shall meet the following requirements: there shall be no transverse cracks at the joint. For secondary and tertiary steel bars, the surface of steel bars in contact with steel bars shall be free from burns. The bending of the joint should not be greater than 4o. The axis deviation of the steel bar at the joint should not be greater than 0. 1 sense diameter, and should not be greater than 2cm at the same time. When a joint does not meet the requirements, all joints shall be inspected and rejected. Unqualified joints can be submitted for secondary acceptance after being removed and re-welded.

3) Precautions

① Install a voltmeter in the power switch of the butt welder and observe the voltage fluctuation. When welding, if the voltage drop is greater than 5%, the number of transformer stages should be appropriately increased; If the voltage drops to 8%, stop welding.

(2) Before formal production every day, try to weld two joints. After the appearance inspection is qualified, the production can be carried out according to the selected welding cursive script.

(3) Before welding, the rust, dirt, etc. on the welded parts of the steel bar and the covered electrode and the contact parts of the steel bar must be removed. Distortion and bending of steel bar ends shall be straightened or cut off.

(4) All links in the operation process should cooperate closely to ensure the welding quality. If there are any abnormal phenomena or welding defects, they should be removed in time.

4.2.2 Negative temperature arc welding of steel bar

1) Scope of application: When the diameter of steel bar is less than or equal to ≤22mm, lap welding is adopted.

2) Selection of covered electrode: Grade I reinforcement e43；; Grade Ⅱ reinforcement e50

3) Preparation before welding

(1) Before welding, remove rust, slag and oil stain. Steel bars and steel plates at welding parts must be removed; Distortion and bending of steel bar ends shall be straightened or cut off.

(2) Double-sided welding should be adopted for lap welding of steel bars, and single-sided welding can be adopted if double-sided welding is not possible.

4) Welding process

Appropriate covered electrode diameter and welding current should be selected according to the grade, diameter, joint type and welding position of reinforcement. Multi-layer temperature control welding technology should be adopted during welding to prevent the cooling speed after welding from being too fast and the joint from overheating. The welding process shall meet the following requirements:

(1) When welding, use two fixings. The locating weld shall be more than 20 mm away from the upper steel strip or lap end.

(2) When welding, the arc striking should start from one end of the lap steel bar, and the arc closing should be at the end of the lap steel bar, and the arc pit should be filled.

(3) During lap welding, the first layer of weld starts arc from the middle, and then carries arc to both ends; In vertical welding, the arc is transmitted from the middle to the top and then from the bottom to the middle. So that the steel bars at the end of the joint can achieve a certain preheating effect. The vendors on the first floor should have sufficient penetration, and the main weld and the positioning weld, especially the beginning and end of the positioning weld, should be well fused. In the future, when welding all layers of welds, the temperature should be controlled by layers for welding. The interlayer temperature is controlled between 150℃-350℃ to slow down the cooling.

(4) The weld thickness h of lap joint should not be less than 0.3 steel bar diameter; Weld width 6 is not less than 0.7 steel bar diameter.

⑤ When multi-layer welding is carried out on the lap welds of Grade II and III steel bars, the "tempering bead welding method" is adopted, that is, the length of the last layer of tempering bead at both ends is 4-6mm shorter than that of the previous layer.

5) Quality acceptance

① Sampling: visual inspection. Visual inspection or measurement shall be carried out one by one after slag removal of joints. Tensile test: three samples are cut from the finished products that have passed the visual inspection for tensile test. For the high-energy champion welded joints of assembled structural joints, simulated specimens can be made according to production conditions. Under the condition of field installation, 300 similar joints (same steel grade, same joint form and same welding position) in each floor are regarded as a batch, and less than 300 joints are still regarded as a batch.

② Visual inspection: The results of visual inspection shall meet the following requirements: the surface of weld shall be smooth, and there shall be no big sag or flash. There shall be no cracks at the joints. The deviation of undercut depth, number and size of air holes and slag inclusions and joint size shall not exceed the specified value. Joints that fail the visual inspection can be submitted for secondary acceptance after finishing or reinforcement.

6) Matters needing attention of joint

When welded joints are used for reinforcement, the welded joints in the same component should be staggered. Within the scope of 30 times the diameter of steel bar (not less than 500mm), a steel bar should not have two joints (welded joints should be set as little as possible for the full-length steel bar of members), and the percentage of the sectional area of steel bar with joints in the total sectional area of steel bar should meet the following requirements:

(1) pulling area-should not exceed 50%;

(2) The joints between the compression zone and the fabricated structure are not restricted.

4.3 concrete engineering

The concrete adopts commercial concrete.

Material requirements of concrete

1) cement: Portland cement or ordinary Portland cement is selected.

2) Aggregate: clean, well-graded, hard, free of ice and snow, and should not contain minerals easily damaged by freezing.

3) Mixing water: water that has passed the inspection.

4) Admixtures: Admixtures that have passed technical appraisal and meet quality standards are selected.

4.3.2 Concrete Mix Proportion

According to the concrete mixture ratio provided by the laboratory.

4.3.3 Concrete mixing control

The mixing time of concrete in winter should be 50% longer than normal temperature.

Transportation of concrete

After the concrete mixture is discharged from the machine, it should be transported to the pouring place in time. During the operation meeting, pay attention to prevent concrete from heat loss, surface freezing, concrete thinning, cement mortar loss and slump change.

concrete pouring

1) General requirements

When pouring concrete, it is necessary to ensure the uniformity and compactness of concrete, the integrity of structure, the accuracy of size, the position of steel bars and embedded parts, and the smoothness of concrete surface after formwork removal.

Before pouring, the snow, ice and dirt on the formwork and reinforcement shall be removed. When pouring, the mortar taken out from the mixing plate, hopper, funnel or various running tools is easy to freeze with the container. Therefore, windproof and antifreezing 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 construction joint should be in the position where the structural shear force is small and convenient for construction. Column should be horizontal seam; Beams, plates and walls should be left with vertical joints. Columns should be left on the top surface of foundation, high beams should be left 20-30 mm below the bottom surface of slab, and flat floor should be left anywhere parallel to the short side of slab. Stairs should be kept within 1/3 of the length of stairs.

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 paved. When the concrete strength is higher than 1.2mpa, it is allowed to continue pouring.

2) Concrete pouring

When the concrete mixture is poured into the formwork, it must be vibrated to make its interior compact, fully fill every corner of the formwork, and make components that meet the design requirements. Vibrating concrete in winter should be mechanically vibrated, and the vibration should be faster. Before pouring, necessary work must be done, such as checking templates, steel bars and embedded parts, removing frozen blocks, erecting scaffolding for pouring, checking anti-skid measures, and preparing vibrating machinery and tools. When pouring columns, each row of columns in a construction period should be poured symmetrically from the outside to the inside, and should not be pushed from one end to the other, so as to prevent the residential formwork from being pushed and gradually inclined, causing error accumulation and being difficult to correct.

Beam and slab are generally poured at the same time, and pushed forward from one end. Only when the beam height is greater than 1m can the beam be poured separately. At this point, the construction joint should be 2-3 cm below the floor surface, and the beam bottom and beam side should be compacted. Vibrators should not be in direct contact with steel bars or embedded parts. The virtual paving thickness at the bottom of floor concrete should be slightly greater than the thickness after work. After vibrating, smooth it with a long-bottom wood trowel, and then spread a plastic film, which should be covered with a protective layer in time.

concrete curing

Thermal storage method should be selected for maintenance: one layer of plastic film and two layers of straw bags for thermal insulation.

Concrete form removal

1) The dismantling time of concrete formwork should be determined according to structural characteristics, natural temperature and concrete strength, and it is generally appropriate to dismantle it slowly.

2) Dismantle the formwork, and the concrete strength must also meet the requirements.

3) When ripping in winter, the surface temperature and natural temperature of concrete should not exceed 20℃.

4) In the process of formwork removal, if the concrete is found to be frozen, the removal shall be suspended, and the removal can be continued only after being treated.

5) The concrete after formwork removal shall be protected by thermal insulation materials. Structural concrete is not allowed to bear load until it reaches the specified strength. Overloading is not allowed in the construction, and too many building materials or machines are not allowed to be piled on it.

Determination of concrete temperature

The air temperature, raw material and concrete temperature shall be measured as follows:

1) At 8: 00, 12, 14 and 20: 00, the temperature was measured four times day and night.

2) The temperature of mixing materials and antifreeze shall be measured at least 3 times per shift.

3) Measure the temperature of concrete mixture when it leaves the mixer at least every 2 hours.

4) Before pouring and after vibrating, the temperature shall be measured at least once every 2h.

5) Measurement of concrete temperature during curing: Before final setting, it shall be measured every 2 hours for the first three days and twice every day and night thereafter.

6) After the curing period, when the temperature changes greatly, the concrete temperature can be sampled.

7) In order to measure the internal temperature of concrete, some closed temperature measuring tubes should be embedded when pouring concrete and covered immediately to avoid being affected by external temperature. Keep the thermometer in the tube for 5 minutes, then take it out and write down the temperature quickly.

8) Temperature measuring holes should be located in representative places with low concrete temperature.

9) All thermometer holes shall be numbered and the layout of thermometer holes shall be drawn. At the same time, the temperature measuring personnel should check the covering insulation to know the pouring date and curing period of the structure and the allowable minimum temperature of concrete. If problems are found, relevant personnel shall be informed immediately, so as to take timely measures to strengthen heat preservation or local short-term heating.

4.3.9 Concrete Specimen and Strength Inspection

Article 4.6.4 of Code for Construction and Acceptance of Reinforced Concrete Engineering shall stipulate the sampling rate of specimens or the concrete bearing capacity that a group of test blocks can represent at most:

1) Each working class has at least one group.

2) Pouring not less than one set of 100m3 concrete.

3) Cast-in-place floor slab, with at least one set for each floor.

In addition, winter construction should be inspected: a batch of beam and frame concrete should be reserved for every 50m3 pouring. At least 4 groups of specimens in each batch shall be tested at -28d, demoulding, steering +28d and delivery. It's best to make more sets as spare specimens. The strength specimen shall be made of concrete mixture poured on the construction site and maintained under the same conditions as the structure or member.

5 Winter construction personnel training

Construction personnel training: organize relevant professionals to learn the theory, norms, procedures and construction technology of winter construction.

6 winter construction safety management

Winter construction should comply with safety laws and regulations, combined with the following contents for safety management.

6. 1 winter construction safety education

1) Conduct regular technical safety education for all employees. Combined with engineering tasks, do a good job in safety technical disclosure before winter construction. Equipped with safety protection articles.

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 made known.

3) Special jobs (including electrical, bent, lifting, boiler, welding, blasting, machinery, vehicles, etc.). ) It can only be operated after professional training and certification by relevant departments. Review is conducted once a year.

4) Adopt new equipment and tools. The new process should provide the operators with safety technical disclosure of mechanical properties and operation methods.

5) All engineering construction organization design and construction scheme must have safety technical measures. Blasting, potholes, shuttering, shelving and other projects must be prepared with a single technical safety plan (also known as safety design) and detailed disclosure, otherwise construction is not allowed.

6.2 Site Safety Management

1) The storage places of various materials, concrete members, acetylene bottles, oxygen, etc. and the acetylene centralized station in the construction site shall meet the safety requirements, and the management shall be strengthened.

2) For pit and groove construction in winter, slope protection measures should be formulated according to soil conditions and engineering characteristics: slope stability should be checked during construction and after thawing, and measures should be taken in time if cracks, loose soil or deformation of slope protection piles are found.

3) Strengthen seasonal labor protection. In winter, we should do a good job in anti-skid, anti-freezing and gas poisoning prevention. Scaffolding, main access and anti-skid measures should be taken. Clean up in time after frost and snow. Check the scaffolding in time after the snowstorm to prevent falling accidents.

6.3 Electrical Safety Management in Winter

1) The time for case prevention and construction organization in winter construction must have on-site electrical circuits and a plan with ten times the location. An electrician should be set up on site to be responsible for the installation, maintenance and management of electrical equipment. It is strictly forbidden for non-electricians to dismantle and change at will.

2) Bare wires are strictly prohibited on the construction site. The laying of electric wires should prevent crushing and rolling, so as to prevent the wires from freezing in snow and ice. After the snowstorm, it is necessary to check the power supply lines to prevent electric shock accidents caused by broken wires.

3) If electric heating equipment is used to raise the temperature of the construction environment, a "Prevention Plan for Strong Electricity Entering the Building" shall be prepared. Electrical equipment adopts special switch box. The plugs of strong current and weak current should be separated to prevent accidents caused by misoperation.

6.4 Cancel the safety management after winter construction.

With the increase of temperature, winter application can only be lifted if there is no negative temperature for seven consecutive days and nights. But pay attention to the following points:

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) During winter construction, the elevated, external elevators, shelves and towers with a height of more than three floors attach importance to subgrade and telephone poles. And a general survey should be conducted to prevent the foundation from collapsing due to freeze-thaw settlement.

3) Masonry built by freeze-thaw method shall be constructed according to masonry engineering when thawed.

4) Take necessary measures according to the provisions of the engineering acceptance specification.

Material yard and large formwork yard shall be inspected and classified. Prevent piles and half-members from collapsing in soil freezing and thawing.