1 winter construction start date
According to the provisions of the "winter construction of construction engineering regulations" (jgj104-97), the average daily outdoor temperature for five consecutive days stable lower than 5 ℃ that is, into the winter construction; when the average daily outdoor temperature for five consecutive days stable higher than 5 ℃ when lifting the winter construction. When the outdoor average daily temperature is steadily higher than 5℃ for five consecutive days, the winter construction period is lifted. The start and end dates of winter construction in Dalian are generally from November 14 to April 1 of the following year. The start and end date can be determined by the actual measurement, can also be negotiated by the A and B parties unified delimitation.
2 winter construction technology preparation
2.1 winter construction technology preparation principles:
1) Ensure the quality of the project.
2) During the winter construction process, do safe production; the construction of the project should be carried out continuously.
3) Formulate the winter construction program (measures) should be adapted to the time and place of the project, which is technically reliable and economically reasonable at the same time.
4) Consideration should be given to the required heat source and materials have a reliable source, reduce energy consumption.
5) Strive to construction points less, construction speed, shorten the construction period.
6) Where there is no winter construction program (measures), or winter construction preparatory work is not done, the project shall not be forced to carry out winter construction.
7) Effective winter construction management measures must be developed.
2.2 Preparation of winter construction program
2.2.1 Preparation before the preparation of winter construction program
1) Into the winter construction, should be carried out a comprehensive research, to master the necessary data: winter construction of the building number of the floor area, the project and its workload, the winter construction parts and their technical requirements.
2) Into the winter construction projects, should be a comprehensive review of drawings. If not suitable for winter construction requirements of the project (or parts), should be timely to the construction unit and the design unit to modify the design requirements.
3) According to the technical requirements of winter construction, grasp the supply of resources.
4) For complex projects and projects with high technical requirements, a comprehensive analysis of the technical feasibility of winter construction should be carried out (including the economy, energy, quality of work, and schedule).
2.2.2 The main content of the winter construction program:
1) Winter construction production task arrangements and construction deployment.
2) The physical volume and workload of the project, construction procedures, progress plans and sub-projects in different winter construction phases of construction methods and technical measures.
3) Heat source equipment plan (including heating heat source and heat conversion equipment).
4) Insulation materials, additives materials plan.
5) Winter construction personnel technical training, labor force plan.
6) Project quality control points.
7) Winter production safety and fire prevention technical measures.
3 winter construction production preparations
3.1 winter construction site preparation
3.1.1 construction site preparation:
1) drain the site of water, the construction site for the necessary repairs, cut off the inflow of water into the site, do a good job of drainage measures, to eliminate the construction of the site with water, with the site of the steam caused by the phenomenon of icing.
2) Construction site snow clearance, should not be placed near the site of mechanical and electrical equipment, components stacking.
3) Ensure the smooth flow of the fire road.
3.1.2 Thermal insulation of mixer shed
The entrances and exits of the front and rear benches of the mixer shed should be well closed and the shed should be heated. Set up hot water irrigation, admixture storage containers. Mixer cleaning sewage should be well organized drainage, closed good sedimentation tank, to prevent freezing, regular cleaning, sewage management to keep open.
3.1.3 Boiler room setup
Before entering the winter construction period, the erection of the boiler room must be completed, as well as the buried pipes. The buried pipes should be buried deeper than the freezing depth, and the overhead pipes should be well insulated.
3.1.4 Upper water pipe, cut-off door well, fire hydrant well should be well insulated.
3.1.5 The entry and erection of raw material heating equipment and facilities, such as mixing water heating equipment and hot pits for sand heating.
3.2 Preparation of winter construction resources
3.2.1 Stabilization of quasi-admixture varieties of additive materials. According to the admixture varieties selected in the winter construction program, combined with the market supply situation, the final admixture use formula, varieties and quantities.
1) Admixture dosage plan. According to the use of additives in the project parts, the amount of work, calculate the dosage plan, reported to the material supply department.
2) Retest of additives. For the market sales of additives, should be done beforehand retesting work to ensure that its performance meets the technical requirements. For single-component additives, determine the content of the active ingredient.
3.2.2 Preparation of insulation materials
1) Selection of insulation materials
The insulation materials used in winter construction require good thermal insulation performance, inexpensive, locally sourced materials. Some requirements have good fire performance. Commonly used insulation materials, according to the use of its parts are broadly divided into:
① steel moldboard insulation: the use of lightweight, fire prevention, good thermal insulation performance of polystyrene foam board, rock wool and so on.
② concrete surface cover insulation: the choice of good insulation properties of plastic film, good insulation properties of rock wool felt, straw compilation of grass curtains. (Straw curtain due to flammable, and easy to disperse, should be used after the glass cloth packaging)
③The base groove, the pit of the heat preservation: the selection of inexpensive thermal insulation materials such as straw curtains and so on.
④Pipe insulation: use perlite insulation tile, grass rope, etc..
5 trolley, mortar drum machine insulation: selection of polystyrene foam board and so on.
6 wind gear, warm shed insulation: generally use reed, canvas canopy.
7 doors and windows opening closed insulation: selection of plastic sheeting, face curtains, etc..
2) the number of insulation materials and plans
According to the winter construction method selected insulation material varieties, specifications, the use of turnover times and the amount of work, calculated the annual plan of dosage, to the material department to put forward the plan and the date of entry.
3.2.3 Winter Construction Fuel Preparation
Winter construction fuel is mainly considered for living coal, engineering heating construction heat source with media, to ensure that the needs of life, production, should be prepared according to the requirements of the construction program.
3.2.4 Preparation of heat source equipment
1) Installation of boiler, pipeline, insulation, test firing.
2) Installation of heat source devices: such as large template for the installation of steam exhaust or steel skewers, electric heaters, etc.; heaters, coal stoves, smoke pipes, etc..
3) construction site of raw material heating facilities, such as hot water furnace, hot water tank sand pit.
4) Installation of coal stoves or heating pipes and heaters for living.
3.2.5 Preparation of construction instrumentation for all phases of construction
Atmospheric temperature test: wooden shuttering box, maximum and minimum thermometer.
Admixture concentration measurement: stick thermometer, electronic induction meter, etc..
Indoor temperature measurement: wet and dry thermometer.
A variety of temperature measurement: forms and stationery.
4 Main construction methods and processes for winter construction
4.1 Excavation and backfilling of frozen soil
4.1.1 Manual excavation of frozen soil square
1) Excavation method: generally 1 person with a sharp pickaxe planing or a group of 3-4 people with iron wedges to split frozen soil square.
2) Construction tools: there are pointed pickaxe, shovel, 18-24 pounds of sledgehammer and iron wedge made of 450-60 round steel, small railway steel, the tip of the crushed flat.
3) operation points: 1 person palms the iron wedge, 2-3 people take turns to hit the sledgehammer, the frozen soil according to the stubble split, generally available 2-3 iron wedge, when the first wedge is not completely split, the second iron wedge is placed on the side of the cracks to add, until the frozen soil is peeled off.
4) Ensure safety measures:
①Take care to remove the flying spikes hit by the head of the iron wedge to avoid injuries.
②The person of the iron wedge and the person hitting the hammer can not face each other, it must be a 90-degree angle, so as not to hurt people with the hammer falling head.
3 ③ iron wedge, to use thick wire or by the steel bar made of handle, to prevent shock hand and accidental injury, etc..
4.1.2 Mechanical excavation of permafrost party
1) Mechanical digging permafrost method: when the thickness of permafrost layer is 0.4m or less, you can choose different types of machinery and equipment to directly excavate, if the thickness of permafrost layer is more than 0.4-1.2m, the permafrost should be crushed with a heavy hammer, and then loaded and transported out with a loader or a reverse and positive shovel.
2) According to the size of the excavation area, shape and depth of the excavation of specific conditions, a reasonable arrangement of excavators, loaders and crusher, etc., the direction of operation, to ensure that the transportation road is smooth, there should be a reasonable in and out of the ring road, to give full play to the efficiency of a variety of operational machinery and equipment.
4.1.3 Frozen backfill
Foundation pit, foundation groove, etc. masonry is completed, allowed to backfill with soil containing frozen soil blocks, frozen soil particles shall not be greater than 5cm in diameter, and the content shall not be more than 15% of the total volume of the fill.
1) Frozen soil backfill is not allowed inside the house.
2) When backfilling the trench of underground pipeline, frozen soil shall not be used to backfill in the range of 50cm thick on the top of the pipeline, and the volume of frozen soil in the part below 50cm shall not exceed 15%.
3) Structures and roads with pavement, pipe trench within the roadbed shall not be backfilled with frozen soil.
4) In order to ensure the quality of winter backfill, for some major projects, sand can be used for backfill if necessary.
5) Ground beams on frozen expansive soils, bearing platforms for pile foundations, which may be augmented by frozen soil below, should be backfilled with loose materials such as slag and slag.
6) All backfill places, must remove water, remove ice and other debris. The thickness of each layer of filling, should be smaller than in summer is appropriate, generally no more than 20cm, with a rammer or roller compaction, guide trench lower dug into a little, but not more than two-thirds of the thickness of the permafrost layer.
4.1.4 pit protection
The pit excavation should take timely thermal insulation measures to prevent permafrost: check the qualified in time to enter the following process.
4.2 Negative Temperature Welding of Reinforcing Steel
In the welding construction of reinforcing steel project, when the ambient temperature is lower than -5 ℃ under the condition of reinforcing steel butt welding or arc welding for the negative temperature welding of reinforcing steel engaged in the production of reinforcing steel welding welders must hold a certificate of qualification of the examination of reinforcing steel welders. Should develop and implement safety technical measures to strengthen the labor protection of welders to prevent burns, electric shock and fire and other accidents. Before welding of reinforcing steel, test welding must be carried out according to the construction conditions, and the welding can be applied only after passing the test: the welder should carry out self-inspection on the appearance quality of all the joints after welding, and eliminate the unqualified. The welding process parameters should be adjusted when welding at negative temperature, so that the weld and heat-affected zone are cooled slowly. When the wind exceeds grade four, wind blocking measures should be taken. Uncooled joints after welding should avoid touching ice and snow. When the ambient temperature is lower than -20 ℃, the welding shall not be carried out.
4.2.1 Negative temperature electroslag pressure welding of reinforcing steel
1) Scope of application: lap welding of reinforcing steel diameter ≥ 22cm
2) Quality acceptance
1) Sampling: 10% of joints in each batch of sampling for appearance inspection, and not less than 10. Mechanical properties of the test, should be from each batch of finished products (by appearance inspection of qualified products) in the cut 6 specimens, 3 tensile test, 3 bending test.
In the same shift, by the same welder, according to the same welding parameters completed 200 of the same type of joint, as a batch. When continuous welding within a week can be cumulative calculation. A total of less than 200 joints in a week is also calculated as a batch. Welding of equal length of prestressing steel (including screws and bars of welded joints), can be made according to the production conditions of the simulation specimens.
② Appearance inspection
Appearance inspection results should meet the following requirements: there shall be no transverse cracks in the joints. The surface of the steel in contact with the steel, for ⅱ, ⅲ grade steel, there shall be no burns. The bending at the joint shall not be more than 4o.The axial deviation of the reinforcement at the joint shall not be more than 0.1 sensory diameter, and at the same time, it shall not be more than 2cm.When there is a joint that does not meet the requirements, all the joints should be inspected, and the unqualified products should be eliminated. Unqualified joints can be submitted to the second acceptance after excision and rewelding.
3) Precautions
①Install a voltmeter in the power switch of the butt welder in order to observe the voltage fluctuation. Welding, such as voltage voltage drop greater than 5%, should be appropriate to increase the number of transformer stages; such as voltage voltage drop to 8%, stop welding.
② daily before the formal production of two joints should be test welding, after passing the appearance check before the selected welding sketch production.
③ Before welding, the welding part of the steel bar and the electrode and steel contact parts of rust, dirt, etc. must be removed; the twisted, bent end of the steel bar should be straightened or removed.
④The various links in the process of joining operations should be closely coordinated to ensure the quality of welding, and if anomalies or welding defects occur, they should be removed in a timely manner.
4.2.2 Negative temperature arc welding of reinforcing steel
1) Scope of application: reinforcing steel diameter ≤ 22mm with lap welding
2) Welding electrode selection: ⅰ reinforcing bar e43; ⅱ reinforcing bar e50
3) Preparation for welding
①Welding must be cleaned up before welding of reinforcing bars, steel welding parts of the rust, slag, grease, etc.; reinforcing bars end of the twisted, bent should be corrected. Twisted, bent should be straightened or removed.
② steel lap welding should be used double-sided welding, can not be double-sided welding can also be used single-sided welding.
4) Welding process
According to the level of steel, diameter, joint type and welding position, select the appropriate electrode diameter and welding current, welding, it is desirable to use a multi-layer temperature-controlled welding process, not only to prevent the welding cooling rate is too fast, but also to prevent overheating of the joint. Welding process should meet the following requirements:
①Lap welding with two points of fixation. The locating weld should be more than 20mm away from the gang or lap end.
②When welding, the arc should start at one end of the lap bar, the arc should be closed at the end of the lap bar, the arc pit should be filled.
3 lap welding, the first layer of weld first from the center of the arc, and then to the ends of the arc; vertical welding first from the middle of the arc to the top, and then from the lower end to the middle of the arc. In order to achieve a certain preheating effect of the steel at the end of the joint. The first layer of rows of vendors should have enough melting depth, the main weld and positioning weld, especially at the beginning and end of the positioning weld, should be well fused. In the subsequent layers of weld welding, take the layered temperature control welding. Interlayer temperature control between 150 ℃ -350 ℃, in order to play the role of slow cooling.
④The thickness h of the weld of the lap joint shall be not less than 0.3 bar diameter; the width 6 of the weld shall be not less than 0.7 bar diameter.
5) When multi-layer welding is carried out in the lap joint of Grade Ⅱ and Ⅲ reinforcement bars, the "tempering welding method" is adopted, i.e., the length of the last tempering weld is 4-6mm shorter than that of the previous weld at each end.
5) Quality Acceptance
1) Sampling: Appearance inspection should be carried out after the slag is cleared. Inspection, should be carried out visually or quantitatively one by one after the joint slagging. Tensile test, from the appearance of the finished product of qualified inspection of each batch of three specimens for tensile test. For high-energy champion welded joints of assembled structural nodes, simulated specimens can be made according to production conditions. In the field installation conditions, 300 similar joints (the same steel grade, the same joint form, the same welding position) in each floor as a batch, less than 300, still as a batch.
② Appearance inspection: the results of the appearance inspection, should meet the following requirements: the weld surface is flat, there shall be no large depression, weld tumor. There shall be no cracks in the joints. Bite depth, porosity, the number and size of slag and joint size deviation, shall not exceed the specified value. Joints that fail the appearance check can be submitted for secondary acceptance after repair or reinforcement.
6) Notes on joints
When welded joints are used for reinforcement bars, welded joints set in the same member should be staggered from each other. In the stress steel diameter 30 times the section range (not less than 500mm), a steel bar shall not have two joints (member of the full length of the steel bar should be as little as possible to set up welded joints), there are joints in the cross-section of the steel bar area accounted for the percentage of the total cross-section area of the steel bar, should be in line with the following provisions:
1) pulling area - should not exceed 50%!
② compression zone - and nodes of assembled structures - no restriction.
4.3 Concrete works
Concrete is commercial concrete.
4.3.1 Material requirements for concrete
1) Cement: choose silicate cement or ordinary silicate cement.
2) Aggregate: it is required to be free of ice and snow mass, should be clean, well graded, hard, and should not contain minerals that are susceptible to freezing.
3) Mixing water: water qualified by laboratory tests.
4) additives: selection of additives through technical appraisal, in line with quality standards.
4.3.2 Concrete proportion
Mixed according to the concrete proportion provided by the laboratory.
4.3.3 Concrete mixing control
The mixing time of winter concrete should be 50% longer than at room temperature.
4.3.4 Transportation of concrete
Concrete mix out of the machine should be transported to the pouring place in time. In the process of running will, bite attention to prevent the concrete heat dissipation, surface freezing, concrete from thinning, cement mortar loss, slump changes and other phenomena.
4.3.5 Pouring of concrete
1) General requirements
Concrete pouring to ensure the uniformity and denseness of the concrete, to ensure the integrity of the structure, the size is accurate, the location of reinforcing steel, pre-buried parts, demolding after the concrete surface is smooth and clean.
Before pouring, the ice, snow and dirt on the template and reinforcement should be removed. When pouring, the mixture from the mixing board, hopper, funnel or all kinds of running tools will be unloaded mortar is easy to freeze with the container, so before pouring should be taken to prevent the wind, freezing protection measures, once the concrete is found to be frozen should be heated for two times to stir, so that the mixture has to adapt to the construction of the ease of pouring again.
Construction joints should be left in the location of the structural shear force is small, and easy to construct parts. Columns should be left in horizontal joints; beams, slabs and walls should be left in vertical joints. Columns should be left at the top of the foundation, high beams should be left at 20-30mm below the bottom of the plate, flat slabs should be left in any position parallel to the short side of the plate. Stairs should be left within the middle 1/3 length of the stair length.
When the concrete is poured at the construction joints, the cement film and loose stones should be removed first, wet rinsed clean, and the temperature of the original concrete at the joints is higher than 2 ℃, and then paved and smeared with a layer of cement slurry or mortar with the same composition as the concrete mortar, and to be poured when the strength of the concrete is higher than 1.2 mpa, allowed to continue pouring.
2) concrete pouring
The concrete mixture into the mold pouring, must be vibrated, so that its internal density, and can fully fill all corners of the template, made in accordance with the design requirements of the components. Winter vibration concrete using mechanical vibration, vibration to be fast, before pouring should do the necessary quasi-energy was work, such as templates, reinforcing steel and embedded parts checking, clearing ice and snow frozen block, pouring so that the use of scaffolding, the horse path of the erection and anti-skid measures to check, vibration machinery and tools ready. Pouring columns to make, a construction section of each row of columns should be poured in a symmetrical order from the outside to the inside, do not advance from one end to the other, in order to prevent the residential template gradually pushed tilt, resulting in the accumulation of errors and difficult to correct.
Beams and slabs are generally poured at the same time, advancing forward from one end. Only when the beam height is greater than 1m is allowed to pour the beam alone, at this time the construction joints should be left in the floor 2-3cm below the surface, the bottom of the beam and the side of the beam should pay attention to the pounding, vibrator do not directly contact and reinforcing bars or embedded parts. Floor concrete bottom thickness should be slightly greater than the class, after vibration with a long bottom wooden trowel smoothing, and then paved plastic film, which is promptly covered with a protective layer.
4.3.6 Concrete maintenance
It is appropriate to choose the heat storage method of maintenance: a layer of plastic film and two layers of straw bags to keep warm.
4.3.7 Concrete dismantling
1) The time of dismantling the concrete formwork should be determined according to the characteristics of the structure, the natural temperature and the strength of the concrete to be achieved, and it is generally preferable to slow dismantling.
2) Remove the template, concrete strength must also meet the requirements.
3) When removing the formwork in winter, the surface temperature of the concrete and the natural air temperature should not exceed 20℃.
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 treatment.
5) The concrete of the removed formwork should be protected by heat preservation materials. Structural concrete to reach the specified strength before allowing load bearing. Construction shall not be overloaded, it is strictly prohibited to pile up excessive construction materials or machinery,
4.3.8 Determination of concrete temperature
The measurement of air temperature, raw materials and concrete temperature shall be carried out in accordance with the following provisions:
1) Measurement of air temperature, every day and night at 8, 12, 14, 20 points **** measured four times.
2) Measurement of the temperature of mixing materials and antifreeze shall be carried out not less than 3 times per working shift.
3) The temperature of the concrete mix at the time of leaving the mixer is measured at least once every 2h.
4) The temperature before filling and after vibration, at least every 2h measurement.
5) Measurement of the temperature of the concrete during the maintenance period: before the final set, every 2h for the first three days, and then every day and night index should be carried out twice.
6) After exceeding the maintenance period, the concrete temperature can be sampled when there is a big change in temperature.
7) In order to measure the temperature inside the concrete, should be pre-buried in the pouring of concrete in some one end of the closed temperature tube, and immediately covered so as not to be affected by the outside air temperature, the thermometer stays in the tube in the index for 5 minutes, and then take out, and quickly write down the temperature.
8) Temperature measurement holes should be located in the concrete temperature is low and representative of the place.
9) All temperature measurement holes should be numbered, should draw the temperature measurement hole layout. Temperature measurement personnel should also check the cover insulation, and understand the structure of the filling date, maintenance period, as well as the allowable minimum temperature of concrete. If problems are found, the relevant personnel should be notified immediately so that timely measures can be taken to strengthen insulation or localized short-term heating.
4.3.9 Concrete specimens and strength test
The sampling rate of specimens or the maximum concrete capacity represented by a group of specimens shall be as stipulated in Article 4.6.4 of the Specification for Construction and Acceptance of Reinforced Concrete Works:
1) Not less than one group for each working shift.
2) Not less than one group per 100m3 of concrete poured.
3) For cast-in-place floors, not less than one group per floor.
In addition, winter construction should also be examined: beams, frames, each pouring 50m3 concrete should be left a batch. Each batch of test pieces at least 4 groups, respectively, in -28d, demolding, turn +28d and delivery of test pressure. It is better to make several more groups as spare specimens. Strength specimens should be made at the site with the concrete mix of the infilled structure and maintained under the same conditions as the structure or component.
5 Winter construction personnel training
Construction personnel training: the organization of the relevant various professionals to learn about the theory of winter construction, norms, regulations and construction technology.
6 Winter construction safety management
Winter construction should comply with safety regulations and procedures, and combined with the following content for safety management.
6.1 Winter construction safety education
1) Regular technical safety education must be provided to all workers. Combined with the engineering tasks in the winter construction before the safety technology briefing. Equipped with good safety protection equipment.
2) Workers must be educated on safety education and operating procedures: for the change of types of work and temporary participation in the production of labor, but also to carry out safety education and safety briefing.
3) Special types of work (including: electrical, erection, lifting, boiler, welding, blasting, machinery, vehicles and other types of work) must be professionally trained by the relevant departments, and the examination and issuance of certificates before operation. An annual review.
4) The use of new equipment, new machinery. The new process should be operated by the operators of mechanical properties, operating methods and other safety technology briefing.
5) The construction organization design and construction program of all projects must have safety technical measures. Blasting, trench pits, supporting molds, shelves and other projects are prepared single technical safety program (also known as safety design), and detailed briefing, otherwise construction is not allowed.
6.2 site safety management
1) the site of a variety of materials, no half, concrete components, acetylene bottles, oxygen and other storage sites and acetylene centralized station should meet the safety requirements, and to strengthen the management,
2) winter pit and trench construction, the program should be based on the soil conditions and engineering characteristics of the development of slope protection measures: construction and thawing after the slopes should be checked to stabilize. Cracks, loose soil or deformation of slope protection piles should be taken timely measures.
3) Strengthen seasonal labor protection. Winter should do a good job of anti-skid, anti-freezing, anti-gas poisoning work. Scaffolding, pedestrian walkway, to operate to anti-skid measures. After the frost and snow days should be cleaned in time. Check the scaffolding in time after the wind and snow to prevent accidents from falling from height.
6.3 winter electrical safety management
1) In the winter construction prevention plan and construction organization time, there must be on-site electrical lines and ten times the location plan. The site should have an electrician responsible for the installation, maintenance and management of electrical equipment. Strictly prohibit non-electrician personnel to dismantle at will.
2) construction site is strictly prohibited the use of bare wire. Wire laying should be anti-smashing, anti-grinding, to prevent the wire from freezing in the ice and snow. After the heavy wind and snow, the power supply line should be inspected to prevent electric shock caused by broken wires.
3) electric heating equipment to raise the temperature of the construction environment, should be prepared "strong electricity into the building to prevent the case. Electricity equipment using a special electric box. Strong power and weak power plugs should be distinguished to prevent accidents caused by misuse.
6.4 Safety management after the lifting of winter construction
With the rise in temperature, there is no negative temperature for seven consecutive days and nights before lifting the winter construction. But pay attention to the following points:
1) Deep pits should be observed at any time to observe the stability of soil slopes, and there should be a person in charge of observation. When conditions are favorable, backfill should be grasped.
2) winter construction erected high car frame, external elevator, the height of more than three floors above the shelf, tower crane depending on the roadbed and utility poles, etc., should be a census to prevent the foundation freezing and thawing subsidence caused by tilting and collapsing.
3) with freeze-thaw method of masonry, in the thaw according to the masonry construction
4) the provisions of the acceptance specification to take the necessary measures.
Material stacking yard, large formwork stacking yard should be inspected and organized. Prevent stacks, no half and components in the soil layer of freezing and thawing collapse.