Preparation for winter construction:

2.1 Winter construction deployment:

1）Construction arrangement:

Before entering the winter, the preparation work required by the winter construction scheme shall be implemented. The supply of equipment, materials, energy and tools shall be gradually mobilized. The materials, equipment and facilities on site shall be arranged and erected according to the winter construction scheme.Establish and improve the safety and fire prevention system, temperature measurement system and quality inspection system.

The project adopts site mixing concrete,.The comprehensive heat storage method is adopted for concrete curing.Concrete placement below 5 layers,

2.2 Personnel preparation:

1）For admixture personnel, temperature measurement and insulation personnel and heating management personnel, special technical disclosure shall be organized, relevant knowledge within the scope of work shall be learned, and responsibilities shall be defined.

2）Set up full-time personnel to listen to the weather station broadcast all day, and collect the future medium and long-term weather forecast information in time.

3）The technical group is responsible for the temperature measurement, the tester is responsible for the implementation, and the quality inspection group is responsible for checking the implementation. The tester will feed back the temperature measurement results to the documenter every day, and the documenter will sort it into the data in time.The construction party shall arrange special personnel to conduct on-site temperature measurement.(see attached figure on page 15 for management system)

2.3 Preparation of winter construction materials;

Before entering winter, the supply of equipment, materials, energy and tools should be gradually mobilized according to the plan, and detailed plans should be made for various insulation materials and heating materials.

① Schedule of main construction insulation materials:

③ Preparation of thermal combustion materials and logistics materials:

The hot water for mixing concrete on site is heated by iron electric box, and special personnel are arranged to measure and control the water temperature.

Temporary boiler room shall be set up at the site office for heating the living area and office area. In addition, the heat preservation work of houses and doors and windows shall be strengthened, and the cold resistant clothes, bedding, shoes and hats, gloves, etc. shall be purchased in time to ensure that the workers have enough energy to put into work.

2.4Preparation for temperature measurement:

1）Conduct disclosure and training for personnel involved in temperature measurement.

2）PVC pipes with reserved temperature measuring holes shall be made in advance, and the air temperature shall be measured by making a hundred leaf box.Thermometer should be tested and qualified before use.Be prepared to fill in the form of temperature measurement data.

3）Arrange special personnel to measure the outdoor temperature, the temperature in the greenhouse, the temperature of mortar and concrete during the construction, and make records, and file them.

4）Educate workers to protect the position of temperature measuring hole.

2.4Other preparatory work:

1）The temporary water supply pipeline and other materials used for wet operation shall be well insulated and antifreeze.

2）Do a good job in the trial mixing and testing of mortar in winter construction, and put forward the construction mix proportion.

3.Technical measures for winter construction:

3.1Winter construction measures of reinforcement engineering:

1）Negative temperature arc welding measures for reinforcement:

In the process of processing and transportation, attention should be paid to prevent the defects such as impact and notch.

① Welding reinforcement under negative temperature in winter should be arranged indoor as far as possible.If it is necessary to weld outdoors, the ambient temperature should not be lower than – 20 ℃. In case of strong wind, bamboo woven board or color strip cloth should be used to form temporary guardrail for wind protection.In rainy and snowy weather, bamboo woven board or asbestos tile shall be used to set up temporary protective shed to cover the rain and snow. It is strictly forbidden to touch the ice and snow immediately for the uncooled joint after welding.The welding rod shall be kept in a dry room, and the wet electrode shall be dried and reused.

1、 (2) in order to prevent the sudden increase of temperature gradient in the heat affected zone of the joint, the arc of the first layer of weld shall be started from the middle and then to the bright end; when vertical welding, the arc shall be run from the middle to the top, and from the bottom to the middle.So that the reinforcement at the end of the joint can be preheated.In the later welding of each layer of welding seam, layered temperature control welding is adopted.The interlayer temperature is controlled between 150 ℃ and 350 ℃ to slow down cooling.Winter construction measures 

1Reinforcement used under negative temperature conditions shall be inspected during construction.During transportation and processing, steel bars shall be protected from impact and scoring.

2When the temperature is lower than – 20 ℃, it is not allowed to cold bend the low alloy grade II and III steel bars, so as to avoid reinforcement at the bending point and cause brittle fracture of the reinforcement.

3Welding methods such as flash butt welding, arc welding and gas pressure welding can be used for negative temperature welding of reinforcement.When the ambient temperature is lower than – 20 ℃, welding is not suitable. 

4When the wind speed exceeds 5.4m/s (Level 3 wind) in snowy days or welding site, shielding measures shall be taken, and the joints cooled after welding shall not touch ice and snow. 

5For negative temperature arc welding of reinforcement, layered temperature control welding should be adopted.The interlayer temperature of hot-rolled steel bar welding should be controlled between 150 ~ 350 ℃, and the interlayer temperature of grade III steel bar welding should be reduced appropriately. 

6In case of negative temperature arc welding of reinforcement, welding rod and welding current can be selected according to the grade, diameter, joint type and welding position of reinforcement.Measures should be taken to prevent overheating, burns, biting and cracks during welding.In structure, the eccentric stress state should be prevented at the joint. 

3.2 Concrete construction measures in winter:

3.2.1Technical requirements for concrete construction:

1）The comprehensive heat storage method is adopted in the winter concrete construction of this project, that is, the method of mixing antifreeze with thermal storage and thermal insulation is adopted.

2）The pouring temperature of pouring concrete shall not be lower than 5 ℃.Before freezing, the compressive strength of concrete shall not be lower than the critical frost resistance strength.

When the outdoor temperature is not lower than – 15 ℃, the critical frost resistance strength of concrete shall not be less than 4.0n/mm2.

3) The concrete used in this project is mixed with early strength compound antifreeze, which can reduce water and air entrainment at the same time. The antifreeze is chlorine free antifreeze

4) In order to reduce the frost damage, the water consumption of concrete should be reduced by controlling the slump and adding superplasticizer.

5) In order to shorten the curing time, ordinary portland cement is used as the cement. The cement permeability in 1m3 concrete shall not be less than 300kg, the water cement ratio shall not be greater than 0.6, and early strength agent shall be added.

6) When the temperature difference between the concrete and the outside is greater than 15 ℃, the concrete surface should be temporarily covered to make it cool slowly.When the concrete strength of the side formwork reaches 1n / mm2, the formwork shall be slightly separated from the concrete, and then the formwork shall be closed and maintained until the formwork is removed.The concrete which is not cooled completely has high brittleness, so it should not be subjected to impact load or dynamic load before cooling.The roof concrete should be covered with plastic film and flame retardant straw curtain in time after the concrete surface is pressed.It is required to cover plastic film first and then fire retardant straw curtain.At the same time, attention should be paid to the protection of finished concrete products, and the footprints should be smoothed in time.

7）Theoretical temperature calculation of concrete mixture:

The concrete in winter construction stage of the project is mixed on site.

① Calculation of concrete casting temperature:

T2=T1－（αtt+0.032n）（T1－Ta）

=15－（0.25×0.4+0.032×2）（15+10）

=10.9℃

Where: T2 is the temperature of concrete from transportation to pouring (℃);

T1 – temperature of concrete transported to the site (℃);

TT – the time from transportation to pouring of concrete on site (H);

N-times of concrete mixture transfer;

Ta – ambient temperature of concrete transportation (set as – ℃);

α – temperature loss coefficient (h-1), 0.25.

② Temperature calculation of concrete after heat absorption due to steel formwork and reinforcement:

T3=（CcmcT2+ CfmfTf+ CsmsTs）/（Ccmc+ Cfmf+ Csms）

=（1×2400×10.9－0.48×450×10－0.48×700×10）/（1×2400+0.48×450+0.48×700）=7℃

Where: T3 – temperature of concrete due to heat absorption of steel formwork and reinforcement (℃);

CC, CF, CS – specific heat capacity of concrete, formwork and reinforcement [kJ / (kg · K)],

1 kJ / (kg · K) for concrete,

48 kJ / (kg · K) for reinforcement and steel formwork;

Mc-1m3 concrete weight (2400KG / m3);

The weight of reinforcement and formwork in contact with MF, ms-1m3 concrete,

MF is 450kg / m3, MS is 700kg / m3;

TF, TS – temperature of formwork and reinforcement, taking the ambient temperature – 10 ℃.

According to the above calculation, the temperature after concrete pouring is 7 ℃.It can meet the requirements of comprehensive heat storage maintenance.

8) Technical requirements for concrete curing by comprehensive thermal storage method

① Process requirements:

The sand and water, which are the constituent materials of concrete, are heated and then mixed. The poured concrete is tightly covered with plastic film and flame retardant straw curtain.Using the pre added heat and the hydration heat of cement, the concrete can be set slowly.At the same time, considering some unforeseen factors, the early strength composite antifreeze is added into the concrete to play the role of antifreeze

3.2.2 Concrete pouring insulation measures:

1）The raw materials used for on-site mixing shall not have frozen block, frost and snow, etc. when pouring concrete in windy weather, the windward side (mainly in the West and North) of the pouring concrete working surface shall be enclosed with colored strip cloth to ensure that the concrete will not be damaged by freezing before being covered.

2）It is forbidden to pour concrete in heavy snow weather.The formwork that has been erected in place shall be covered to prevent snow.

3）Before concrete pouring, if there is snow and ice in the formwork, it should be cleaned or washed with hot water before pouring immediately.

3.2.3Thermal insulation and anti freezing measures for molding concrete:

1）Roof concrete insulation and anti freezing measures:

After the concrete surface is plastered, the concrete shall be covered in time by sections. First, a layer of film shall be covered, and then a layer of flame-retardant straw curtain shall be covered. It is required that the adjacent grass curtain shall be overlapped by 200 mm and shall be paved against the wind direction.In the process of paving, attention should be paid to the protection of the finished concrete. It is not allowed to step on the concrete at will. If it is not careful, it should be repaired in time.

In case of windy weather, the fire-retardant straw curtain should be pressed with wooden square or steel pipe, so as to prevent the thermal insulation layer from being blown over by strong wind.

The edges and corners of the concrete shall be covered with 2-3 layers of flame retardant grass curtain.Special personnel shall be assigned to be responsible for the inspection of concrete coverage, especially in windy weather and at night. If there is strong wind or artificial uncovering, the concrete shall be covered in time.At the same time, the workers should be educated to pay attention to the protection of the concrete cover during the concrete insulation period. If the covering is to be uncovered due to the work needs during the concrete insulation period, the consent of the relevant management personnel should be obtained, and other effective insulation measures should be taken at the same time.

In order to prevent the cold air flow or cold current attack, the bottom of the roof concrete shall be sealed with color strip cloth (flame retardant straw curtain shall be used for local inconvenient shelter), and temporary straw curtain shall be hung at the stairway and doors and windows to keep the bottom of the roof in a positive temperature.

2）Wall column concrete insulation measures:

The wall column formwork is made of steel, and the secondary ribs on the back of the steel formwork are filled with 50 mm thick polystyrene board and pasted firmly with adhesive tape.After the concrete pouring is completed, the fire-retardant straw curtain shall be used to cover tightly, the edges and corners shall be covered tightly, and the connection between the fire-retardant straw curtains can be tied with wire, but the lap joint shall not be less than 200 mm.

The exposed part of wall column concrete top is covered with 2-3 layers of flame retardant straw curtain.

3.2.4 Test block retention:

1）Test block fabrication requirements:

The test block shall be made at the pouring site, and the curing test block under the same conditions shall be placed at the corresponding part of the concrete sampled in the floor, and the reinforcement cage shall be set for protection.

2）Retention type of test block under the same condition:

(the number of retention groups of each curing test block under the same conditions shall not be less than one group)

① The critical strength test block was applied in winter;

② After 28 days of curing at normal temperature, the test block was applied in winter;

③ Test block for strength of formwork removal;

④ Spare test block.

3）Retention of standard curing test block: the number of retention groups of standard curing test block in each sampling unit shall not be less than one group.

3.3Winter construction measures of masonry engineering:

3.3.1Masonry engineering construction technical requirements:

Before masonry, the surface dirt, ice and snow, etc. of ordinary bricks shall be removed, and bricks soaked in water or frozen shall not be used.

(2) The mortar should be mixed with ordinary portland cement preferentially.Mortar without cement shall not be used for masonry in winter.

(3) Lime paste should be heat preservation and antifreeze. When frozen, it should be melted before use.

(4) The sand used for mixing mortar shall not contain frozen block or ice block with diameter greater than 1 cm.

(5) When mixing mortar, the temperature of water shall not exceed 80 ℃, the temperature of sand shall not exceed 40 ℃, and the consistency of mortar shall be appropriately increased compared with normal temperature.

L the brick masonry construction in winter should be carried out according to the “three one” bricklaying method, and the mortar joint should not be greater than 1 cm.

L in winter construction, after daily masonry, the masonry surface should be covered in a timely manner, and no mortar should be left on the masonry surface.The masonry surface shall be cleaned before the masonry is continued.

The admixture method should be preferred in the winter construction of masonry engineering.Other methods can be used for projects with special requirements for insulation and decoration.

1. Quality control shall be carried out for masonry works in winter. In addition to routine requirements, outdoor air temperature, greenhouse temperature, mortar temperature during masonry, admixture content and other relevant data shall be recorded in the construction diary.

The retention of mortar test block shall be in accordance with the requirements of normal temperature, and not less than two groups of test blocks shall be added under the same conditions as the masonry to test the strength of each age and the mortar strength transferred to normal temperature for 28 days.

3.4 Measures for heat preservation and heating in living area:

Before winter construction of workers’ dormitories and canteens, windows and doors of dormitories shall be fully installed and airtight after doors and windows are closed.

During the winter construction, the material group of the project department timely purchased all kinds of cold proof clothing and labor protection articles, such as warm gloves, shoes and hats, cotton padded clothes, etc.Avoid frostbite of workers’ hands and feet due to the sudden attack of cold current.

Special personnel shall be arranged in the boiling room to supply hot water for drinking, bathing and washing face in time.

4. quality assurance measures:

1）The quality inspector is responsible for collecting the weather forecast and supervising the implementation of the comprehensive heat storage of concrete. In case of cold current or snowy weather, the insulation layer of concrete shall be inspected frequently, and the non intact parts shall be covered and reinforced in time.

For the concrete with low strength not covered, cover measures should be taken in rainy and snowy days, so as to prevent the concrete from being damaged by cold current after wetting.For the wet concrete, cover measures or heating should be taken before freezing to make the water evaporate.

2）Quality control of concrete temperature measurement:

1Concrete temperature measurement management measures:

The temperature measurement system shall be strictly implemented after the concrete pouring. If the concrete temperature drops too fast or is attacked by cold current, the additional insulation layer or artificial heating measures shall be taken immediately.

The test group manages the temperature measurement construction, and arranges full-time temperature measurement personnel to reserve holes for the poured concrete in time, arrange the hole position according to the technical requirements, measure the temperature according to the required interval time and fill in the form and record. The record shall be true. The test group shall sort out and report it to the technical group in time. The technical group shall analyze the thermal insulation of concrete and the rise of concrete strength according to the temperature measurement records And make the time requirements of whether to strengthen the insulation and when to remove the insulation layer.

② Temperature measurement items and times of winter construction:

Note: the starting and ending date of outdoor maximum and minimum temperature is from the beginning to the end of winter construction in this area.

③ Concrete temperature measurement and inspection system:

a. Arrange one person to take charge of temperature measurement construction and record work.And report the daily record form to the test group in time.

b. The thermometer shall be stored in the incubator.When measuring, the thermometer should be isolated from the outside air temperature. The method of setting temperature measuring hole is as follows:

According to the layout of temperature measuring hole, insert the PVC pipe (DN 15) closed at the bottom into the concrete, with the depth of 100-150 mm, or 1 / 2 of the thickness of the wall panel. After the initial setting of the concrete, pull out in time, and then insert the thermometer,Plug the orifice, keep the thermometer in the hole for at least 3 min, then take it out immediately to make the thermometer level with the line of sight, read carefully, and fill the measured data into the temperature measurement record sheet according to the number.After the concrete curing period, the sampling test is conducted when the temperature changes greatly.When the atmospheric temperature is above 0 ℃, stop the temperature measurement.

c. In addition, check whether the concrete surface is frozen, adhesive, shrinkage cracks, whether the corners fall off, and whether there are frost marks at the construction joints.

d. Check whether the curing conditions of the test block under the same conditions are consistent with the structural maintenance conditions at the construction site, otherwise, it shall be adjusted.

④ Air temperature measuring box: the specification is not less than 300mm × 300mm × 400mm, it is installed 10m away from the structure, about 1.5m away from the ground, and has good ventilation conditions.The outer surface is painted with white paint.

The holes on the roof are arranged preferentially at the periphery and the opening, and then at the frame column head.

3) According to the temperature measurement records of concrete curing, the technical group calculates the concrete strength growth, determines the pressure test time of the curing test block under the same conditions, the concrete formwork removal time, and the thermal insulation measures for the concrete surface after the formwork removal.

5. safety measures:

1) The construction work shall comply with the safety operation regulations. When entering the site, safety helmet must be worn. When smoking in the designated smoking room, the safety belt shall be fastened when working at height.Establish the safety awareness of prevention first.

2) Check whether the fire protection, protective fence and other safety facilities are perfect, and repair or supplement the imperfect ones.

3) The ice and snow on various roads and horse tracks should be cleaned up in time, and attention should be paid to anti-skid and falling injuries.If it can not be removed in time, anti-skid measures such as laying straw curtain and wood board should be taken.

4) The electric heating pipe of sand material shall be grounded to prevent electric leakage.

5) Open fire construction should be far away from inflammables, or isolation measures should be taken.Strictly implement the fire certificate system.Fire buckets shall be carried and special personnel shall be assigned to watch the fire.

6) In order to ensure the personal safety of workers, it is forbidden to use electric furnace or other dangerous electrical equipment for heating in the dormitory.

7) To prevent frostbite of winter construction personnel or gas poisoning accidents.

Winter construction deployment and preparation

(1) In winter construction, the comprehensive heat storage method is adopted to heat the concrete raw materials and use admixtures, and the concrete after pouring is properly insulated.Wdn-3 composite antifreeze is used as concrete admixture;

(2) Commercial concrete is used in the project, and the temperature at the site shall not be lower than 100C;

(3) The pump pipe on site shall be wrapped with fireproof straw curtain;

(4) The large steel formwork of the wall is insulated with polystyrene board;

(5) The outside of the external wall pylon and bracket is enclosed with colored strip cloth, and the dense mesh safety net is hung at the same time;

(6) The subcontract team shall contact the central heating unit for heating;

(7) The above ground part of temporary water supply is insulated with Pool (filled with insulation material) and pipeline insulation material;

(8) The laboratory should listen to the weather forecast well.When the air temperature is lower than – 150C, no concrete pouring shall be carried out;

(9) The atmospheric temperature will be measured from November 1, and the preparations for winter construction will be completed before November 10 to prevent sudden cooling.

4、 Winter construction measures of concrete engineering

4.1 general provisions

(1) Reinforcement processing shall be carried out on site; welding shall not be carried out on site in snowy days. When welding must be carried out, effective shielding measures shall be taken. For Uncooled joints after welding, ice and snow shall be avoided; when the ambient temperature is lower than – 200C, welding is not allowed. 

(2) The comprehensive heat storage method is adopted for the concrete structure of the project, that is, the raw materials are heated, the poured concrete is insulated, and a certain amount of additives are added to make the temperature reach the critical strength before freezing. 

(3) Critical strength of concrete for winter construction: the compressive strength of concrete poured in winter before freezing shall not be less than 30% of the design strength, and generally not less than 4.0n/mm2. 

(4) Heating of raw materials: the concrete mixed in winter shall be heated with water, and the cement shall not be heated directly, and shall be transported to the warm shed for storage before use.According to the thermal calculation, when the minimum temperature is above – 150C, the mixing water can be heated to 800C without heating the aggregate.When the minimum temperature exceeds the normal, additional measures should be taken. 

(5) Requirements for concrete preparation: Ordinary portland cement shall be selected for concrete prepared in winter construction, with cement grade no less than po.42.5r, minimum cement dosage no less than 300kg / m3, water cement ratio no more than 0.6. High alumina cement is strictly prohibited due to the addition of antifreeze. 

(6) The concrete mixed with antifreeze agent shall meet the following requirements: 

A. The preparation of antifreeze solution and the content of antifreeze should meet the relevant provisions of current national standards; 

B. The water cement ratio of concrete shall be strictly controlled, and the moisture brought in by aggregate and antifreeze solution shall be deducted from the mixing water; 

C. Before mixing, hot water or steam should be used to wash the mixer, and the mixing time should be 1.5 times (135 seconds) of the normal temperature mixing time; 

D. The temperature of concrete mixture to the site should not be lower than 100C, and the temperature of formwork should not be lower than 50c. 

(7) Wdn-3 composite antifreeze agent is selected as the concrete admixture of the project, and the content is as follows: 

(8) Before concrete pouring, the ice and snow and dirt on the formwork and reinforcement shall be removed, and the concrete pump pipe shall be insulated with flame retardant straw curtain.

(9) The total time of concrete transportation, pouring and intermission shall not exceed 180 minutes.

4.2 Concrete curing

(1) After the roof concrete is poured, a layer of recycled plastic film shall be covered immediately, and a layer of fireproof straw curtain shall be covered on the plastic film for insulation.Depending on the atmospheric temperature, if the temperature measurement results show that it is low, it can be covered with two layers of fire curtain. In extreme cases, even the fire curtain can be covered with plastic film.In the room at the bottom of the board, if it can not meet the requirements of the time for formwork removal, a furnace can be set up every 50m2, and the door and window openings of the room shall be sealed with plastic film.

(2) Polystyrene board is used for thermal insulation of wall structure wall formwork. Polystyrene board is cut according to the length and width of the back edge of large formwork, embedded in the back of large formwork, and the joint of external formwork at large corner of external wall is hung and sealed with fire-proof straw curtain, and the wall mouth is tightly sealed with straw curtain; if the temperature measurement still fails to meet the requirements, straw curtain shall be added to the external formwork of external wall, and the test block under the same conditions shall be placed in the construction layer, and the insulation method with concrete shall be adoptedagreement.

(3) When curing under negative temperature, watering is strictly prohibited and the exposed surface must be covered.

(4) The initial curing temperature of concrete shall not be lower than the specified temperature of antifreeze, and insulation measures shall be taken if the temperature fails to reach the specified value.If it is the roof, it should be covered with fire-proof straw curtain; if it is a wall, it should be hung on the wall.

(5) When the temperature of concrete mixed with antifreeze is lower than the specified temperature of antifreeze, its strength shall not be lower than 3.5 n / mm2.

(6) The formwork and insulation layer can be removed after the concrete is cooled to 5 ℃.And for the wall column concrete, the side formwork can be removed only when the test block strength reaches 3.5Mpa according to the same conditions.When the difference between the surface temperature of the concrete and the ambient temperature is greater than 15 ℃, the concrete shall be covered with straw curtain or hung with straw curtain on the wall.

(7) When furnace heating is adopted, the following requirements shall be met:

A. When the warm shed method is adopted, the temperature of each measuring point in the shed shall not be lower than 5 ℃, and special personnel shall be assigned to detect the temperature of concrete and shed.The temperature measuring points in the greenhouse should be arranged in representative positions, and the points must be set at the height of 1250px from the ground, and the temperature measurement should not be less than 4 times every day and night.

B. During the curing period, the humidity in the shed shall be measured, and the concrete shall not have water loss.In case of water loss, humidification measures or watering on concrete surface shall be taken in time.

C. The entrance and exit of the greenhouse should be managed by special personnel, and measures should be taken to prevent the temperature drop in the shed or the concrete at the air outlet from freezing.

D. During the concrete curing period, the smoke or combustion gas should be discharged outside the shed, and the smoke poisoning and fire prevention measures should be taken.

4.3 Quality inspection of concrete

(1) In the process of concrete pouring, inspection shall be carried out according to the following provisions:

A. Check the slump of concrete at the place of pouring; 

B. In a work shift, when the concrete mix proportion changes by external influence, it should be checked in time; 

C. Check the amount of admixture; 

D. Measure the temperature of concrete when it is discharged from the mixer and when it is poured. 

Each shift shall be measured and checked at least four times

(2) The temperature measurement of concrete curing temperature shall meet the following requirements:

A. When the heat storage method is adopted, it shall be maintained at least once every 6 hours during the curing period. 

B. For the concrete mixed with antifreeze agent, it should be measured every 2 hours before the strength does not reach 3.5 n / mm2, and then every 6 hours. The relationship between time and strength curve is used to determine the concrete pressure test. 

C. Outdoor temperature and ambient temperature should be measured at least four times every day and night.The determination time was 7:30 am, 14:00 am, 19:00 PM and 02:00 PM. 

(3) The temperature measurement method of concrete curing temperature shall meet the following requirements:

A. All temperature measuring holes shall be numbered and the layout of temperature measuring holes shall be drawn (see temperature measurement diagram). 

B. When measuring the temperature of concrete, the thermometer shall be isolated from the outside temperature; the time for the thermometer to stay in the temperature measuring hole shall not be less than 3 minutes. 

C. When the heat storage method is adopted for curing, the temperature measuring hole shall be set at the position easy to open for heat dissipation; when the heating method is adopted, it shall be set at different positions from the heat source. 

D. When pouring concrete, the galvanized temperature measuring pipe is inserted into the specified position, and 125px high kerosene is added in the hole for accurate temperature measurement. 

(4) The test pieces used to check the concrete quality of structural members shall be randomly sampled and manufactured at the concrete pouring place, and the retention of test blocks shall meet the following requirements:

A. The sampling shall not be less than once for every 100 plates of concrete with the same mix proportion and no more than 100m3. 

B. When the concrete of the same mix proportion is less than 100 plates, the sampling shall not be less than once. 

C. For the cast-in-place concrete structure, the test block reserve shall meet the following requirements: 

For each cast-in-place floor with the same mix proportion, the sampling shall not be less than once.

The sampling of concrete with the same mix proportion in each acceptance project of the same unit project shall not be less than once.

D. In addition to the provisions of a, B and C above, at least three groups of test blocks with the same curing conditions as the structure shall be added in winter construction to check the strength of concrete before freezing, the strength of concrete cured at room temperature for 28 days and the strength of concrete used for formwork removal. 

E. At least one group of standard test pieces shall be retained for each sampling, and the test blocks shall be made at the pouring site. The number of retention groups of the specimens cured under the same conditions can be determined according to the actual needs, and shall be placed on the construction site for curing together with the concrete at the pouring point. 

F. The frozen concrete specimens cured under the same conditions as structural members can be tested after thawing. 

(5) All the measurement and inspection results shall be filled in “concrete engineering construction record” and “concrete winter construction daily report”, and shall be recorded clearly and accurately, and submitted to the technical department in time, so as to take measures to solve the special situation at any time.

5、 Special construction measures

5.1 Reinforcement works

Reinforcement used in negative temperature conditions should be inspected during construction.During transportation and processing, steel bars shall be protected from impact and scoring.

When the temperature is lower than – 20 ℃, the cold bending operation of low alloy grade II and III reinforcement is not allowed, so as to avoid reinforcement at the bending point and cause brittle fracture of reinforcement.Click here to download construction technical data for free

Welding methods such as flash butt welding, arc welding and gas pressure welding can be used for negative temperature welding of reinforcement.When the ambient temperature is lower than – 20 ℃, welding is not suitable.

When the wind speed exceeds 5.4m/s (Level 3 wind) on snowy days or welding site, shielding measures shall be taken, and the joints cooled after welding shall not touch ice and snow.

For negative temperature arc welding of reinforcing steel bar, layered temperature control welding should be adopted.The interlayer temperature of hot-rolled steel bar welding should be controlled between 150 ~ 350 ℃, and the interlayer temperature of grade III steel bar welding should be reduced appropriately.

When negative temperature arc welding of steel bar, welding rod and welding current can be selected according to the grade, diameter, joint type and welding position of reinforcement.Measures should be taken to prevent overheating, burns, biting and cracks during welding.In structure, the eccentric stress state should be prevented at the joint.

The welding process of negative temperature side bar welding or lap welding of reinforcement shall meet the following requirements:

(1) Four point positioning welding shall be applied between the upper bar and the main reinforcement, and two points shall be used for the overlap welding. The distance between the positioning weld and the rib or lap end shall be equal to or greater than 20 mm.

(2) At the end of the reinforcement, the arc bar shall be filled at the end of the arc bar.

(3) During welding, the first layer of weld should have enough penetration, and the main weld or positioning weld should have good fusion.For flat welding, the arc of the first layer of weld should be started from the middle and then to both ends. For vertical welding, the arc should be moved from the middle to the top, and then from the bottom to the middle.In the later welding of each layer of weld, the layered temperature control welding should be adopted.

(4) The thickness of the weld seam of the rib joint or lap joint shall not be less than 0.3 times of the reinforcement diameter, and the weld width shall not be less than 0.7 times of the reinforcement diameter.

When the hot-rolled grade II and grade III steel bars are welded in multi-layer way, the tempered weld bead can be used after welding, and the length of the tempered weld bead shall be 4-6 mm shorter than that of the previous layer at both ends.

5.2 Earthwork

L general provisions

(1) For the winter construction of earthwork, the preparatory work should be done before the construction, and the construction should be continuous.

(2) During winter construction, anti slip and fire prevention measures shall be taken for transportation road and construction site.

Earthwork backfilling

(1) In winter, the thickness of each layer should be reduced by 20% ~ 25% compared with that under normal temperature.The reserved settlement should be increased compared with the normal temperature construction.

For large-area backfill, soil containing frozen soil block can be used, but the particle size of frozen soil block shall not be greater than 375px, and its content (by volume) shall not exceed 30%.The frozen soil blocks shall be divided into scattered parts and compacted layer by layer.

(2) In winter filling construction, ice and snow and thermal insulation materials on the base shall be removed before filling; soil containing frozen soil block shall not be used for filling within 100 cm of the surface layer of filling slope, and the whole upper part of filling shall be backfilled with unfrozen or good permeable soil, and its thickness shall meet the design requirements.

The height of filling in winter should not exceed the following table:

Note: when stone, sand (excluding silt) and gravel soil are used for backfilling, the height of filling can not be limited by the above table.

(3) The foundation trench (PIT) or pipe trench outdoor can be backfilled with soil containing frozen soil block.However, the content of frozen soil should not be more than 1250x.

Indoor foundation trench (PIT) or pipe trench shall not be backfilled with soil containing frozen soil block.The backfill construction shall be carried out continuously and compacted.When manual compaction is adopted, the thickness of each layer of soil shall not exceed 500px, and the tamping thickness shall be 10 ~ 375px.

(4) The earthwork backfilled under the indoor ground cushion shall not contain frozen soil block, and shall be compacted in time.Anti freezing measures should be taken from the completion of filling to the ground construction.

5.3 masonry engineering

L the materials used in winter construction shall meet the following requirements:

(1) Before laying ordinary bricks, hollow bricks, lime sand bricks, small-sized concrete hollow blocks, aerated concrete blocks and stone materials, the surface dirt, ice and snow, etc. shall be removed, and the bricks or blocks that have been soaked or frozen shall not be used.

(2) The mortar should be mixed with ordinary portland cement preferentially.Mortar without cement shall not be used for masonry in winter.

(3) Lime paste, clay paste or electric gypsum should be kept warm and antifreeze. When frozen, they can be used after melting.

(4) The sand used for mixing mortar shall not contain frozen block or ice block with diameter greater than 1 cm.

(5) When mixing mortar, the temperature of water shall not exceed 80 ℃, the temperature of sand shall not exceed 40 ℃, and the consistency of mortar shall be appropriately increased compared with normal temperature.

L the brick masonry construction in winter should be carried out according to the “three one” bricklaying method, and the mortar joint should not be greater than 1 cm.

L in winter construction, after daily masonry, the masonry surface should be covered in a timely manner, and no mortar should be left on the masonry surface.The masonry surface shall be cleaned before the masonry is continued.

The admixture method should be preferred in the winter construction of masonry engineering.Other methods can be used for projects with special requirements for insulation and decoration.

L. the freezing method is not allowed for the construction of small-sized concrete hollow blocks, and the bearing walls of aerated concrete blocks and the maintenance of external walls are not suitable for winter construction.

1. Quality control shall be carried out for masonry works in winter. In addition to routine requirements, outdoor air temperature, greenhouse temperature, mortar temperature during masonry, admixture content and other relevant data shall be recorded in the construction diary.

L the retention of mortar test block shall be in accordance with the requirements of normal temperature, and not less than two groups of test blocks shall be added under the same conditions as the masonry to test the strength of each age and the mortar strength transferred to normal temperature for 28 days.

5.4 Waterproofing works

L the high polymer modified asphalt waterproofing membrane should be used for hot melt construction, and the physical properties of the coiled material should meet the following table:

Note: class I to IV are the coil materials of polyester felt, linen, polyethylene film and glass fiber mat respectively.

L. the hot-melt method shall meet the following requirements:

(1) The base treatment agent should be prepared with fast volatile solvent, which should be dried for more than 10 hours after brushing, and be paved in time after drying.

(2) Full bonding method shall be adopted for hot melt paving waterproof layer.When the slope is less than 3%, the coiled material and the cushion should be laid in parallel. When the slope is greater than 15%, the coiled material and cushion should be laid vertically. When the slope is 3% – 15%, parallel or vertical bedding can be paved.Spray lamp (or thermal spray gun) shall be used for uniform heating during paving. The distance between blowtorch or thermal spray gun and the coiled material should be 0.5m. Excessive heating or burning through is not allowed. After the surface of coiled material is melted, roll paving and paving slowly.

(3) The lap joint of coiled materials shall be in accordance with the design requirements. When there is no design specification, the transverse lap width should be 120 mm, and the longitudinal lap width should be 100 mm.When lapping, the lap joint shall be heated by a blowtorch (hot spray gun). When the coil material is melted and not cooled, the joint edge shall be plastered with an iron trowel, and then the torch (or thermal spray gun) shall be used for uniform and meticulous sealing.

The coiled material connecting the plane and the facade shall be paved from the bottom to the top, and the coiled material shall be close to the internal corner without hollowing.

(4) The edge of lap joint and end closing part of coiled material shall be caulked with sealing material. If necessary, cement mortar mixed with antifreeze can be used for caulking treatment at the end joint after sealing treatment.