Winter construction plan

Winter construction plan

Winter is coming, and the cold climate conditions during winter construction will directly affect the construction quality, safety and progress of the project under construction. The start and end dates of winter construction are: when winter comes, if the daily average temperature for five consecutive days is stable below 5℃, the first day of the 5 days will be the first day of winter construction. When the temperature gets warmer, the last 5 days will If the daily average temperature is stable above 5℃, then the last day of this 5-day period is the last day of winter construction (the daily average temperature is the average of four outdoor temperature observations at 2, 8, 14 and 20 o'clock in 1 day. This is the Measured 1.5m above the ground and away from heat sources). In order to ensure the smooth progress of winter construction, since the eve of the start of winter construction, our project management department has established a construction site winter construction leading group with the project manager as the first responsible person to make necessary preliminary preparations and prepare a winter construction plan.

1. Preparation Principles

Ensure the quality of the project; be economical and reasonable to minimize the additional cost; have reliable sources of heat and materials required, and minimize energy consumption; be sure Can shorten the construction period.

2. Characteristics of winter construction

1. Due to the unfavorable construction conditions and environment, winter construction is a season prone to engineering quality accidents, especially in concrete projects.

2. The concealment and hysteresis of quality accidents. That is to say, the project was carried out in winter, and most of them began to be exposed in spring, which made it very difficult to deal with the accident. In the case of minor cases, repairs were carried out, and in serious cases, it was repeated, which not only caused losses to the project, but also affected the quality of the project. service life.

3. Winter construction requires strong planning and preparation time. This is due to the short preparation time and complex technical requirements. Quality accidents often occur because this link cannot keep up and construction is hasty.

3. Construction preparation

When the temperature is below 0℃, winter construction measures should be taken immediately to prevent the construction project under construction from freezing damage.

1. Establish a winter construction leadership group

Team leader:

Deputy team leader:

Team members:

① For engineering projects undergoing winter construction, a dedicated person should be organized to prepare a winter construction plan before winter begins. The winter construction plan should include the following: construction procedures; construction methods; site layout; supply plans for equipment, materials, energy, and tools; safety and fire prevention measures; temperature measurement system and quality inspection system, etc. After the plan is determined, it is necessary to organize relevant personnel to study and explain it to the team.

② Before entering winter construction, technical and professional training should be specially organized for management personnel to learn relevant knowledge within the scope of their work and clarify their responsibilities. Only after passing the examination can they be allowed to work.

③ Keep in touch with local weather stations to receive timely weather forecasts to prevent sudden cold wave attacks.

④ Arrange special personnel to measure the outdoor temperature, the temperature in the greenhouse, the temperature of mortar and concrete during the construction period and keep records.

3. Drawing preparation

For any engineering project that will be constructed in winter, the construction drawings must be reviewed to check whether they can adapt to winter construction requirements. For example, issues related to the height-to-thickness ratio of the wall, the spacing between horizontal walls, and whether the engineering structure can survive the winter safely in cold conditions should be resolved through drawing review.

4. On-site preparation

1. Organize the arrival of relevant machinery, admixtures and insulation materials in advance based on the physical project quantities.

2． Temporary water supply pipes and other materials at the construction site should be well insulated and anti-freeze.

3. Do a good job in the trial mix test of concrete, mortar and admixtures for winter construction, and propose the construction mix ratio.

IV. Temperature measurement for winter construction

1. Relevant regulations for temperature measurement during winter construction

1. Temperature measurement range for winter construction

Temperature measurement range for winter construction: atmospheric temperature, temperature of cement, water, sand, gravel and other raw materials, indoor temperature of concrete or mortar shed, temperature of concrete or mortar coming out of the tank, temperature of entering the mold or on the wall, and initial temperature after the concrete is placed in the mold. and curing temperature, etc.

2. Responsibilities of temperature measuring personnel

(1) Record the atmospheric temperature every day and report to the person in charge of the construction site;

(2) Concrete mixture Temperature, temperature of concrete coming out of the tank, temperature of concrete entering the mold;

(3) Measurement of concrete curing temperature: Arrange the temperature measurement holes as required, and draw the distribution map and number of the temperature measurement holes. Measure the initial temperature and atmospheric temperature of concrete curing as required. Control the initial temperature and time of concrete curing.

2. Temperature measurement management

1. Under the guidance of technical personnel, the construction site foreman is responsible for the leadership work of the project such as temperature measurement, insulation, and admixture. Every day It is necessary to check the temperature measurement records, take timely measures if any abnormalities are found, and report to the relevant leaders and technical persons in charge.

2. Project technical personnel should check the temperature measurement, insulation, and heating conditions and existing problems every day, report to the supervisor in a timely manner, and assist the on-site construction management personnel to solve difficult winter construction problems.

3. Construction temperature measurement personnel should submit a temperature measurement record when temperature measurement is stopped on each floor or section. Problems found should be reported to the on-site management personnel and technical personnel in a timely manner so that immediate measures can be taken.

4. Temperature measuring personnel should be on duty 24 hours a day, and a strict handover system should be implemented. Temperature measuring personnel should fill in the sections and items and keep them properly.

5. Temperature measurement records must be handed over to technical personnel for archiving and reference.

3. Winter construction measures

1. Winter construction of concrete

1. Requirements for raw materials for concrete construction in winter

(1 ) Portland cement and ordinary Portland cement are preferred for cement. Attention should be paid to the impact of the blended materials on the anti-freeze and anti-permeability properties of the concrete. The cement number should not be lower than No. 425, and the minimum amount of cement used in the concrete should not be less. At 300kg/m3, the water-cement ratio should not be greater than 0.6. For concrete mixed with antifreeze, it is strictly prohibited to use high-lead cement.

(2) The aggregate used in concrete must be clean and must not contain frozen matter such as ice and snow and minerals that are prone to freeze cracking. In the concrete containing antifreeze containing potassium and sodium ions, the aggregates must not be mixed with active materials to avoid alkali-aggregate reaction.

(3) For concrete projects poured in winter, various admixtures should be reasonably selected according to the construction method. Attention should be paid to the corrosion effect of chlorine-containing salt admixtures on steel bars. It is advisable to use chlorine-free antifreeze. When using chlorine salt admixtures for concrete in non-load-bearing structures, protective measures such as chlorine salt rust inhibitors should be included. The chlorine salt content shall not exceed 1% of the cement weight, and the chlorine salt content in plain concrete shall not exceed 3% of the cement weight. The types and uses of admixtures are shown in the attached table.

(4) Mixing water, generally drinking tap water and clean natural water can be used for mixing concrete, but sewage, industrial wastewater, acidic water with a small pH value, and sulfate content (according to so4 ) exceeding approximately 1% by weight of water shall not be used in concrete. To reduce freezing damage, water consumption in the mix should be reduced to a minimum. The method is: control the slump, add water-reducing agent, and give priority to high-efficiency water-reducing agent.

2. Mixing of concrete

1) Admixtures

a. Selection of admixtures

In winter construction, from this Select admixtures based on the structural type, nature, construction site and purpose of using the admixtures of the project. When choosing, you should consider: improving the workability of concrete or mortar, reducing water consumption, improving the quality of the mixture, and increasing the early strength of the concrete; lowering the freezing point of the mixture to promote accelerated hydration of cement at low or negative temperatures. ; Promote the growth of strength in the early and middle stages, reduce drying shrinkage, and improve freeze-thaw resistance; while ensuring quality, increase the turnover speed of the formwork, shorten the construction period, shorten or cancel heating maintenance, and reduce costs; the selection of admixtures must be Pay attention to its impact on the later strength of the concrete, the corrosion effect on the steel bars and the impact on the environment, such as ammonia-containing concrete admixtures; try not to use slag cement with a small hydration heat during winter construction.

b. Test of admixtures

The technical indicators of all admixtures for winter construction must meet the corresponding quality standards and should have product certificates. If there is any doubt about the performance of an additive that has already entered the site, additional testing must be done and it can be used only after it is confirmed to be qualified. The inspection content of admixture components includes: composition, content, purity, concentration, etc. The dosage of commonly used additives can be used in accordance with relevant regulations under normal circumstances. In case of special circumstances, the amount of additives to be added must be determined through tests based on the structure type, usage requirements, climate conditions, and maintenance methods.

c. Management of admixtures

A dedicated person should be responsible for the configuration and mixing of admixtures used in mixing concrete and mortar during winter construction, and records should be carefully kept. The admixture solution should be prepared into a standard concentration in advance, and then the mixed solution should be prepared according to the usage requirements. Various admixtures should be placed in clearly marked containers and should not be confused. Each batch of solution prepared should meet at least one day's usage.

When using admixtures, the concentration should be measured frequently, and attention should be paid to strengthening stirring to maintain uniform concentration.

2) Mixing of concrete

The concrete mixing station strictly follows the mix ratio notice issued by the laboratory, and the mix ratio is not allowed to be modified without authorization. Before mixing, rinse the mixer with hot water for 10 minutes, and the mixing time is 47.5?.5s (1.5 times the mixing time at room temperature). The order of feeding during mixing is stone → sand → water → cement and admixtures → admixtures. During the production period, a dedicated person is assigned to unload the aggregate warehouse to remove frozen blocks of sand and gravel. Ensure that the water-cement ratio is not greater than 0.6, deduct the moisture brought in by the aggregate and antifreeze solution from the mixing water, and strictly control the maximum replacement value of fly ash. The mixing station must maintain close contact with the meteorological unit, carefully analyze the forecast temperature to obtain insurance values, test antifreeze at -5°C, -10°C and -15°C, and strictly control its dosage. The temperature of the mixing water must be measured at any time, and the water temperature should be controlled at 50-0°C, and the sand temperature should be controlled at 20-40°C to ensure that the cement is not in direct contact with water with a temperature of ≥80°C. Ensure that the slump of concrete does not exceed 200mm.

3. Transportation of concrete

The pipes for pumping concrete should be wrapped with insulation materials to ensure that there is no surface freezing, concrete segregation, cement mortar loss, or slump during transportation. losses, etc. Ensure that the temperature drop rate of the concrete during transportation shall not exceed 5°C/h, and the temperature of the concrete entering the mold shall not be lower than 5°C. It is strictly prohibited to use concrete with freezing phenomenon.

4. Concrete pouring

1) Checking of mold entry temperature

Before pouring concrete, the mold entry temperature must be calculated.

2) On-site pouring of concrete

In snowy weather, tie steel bars and cover the tied steel bars with plastic sheeting to reduce the difficulty of snow collection and cleanup. Before pouring concrete, clean the ice and snow on the formwork in time. Make preparations to increase the speed of concrete pouring. Wrap flame-retardant straw curtains on the concrete pump body hopper and pump pipes.

3) Concrete maintenance

Maintenance measures are very critical. Correct maintenance can avoid unnecessary temperature shrinkage, cracks and freezing of concrete. Under winter application conditions, winter application temperature measurement must be adopted to monitor that the temperature difference between the concrete surface and the interior does not exceed 25°C.

Concrete maintenance can take a variety of measures, such as thermal storage method maintenance and comprehensive thermal storage method maintenance. Plastic film can be used to cover the insulating straw curtains to prevent freezing and control the temperature difference between the concrete surface and the interior.

The comprehensive thermal storage method uses a small amount of antifreeze combined with thermal storage and insulation. The following is the specific implementation method of the comprehensive thermal storage method for reference.

a. Column concrete maintenance:

The steel column formwork is filled with 50mm thick polystyrene boards between the back frames of the formwork. After the formwork support is completed, the flame-retardant felt curtain is fixed with iron wire. Tower connections must be ensured on the outside and at corners.

b. Maintenance of roof and beam concrete:

The upper and lower parts of the roof and beam concrete are insulated close to the surroundings of the building (whole floor height) on the lower floor by attaching cross bars to the scaffolding. Colorful strips of cloth are hung, and straw curtains are tied to the edges of the beams. The surface of the newly poured concrete is first covered with plastic sheeting, and then covered with a second layer of felt curtains. For weak parts such as corners or windward sides, felt curtains should be covered and tower connections should be made.

c. Precautions during maintenance:

When the insulation material (above 5℃) must be opened for measurement and laying out, the line must be covered immediately after laying out; lay it on the surface of the newly poured concrete first A layer of plastic film, and then tightly covered with flame-retardant felt curtains. The weakest parts of the wall and column tops are first covered with a layer of plastic sheeting, and then covered with two layers of small felt curtains, which are compacted and filled, and the circumference is sealed. After the formwork is removed, the concrete is cured with brush curing fluid. The initial curing temperature of concrete must not be lower than -15°C. If this temperature condition cannot be met, a covering felt curtain must be immediately added for insulation. When the temperature difference between the concrete surface and the outside temperature after the formwork is removed is greater than 15°C, the concrete surface must continue to be covered with felt curtains; weak parts such as corners and corners must be covered with felt curtains and sealed tightly.

5. Dismantle the mold

Send the test block to the project management department laboratory in time for strength inspection of the test block. When the concrete does not reach the critical strength due to freezing, the insulation and heating equipment shall not be removed. The formwork can only be removed when the concrete is cooled to 5°C, exceeds the critical strength and meets the requirements for formwork removal of concrete at room temperature. The concrete temperature is measured by a thermometer; it can be measured through a 3-day test under the same conditions and at 4MPa, the column formwork is gently separated from the concrete and continues to be cured until the formwork is removed. The foreman fills in an application for concrete formwork removal based on the test results and submits it to the project chief engineer and relevant personnel for approval. Special approval is required for formwork removal in key locations or structures with special requirements.

6. Preparation of test blocks

During the concrete construction process, random samples should be taken at the pouring site to make test pieces. Each time sampling should be made, 3 sets of test pieces should be made at the same time. Group 1 is cured under standard conditions until 28 days of pressure testing, and the strength is f28; Group 1 is cured under the same conditions as the components, when the concrete temperature drops to 0°C (negative temperature concrete means when the temperature drops below the specified temperature of the antifreeze) Pressure test is used to check whether the concrete has reached the critical temperature of anti-freeze; Group 1 and the components are cured under the same conditions for 14 days, and then transferred to the standard conditions of 20°C to continue curing for 21 days. The pressure test is performed when the total age is 35 days to obtain the strength. f14'21. If f14' 21 ≥ f28, it can be proved that the concrete has not been damaged by freezing, and f28 can be used as the basis for strength evaluation.

7. Winter construction records

1) Winter construction data classification

a. Winter construction daily report;

b. Winter construction Statistical table of temperature of concrete entering mold;

c. Temperature measurement record table of concrete maintenance in winter.

2) Analysis, collection and cataloging of winter construction data

a. Daily average temperature during winter construction, daily temperature in each time period, concrete temperature measurement, formwork removal, formulation and Taking emergency measures has a great decisive role. In order to better ensure the quality of the winter construction project, the outdoor temperature will be measured at 3:00, 9:00, 15:00 and 21:00 every day during the winter construction period. Calculate the average value, prepare a winter construction daily report, and establish a winter construction daily report system so that you can grasp the temperature conditions on winter construction days at any time and take necessary measures. The winter construction daily report also indicates the weather forecast for the day, making it easier for technicians to check and compare.

b. The temperature of concrete entering the mold during winter construction is a very important internal factor in pre-controlling the quality of concrete. Establish a statistical table of the temperature of concrete entering the mold during winter construction to keep track of the temperature of concrete entering the mold at any time.

c. The concrete maintenance temperature measurement record sheet is cataloged by location and date, and is attached with a floor plan of the temperature measurement points. The temperature measurement personnel must feedback the concrete maintenance temperature measurement records to the project technology before 9:00 on the same day. Quality Department. In case of a sudden drop in temperature or other situations, timely feedback will be given to the project technical quality department or the project personnel on duty so that effective measures can be taken in a timely manner. After the temperature measurement record is completed, the temperature measurement personnel, auditors, and technical persons in charge must sign completely and file it in the construction record.

2. Winter construction of steel bars

1) Cold drawing and cold bending of steel bars

①The cold drawing temperature of steel bars should not be lower than -20℃, prestressing The tensioning temperature of steel bars should not be lower than -15℃.

② The negative temperature cold drawing method of steel bars can adopt the stress control method or the cold drawing rate control method. For prestressed bars used as prestressed concrete structures, stress control methods should be used; for hot-rolled steel bars that cannot be divided into batches for cold drawing, the cold drawing rate control method should not be used.

③When cold drawing steel bars using the controlled stress method under negative temperature conditions, since the elongation decreases as the temperature decreases, if the control stress remains unchanged, the elongation will be insufficient and the strength of the steel bars will not reach the level. To meet the design requirements, the control stress of cold drawing at negative temperature should be higher than that at normal temperature. The determination of the cold drawing rate should be the same as that for normal temperature construction.

④The instrumentation and hydraulic working system oil of steel bar cold drawing equipment should be selected according to the ambient temperature, and should be calibrated under the operating temperature conditions.

⑤ When the temperature is lower than -20℃, cold bending of low alloy grade II and III steel bars is strictly prohibited to avoid strengthening at the bending point of the steel bar and causing brittle fracture of the steel bar.

2) Steel bar welding

① When welding steel bars under negative temperature conditions in winter, we should try to arrange it indoors. If welding must be done outdoors, the ambient temperature should not be lower than -20°C, and wind protection measures should be taken when the wind force exceeds Level 3. Uncooled joints after welding must not be exposed to ice or snow.

② Negative temperature flash butt welding. Negative temperature flash butt welding should use preheated flash welding or flash-preheat-flash welding process. When the end face of the steel bar is relatively flat, preheated flash welding should be used; when the end face is uneven, flash-preheat-flash welding should be used.

③ Negative temperature arc welding. When negative temperature arc welding of steel bars, defects such as overheating, burns, meat bites and cracks must be prevented, and the structure should prevent eccentric stress states at the joints.

④ Negative temperature automatic electroslag pressure welding. The welding steps of negative temperature automatic electroslag pressure welding are the same as those at normal temperature, but the welding current and power-on time should be appropriately increased. The time for removing the joint pill box should be extended by about 2 minutes, and the slag shell of the joint should be extended for 5 minutes before slag can be broken.

⑤ When the ambient temperature reaches -5°C, the steel bars are "low-temperature welded". The low-temperature welding process of steel bars is strictly implemented, and direct contact with ice and snow during the welding process is strictly prohibited. In windy and snowy weather, the welding operation part must be enclosed and insulated to slowly cool down the welding part to prevent the joint temperature from dropping too quickly after welding, causing cold brittleness and affecting the welding quality.

⑥The welding steps of negative temperature automatic electroslag pressure welding are the same as those at normal temperature, but the welding parameters need to be adjusted appropriately. The size of the welding current should be determined according to the diameter of the steel bar and the ambient temperature during welding. It affects the slag pool temperature, viscosity, stability of the electroslag process and steel melting speed. The welding energization time should also be adjusted according to the steel bar diameter and ambient temperature. If the welding energization time is too short, the end faces of the steel bars will melt unevenly and cannot be in close contact, making it difficult to ensure the fusion of the joints. Therefore, the energization time should be appropriately increased.

⑦ Negative temperature flash butt welding: Preheated flash welding or flash-preheat-flash welding process should be used. When the end face of the steel bar is relatively flat, preheated flash welding should be used; when the end face is uneven, flash-preheat-flash welding should be used.

Compared with normal temperature welding, the following measures should be taken for negative temperature flash butt welding:

The elongation length should be increased by 10% to 20% to increase the heating range and increase preheating The remaining amount, preheating times, preheating interval time and preheating contact pressure can reduce the cooling speed and improve the joint performance.

Control the length of the heat affected zone. The length of the heat affected zone increases appropriately with the increase in steel grade and diameter.

The number of transformer stages should be reduced by 1 to 2 stages to ensure smooth flashing.

Before the flashing process begins, the steel bars can be contacted several times to increase the temperature of the steel bars to facilitate the smooth progress of the flashing process. The speed in the middle of the burning process slows down appropriately.

Before welding steel bars in winter, trial welding must be carried out according to the construction conditions. Only after passing the test can formal welding be carried out.

3) In case of rain or snow, the ice and snow in the template (top) need to be cleaned. For rain, snow and other debris that are difficult to clean in the template (top), you can use a heater, vacuum cleaner and gasoline. Blowtorch cleaning. It is best to use plastic film to cover the formwork and steel construction operating surfaces before rain or snow comes to minimize a lot of cleaning work.

3. Winter construction measures for earthworks

1) For winter construction of earthworks, preparations must be made before construction and continuous construction must be ensured.

2) During winter construction, anti-slip and fire prevention measures will be taken on transport roads and construction sites.

3) When earthwork is backfilled in winter, the thickness of each layer of soil should be reduced by 20% to 25% compared with that during normal temperature construction, and the reserved settlement should be increased than during normal temperature construction.

4) During winter filling construction, the ice, snow and insulation materials on the base should be removed before filling. After the filling is completed and before ground construction, anti-freeze measures should be taken and the surface layer should be covered with insulation materials.

5) In winter, soil becomes hard due to freezing, making excavation difficult and construction costs higher than at normal temperatures. Therefore, earthwork and foundation works for newly started projects should be completed before winter construction.

6) For earthwork that must be excavated in winter, an economical and reasonable construction plan and practical technical measures must be determined according to local conditions to achieve quick earth excavation, quick foundation construction, and quick backfilling.

7) The foundation soil is mainly covered with grass mats for heat preservation. For large-area earth excavations, the topsoil should be loosened and raked to prevent freezing. The soil loosening depth is 30-40cm.

8) During winter construction, if foundation construction cannot be carried out immediately after excavation of the foundation trench, 300mm of remaining soil should be reserved according to the designed trench bottom elevation, and the edge of the trench should be cleared as the foundation. Generally, when the temperature is 0 ℃ to -10 ℃, it is covered with two layers of straw mats, and when the temperature is below -10 ℃, it is covered with three to four layers of straw mats.

9) The earth to be used for winter backfilling should be stacked in large piles and covered with two layers of straw mats to prevent freezing.

10) Before backfilling the earthwork, ice, snow and insulation materials on the base should be removed.

11) The thickness of each layer of earthwork backfill should be reduced by 20-25% compared to normal temperature construction, and the reserved settlement amount should be appropriately increased compared to normal temperature construction. When manually tamped, the thickness of each layer of soil shall not exceed 20cm, and the compacted thickness shall be 10-15cm.

12) When soil materials containing frozen soil blocks are used as fill, indoor foundation pits (troughs) or pipe trenches must not be backfilled with soil containing frozen soil blocks; outdoor foundation pits (troughs) ) or the pipe trench can be backfilled with soil containing frozen soil blocks, but the volume of frozen soil blocks shall not exceed 15% of the total volume of the filling soil. The range of 0.5m from the bottom of the pipe trench to the top of the pipe shall not be backfilled with soil containing frozen soil blocks. Frozen soil The particle size of the blocks should not be larger than 15cm. When filling, the frozen soil blocks should be dispersed and compacted layer by layer.

13) The lime-soil cushion can be constructed when the temperature is not lower than -10℃, but insulation measures must be taken to prevent the foundation trench, plain soil and white ash from freezing. The "five follow" measures of sifting, mixing, tamping and covering are followed by tamping on the same day and covering with two to three layers of straw mats.

14) Earthwork construction should comply with the current specifications regarding winter construction.

IV. Winter construction measures for masonry projects

1. Before masonry, ordinary bricks, hollow bricks, lime sand bricks, small concrete hollow blocks, and aerated concrete blocks should be Dirt, ice, snow, and frost on the surface of the stone must be removed. Bricks or blocks that have been soaked in water and frozen must not be used.

2. Lime plaster, clay plaster or electrogypsum should be kept warm and anti-freeze. If frozen, they should be thawed before use.

3. The sand used for mixing mortar shall not contain frozen blocks and ice cubes with a diameter greater than 1cm.

4. The consistency of masonry mortar in winter should be appropriately higher than that during normal temperature construction. This can be solved by adding lime paste or clay paste.

5. The grade of masonry mortar should generally not be lower than M2.5, and important parts and structures should not be lower than M5. It should be mixed with ordinary Portland cement. No cement-free mix should be used for masonry construction in winter. Made mortar. The chemical composition and performance of admixtures used in mortar must be understood before use, and the dosage must be accurate.

6. When mixing mortar, the temperature of the water shall not exceed 80°C and the temperature of the sand shall not exceed 40°C. The temperature of the mortar during use should not be lower than 5℃ when the lowest ambient temperature is below -10℃. When the ambient temperature is between -10℃ and -20℃, it should not be lower than 10℃. During masonry, the temperature difference between the brick surface and the mortar should not exceed 30°C, and the temperature difference between the stone surface and the mortar should not exceed 20°C. During construction, the consistency of mortar is generally controlled at 9-12cm.

7. For winter construction of masonry projects, admixture method, freezing method and greenhouse method can be used. For freezing method construction, the design should be contacted in advance for reinforcement matters. Generally, hot-mix mortar mixed with chlorine salt is used.

When using salt-mixed mortar, the steel bars and steel embedded parts in the masonry should be treated with anti-corrosion. The anti-corrosion methods include: ① Apply two coats of camphor dandruff. ② Apply asphalt paint. The ratio is No. 30 asphalt: No. 10 asphalt: gasoline = 1:1:2; ③ Apply anti-rust paint and the ratio of cement: sodium nitrite: sodium methylsilanolate: water = 100:6:2:30, The prepared paint is applied to the surface of the steel bar with a thickness of about 1.5mm and can be used after drying.

8. Precautions for the salt-mixed mortar method:

(1) The amount of salt added is based on anhydrous sodium chloride and calcium chloride.

(2) When the daily minimum temperature is below -20℃, masonry construction is not suitable.

(3) When adding microfoaming agent to salt-mixed mortar, the salt solution and microfoaming agent solution must be stored separately and added one after another during mixing.

(4) During winter construction, after daily masonry construction, the upper surface of the masonry should be covered with insulation material.

Due to the high hygroscopicity of chlorine salt mortar, the thermal insulation performance is reduced and salt precipitation occurs.

The following projects shall not use the salt-mixed mortar method:

A. Projects with special requirements for decoration.

B. Buildings close to high-voltage wires (such as substations, power stations, etc.).

C. Design projects with high thermal requirements.

D. Buildings with humidity greater than 80% when the house is in use.

E. Buildings that are often affected by high temperatures above 40°C.

F. Structures that are often within the range of changes in groundwater levels and have no waterproof layer underwater.

G. Masonry without reliable anti-corrosion treatment measures for reinforcement and steel embedded parts.

9. For projects that are not suitable for adding chlorine salt, adopt freezing method, greenhouse method and other methods.

10. Quality requirements for the salt-mixed mortar method:

(1) The preparation of salt-mixed mortar must be based on the temperature of the day, and the amount of salt in the masonry parts must be strictly controlled.

(2) A dedicated person should be responsible for the preparation of the salt solution. Use a hydrometer to measure the concentration of the solution at any time and grasp the salt content of solutions with different specific gravity.

(3) The temperature of the salt-mixed mortar should not exceed 35℃ when it leaves the tank, and the minimum temperature during use should not be less than 5℃.

(4) It is not allowed to increase the amount of microfoaming agent to improve the workability of mortar, in case increasing the amount will reduce the strength of the mortar.

(5) Salt-incorporated mortar should have good workability.

(6) The measurement of mortar proportions must be accurate, mainly based on weight ratio, and the error of cement and organic plasticizer dosage should be controlled within ?%; the dosage of sand, lime paste, fly ash, etc. The error is controlled within ?%.

11. The temperature of the mortar after stirring can be calculated according to the following formula

Tp=〔0.9(MceTce+0.5MlTl+MsaTsa)+4.2Tw(Mw-0.5Ml-WsaMsa)〕〔4.2 (Mw＋0.5Ml)＋0.9(Mce＋0.5Ml＋Msa)〕

Tp---The temperature of the mortar after stirring (℃);

Mw, Mce, Ml, Msa- --Amount of water, cement, lime paste and sand (Kg);

Tw, Tce, Tl, Tsa---Temperature of water, cement, lime paste and sand (℃);

Wsa---Moisture content of sand.

The outlet temperature should consider the temperature drop during mixing, transportation and storage. If there is no basis for actual measurement data, an approximate estimate can be made first, and then adjusted according to the actual measurement value during construction.

The sand can be heated by: steam pipe, puddle heating, or the steam pipe can be inserted into the sand to directly supply steam. When directly venting steam, attention should be paid to changes in the moisture content of the sand. When using steam pipes or fire pits for heating, you can pour some warm water on the sand (the amount of water added should not exceed 5%) to avoid uneven cold and heat and speed up the heating speed.

Water heating can be divided into two heating methods: direct and indirect.

Direct heating means that iron barrels, cauldrons, and hot water boilers directly use open flames to increase the temperature of water.

Indirect heating can directly pass steam into the water storage tank to increase the temperature of the water, or a high-power water heater can be added to the water tank to increase the water temperature.

IV. Safety and Fire Prevention

1. During winter construction, anti-slip measures must be taken. Domestic and construction roads, shelves, and ramps must be regularly cleared of accumulated water, snow, and ice. Inclined runways must have reliable anti-slip strips.

2. It is strictly forbidden to use open fires for heating at construction sites and temporary sheds in winter. Specific fire safety precautions should be formulated and responsibilities should be assigned to individuals.

3. When there is ice and snow accumulation on scaffolding and scaffolding boards, they should be cleared before construction. Sliders or straw bales should be nailed on the sloped springboard, and the frame should be checked at any time for looseness and sinking. for prompt processing.

4. Strengthen the management of on-site fire sources; when using natural gas and coal gas, prevent explosions; when using coke ovens, coal stoves or natural gas and coal gas, pay attention to ventilation to prevent gas poisoning .

5. Power switches, control boxes and other facilities should be arranged in a unified manner, locked and protected to prevent random pulling of wires, and designated personnel should be responsible for management to prevent electric shock due to leakage. The wires of frequently moved equipment must not be dragged on the ground or immersed in water, and must be overhead and well insulated.

6. During winter construction, anyone working at heights should wear safety belts and rubber-soled shoes to prevent slipping and falling from heights.

7. There must be protective sheds or other isolation measures around the entrances and exits of the upper and lower three-dimensional crossing operations and the derrick.

8. Safety belts must be worn when working at high levels, and safety helmets must be worn when entering the construction site. Enclosure and warning measures should be taken when dismantling scaffolding during winter construction, and throwing downwards from high altitudes is strictly prohibited.

9. Temporary water pipes on the construction site should be buried in the soil or wrapped with insulation materials such as straw bags, and covered with paper tendons. The water tank stores water and should be drained before leaving get off work.

10. Insulation materials such as straw bales and straw curtains must not be placed in the open to avoid moisture and loss of insulation effect.

11. Water sources and fire hydrants at the construction site should be marked.