Key points and precautions in winter construction?

The following are the key points and matters needing attention in winter construction brought by Zhong Da Consulting for your reference.

A, winter construction period division

1, specification: according to the statistics of local meteorological data for many years, the winter construction will be started when the outdoor daily average temperature is steadily lower than 5℃ for five consecutive days; When the daily average outdoor temperature is higher than 5℃ for five consecutive days, the winter construction will be terminated.

2. Comply with the regulations of local government departments (such as relevant documents or requirements issued by the Construction Committee, quality supervision stations and other departments).

3. Reference materials of winter days in some areas throughout the year.

4. Due to the possibility of cold weather sooner or later, the project should start and end the winter construction according to the measured temperature.

Second, the technical management

2. 1 technical standards and standardized management

2. 1. 1 Main standards and specifications for winter construction

(1) Code for Winter Construction of Building Engineering JJ104-2011.

(2) Code for Acceptance of Construction Quality of Concrete Structure Engineering (version 20 1 1).

(3) Technical Specification for Winter Construction of Building Engineering DB2 1/T 1692-2008.

2. 1.2 Technology Department organizes the study of relevant standards and specifications.

2.2 Construction scheme management

Process: scheme preparation → scheme planning meeting → preparation → internal joint review of scheme → company approval → supervision and construction unit approval.

2.3 technical disclosure

2.3. 1 process: scheme disclosure → quality (safety) technical disclosure → operation disclosure.

2.3.2 Concrete subdivisional work shall be disclosed according to each specific part (divided into buildings and layers).

2.4 process acceptance and technical review

Acceptance and inspection (pre-inspection, self-inspection and re-inspection) of technical disclosure (quality and safety technical measures), design drawings and standards and specifications at all levels, and inspection of the actual implementation and implementation of the construction site.

2.5 technical summary

2.5. 1 including: technical summary of the project; Summary of special plan; Summary of quality (safety) technical measures.

2.5.2 Summary of quality (safety) technical measures: after the implementation of a scheme, summarize the problems in the process of project implementation, find out the causes of the problems and propose improvement measures; The good aspects in the process of project implementation should also be summarized and continued to be applied.

2.6 process data

2.6. 1 temperature record (including winter vacation)

2.6.2 Record of concrete pouring temperature measurement (temperature measurement of concrete leaving the tank, temperature measurement of concrete entering the mold and temperature measurement of indoor insulation floor)

2.6.3 Layout of temperature measuring points

2.6.4 concrete curing temperature record

2.6.5 thermal insulation material removal sequence

2.6.6 Concrete strength inspection summary table

Data standardization: tables

Third, quality management.

Common sub-projects in winter construction include: earthwork backfilling, masonry engineering, waterproof engineering, reinforcement engineering, concrete engineering, plastering engineering, etc.

3. 1 earthwork backfilling

3. When1.1plain soil contains frozen soil, the particle size of frozen soil shall not be greater than 15cm, and its content shall not exceed 30% of the total volume of backfill soil. When paving and filling, the frozen soil should be dispersed and compacted layer by layer.

3. 1.2 The paving thickness of each layer should be reduced by 20% ~ 25% compared with that during normal temperature construction, and the thickness of each layer of filled soil should be 200 ㎜ ~ 250 ㎜ during winter construction, the thickness of filled soil should be controlled at 150 ㎜ ~ 200 ㎜.

3. 1.3 indoor foundation trench (pit) or pipe trench shall not be backfilled with frozen soil. Backfill construction shall be continuous and compacted. When artificial compaction is used, the thickness of each layer of soil shall not exceed 20cm, and the compaction thickness should be 10 cm ~ 15 cm.

3. 1.4 When backfilling pipelines and their sites temporarily not used during the freezing period, the content and particle size of frozen soil blocks are not limited, but they should be properly handled after melting.

3. 1.5 The earthwork backfilled under the indoor ground cushion shall not contain frozen soil, and shall be compacted (compacted) in time and verified by tests. After the completion of filling and before the ground construction, anti-freezing measures should be taken.

3.2 Masonry engineering

3.2. 1 The temperature of commercial mortar shall not be lower than 5℃.

3.2.2 Admixture method should be preferred for self-mixing mortar, and chloride salt or nitrite antifreeze can be used to mix mortar. Chlorine salt should be mainly sodium chloride, and the specific dosage should meet the requirements of antifreeze instruction manual and instruction manual.

3.2.3 After daily masonry, the masonry surface shall be protected and covered in time, and mortar shall not be left on the masonry surface. Before continuing masonry, the masonry surface should be cleaned.

3.2.4 Retention of test blocks: not less than two groups.

3.3 Waterproof works

Hot-melt method and cold-stick method can be used for waterproofing construction of coiled materials. The construction temperature of hot melt method should not be lower than-10℃, and the construction temperature of cold glue method should not be lower than -5℃. When coating is used as waterproof layer, solvent-based coating should be adopted, and the construction temperature should not be lower than -5℃.

3.4 reinforcement engineering

3.4. 1 Key points of steel bar welding quality control

A before welding, the dirt and sundries on the surface of embedded parts or joints shall be removed. When welding, the welding process parameters should be adjusted to make the weld and heat affected zone cool slowly. When the wind force exceeds level 3, corresponding windproof measures should be taken before welding; Joints that are not cooled after welding shall be protected from rain and snow, and construction in the open air on rainy and snowy days shall be avoided. When the ambient temperature is lower than -20℃, welding is not allowed.

B, when electroslag pressure welding welding long ribs, should be removed as late as possible medicine cabinet to ensure the slow cooling of welding head. Generally, it takes about 2 minutes to remove the joint medicine box, and 5 minutes to extend the joint welding slag shell before slagging.

C, lap welding or welding process shall meet the following requirements:

(1) The lap joint between reinforcement shall be fixed by two-point welding. The distance between the locating weld and the lap end is equal to or greater than 20mm.

⑵ When welding, the first layer of weld should have enough penetration, and the main weld or locating weld is well fused. When flat welding, the first layer of weld should start from the middle and then be transported to both ends; During vertical welding, the arc should be transported from the middle to the top and then from the bottom to the middle. In the future, when welding all layers of welds, layered temperature control should be adopted.

(3) The weld thickness of lap joint should not be less than 0.3 times of the diameter of steel bar, and the weld width should not be less than 0.7 times of the diameter of steel bar.

3.4.2 Quality control points of negative temperature cold drawing and cold bending of steel bars

A, steel cold-drawn temperature should not be lower than -20℃, steel cold-drawn at negative temperature, should check the appearance quality one by one, the surface can not have cracks and local necking.

B, steel processing equipment, instruments and hydraulic working system oil should be selected according to the ambient temperature, and should be calibrated under the condition of temperature matching.

C, under the condition of negative temperature, steel bars should be checked during construction. During transportation, unloading and processing, attention should be paid to prevent impact and scratch. When the temperature is lower than -20℃, the low-alloy second-and third-grade steel bars should not be cold-bent, so as to avoid strengthening the bending point of steel bars and causing brittle fracture of steel bars.

3.4.3 Quality Control Points of Straight Thread Connection of Steel Bar

The design, application and acceptance of reinforced mechanical connection joints shall comply with the General Technical Specification for Reinforced Mechanical Connection (JGJ 107).

The rebar used for mechanical connection shall comply with the current national standards "Rebar for Reinforced Concrete Part 2: Hot Rolled Ribbed Rebar" GB 1499.2 and "Rebar for Residual Heat Treatment of Reinforced Concrete" GB 130 14.

When the temperature of steel bar joints in concrete structures is lower than-10℃, special tests should be conducted.

3.5 concrete engineering

3.5. 1 critical freezing strength

(1) The concrete, mortar and cement slurry used in winter construction must reach the minimum strength before freezing.

(2) When ordinary concrete is prepared with portland cement or ordinary portland cement, it shall be 30% of the standard value of design concrete strength. The concrete prepared with slag portland cement should be 40% of the design concrete strength standard value, but when the concrete strength grade is C 10, it should not be less than 5.0MPa. When the construction needs to improve the concrete strength grade, it should be determined according to the improved strength grade.

(3) The concrete mixed with antifreeze shall not be less than 4MPa when the outdoor minimum temperature is not lower than-15℃, and not less than 5.0MPa when the outdoor minimum temperature is not lower than -25℃.

Requirements for concrete:

Cement variety and strength grade, minimum cement dosage, water-binder ratio, aggregate, admixture (national 3C certification), slump, initial setting time, tank temperature, etc.

concrete curing

Negative temperature curing method: concrete, mortar and mud mixed with antifreeze can be continuously hardened at negative temperature, and there is no need for heating or heat storage and thermal insulation curing during construction.

Heat storage method: A construction method that uses the heat of raw materials heating and the hydration heat of cement to delay cooling through proper heat preservation, so that concrete, mortar and mud can reach the expected required strength before cooling to 0℃.

Comprehensive heat storage method; Warm shed method;

Electric blanket method: after concrete pouring, cover the concrete surface or the outside of the formwork with a flexible electric blanket, and heat and cure the concrete with electricity.

Concrete temperature measurement

Temperature measurement items and time

Temperature measurement during concrete curing in 3.5.4.2.

(1) temperature measuring point arrangement

(2) Temperature measurement method: thermometer; Electronic thermometer;

(3) Requirements for temperature measurement: from the time the concrete enters the mold to the critical strength of freezing, it shall be measured every 2 hours, and once every 6 hours after reaching the critical strength of freezing.

3.5.5 concrete block lien

① Requirements for retention of test blocks: In addition to the corresponding group of 28d standard maintenance test blocks, test blocks with the same maintenance conditions as the structure should be added at one time. The same curing test block should be placed in the appropriate position of the construction site represented by the test block to ensure that it is stored at the same temperature or curing conditions as the original concrete.

② Number and use of retained test blocks: No less than 5 test blocks shall be retained for wall and column concrete each time, which is used to test the strength of concrete before freezing and after 28 days of curing at normal temperature. At least 2 groups (1 group for standby) shall be retained at different temperature stages (and ≤3d), and 1 group of test blocks shall be retained when the concrete reaches 600℃. D's strength; There shall be no less than 5 groups of floor concrete test blocks each time, of which 2 groups are used to test the strength of concrete before freezing and the strength of concrete after curing at room temperature for 28 days; Two groups (one standby group) are used to control the time of floor formwork removal; At the same time, keep a set of test blocks to check that the concrete reaches 600℃. D the strength of the test block shall be clearly marked with the specific production time, representative parts, strength grade and other technical requirements.

③ Pressure test time of co-culture test block: the test block used to control the time of wall formwork removal should be tested when the test block reaches the condition of formwork removal, the test block used to test the concrete strength before freezing should be tested before the concrete temperature drops to the freezing point (and ≤30h), and the test block used to control the time of floor formwork removal should be tested before formwork removal to test the concrete at 600℃. When the test block with strength d reaches the equivalent age, it should be subjected to pressure test.

3.5.6 Insulation layer and formwork removal

3.5.6. 1 The concrete insulation layer can only be removed after the pressure test strength of the test block with the same conditions as the structure meets the requirements and is cooled to 5℃. In general, when the temperature is 0 ~-5℃, the heat preservation covering time shall not be less than 3 days; When the temperature is lower than -5℃ but not lower than-10℃, the heat preservation and covering time shall not be less than 5 days; When the temperature is lower than-10℃, the heat preservation and covering time shall not be less than 7 days. Only when the strength of concrete strength test block before freezing is greater than the critical strength of concrete freezing, and the difference between concrete temperature and ambient temperature is less than 20℃, can the final insulation layer be removed.

Demolition of concrete insulation layer in 3.5.6.2 must fill in the application for demolition, which can only be removed after it is approved by the chief engineer of the project and approved by the supervision unit.

3.5.6.3 winter construction template demolition, concrete strength must meet the requirements of the table below, the specific demolition time is determined according to the test results of the same condition block.

3.5.7 Strength test of concrete structure in winter construction site.

3.6 Plastering project

3.6. 1 Indoor plastering

(1) Before plastering indoors, doors and windows should be sealed, and the edges of doors and windows and external walls, feet, eyes or holes should also be blocked. Construction holes, air outlets and stairwells should be closed for thermal insulation; The lowest temperature in the north house 50 cm above the ground is not lower than 5℃.

⑵ Mortar should be mixed indoors or in a mixing shed. Mortar temperature should be above 5℃, and it should be kept warm during transportation. It should be mixed because it is used to prevent mortar from freezing.

(3) After the indoor plastering project is completed, the indoor temperature shall be kept at not less than 5℃ within 7d. The gypsum layer can be heated to accelerate drying. When heating with hot air, pay attention to ventilation and eliminate moisture.

Outdoor plastering

(1) Generally, the cold construction method is adopted, and compound antifreeze and chloride antifreeze can be used, and the dosage of antifreeze should meet the requirements of the operating instructions and specifications.

(2) Mortar mixed with compound antifreeze shall be plastered at an ambient temperature not lower than -5℃.

(3) Mortar mixed with chlorine salt shall be plastered during cold operation, and the temperature shall not be lower than-15℃. Chlorine salt antifreeze can be mixed into mortar mixed with portland cement, ordinary portland cement and slag portland cement, but not into high alumina cement mortar.

(4) Chlorine-containing antifreeze shall not be used for high-voltage power supply and cement mortar base for painting walls.

3.7 Heat preservation and snow removal measures

1, facilities insulation measures

2, the construction floor insulation measures

3, ice and snow removal measures

Melt ice and snow with spray gun liquefied gas or boiling water.

3.8 Snow Emergency Plan

Emergency measures before snow:

(1) Pay attention to the weather in time.

⑵ Cover the parts where the steel bars have been bound with colored strips (the wall column parts are covered with cotton curtains) to reduce the snow falling into the formwork.

(3) Comprehensively check the coverage of thermal insulation materials on the poured concrete surface to ensure that the thermal insulation materials are tightly covered.

(4) Check whether the thermal insulation measures for temporary water pipelines are in place.

Emergency measures in case of snow:

1, concrete pouring shall be carried out as far as possible to avoid snowy days. In case of sudden snowfall during pouring, the snow and ice blocks in the formwork should be cleaned before pouring, or construction joints should be left in the allowable parts of the structure before pouring.

2. Covered striped cloth should be hoisted and poured with concrete. If it freezes, use a liquefied gas tank with a spray gun or boiled hydrated ice to melt the snow. After the completion of concrete pouring, the concrete surface shall be covered and insulated immediately according to the technical disclosure requirements.

Fourth, safety management.

4. 1 fire protection

4.2 Anti-skid

4.3 Prevention of Gas Poisoning

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