Technical quality measures for construction in the

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Technical quality measures for winter construction

preparation for winter construction, main technical quality control for winter construction and common quality problems and preventive measures for concrete in winter construction

II. Preparation for winter construction

(I) technical preparation

1. The formulation of construction technical scheme (measures) must be based on the premise of ensuring construction quality and production safety, with certain technical reliability and economic rationality

2. The formulated construction technical scheme (measures) shall include the following contents: Construction deployment (schedule), construction procedures, construction methods, allocation plan of machines, tools and materials, technical training of construction personnel (temperature measurement personnel, admixture personnel) and labor plan, plan of thermal insulation materials and admixture materials, key points of operation, key points of quality control, testing items, etc

(II) production preparation

arrange construction tasks and site preparations according to the formulated schedule For example, the heat preservation and anti freezing of on-site water supply pipeline, the heat preservation of mixer shed, the leveling of the site and the setting of temporary roads, and the sealing and heat preservation of door and window openings of decoration works

(III) resource preparation

organize the preparation of admixture materials, thermal insulation materials, construction instruments (temperature measuring agents), labor protection articles for employees, etc. according to the formulated plan

III. main technical measures for winter construction

(I) earthworks

1. Foundation earthworks should avoid construction in winter as far as possible. If construction in winter is required, detailed construction plans, reasonable construction schemes and practical technical measures should be formulated. At the same time, construction management should be organized to strive to complete the construction in a short time

2. The roads on the construction site shall be kept unblocked, and necessary anti-skid measures shall be added for transport vehicles and driving roads (such as covering straw bags along the road)

3. When excavating earthwork at the side of adjacent buildings, measures shall be taken to protect the foundation soil of old buildings from freezing damage During construction, try to dig and fill quickly to prevent the foundation from freezing

4. Drainage measures shall be taken in the foundation pit groove to prevent ponding, resulting in collapse due to multiple freeze-thaw cycles at the lower part of the soil wall

5. Necessary thermal insulation measures shall be taken at the bottom of the excavated foundation pit, such as retaining foot mud or laying straw bags

6. Before earthwork backfilling, the ice, snow and thermal insulation materials at the bottom of the foundation pit shall be cleaned

7. Outdoor foundation pit or 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 filling Indoor pits, grooves and pipe trenches shall not be backfilled with soil containing frozen soil blocks

8. When manual backfilling is used for backfilling, the thickness of each layer shall not exceed 20cm, and the compaction thickness shall be 10-15cm

9. The backfilling work shall be carried out continuously to prevent the foundation soil or filling layer from freezing

(II) pile foundation works

1. Before construction, special construction schemes and technical measures shall be prepared

2. The distance from the axis of the pile foundation shall be appropriately increased to avoid being affected by the frozen soil crust during pile driving The number of benchmarks shall not be less than two In recent years, many heads of state, dignitaries and delegations have inspected China's high-speed railway

3. The concrete of precast piles can be lifted only when the strength reaches 70% of the design strength standard value, and can be transported and driven only when the strength reaches 100% of the design strength standard value

4. Pile stacking shall consider the driving route and driving sequence of the pile driver, and the number of pile stacking layers shall not exceed 4

(III) reinforcement engineering

1. Cold drawing of reinforcement

(1) when the reinforcement is cold drawn at negative temperature, the stress control method or the cold drawing rate control method can be used It is not suitable to control the cold drawing rate for hot rolled steel bars that can not distinguish the furnace batch

(2) when the control stress method is used to cold draw the reinforcement under negative temperature, the elongation decreases with the temperature. If the control stress remains unchanged, the elongation is insufficient, and the reinforcement strength will not meet the design requirements. Therefore, the control stress of various experimental data and curve drawing under negative temperature is higher than that under normal temperature Cold drawing control the maximum cold drawing rate of the factory made stress of Jinan steel bar bending testing machine shall meet the requirements of the following table:

2. Steel bar negative temperature welding

(1) the construction personnel engaged in steel bar welding construction must hold the welder's certificate before they can work

(2) for reinforcement welding construction under negative temperature, flash butt welding, electric arc welding (upper strip, overlap, groove welding) and electroslag pressure welding can be used

(3) the welding of steel bars should be arranged indoors as far as possible. If it is necessary to weld outdoors, the ambient temperature should not be too low. In windy and snowy weather, certain shielding measures should be taken Do not touch snow and ice when welding uncooled joints

(4) flash butt welding:

1) preheating flash welding or Flash preheating flash welding process should be adopted for negative temperature flash butt welding When the end face of the reinforcement is relatively flat, preheating flash welding should be adopted; When the end face is uneven, the flash preheating flash welding process should be adopted

2) compared with normal temperature welding, corresponding measures should be taken, such as increasing the stretching length by about 10% to 20%, increasing the contact pressure during preheating, and increasing the preheating interval

3) the parameters selected during welding can be flexibly selected according to the steel type, diameter, welding temperature and welder's technical level of the weldment

(May 1969) arc welding

1) overheating, burns, biting, cracks and other defects must be prevented during welding, and the eccentric stress state at the joint shall be prevented in structure

2) in order to prevent the temperature in the heat affected zone of the joint from suddenly increasing, the bonding and lap arc welding shall be carried out, and the layered temperature control welding shall be adopted When welding the upper strip, the upper strip and the main reinforcement shall be fixed by four point tack welding Two points shall be used for fixing during lap welding, and the fixed-point weld shall be more than 20mm away from the upper strip or lap end

3) during groove welding, the weld root, groove end face and the steel bar and steel base plate shall be well fused

(6) electroslag pressure welding

1) the size of welding current shall be determined according to the diameter of reinforcement and the ambient temperature during welding

2) the removal time of the joint kit should be extended for about 2min; The slag shell of the joint should be extended for 5min before slagging

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