Quality assurance measures for winter construction

Quality Assurance Measures for Winter Construction of Bid B 1 Project

I. Overview of the Climate Situation

Nantong City, where Sutong Bridge is located, has the lowest temperature and the least precipitation in winter. Previous statistics show that 1 month is the coldest in winter, and the monthly average temperature is around 3℃. Extreme minimum temperature-12.7℃, extreme maximum frozen soil depth-0/2cm, extreme maximum snow depth-0/7cm.

The winter climate characteristic values of the bridge site area are shown in the following table:

Table 5. 1. 1 winter climate characteristic value of bridge area

Element in Changshu City, Nantong City

Gas temperature extreme minimum temperature-12.7℃-11.3℃

The lowest annual average temperature is 14.4℃ 14.5℃

The lowest monthly average temperature is-0.2℃ 0.3℃

Extreme maximum frozen soil depth (cm) 12-

Extreme maximum snow depth

(cm) 65438+February 7th 7

65438+ 10 month 17 15

February 16

March 13 1 1

The outdoor daily average temperature is lower than 5℃ for five consecutive days, which is winter construction. According to the above climate statistics, the outdoor average temperature in some weather periods of 65438+ 10 in Nantong area was lower than 5℃ for five consecutive days, which had a certain impact on the construction of reinforced concrete and prestressed concrete. It belongs to winter construction, so it is necessary to take winter construction quality assurance measures.

Second, the winter construction measures

The duration of this contract is 36 months, and the whole project lasts for three winters, in which the concrete such as pile caps, piers and box girders constructed in 2004 and 2005 are exposed to the air, which is greatly affected by temperature. Therefore, winter construction must be well prepared in advance and take reliable technical guarantee measures.

1, winter construction preparation

B 1 contract section of Sutong Bridge is under normal construction in winter. In order to better ensure the quality and progress of winter construction, the following preparations should be made.

1. 1 Make a plan for winter construction quality assurance measures;

1.2 do a good job of snow prevention and freezing prevention for all facilities and materials in advance;

1.3 The construction technical requirements and safety measures shall be specially formulated for prestressed tensioning;

1.4 winter construction should be considered for concrete mixture ratio;

1.5 laying waterproof layer shall be carried out according to the relevant provisions of waterproof layer construction in winter;

1.6 Formulate safety measures such as fire prevention, freezing prevention and gas poisoning prevention in winter construction;

1.7 Technical disclosure of winter construction for workers in advance;

1.8 contact the meteorological department to make a good winter temperature forecast.

2, winter construction measures in the process of construction

2. 1, winter construction measures for steel bars and prestressed beams

2. 1.65438+

2. 1.2 When tensioning prestressed reinforcement, the temperature should not be lower than-15℃.

2. 1.3 the working oil of prestressed tensioning equipment and instruments shall be selected according to the actual ambient temperature, and calibrated at the ambient temperature.

2. 1.4 prestressed concrete channel grouting should be carried out at room temperature.

2.2, template winter construction measures

The back of the steel formwork is wrapped with 30mm thick hard foam insulation layer, and the wooden formwork is wrapped with 20mm thick cotton felt, which is welded and fixed with adhesive tape and steel bars. During winter construction, the formwork requiring auxiliary maintenance shall be appropriately extended according to the weather conditions.

2.3, concrete construction measures in winter

2.3. 1 concrete mixture ratio

Ordinary portland cement is selected for concrete mixing, and the cement strength grade is 42.5. The water-cement ratio is not greater than 0.5 (now the concrete mix ratio used in the construction site is: pile foundation ((c+f): s: g: w =1:kloc-0/.795: 2.476: 0.43) and cap ((c+f): s: g: w = 655). Pier ((C+F): S: G: W =1:kloc-0/.890: 2.683: 0.373), box girder ((C+F): S: G: W =1:/kloc-

The mix proportion design of concrete in winter should be comprehensively considered according to the pouring strength and transportation mode of concrete, and the admixture content must be implemented according to the specifications.

Concrete mixing

Materials used for mixing concrete in winter construction, such as sand, stone and water. , should be kept at a positive temperature. In order to ensure that the temperature of concrete mixture entering the mold is not lower than 10℃, the temperature of concrete mixture leaving the tank should generally be controlled at 13℃ ~ 18℃. In order to ensure the temperature of the tank, first consider heating the mixing water, and if it still cannot meet the needs, then consider heating the aggregate.

There is a10.5m3 steam boiler in the back mixing station for heating the mixed water.

For concrete mixing in winter, we should also pay attention to the following items:

First, cement can only be kept warm and cannot be heated;

B, pay attention to the mixing water heating water temperature shall not be higher than 60℃, aggregate temperature shall not be higher than 40℃ when heating;

C, before concrete mixing, rinse the mixer with hot water or warm water;

D, clean up the snow and frozen aggregate, don't stir in the blender;

E, according to the actual temperature on the day of concrete pouring, convert the temperature that each material needs to be heated, but it shall not exceed the above-mentioned maximum temperature regulation;

F, in order to ensure the workability and fluidity of concrete, mixing time can be extended, generally 50% longer than normal temperature.

G, in order to ensure the concrete does not appear false setting phenomenon, concrete mixing should be carried out in the order of sand, water and cement, and shall not be reversed.

Concrete transportation

In winter concrete construction, in order to prevent excessive temperature loss during transportation, the following measures should be taken:

A, clean up the concrete tanker transportation road, ensure the smooth road, and shorten the concrete transportation time as much as possible;

B, the construction site reasonable control of concrete pouring speed, try to reduce or avoid the waiting time of concrete tank car;

concrete pouring

Before pouring concrete, the snow, ice and dirt on the formwork and steel bar should be removed.

When constructing joint concrete in winter, before pouring new concrete, iodine tungsten lamp or hot water should be used to pour the summer-planting part of the concrete contact surface, to ensure that the concrete temperature at the joint is not lower than 5℃, the heating depth is not less than 30cm, and the preheating length is controlled at around1m.. After pouring is completed, measures should be taken to keep the concrete joint surface at a positive temperature until the newly poured concrete reaches the specified frost resistance strength.

2.3.5 Technical requirements for concrete curing

Cover and maintain the poured concrete in time. Temperature requirements during curing: when curing by heat storage method, it shall not be lower than 65438 00℃; Steam curing shall not be lower than 5℃, and thin structure shall not be lower than 8℃.

The curing method of concrete should be calculated and determined according to the technical and economic comparison and the "Thermal Calculation Formula for Winter Construction" in the specification. The curing method should be based on various factors, such as site temperature and structural surface coefficient. , and can choose heat storage method, steam heating method, greenhouse heating method or electric heating method, etc., to ensure that the concrete structure is not damaged by freezing.

In winter construction, before the compressive strength reaches 40% of the design strength, it is necessary to prevent freezing.

When the temperature is lower than 5℃, it is not allowed to spray water on concrete and mulch for curing.

3. Winter construction measures of this project

3. 1 winter construction of bored pile

The winter construction of bored pile concrete is mainly to ensure that the concrete will not freeze during pouring and can be poured smoothly.

When the pile head is exposed out of the water (or ground) or not, but it is within the freezing range, the pile head concrete shall be covered for thermal insulation and curing.

Note: The temperature of concrete mixture during pouring should not be lower than 5℃; No antifreeze or antifreeze is allowed in concrete.

3.2 Winter construction of pile caps and pier shafts

In order to ensure the construction quality of concrete for pile caps and piers in winter, the following measures should be taken:

A, 20mm thick felt is wrapped behind the steel box template of bearing platform and the steel box template of pier column, and welded and fixed with steel bars;

B, 30mm thick rock wool felt is wrapped behind the pier formwork and fixed with adhesive tape;

C, concrete pouring of pile caps and piers should be arranged during the day as far as possible;

D, concrete curing of pile caps and piers, mainly using geotextile to cover the concrete surface for temperature storage and curing, especially for individual parts that are easy to cool down (such as exposed positions of steel bars).

3.3 Box girder construction in winter

When box girder concrete is constructed in winter, the following measures should be taken to ensure the construction quality:

A, 30m box girder external formwork adopts wooden formwork. When pouring concrete below 5℃, the scaffolding outside the external formwork is wrapped and sealed with colored strips of cloth to form a greenhouse, which can be heated by a stove or an electric heater; The surface layer adopts plastic water-retaining curing method. After the concrete pouring is completed, the roof is immediately covered with 0.03mm thick plastic sheet, and then covered with cold-proof quilt.

B, 50mm thick felt is wrapped outside the formwork of 50 m box girder, which is welded and fixed with steel bars. Surface maintenance is the same as 30m box girder.

C, box girder before concrete pouring, pay attention to listen to the weather forecast, according to the weather forecast, avoid heavy snow, heavy rain, cold wave and other weather when concrete pouring.

D, drag pump pipe covered with sacks or geotextiles. , in order to reduce the temperature loss in the process of concrete pouring.

E, construction joint concrete with iodine tungsten lamp or hot water pouring summer-planting parts heating (mainly floor, roof position) to more than 5℃, after the completion of concrete pouring, continue to heat to ensure that the joint is maintained at a positive temperature;

F, when the temperature is too low, after the completion of concrete pouring, seal the cavity and measure the temperature of the cavity. If the indoor temperature is lower than 5℃, set a heater indoors for heating and curing. Observe the surface humidity of concrete during curing, stop heating when drying, and wet the surface with warm water;

G, prestressed pipe grouting above 5℃;

H, maintenance, it is forbidden to negative temperature concrete surface water.

3.4 Bridge deck system construction in winter

When the bridge deck concrete is constructed in winter, the following measures should be taken to ensure the construction quality:

A, 30mm thick felt is wrapped behind the steel formwork of the crash barrier, which is welded and fixed with steel bars;

B, concrete pouring as far as possible in the daytime;

C, when pouring concrete for crash barrier, in order to reduce the temperature loss of concrete when shoveling materials manually, an ignition lamp is set at the concrete accumulation place for heating;

D, leveling layer concrete pouring, cloth, vibrating, surface should cooperate well, try to reduce the construction operation time;

E, after the concrete pouring is completed, cover it with geotextile for heat preservation and maintenance;

F, collision guardrail template is dismantled, should cover geotextile to continue maintenance.

Third, the winter construction quality inspection

In winter construction, in addition to the quality inspection according to the routine construction, the ambient temperature during concrete pouring and curing should also be checked, and the following inspections should be carried out:

1, concrete water heating temperature;

2, concrete heating curing method and time, etc. , the inspection results should be recorded in the concrete engineering construction record and the temperature inspection record;

3. The temperature of aggregate and mixing water entering the mixer, the temperature of concrete poured from the mixer and the temperature at the time of pouring shall be checked at least 3 times per shift;

4, during the period of concrete curing, indoor and outdoor environmental temperature, fixed point 4 times a day and night;

5, concrete construction in winter, in addition to the standard curing specimens, should make the same number and the same conditions as the structure of curing specimens.

Four, other matters needing attention in winter construction

1, when working at height, strengthen safety management and safety measures, and take reliable windproof measures;

2. When welding steel structure in winter, corresponding welding technology should be adopted to ensure welding quality;

3. Strengthen the warm maintenance of mechanical equipment during winter construction to ensure the normal operation of the equipment;

4. Construction should be stopped in windy, snowy and foggy days;

5. If it is continuously attacked by cold weather, the construction of surface concrete such as pier and box girder can be suspended, and the construction can be carried out after the temperature warms up.

6. Clear the snow on the upper and lower ladders in time, and there should be anti-skid measures at special positions.