1. Organizational guarantee measures:
The engineering department, quality inspection department and laboratory are responsible for the prevention and control of concrete construction in winter The main body of the measures, technical managers at the construction site, are directly responsible. Strengthening the temperature control of concrete entering molds, time control of mold removal, insulation covering and maintenance, and tension and grouting temperature control are the key to process control of the concrete construction process in winter.
2. Construction facilities and material requirements
Winter concrete construction refers to the average daily outdoor temperature Construction of concrete, reinforced concrete, prestressed concrete and masonry projects when the temperature is stably below 5 degrees for 5 consecutive days. For projects constructed in winter, various winter preparations should be made in advance, and anti-snow, anti-freeze and other measures should be taken in advance for various facilities and materials (to prevent materials from being soaked with water and freezing and snow, etc.) to prevent construction facilities from being damaged by water and freezing. Affect the quality of construction operations. Therefore, it is very important to cover and protect materials and facilities. During winter construction, anti-freezing measures should be formulated, and the local meteorological department should be contacted to conduct temperature observations.
Welding steel bars should be done indoors. When it must be done outdoors, the lowest temperature
The temperature should not be lower than -20 degrees, and snow and wind protection measures should be taken to reduce the temperature difference of the welded parts. The joints after welding are strictly prohibited from contacting ice and snow immediately.
The mixing water for concrete, grouting, mortar, etc. should generally not be lower than 5 degrees. If the temperature is low, construction must be carried out, and the construction water should be added. temperature treatment.
Mainly used pulping machines, grout presses, tensioners, instruments and other equipment should be placed back indoors or in a warm place after use to prevent freezing damage during secondary use. .
3. Technical requirements for concrete preparation and mixing
1. When preparing concrete, it is advisable to Portland cement and ordinary Portland cement are preferred. The strength grade of the cement should not be less than 42.5#, and the water-cement ratio should not be greater than 0.5.
2. When curing concrete mixed with admixtures by heating, the use of high-alumina cement is strictly prohibited. When using other types of cement, attention should be paid to the impact of its blending materials on concrete strength, frost resistance, impermeability and other properties.
3. When pouring concrete, it is advisable to mix air-entraining agent, air-entraining water-reducing agent and other admixtures to improve the frost resistance of concrete.
4. The temperature of each material used to make concrete should meet the temperature required after the concrete mixture is mixed and synthesized. When the original temperature of the material cannot meet the needs, heating of the mixing water should first be considered. If the original temperature still cannot meet the needs, heating of the aggregates should then be considered. Cement only insulates and must not be heated.
5. When mixing concrete in winter, the aggregates must not contain ice, snow and frozen clumps. Strictly control the mix ratio and slump of concrete; before feeding, the mixer should be flushed with hot water or steam. The feeding sequence is aggregate, water, mixing, then cement mixing. The mixing time should be 50% longer than at normal temperature. The exit temperature of the concrete mixture should not be lower than 10 degrees, and the mold entry temperature should not be lower than 5 degrees.
4. Technical requirements for concrete transportation and pouring
1. The transportation time of concrete should be Keep it as short as possible, and containers for transporting concrete should be insulated.
2. When constructing joint concrete in winter, the joint surface should be heated to a temperature of more than 5 degrees before the new concrete is poured. After the pouring is completed, measures should be taken Keep the concrete joint surface at a positive temperature until the newly poured concrete acquires the specified frost resistance.
5. Technical requirements for concrete curing
1. The curing method of concrete should be based on Determined by technical requirements and on-site construction. When the temperature is low and the structural surface coefficient is large, methods such as greenhouse heating or wrapping insulation can be used.
2. The removal of formwork should comply with the following regulations:
1. According to the same as the structure After the test of the conditional curing specimen proves that the concrete has reached the required frost resistance strength and form removal strength, the formwork can be removed. And according to the owner’s documents: the formwork removal time should be no less than 30 hours, and the formwork can only be removed after the load-bearing formwork concrete reaches the strength and elastic modulus.
2. The formwork and insulation layer of the heated curing structure can only be removed after the concrete has cooled to 5 degrees. When the difference between the concrete and the outside temperature is greater than 20 degrees, the concrete surface after removing the formwork should be covered.
3. The maintenance of concrete mixed with antifreeze should comply with the following regulations:
Under load Watering is strictly prohibited under warm conditions, and exposed surfaces must be covered and maintained.
The curing temperature shall not be lower than the temperature specified by the antifreeze. When the specified temperature is not reached and the concrete strength is less than 3.5mpa, heating and insulation measures should be taken.
When the difference between the surface temperature of the concrete after the formwork is removed and the ambient temperature is greater than 15 degrees, the surface of the concrete should be covered with thermal insulation and curing.
6. Prestressed tensioning
1. Before the tensioning operation, first deal with Preheat the tensioning equipment, check the oil top, instrumentWhether the gauge is sensitive and accurate, and at the same time, the pressure gauge is kept stable during the tensioning process.
2. When prestressing is being tensioned, in addition to the time requirements, the strength of the concrete and whether the concrete is damaged by freezing damage must be checked. If there is no abnormality, tensioning should be carried out again. pull.
7. Pipeline grouting requirements
1. Before grouting, first check whether the pipeline is Check whether the concrete is blocked or the residual water is frozen and blocked; use warm water to check.
2. Check whether the grouting pipeline is damaged and whether the normal grouting pressure can be guaranteed;
3. Grouting should be carried out when the temperature of the concrete body is above 5 degrees, or heating methods should be used;
8. Construction of masonry projects in winter
1. In terms of materials:
The blocks should be clean and free of ice and frost; the sand must not contain ice or Freeze clumps. Blocks that have been frozen after being soaked in water cannot be used.
2. The masonry mortar constructed in winter must be kept at a positive temperature, and the temperature difference between the mortar and the stone surface should not exceed 20 degrees. Mortar should be mixed with ordinary Portland cement. The mortar should be mixed and used. The mixing time should be doubled compared with normal temperature. The consistency of the masonry mortar should be 40-60.
3. When the temperature suddenly drops before and after winter construction, the following measures should be taken for the masonry project under construction:
1. When heating the materials for mixing mortar, the water temperature should not exceed 80 degrees, the sand should not exceed 40 degrees, and the mortar temperature should not be lower than 5 degrees.
2. The speed of mixing the mortar is closely coordinated with the progress of the masonry, and it can be used as needed.
3. The completed part should be covered with insulation materials. When the temperature is lower than 5 degrees, watering cannot be sprinkled for maintenance.
<img src="/upfile/202210/2022101830586343.jpg"/
微信扫一扫打赏
Chinese