Does winter construction have hidden dangers to housing quality?
1, winter construction is the season with frequent engineering quality accidents due to unfavorable construction conditions and environment, especially concrete projects.
2. The concealment and lag of quality accidents. That is to say, the project was done in winter, and most of it began to be exposed in spring, which brought great difficulty to the accident handling. The light ones are repaired and the heavy ones are restarted, which not only brings losses to the project, but also affects its service life.
3. The winter construction is planned, and the preparations are timely. This is due to the short preparation time and complicated technical requirements. There are often some quality accidents, all because this link has not kept up and the construction has been rushed.
Second, the winter regulations:
Masonry engineering: it is predicted that the daily average temperature of 10 will be lower than 5℃, that is, it will enter the winter construction stage.
Concrete construction: When the daily average outdoor temperature is lower than 5℃ or the lowest outdoor temperature is lower than 0℃ or below for five consecutive days, concrete construction will enter winter construction.
Plastering works: When the minimum ambient temperature is lower than +5℃, it shall be carried out according to the relevant regulations of winter construction.
After entering 1 1, all units should pay attention to the local weather forecast at any time, start measuring the temperature every day, and prepare for the sudden drop of temperature.
Third, the temperature characteristics:
According to the characteristics of temperature in Tianjin, the starting and ending time of the average temperature below 5℃ is 1 15 in October to 15 in March of the following year, totaling 128 days. However, according to the law of temperature change over the years, winter construction can be divided into general low temperature stage and extremely low temperature stage. Generally, the low temperature period is1October 1 15 to mid-February of the following year 15 and mid-February to March of the following year 15, which is about 70-80 days, accounting for about 60% of the whole application time in winter. During the day, the working environment is basically normal temperature, and concrete construction adopts mixing.
The extreme low temperature period is from the end of June 65438+February to the middle of February of the following year, especially in June 65438+10, which belongs to Leng Yue with the highest temperature in Tianjin. The daily minimum temperature is about-10 C. During this period, the water and sand used in the mixture must be heated and mixed with concrete antifreeze for construction. After concrete pouring, cover with plastic film and straw bag for insulation.
Fourth, winter preparations
1, organizational measures
(1), winter construction projects, should organize personnel to prepare the winter construction plan before winter. The principles of compilation are: to ensure the quality of the project; Economical and reasonable, try to reduce the increase of cost; The required heat source and materials are reliable, and the energy consumption is minimal; It can really shorten the construction period. The winter construction plan should include the following contents: construction procedures; Construction method; Website layout; Supply plan of equipment, materials, energy and tools; Safety fire prevention measures; Temperature measuring system and quality inspection system. After the scheme is determined, it is necessary to organize relevant personnel to study and make disclosure to the team.
(2) Before entering the winter construction, special technical business training should be given to admixture personnel, temperature measuring and insulation personnel, boiler stoker personnel and furnace management personnel to learn relevant knowledge within the scope of work and clarify their responsibilities. Only after passing the exam can they go to work.
(3) Keep in touch with the local meteorological station, receive the weather forecast in time, and prevent the cold current from coming.
(4) During the construction, assign special personnel to measure the outdoor temperature, the temperature in the greenhouse, the temperature of mortar and concrete and make records.
2, drawing preparation
All winter construction projects must review the construction drawings to check whether they can meet the requirements of winter construction. For example, the structural stability related to the wall height-thickness ratio and the distance between transverse walls, the change from cast-in-place to prefabrication, and whether the engineering structure can survive the winter safely in cold conditions, etc., must be solved through the blue prints.the design.
3. Site preparation
(1), organize related machines and tools, additives and insulation materials in advance according to the physical quantities.
(2), the construction of boiler room for heating, mixing station, laying pipes, boiler fire and pressure test, and check the safety and reliability of all kinds of heating materials and equipment.
(3) Calculate the transformer capacity and turn on the power supply.
(4), the scene of the temporary water supply pipes and plastering materials to do a good job of heat preservation and antifreeze.
(5) do a good job in the trial mixing test of concrete, mortar and admixture for winter construction, and put forward the construction mixture ratio.
4, safety and fire prevention
(1), winter construction, anti-skid measures should be taken. Living and construction roads, shelves and ramps are often cleaned of accumulated water, ice and snow, and inclined runways should have reliable anti-skid strips.
(2) After the heavy snow, the snow on the shelf must be cleaned and inspected. If the platform is loose and sinks, it must be handled in time.
(3), such as contact with steam source and hot water during construction, to prevent burns; When using calcium chloride and bleaching powder, skin corrosion should be prevented.
(4) Sodium nitrite is highly toxic and should be kept strictly to prevent accidental poisoning.
(5), fire prevention, strengthen management; When using natural gas and coal gas, it is necessary to prevent explosion; When using coke oven, coal stove or natural gas and gas, pay attention to ventilation to prevent gas poisoning.
6, power switch, control box and other facilities should be unified layout, lock protection, prevent disorderly pull wires, designated persons responsible for the management, to prevent leakage and electric shock.
All landowners, winter construction, all aerial work should wear a seat belt, wear rubber shoes, to prevent slipping and falling.
Today, the construction site water and fire hydrants should be marked.
5. The winter construction projects this year include Longsheng Garden, Wang Di, Science Park, Wuqing Vacuum Factory, Juchuan Project, Longdu, Meijiang, and some undetermined projects. Please make all preparations for winter construction in advance, and submit detailed material plans to ministry of materials and equipment, which will be purchased by ministry of materials and equipment for convenient deployment. When purchasing antifreeze, it must be implemented in accordance with the Notice on Strengthening the Quality Monitoring of Concrete Antifreeze for Winter Construction issued by Tianjin Construction Committee, that is, the antifreeze used must have "three certificates" (certificate, 24-station test report and factory certificate). Pay special attention. According to the Technical Management Regulations for Preventing Alkali-aggregate Reaction of Concrete in Tianjin (Trial) (JJG 14-2000), low-alkali admixture should be selected when adding admixture to concrete, so that the total alkali content of concrete does not exceed the specified value.
Five, winter construction measures
(a), pile foundation engineering:
In winter, the construction of concrete cast-in-place piles should be carried out by heating raw materials or mixing antifreeze, and the concrete pouring temperature should not be lower than 5℃. When the concrete pile body is located in the frozen soil layer, the top of the concrete after pouring should be covered with heat preservation to ensure that the concrete strength reaches 50% of the design mark without freezing.
(2), earthwork:
1 In winter, the soil becomes hard and difficult to dig because of freezing, and the construction cost is higher than that at room temperature. Therefore, the earthwork and foundation works of the new project should be completed as far as possible before the winter construction.
2. For the earthwork that must be excavated in winter, it is necessary to determine the economic and reasonable construction scheme according to local conditions and formulate practical technical measures to achieve rapid excavation, rapid foundation construction and rapid backfill.
3. The foundation soil is mainly covered with straw mats for insulation. During large-scale earthwork excavation, the topsoil should be turned loose and raked flat to prevent freezing, and the turning depth should be 30-40 cm.
4. In winter construction, if foundation construction cannot be carried out immediately after foundation trench excavation, more than 300mm of soil shall be reserved according to the designed trench bottom elevation, and the trench shall be cleaned as the foundation. Generally, the temperature of two-layer straw mats is between 0℃ and-10℃, and the temperature of three-layer or four-layer straw mats is below-10℃.
5. Earthwork used for backfilling in winter should be piled up in piles and covered with straw mats on the second floor to prevent freezing.
6, before earthwork backfill, should remove the ice and snow on the grass-roots and thermal insulation materials.
7. The thickness of each layer of earthwork backfill soil should be reduced by 20-25% compared with normal temperature construction, and the reserved settlement should be appropriately increased compared with normal temperature construction. When tamping manually, the thickness of each layer of soil shall not exceed 20cm, and the tamping thickness shall be 10- 15cm.
8, when using frozen soil as fill, indoor foundation pit (groove) or pipe trench shall not backfill frozen soil; Outdoor foundation pit (ditch) or pipe trench can be backfilled with soil containing frozen blocks, but the volume of frozen blocks shall not exceed 15% of the total volume of filled soil, and the soil containing frozen blocks shall not be backfilled within 0.5m from the bottom of pipe trench to the top of pipe, and the particle size of frozen blocks shall not exceed 15cm. When paving and filling, frozen blocks should be dispersed and compacted layer by layer.
9. The lime-soil cushion can be constructed when the temperature is not lower than-10℃, but thermal insulation measures must be taken to prevent the foundation trench, plain soil and lime from freezing. "Five-in-one" measures should be taken in lime construction, that is, drilling, screening, mixing and tamping and covering. The compacted straw mat will cover two or three layers.
10, earthwork construction should follow the provisions of the current code on winter construction.