Key points of concrete construction in water conservancy project in winter?
1 concrete winter construction temperature standard
In winter construction of water conservancy projects, the temperature standards are as follows: First, in relatively cold areas, the temperature should be controlled below 5℃; Second, for mild areas, the temperature should be controlled below 3℃; Third, in the process of winter construction, thermal insulation measures should be implemented.
2 winter concrete matters needing attention
2. 1 meets relevant requirements.
In the process of batching, it is necessary to ensure the strength and workability of concrete, mainly including the water retention, cohesiveness and fluidity of concrete. Water retention refers to the fact that if there is water precipitation on the surface of concrete during construction, it means that the compactness and water retention of concrete are poor, which will have a certain impact on the durability and strength of concrete. Cohesion mainly means that concrete does not segregate during pouring and transportation. After vibrating in the mould, if the cement slurry can't wrap the stones, the uniformity and integrity of concrete can't be guaranteed. Liquidity mainly refers to the ability of concrete to fill the formwork evenly, and its size reflects the thinness of concrete. Liquidity directly affects the construction time and difficulty, and also affects the quality of the project.
2.2 to prevent cracks
In winter construction, the temperature difference of concrete should be controlled within a reasonable range. The mix proportion of concrete and the quality of raw materials determine its mechanical and thermal properties, so controlling its temperature difference can effectively prevent cracks. It is necessary to choose cement with low heat release, reduce its dosage as much as possible, and prevent concrete from rising in temperature. At the same time, a certain amount of admixture, including admixture and water reducer, should be added to reduce water consumption and improve the strength and workability of concrete. It is necessary to select aggregate with good gradation and material, reduce its linear expansion coefficient, and add shrinkage reducing agent and expansion agent. Construction personnel should reasonably control the water-cement ratio of concrete, improve the strength of concrete and control the sand-water ratio. M When the sand quantity increases and the water consumption decreases, the most reasonable proportion can be achieved. It is also necessary to dynamically monitor the water content of sand, adjust the proportion according to the actual situation, and scientifically adjust the sand water compensation through calculation during the batching process.
2.3 Arrange the pouring sequence
In the process of construction, the construction personnel should carry out the construction according to the design requirements, and arrange the pouring sequence reasonably to prevent the weak parts from appearing due to the long pouring interval. In mass construction, the method of uniform rising, short interval and thin layer pouring should be adopted to prevent the long-term shutdown from affecting the engineering quality. After the initial setting of concrete, secondary plastering should be carried out immediately, and the accumulated water on the surface should be cleaned in time to prevent cracks.
3 concrete pouring and mixing requirements
3. 1 mixed antifreeze
There are many concrete construction methods in winter, and adding antifreeze is the most economical and simple method. Compared with far infrared method, warm grid method, steam method and electric heating method, there is no need to invest in equipment maintenance, energy consumption and equipment investment, which saves the cost for the construction unit.
3.2 Material preheating
The mixed water and sand are preheated and then concrete is added. Aggregate can be heated by steam or copied by iron plate. In the process of heating sand and water, the temperature should be controlled at about 60℃ and the water temperature should be controlled at about 80℃ to prevent false condensation caused by excessive temperature. The preheating of materials can ensure that the cement is in good condition, and if the heat preservation work is done properly, the construction quality can be effectively guaranteed.
3.3 Heat storage and heat insulation
Mainly to prevent concrete temperature from escaping through the protective layer, so as to avoid the influence of low temperature in winter. Thermal storage and insulation is the most commonly used method in winter construction in China, with low cost, simple operation and good effect. Plastic film and rock wool are usually selected as covering materials. Without the above materials, rice husk, sawdust, straw bag and straw curtain can also be used, but attention should be paid to fire safety. At present, plastic film and rock wool quilt are still the main covers selected by construction units, which not only keep warm, but also retain water.
3.4 Thermal storage and insulation and admixture mixing
In winter construction of water conservancy projects, in order to ensure the temperature of concrete, a comprehensive method of thermal storage and insulation and additives is usually adopted. After adding antifreeze, it is necessary to cover a layer of plastic film or rock wool quilt to improve the insulation effect. This method is better than simply adding antifreeze, which can not only ensure the quality of concrete, but also speed up the construction progress.
4 concrete curing
During winter construction of water conservancy projects, concrete maintenance is very important. Because winter construction is prone to quality problems, and these problems are usually not easy to find, it is difficult to meet the quality requirements after the temperature rises. Early frost damage is mainly due to internal freezing of concrete. Under the condition of constant ambient temperature, it is necessary to increase the condensation effect of concrete and add a certain amount of antifreeze. In order to ensure the concrete quality problems caused by early freezing injury, technicians should communicate with construction workers in time, grasp the weather conditions and adjust the material consumption reasonably. The curing agent is used for curing to ensure that the internal structure of concrete is not destroyed, reduce the internal porosity, and improve the compactness, durability and frost resistance.
5 conclusion
In the winter construction process, we should master the key points of concrete construction and control the quality of concrete according to the construction requirements. Through scientific and reasonable measures, it is of positive significance to ensure the overall quality of the project and save the project cost, which will promote the development of water conservancy projects in China.
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