Nuclear power project is less than hydropower project in concrete pouring volume, but compared with other projects, it still needs a large volume of concrete and its structure is more complex than hydropower project. Because of the requirements for preventing radiation and controlling crack degree, there are a series of stringent standards and requirements in concrete mixture ratio, raw materials' selection, pouring, curing, density, capacity and monitoring, especially the mixture ratio and selection of raw materials.
Raw materials: cement, fly ash, additives, gravel, fiber, corrosion inhibitor, etc.
Cement: nuclear power construction requires manufacturers produce cement in special line and special kiln and store cement in a special storeroom. At the same time cement manufacturers should promise to establish the quality assurance system and provide products in line with national standards and nuclear power concrete technical specifications. Fly ash: use Grade 1 fly ash, and the maximum dosage is 20%. Additives: it is necessary for users to examine whether additives can improve concrete strength and workability, and the dosage should not exceed 5% of the cement weight. Gravel: you can choose good gradation and self-produced artificial gravel. Fiber: fiber can effectively improve concrete workability and the internal stress of later concrete, prevent concrete from cracking, significantly improve concrete permeability. Corrosion Inhibitor: you can use compound amino alcohol, multi-functional and active corrosion inhibitor. Water: use clean groundwater or tap water and its content of harmful ions(for example chlorine ion, sulfate ion) cannot exceed standards.
When the raw materials have been prepared, they will be sent to the central mixing station according to the pre-set formula. The most important equipment of the central mixing station is one or more mixers. The raw materials stored in the barrel will be fed into the mixer by a screw conveyor. The central control room can control the proportion of raw materials and the time of stirring. After raw materials are stirred and mixed, next step can go on.
Concrete transportation should be compatible with production capacity, pouring capacity, the demand for concrete, and you should take method to shorten transport, reversed transport, intermittent time. Concrete vibrating time test shows that the vibrating time of concrete should be within 2.5h~3.5h. Additionally, you should spare adequate time for pouring and vibrating, so concrete transport time should not be over 1h, and you are not supposed to randomly add water or additives during the transport process. If the intermittent time is too long and the concrete has solidified or lost plasticity, it must be discarded.