Study And Practice On The Concrete Crack Prevention Of The Large Pumping Station

1 jv/-v\_, 1Both the research about the minute observation concrete intensity and the experience provided by a quantity of engineering practice in the modern science show that crevice happening to hydraulic structures espetially the giant pumping station projects is inevitable,because of their special structure,environment and geological conditiona]s,but their injurious extent can be controlled if the practical and effective integrated measures against their crack are adopted. This task summarizes the experiences and lessons defending and bounding the crack(s) on HUAIYIN PUMP STATION NO. 2 having been built for SOUTH-TONORTH WATER TRANSFER, integrates the other giant pumping stations having been set up and those to be built in future for SOUTH-TO-NORTH WATER TRANSFER, and makes system analysis about the basic theories and means on cracks for giant pumping station projects in poin. Contemporarily the task thinks that the temperaturer controlling measures are integrated and scientific only when the more advanced calculation technology of a three-dimensions FEM dynamic stimulationis adopted,because the dynamic stimulation computing technology utilizes the more mature non-linear software, more exactly stimulates the temperature field of concrete structure, nicely reflects the changing of the whole construction and its exterior surroundings' conditions, achieves more precise solution, more integratively and more particularly reflects the movements of the temperature and stress at various moments, and instructs the design and construction in time.Therefore the author elicits the part and the types easily happening to a giant pumping station and put forward that the integrated measures of preventing and limiting cracks are adopted with the structure's design,choices and utilization of the raw materials, constructional plan and temperature controlling.These above will be used for good references when the other tens of giant pumping stations are built for south-to-north water transfers. The main contents are researched in this articl as follows:1. Both of the status quo of crack's research about the concrete of hydraulic structure and the important significance of making research about preventing against crack of giant pumping station projects are introduced.The basic concepts of crack, the practical basic theories and basic methods of crack's analysis of pump station engineering are elaborated.2. The various methods about how to check and deal with crack are introduced.. The author makes analysis and research about the principles and plans of crack's handling, the chosen materials for repairation, the repairation technique and the evaluation of the effective handling on crack, which are fitted for pumping station engineering. After making final analysis about the handling plans and effectiveness of the crack of the intake flow course on Huaiyin Second Pump Station, the author thinks the crack's repairation is dense and highly strong and the crack's handling is successful.3. The preventing measures on preventing againt crack and limiting crack on giant pumping stations are elaborated as foolows: pay attention to reasonable structure form with respect to the design; make the exact compute about the capacity of the structure's anti-crack and put forward the index of the temperature control in reason.; especially give more effective enhancement on the design of the easily crackable parts; improve the capacity of anti-crack with the tecknology of using steel-fibre concrete and shrinkage-compensating concrete on the easily crackable parts; make obligation for the post-pouring belts and make reasonable parting and blocking for the excessive-length structur; make full use of anaphase strength of concrete, make r(?)nable application on concerete intensity and grade, reduce theusage of cement, and reduce hydration heat to prevent crack ; properly choose the raw materials; properly choose concrete mix-proportion with doubl-mixingtechnology. In regarding to temperatur control, the temperatur of concrete leaving the mixer and the placing temperature of concrete have to be controlled strictly, and both the thermal stresses and the temperature differences between the inside and outside, the up and down of concrete are reduced with the technology of lowering temperature by water flowing in cooling pipe adopted.. Strengthening superficial handling and curing of mass concrete are the key measures preventing cracks in the early and later stages. In regarding of construction, quality control has to be strengthened, distribution on construction has to be made scientifically and rationally., the construction technique needs to be improved, and the the performance of concrete's anti-crack also needs to be improved.4. Integrating with the design on the main body of Huaiyin Second Pumping Station, its construction and the management for its operation especially the chosen raw materials during the construction of the intake channel, the concrete mix-proportion, the construction measures and placing plan of concrete, the local environment, the situation of weather and placing of concrete, the inside and ouside temperature of concrete, the applied measures of temperature control and the strength of the experimented conrete block, the author makes analysis and research about the crack's distribution and development and classification of the intake channel of Huaiyin Second Pumping Station and make qualitative analysis about the cause of crack's formation based on the structure's design, the choice and utilization of raw materials,temperature's control in the period of construction, the construction's technique,the excessive-strength of concrete and etc. , and make quantitative analysis about the cause of crack's formation by the compute achivement of three-dimentions FEM stimulation for the intake flowing course. The author thinks the thermal stresses appearing during lowering the temperature of concrete in the intake flowing course is the direct cause of the early crack. The technique of pumped-transportation concrete during construction are the indirect cause of the crack because the value of the temperature's going up depends on the cement's usage per unit volumn. Drying shrinkage pressure is not the main cause of the early crack of the intake flowing course in the project and the weak curing and the measures of thermal insulation, producing the big shrinkage prsseure and the thermal streese, are the main causes of the crack The crack makes little influences on the whole pressure of the flowing course working with conventional load. The crack would not be expanded with the conventional load if the anti-pull stresses of the structure loaded conventionally not more than the anti-pull strength of concrete.5. Making integration with the three-dimention FEM simulation compute of the intake flowing course of Huaiyin Second Pump Station, the author elaborates the compute methods, course and the chosen parameters with thee-dementions FEM compute applied for a giant pump station and obtains the solutions with higher accuracy. Contemporarily both the technologies of the more advanced reversed temperature analysis and construction pre-determination are introduced and can make pre-determination about the temperature and stresses og concrete of a giant pumping station very well and the design of a pump station and its construction can be directed in time.