Research And Application Of Construction Technology Of Deep Foundation Pit Super Large Volume Concrete

With the increasing development of urbanization in China,the height and scale of buildings grow with it.Therefore,mass concrete is playing a more important role in building construction.Temperature control is the key technology in mass concrete construction.The heat of hydration may cause cracks in poured concrete and cause damaging effects.Meanwhile,the mass concrete underground construction requires deep foundation operation,which will be largely effected by conditions like environment,temperature.It faces many difficulties in the real construction process.The article studies the base plank mass concrete pouring of the Chinese Railway Trust Mansion.It optimizes the mix proportion,innovates the construction and maintenance and effectively solve the difficulties in mass concrete testing technology and construction.First,the research finds a way of concrete construction that meet the demand of the project by site survey and calculation.The construction site is limited,the time is limited and the conveying height is 19 meters.The design innovatively combining the steel sleeve conveying shuttle slot and ground pump in the pouring.Second,it designs C35P10shrinkage-compensating concrete mix proportion with high quality material to reduce the cement use so that the cracks caused by hydration heat can be reduced,and the intensity and construction are guaranteed.Third,in this project,the base plank is thick(6200mm)and has a great square amount(20100 m~3),the traditional way of maintenance cannot meet the requirements.The design solves the maintenance problems innovatively by storing water in base plank to preserve heat,which can effectively control the concrete temperature and cracks on the surface.(1)The new conveying system study on combining steel sleeve conveying shuttle slot and ground pumpThe design thinking:the concrete conveying tank truck transits the concrete from the ground to the cylinder sleeve hopper,the concrete flows through steel sleeve conveying shuttle slot to the concrete ground pump hopper in the foundation pit.After the second stirring,the concrete is sent to the ground by ground pump.Practical significance:Firstly,it solves the construction difficulties like site restriction,no berm,pipe blockage and segregation easily caused by vertical transportation in the deep foundation pit.Second,three concrete tank trucks conveying materials and three ground pumps working together has greatly improved the construction efficiency.Third,the cost of ground pump is lower than car pump.The design lowers the cost and helps to gain more profit.(2)C35P10 shrinkage-compensating concrete mix proportionFirst,it can lower cement amount.The heat of hydration when mixing water and cement is the main reason that makes the concrete's temperature rise.The amount of cement used in the construction and the concrete temperature are positively correlated.Therefore,the amount of cement should be reduced reasonably.Second,blending fly ash and mineral powder.Blend fly ash in the concrete can improve the intensity of concrete and reduce the amount of cement.Therefore,the heat of hydration decreases,so as the concrete cracking problems.Third,use high quality aggregate.The coarse aggregate uses continuous grading,which can upgrade the workability and intensity of concrete and reduce the consumption of water and cement.The bigger particle size,the better effect.However,if the particle size is too big,the concrete might has constituent isolation.The particle size is restricted according to construction conditions,usually 5-31.5mm.Finally,blend some additives.The sweller and cement's chemical effect will strengthen the intensity of concrete and restrain the concrete to shrink.Therefore,the structure can avoid shrinkage cracks.(3)Research on water storage heat preservation maintenanceBecause the project is tight,the base plank is thick;the concrete square amount is huge.The traditional maintenance cannot satisfy the need,so the research innovatively preserves the temperature by storing water in the mass base plank.Water storage skills:set water pipes at the four corners of the base plank.The boiler at the living area will heat the water to 43.5?,it's the temperature of the concrete surface.The water will be injected into the surface of the concrete covered by thin film.The centre of the surface,corners,prevailing wind direction part has maximum adiabatic temperature rise and shrinkage stress.These are the best places to set temperature testing sites because they have high heat radiation and can be easily influenced by the environment.The temperature is tested at regular time.If the temperature range between the concrete surface and concrete inside reaches 20?,the water must be drawn off immediately and water heated to 43?will be injected again to maintain the temperature.If the temperature range is larger than 20?,the water storage depth must be adjusted and more hot water are needed.Chinese Railway Trust Mansion base plank mass concrete pouring has effectively solved the difficulties in construction and maintenance.The appearance and quality of the concreate is superior without any cracks.Meanwhile,the new construction style and maintenance has greatly improved construction efficiency and brought better profits.The experience and study results can be applied into mass concrete construction at restricted sites.