Study On Crack Control Technology In Pier Shaft Mass Concrete Of Luobu Bridge

This paper is based on the construction of Luobu Bridge in Sanming city,Fujian province,which consists of 2(32.65+4 × 32.7+32.65)m continuous beams.Maximum size for a single pile caps is 21/m × 9/m × 3/m,contained C35 concrete 6 892 m~3,steel bar 67.6 t.For circular shafts of the type,the biggest shafts of up to 18.5 m,contained C35 concrete 1 357 m~3,steel bar 30 t,14 m,the average height of 11 piers is 14 m,contained C35 concrete 10 528.7 m~3,steel bar 30 t.The bearing platform and bridge pier body belong to mass concrete structures and have inherent characteristics of mass concrete.And the concrete sets will produce a large amount of hydration heat,thermal conductivity due to the large volume concrete performance is poor,the hydration heat is not released in time,the internal temperature rapid growth,which causes large temperature difference between inside and outside,leading to the cracks of temperature.The large volume concrete temperature crack to cause a decline in caps and shafts of carrying capacity,reduce the concrete durability,great safety hidden trouble,so it is necessary to research the crack control of mass concrete of the bridge pier technology.(1)This paper elaborates the formation mechanism and the harm of temperature crack in pier shaft mass concrete,demonstrates the necessity and feasibility of controlling temperature crack.(2)Introducing heat conduction equation and the calculating method of temperature field in pier shaft concrete,discussing all effect factors of it,and putting forward an approach which is available to reduce initial maximum temperature of concrete,to depress difference in temperature between interior and exterior and thus to prevent it's temperature crack.(3)On the base of the engineering case of Luobu bridge,a series of temperature control measures of mass concrete are proposed.The result indicates that it is very successful to take these measures.Research shows: rational concrete mix proportioning and high-quality material are the basis to control the temperature of pier shaft mass concrete successfully;Besides,Optimized construction management,the effective scheme of temperature controlling and correct construction plan are also very important to mass concrete;In addition,concrete temperature field is sensitive to the boundary condition and we need to do in-depth study on the temperature difference and temperature gradient in mass concrete.