Research On Preparation And Crack Control Technology Of Main Pier Concrete In Jiayu Yangtze River Highway Bridge

In order to solve the problem of temperature control and crack prevention in pile cap,cable bent tower mass concrete and elevation pumping,durability in cable bent tower concrete.Based on Jiayu Yangtze River Highway Bridge,the optimum design of mix proportion and performance research in pile cap mass concrete and cable bent tower concrete had been carried out.Besides the development of temperature field and temperature-stress field of mass concrete in pile cap,cable bent tower which under different working conditions were discussed.The optimal conditions had been selected,reasonable temperature control measures had been formulated,and they are successful applied in mass concrete construction.First of all,the effects of retarder type,content of fly ash-slag powder composite mineral admixture and PAN fiber on concrete setting time,workability,mechanical properties,adiabatic temperature rise and durability were systematically investigated.Additionally,a kind of C40 pile cap concrete with super retarding and low hydration heat has been successfully cast.Secondly,From the aspect of the amount of cementitious materials and the content of fly ash,the mixing ratio is optimized according to the requirement of pumping performance and crack resistance of cable bent tower concrete.Moreover three high performence fly concrete mixtures proportion are presented,whose workability,mechanical properties,adiabatic temperature rise meet the preparation requirements.They are S2(the amount of cementitious materials is 475kg·m^-3,the content of fly ash is 22.5%),S5(the amount of cementitious materials is 485kg·m^-3,the content of fly ash is 20.0%),S8(the amount of cementitious materials is 495kg·m^-3,the content of fly ash is 17.5%).The effects of PAN fiber and PAN fiber-PP crude fiber recombination on concrete workability,mechanical properties,early plastic shrinkage cracking,flexural toughness and durability of concrete were studied.The results show that the concrete has good workability,mechanical properties,anti-early plastic cracking,toughness and durability when the content pf PAN is 0.9kg·m^-3,and compared with mixing PAN fiber singly,the comprehensive performance of concrete mixed with 0.9kg·m^-33 PAN fiber+2.7kg·m^-3 PP crude fiber were further improved.Finally,The distribution and development of temperature field and temperature stress field of pile cap,pedestal,first section of tower column in different pouring temperature,stratified thickness,cooling water pipe and fiber were investigated.On this basis,the working conditions whose internal maximum temperature,temperature difference in the table meet the standards and the minimum anti-cracking safety factor>1.4 had been choosed.The working conditions of pile cap contain layered casting4m+4m,pouring temperature of 28?,setting up cooling water pipe.The working conditions of pedestal,first section of tower column contain pouring temperature of 28?,setting up cooling water pipe,mixtures proportion of C40pedestal concrete incorporate with 0.75kg·m^-3 PAN fiber,mixtures proportion of C50tower column concrete incorporate with 0.9kg·m^-3PAN fiber+2.7kg·m^-3PP crude fiber.Combined with the temperature control measures on the concrete temperature control and monitoring,the results show that a sequence of efficient temperature control measurements including reducing the pouring temperature of concrete,setting up cooling water pipe in a reasonable way and heat and moisture preservation were adopted.,and its temperature control index met all the requirements of the temperature control standards.