Influence Of Temperature And Water-Binder Ratio On Hydration Process And Mechhanism Of Fly Ash Concrete

At present,fly ash is more and more widely used in mass concrete due to its advantages of reducing hydration heat,green environmental protection and economic applicability.However,the crack problem of mass fly ash concrete is widespread,crack prevention and control is still the key and difficult point of mass concrete construction.The crack is caused by the temperature difference between inside and outside the structure caused by the hydration heat release of the cementitious material in concrete,and the common solution of temperature control and crack prevention in engineering is to reduce the hydration heat by adding fly ash into the concrete cementitious material.Therefore,only by studying the hydration process and hydration mechanism of fly ash concrete,can we effectively solve the problem of temperature control and crack prevention of large volume fly ash concrete.It is found that the hydration reaction process and mechanism of concrete are affected by thermodynamic factors such as cement type and cement amount and dynamic factors such as temperature,water-binder ratio and admixture.Among them,the kinetic factors on the hydration process and mechanism of the influence of the more significant,in the dynamic factor,the initial temperature and the mechanism of waterbinder ratio on the hydration process of fly ash concrete and most important,and the present study is of cement hydration process and mechanism of mineral admixtures,and the study of concrete hydration process and mechanism of less.The adiabatic temperature rise of 35% fly ash concrete with 5 kinds of water-binder ratio and 3 kinds of initial temperature was measured by hr-4A type concrete thermal physical parameter tester.By using hydration kinetics method,the hydration reaction rate constant K,hydration degree α and reaction order n of fly ash concrete under different initial temperature and water-binder ratio were calculated.The hydration kinetics model of fly ash concrete considering initial temperature and water-binder ratio was established.The influence of different initial temperature and water-binder ratio on hydration process and mechanism of fly ash concrete was evaluated according to dynamic differential curve.The effect of initial temperature and water-binder ratio on the pore structure of fly ash concrete was studied by industrial CT technique.SEM scanning was used to observe hydration products through backscattering electronic images of fly ash concrete of different ages,and the influence of initial temperature and water-binder ratio on hydration mechanism of fly ash concrete was studied.It’s indicate that:(1)According to the kinetic parameters and dynamic differential curve,and found that the hydration process of fly ash concrete by crystallization nucleation and crystal growth(NG),phase boundary reaction(I),diffusion(D)of three phase,and the dynamic model can better simulate the actual hydration process of fly ash concrete,hydration kinetics model applies to fly ash concrete.(2)With the increase of initial temperature or the decrease of water-binder ratio,the adiabatic temperature of fly ash concrete increases more and the temperature rise rate increases faster.The hydration process changes from NG→I→D control to NG→D control,and the duration of stage I is gradually shortened until it disappears.The initial temperature is 5℃ and 15℃,and the hydration process is controlled by NG→I→D.The initial temperature is 25℃,and the hydration process is controlled by two stages NG→D.The water-binder ratio was 0.5,0.55,0.6,and the hydration process was controlled by NG→I→D.The water-binder ratio was 0.4 and 0.45,and the hydration process was controlled by NG→D stages.The reaction order N decreases with the increase of the initial temperature or the decrease of the water-binder ratio,and the reaction rate constant K increases with the increase of the initial temperature or the decrease of the water-binder ratio.(3)With the increase of initial temperature or the decrease of water-binder ratio,the porosity of fly ash concrete decreases faster and more.The higher the initial temperature is,the faster the hydration rate is,the more hydration products are generated in the early stage,and the pores are filled,the large pores are reduced,the small pores are increased,and the porosity is reduced.The lower the water-binder ratio is,the faster the hydration rate is,the more hydration products are generated in the early stage,and the earlier the pore structure changes.