Research On Adiabatic Temperature Rise Model Of Fly Ash Concrete Based On The Chemical Reaction Rate

Concrete structure is one of the most common structural forms of buildings,concrete structure often work with cracks,cracks of mass concrete structure is particularly significant,and even the phenomenon of"no dam,no crack"appears in hydraulic dams.At present,measures to reduce hydration heat and physical cooling of cementing materials are often used in temperature control and crack prevention of mass concrete structures.The most common method to reduce hydration heat is to add mineral admixtures such as fly ash,slag and silica powder into concrete.Adiabatic temperature rise is a key index of temperature control crack prevention and temperature stress simulation of concrete,and the rate of temperature rise is the key to affect adiabatic temperature rise.Adiabatic temperature rise rate is affected by thermal factors such as cement dosage,variety,admixture dosage,water-binder ratio,temperature（initial temperature,ambient temperature）,admixture and other dynamic factors,among which water-binder ratio and temperature have the most significant impact.Therefore,only the relationship between temperature rise rate and water-binder ratio and temperature can be established.In order to accurately predict the adiabatic temperature rise of mass concrete and accurately simulate the temperature field of concrete.First of all,the adiabatic temperature rise experiment of 35%fly ash concrete、water binder ratio and three initial temperatures is carried out in this paper.The characteristics of adiabatic temperature rise and temperature rise rate curve are analyzed,and the influence laws of various factors on adiabatic temperature rise and temperature rise rate are studied.Secondly,according to the"temperature-time"rate curves and"time-temperature rise rate curve,the characteristics of reasonable division of fly ash concrete hydration temperature rising stage,the research in each stage of hydration temperature rise of adiabatic temperature rise and the rule of the adiabatic temperature rise rate,with every hydration of fly ash concrete stage start time and end time of temperature rise rate of key nodes and each time adiabatic temperature rise rate model is set up;Then,Thermogravimetric Analysis（TGA）is used to verify the law of temperature rise rate of fly ash concrete in each hydration temperature rise stage.Finally,the hyperbolic velocity expression is optimized into the temperature rise rate model established in this paper,and the concrete pouring project of Jinghong Hydropower Station is taken as an example to verify the model.Research shows that:the fly ash concrete hydration temperature rise can be divided into the induction period,the temperature rise rate acceleration period,the temperature rise rate reduction stage and failure stage four stages,with the decrease of water binder ratio,initial temperature increase,the adiabatic temperature rise and temperature rise rate increases,the peak point of temperature rise rate,temperature rise rate is increased by 30.1%from 0.4 to0.6,temperature rise rate increased by 119.3 from 25℃to 5℃%;According to the temperature rise rate curve,the four stages of hydration temperature rise are divided and the criterion of ageτis determined.According to the law of hydration temperature rise rate of adiabatic temperature rise test,a four-stage model of temperature rise rate considering water-binder ratio,initial temperature and age was established.The rate of change of Ca（OH）₂ mass in thermogravimetric analysis is consistent with the rate reflected by adiabatic temperature rise.The established temperature rise model considering chemical reaction rate has clear physical meaning,can better reflect the characteristics of the temperature rise rate at each stage of hydration of pulverized coal concrete,and accurately predict the adiabatic temperature rise of fly ash concrete.