Study On Hydration Characteristics And Kinetics Of Geopolymer

Cement is the most demanding building material in the world today,and it consumes a lot of cement every year.In the cement production process,it consumes a lot of energy and emits C02,which puts a burden on the environment.It is urgent to find an effective method to reduce energy consumption and CO2 emissions.Geopolymer is a kind of cementitious material which is produced by reacting industrial waste as the main raw material.It has good economic and environmental benefits,and has high early strength,antifreeze and acid resistance.Excellent performance such as alkali corrosion is a new type of green cementitious material.Based on the formation mechanism of geopolymer,the hydration properties and hydration kinetics of the cementitious materials were studied.According to the preliminary research results of the research group,according to the CaO composition,the SiO2-Al2O3-CaO ternary oxide molar composition system Different proportions are divided into low calcium system(CaO content is 0?10%),medium calcium system(CaO content is 10%-40%)and high calcium system(CaO content is 40%-50%).In this paper,slag,metakaolin and silica fume were used as raw materials,and NaOH modified water glass was used as alkali activator to prepare geopolymeric cement at room temperature.TAM Air isothermal calorimeter was used to measure the hydration heat release rate of geopolymer.The heat release rate,using the hydration rate,hydration heat release and hydration heat release peak index as the characterization parameters of the hydration performance of the geopolymer,discussed the influence of the alkali-exciting conditions on the hydration performance of different calcium-containing systems.The paper explored the characteristics of the exothermic peak of geopolymeric cement in the SiO2-Al2O3-CaO ternary oxide molar composition system.Based on Krostulovic-Dabic and Kondon equations,the hydration kinetics of geopolymer with different CaO content and different water glass content were established.The effect of composition on the hydration properties of geopolymers was investigated.The results show that with the increase of the modulus of water glass,the hydration heat of geopolymers continues reducing.As the amount increases,the hydration heat of the geopolymer increases.Under the same alkali excitation condition,the hydration heat release of the high calcium system is greater than the hydration heat release of the medium calcium system than the hydration heat release of the low calcium system;The low-calcium system has only one exothermic peak.When the medium-and high-calcium system has a water glass modulus of 1.0 to 1.6 and a water glass content of more than 50%,a second exothermic peak appears.The formation range has a great relationship with the CaO content.The CaO composition of the first type hydration heat release curve(number of peaks=1)is between 0%and 22%,and the CaO composition of the second type of hydration heat release curve(number of peaks=2)is between 22%and 43%.The CaO composition of the hydration-like exothermic curve(number of peaks=3)is 43%to 50%.The water glass modulus is 1.2,the water glass content is 90%,and the CaO content is 43%.The compressive strength of the geopolymer cement reaches the maximum value of 67.85MPa.The results of orthogonal test show that the primary and secondary order factors affecting the compressive strength of geopolymer are CaO content greater than that of water glass,which is greater than the water glass modulus.The optimization scheme at this time is C3B3A2.When the water glass modulus is 1.2,the water glass content is 90%,and the CaO content is 43%.The 3d compressive strength of the geopolymeric cement reached a maximum of 67.85 MPa.The hydration kinetics equation of the first exothermic peak of geopolymer based on Krostulovic-Dabic was established,and the hydration process of geopolymer was divided into three stages NG,I and D.For different hydration processes under CaO content,when the CaO content is less than 26%,it is suitable for the Krostulovic-Dabic equation.The hydration mechanism is NG?I?D;the water content of different calcium-containing systems is different.The application range of the Krostulovic-Dabic equation is different.In the low calcium system,when the water glass content changes from 30%to 90%,the hydration mechanism is NG?I?D;the water glass content in the medium calcium system is When the temperature is changed from 30%to 50%,the hydration mechanism is NG?I?D.When the water glass content in the high calcium system is only 30%,the hydration mechanism is NG?I?D.The hydration kinetics of the second exothermic peak of geopolymeric cement based on the Kondon equation was established.The hydration process of the second exothermic peak of the geopolymeric cement is a diffusion process,and the hydration rate during the acceleration period is the slowest.