Study On Hydration Mechanism Of Solid Waste Based Cementitious Materials Based On AC Impedance Technology

With the acceleration of industrialization process in China,problems such as large consumption of natural resources,continuous storage of solid waste,and excessive carbon dioxide emissions have emerged one after another,becoming the main factors hindering the green development of society.How to effectively use solid waste,play their potential value and reduce environmental pollution has become an urgent problem to be solved.In this paper,coal gangue,carbide slag and desulfurization gypsum are used as the main raw materials to prepare solid waste based cementitious materials with excellent performance.The feasibility of using industrial solid waste to prepare solid waste based cementitious materials was confirmed by studying the hydration mechanism of cementitious materials.As a non-destructive testing method,AC impedance technology is more and more widely used in the study of hydration and microstructure development of cementitious materials.In this paper,the hydration degree and microstructure evolution of solid waste based cementitious materials are analyzed by AC impedance technology.The main research contents and conclusions are as follows:（1）The solid waste based cementitious materials were prepared by using coal gangue,carbide slag and desulfurization gypsum as raw materials,and their mechanical properties and hydration products were tested.The test results showed that the compressive strength of the solid waste based cementitious material with a water-binder ratio of 0.47 was 52.52 MPa at 3 days of hydration,reaching 83.13%of the compressive strength at 28 days of hydration.The main mineral components of the solid waste based cementitious material were calcium sulphoaluminate（C₄A₃S）,dicalcium silicate（C₂S）,calcium sulfate（Ca SO₄）.The hydration of C₄A₃Sprovides early strength for cementitious materials,and the hydration of C₂S can improve the compressive strength of cementitious materials in the later stage of hydration.（2）Taking different water-binder ratios and different hydration ages as research variables,the AC impedance test of solid waste based cementitious materials was carried out,and an equivalent circuit model capable of characterizing the hydration degree of cementitious materials was established to study the variation of different impedance parameter values.Combined with the test results of hydration heat and chemically bound water,the relationship between different impedance parameters and hydration degree was explored.It was found that with the increase of age,the high-frequency semi-circle in the AC impedance curve expanded and moved to the right.The impedance parameter values R_sand R_ct1 gradually increased with the extension of hydration age,and CPE gradually decreased with the increase of hydration time.The impedance parameter values had a good correlation with the compressive strength,cumulative hydration heat and chemically bound water content of solid waste based cementitious materials.（3）Based on the microstructure of solid waste based cementitious materials,the corresponding equivalent circuit model was established,and the variation of different impedance parameters was studied with different water-binder ratios and different hydration ages as variables.The microstructure and pore structure of solid waste based cementitious materials with different water-binder ratios and different hydration ages were tested to explore the relationship between impedance parameters and pore structure parameters.It was found that the impedance parameters R_CP/R_CCP and C_DP decreased with the increase of hydration age,while R_CP and R_CCP showed the opposite trend.The impedance parameter R_CCP was exponentially correlated with the product of the most probable pore size and porosity,and the impedance parameter R_CP/R_CCP was linearly correlated with porosity.（4）Based on the differential integrated moving average autoregressive model（ARIMA）,the impedance parameter values,chemically bound water content and porosity of solid waste based cementitious materials with different water-binder ratios were verified and predicted.Through analysis,it was found that the average relative error between the experimental value and the predicted value was within 5%,and the prediction result had high accuracy and conformed to the actual change rule.