| Coal gangue is one of the solid wastes with huge accumulation.Many scholars have studied the resource utilization of coal gangue.Still,there are few studies on the secondary waste coal gangue fines directly produced in coal gangue collection.This paper uses the secondary waste coal 4angue fines(CGF)made in coal gangue collection as the alkali-activated cementitious material.The original coal gangue fines are activated by high-temperature calcination.The activity of calcined coal gangue fines and its replacement of fly ash and slag to prepare new alkali-activated cementitious materials are studied using XRD,SEM,and FT-IR.The main research conclusion is as follows:(1)The effect of calcination temperature on the activity of CGF was studied.The coal gangue fines were activated by thermal activation at different temperatures(500°C,600°C,700°C,800°C,900°C).The phase change,performance change,and internal characterization of coal gangue fines before and after calcination were observed by XRD,SEM,and FT-IR.The effect of different temperature calcination on coal gangue fines was analyzed.Studies have shown that high-temperature calcination of CGF transforms kaolinite into metakaolinite.Kaolinite becomes amorphous at high-temperature calcination,resulting in an enhanced activity.However,when the heating temperature reaches 900°C,the internal material will be recrystallized into mullite,reducing activity.Calcination at 800°C makes coal gangue fines have the best reactivity.(2)The feasibility of calcined coal gangue fines completely replacing fly ash to prepare alkali-activated slag materials(AASM)was studied.Based on previous studies,CGF was calcined at five different calcination temperatures of 500°C,600°C,700°C,800°C,and 900°C.The effects of CGF calcined at different temperatures on the fluidity,hydration heat,hydration products,compressive strength,and microstructure of AASM were studied.The test proves that it is completely feasible to replace fly ash with calcined CGF,and the alkali-activated cementitious material after the replacement has better mechanical properties than the control group.The metakaolinite in calcined coal gangue fines has a certain pozzolanic effect,which can promote the formation of hydration products.The C-(A)-S-H,C-S-H,and N-A-S-H gel products generated in the cementation process are compatible.(3)The development of mechanical properties of slag in AASM with different amounts of calcined CGF was studied,and the hydration products and microstructure of AASM were tested and analyzed.The main component of slag is calcium oxide,while the calcined CGF is mainly active silica and alumina.Under the action of an alkaline activator,the chemical bonds of the substances are broken and recombined to form gel products.The gel products are combined to create a disordered network structure.The internal Ca/Si of the experimental group doped with calcined CGF changed,which affected the strength development.The experimental results show that the calcined CGF can replace a small amount of slag.At 10% CGF content,the 3d,7d,and 28 d compressive strength of AASM increased by 8%,25%,and 13%,respectively.It is feasible to use an appropriate amount of calcined CGF to replace slag to reduce the use of slag.This paper focuses on the resource application of coal gangue fines,which provides a feasible experimental basis for CGF resource utilization.The research results offer a new idea and important reference for preparing new alkali-activated cementitious materials and expanding the application range of coal gangue fines in engineering.Figure [39] Table [5] Reference [92]... |
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