Study On Structure Design And Application Of Fly Ash-based Geopolymer

With the increase of coal energy application,tens of thousands of Fly ash（FA）are produced.Due to the limited traditional storage and disposal capacity,FA poses a serious threat to the ecology.Therefore,it is urgent to develop a new green product flow from FA to reduce the threat of massive accumulation of FA to the environment.Fly ash-based geopolymer（FGPC）is a method of resource recovery of FA with large dosage.Due to the limitation of application performance and added value,FGPC has not been widely promoted at present.In this paper,the problems existing in the application of Fly ash-based geopolymer are studied.Through the method of structural design,Fly ash-based geopolymer,organic modified Fly ash-based geopolymer and Fly ash-based porous geopolymer（FPGPC）with excellent mechanical properties are prepared,and their performance in different application scenarios are evaluated.（1）Structural design and performance analysis of high strength FGPC.FGPC was prepared with FA as the main raw material and Na OH as the main component of alkali activator.By studying the changes of FGPC structure under different influencing factors such as the ratio of alkali activator,curing temperature,curing time and curing age,etc.That is,the development of hydroxy sodalite(Na₄Al₃Si₃O₁₂OH)and the microstructure of matrix section were analyzed to analyze the reasons for the improvement of FGPC compressive strength.The test results show that when Na₂Si O₃/Na OH is 1.7.Alkali activator/Fly ash is 0.58,curing temperature is 75℃,curing time is 24 h,the compressive property of the sample is the best,and can reach 110.2MPa after 28 days.At the same time,by comparing the compressive strength of FGPC under different preparation parameters,the microstructure of hydroxyl sodalite in FGPC was observed by SEM,XRD and FT-IR analysis.It is found that increasing the concentration of Na OH solution,curing temperature and curing time in a certain range can effectively improve the activity of FA,promote the formation of N-A-S-H gel and hydroxyl sodalite,and the matrix structure tends to densify,so as to fully explore the compressive strength of FGPC and prepare FGPC with high compressive strength.（2）Structural design and performance analysis of organic compound FGPC.The addition of organic compounds in FGPC is the development trend of composite materials,so the influence of the addition of organic compounds on the structure and performance of geopolymers is studied.Organic bases and hydrophilic organic polymers were combined with FA to prepare geopolymer composites.The compressive properties of geopolymer prepared at different ages and types of organic compounds were investigated,and the microstructure morphology of fracture surface of geopolymer was analyzed.The experimental results show that a small amount of 2-amino-2-methyl-1-propanol（AMP-95）can improve the compressive strength of the geopolymer,while hydroxyethyl cellulose（HEC）and polyurethane（PU）can not effectively improve the compressive strength of the polymer,but both improve the compressive failure characteristics of the geopolymer.The influence of organic matter addition on the compressive properties of geopolymer was summarized,which provided reference for the application research of organic-inorganic composite geopolymer based on FA.（3）With FA as the main raw material,Al and H₂O₂ as foaming agents and calcium stearate（CS）as foam stabilizer,the density,compressive strength and pore structure characteristics of FPGPC can be regulated through the structural design of FPGPC.The results show that when0.195 g Al and 0.65 g CS are added,the density and compressive strength of the geopolymer porous material can reach 459.4 kg/m³ and 3.1 MPa respectively.When 2.6 g of H₂O₂ and 0.65g of CS were added,the density and compressive strength of the prepared FPGPC reached 478.8kg/m³ and 3.2 MPa respectively.Combined with SEM and water absorption results,it is found that Al-H₂O₂ composite foam at 9:1 or 1:9,this specific ratio of composite foaming agent can enhance the volume water absorption and compressive strength of FPGPC,and can compound the water absorption characteristics of a single foaming agent,which will greatly enrich the pore structure characteristics of porous materials.From single foaming agent to compound foaming agent,it provides a new method for controlling the pore structure of porous materials.（4）Application research of FGPC Samples of FGPC formulated with the best compressive strength were tested under different application scenarios and soaked at 75～1000℃with 0.2～1.2 mol/L H₂SO₄ and Na OH solution to test their mechanical properties.The results of high temperature environmental test show that the mass loss of samples is the largest when the temperature is 200℃,and the mass loss is small when the temperature is 400～1000℃.The compressive strength decreases at 200℃and reaches 28.2 MPa at 1000℃.Combined with XRD and SEM,it was found that the main reasons for the decrease of compressive strength were the cracking of FGPC microstructure and the decomposition of N-A-S-H gel and hydroxyl sodalite at high temperature.The results of acid and alkali environment experiments show that the compressive strength and mass decrease with the increase of concentration and age of H₂SO₄ solution in H₂SO₄ immersion,and the compressive strength is still 70.9 MPa after immersion in 1.2 mol/L H₂SO₄ solution for 28 days.In Na OH solution soaking,the mass increases with the increase of Na OH concentration and soaking age,while the compressive strength decreases with the increase of Na OH concentration and soaking age,and the compressive strength is still 89.3 MPa after soaking in 1.2 mol/L Na OH solution for 28 days.Combined with SEM and XRD,it is found that the decrease of compressive strength in acid and alkali immersion is caused by the corrosion of microstructure by H₂SO₄ and Na OH.Howe show that the FGPC prepared in this paper still has good resistance to high temperature,acid and alkali.FPGPC also shows good compressive resistance in alkali environment,and after soaking in H₂SO₄ solution,the adsorption rate of FPGPC to methylene blue（MB）solution is greatly improved,that is,the absorption wavelength of MB solution under ultraviolet and visible light disappears after 5 days of adsorption,and the highest 5 days can reach 100%,so that this material shows a good adsorption effect on organic wastewater.To sum up,fully using FA to prepare geopolymer materials can obtain a substitute with compressive strength far higher than ordinary portland cement,which can not only promote the reuse of FA solid waste,but also reduce the harm of FA to the environment.On the other hand,the prepared Fly ash-based geopolymer material can be applied in harsh environment,and can also be effectively applied in organic printing and dyeing wastewater treatment after structural design.It solves the problems of poor application performance and low added value in the utilization of FA in the past,which is of dual significance to environmental protection and economic benefit improvement.Figure[63]Table[18]Reference[185]...