Experimental Study On The Effect Of Fly Ash On Calcium-based Solid Waste Cementitious Materials

With the rapid development of my country’s industry,coal-fired power generation plays an important role in my country’s power industry.The large amount of coal-based solid wastes such as fly ash and desulfurized gypsum are stacked,causing serious damage to land resources,water quality,atmosphere,soil,etc.Influence.At present,my country’s comprehensive utilization of industrial solid waste has achieved good results,but there is still a big gap with developed countries.In this thesis,fly ash from three power plants is selected to prepare composite cementitious materials under the condition that desulfurized gypsum,calcium carbide mud and cement remain unchanged,and the reaction mechanism of fly ash and calcium-based solid waste is studied.The main research results are as follows:(1)The optimal ratio of composite cementitious materials prepared by three kinds of fly ash was obtained by orthogonal test with 7d and 28 d unconfined compressive strength as the index.The optimal proportion of composite cementitious material prepared by fly ash A is calcium carbide mud content of 10%,cement content of 15%,fly ash content of 56.25%,desulfurization gypsum content of 18.75%,age 28 d The compressive strength is 3.16MPa;the optimal proportion of the composite cementitious material prepared by fly ash B is 10%calcium carbide mud,10% cement,60% fly ash,and desulfurized gypsum is 20%,and the compressive strength at 28 days of age is 13.86MPa;The optimal proportion of the composite cementitious material prepared by fly ash C is that the content of calcium carbide mud is 10%,the content of cement is 15%,and the content of fly ash is 50%,the content of desulfurized gypsum is 25%,and the compressive strength at 28 d age is 13.41 MPa.(2)By comparing the macroscopic properties of the composite cementitious systems prepared by different types of fly ash,it is found that the content of calcium oxide in the fly ash has a great influence on the performance of the composite cementitious system.The fluidity of the composite cementitious system prepared by high-calcium fly ash B and C is small,and the fluidity of the composite cementitious system prepared by low-calcium fly ash A is twice that of the high-calcium ash cementitious system.The composite cementitious system prepared with low calcium fly ash A has a 2h water separation rate of more than 5%,a 28 d compressive strength of only 3.12 MPa,and a softening coefficient of less than 0.85,which shows a large water separation rate,poor slurry stability,low compressive strength,and water resistance.However,the composite gelling system prepared by high calcium fly ash B and C is the opposite.(3)The hydration products and microstructures of composite cementitious materials prepared by different types of fly ash were analyzed by XRD and SEM,and it was found that the reaction degree of high-calcium fly ash B and C was higher than that of low-calcium fly ash B and C,the composite cementitious material they participate in can better exert the pozzolanic effect to produce more hydration products during the hydration process,so that the microstructure of the composite cementitious material becomes very compact and contributes to the improvement of the compressive strength.(4)The hydration mechanism of composite cementitious materials is a process of mutual excitation and influence between raw materials.Desulfurized gypsum and cement provide early strength for composite cementitious materials.Under the alkaline conditions provided by cement clinker and calcium carbide mud,pulverized coal The pozzolanic activity of ash is continuously stimulated,and at the same time,a large amount of ettringite,hydrated calcium silicate gel and hydrated calcium aluminate gel are produced under the secondary excitation of desulfurized gypsum,which promotes the continuous mechanical properties of composite cementitious materials.Through this experiment,the reaction mechanism of fly ash,desulfurized gypsum and calcium carbide mud three solid wastes combined with cement to prepare composite cementitious materials was found out,which has certain theoretical guiding significance for the later application of composite cementitious materials in different industrial fields.