Study On Preparation And Hydration Mechanism Of Cementitious Materials From Diatomite And Steel Slag

Diatomite,as a widely distributed mineral natural resource in the world,has many kinds,large quantities and special pore structure.However,the utilization rate of diatomite in China is less than 30%.The preparation of building environmental protection materials is one of the main application directions of diatomite.The low activity of diatomite restricts its wide application in the field of building materials.In this study,a new type of diatomite-steel slag based composite cementitious materials was prepared by using diatomite and steel slag as the main raw materials and physical and chemical activation methods through double optimization of particle size and activity.The following conclusions were drawn:?1?The characteristics of diatomite were analyzed by chemical analysis,XRD,FT-IR and DSC-TG.It was found that the content of SiO₂ in diatomite was as high as81%,and its mineral composition was quartz,opal,montmorillonite and illite.Through mechanical grinding and high temperature calcination,the crystalline state and phase composition of diatomite were changed,and the gelling activity of diatomite was stimulated.The activity test showed that the optimum grinding time and calcination temperature of diatomite were 15 min and 450 ^oCrespectively,and the highest activity index was 80.74.?2?A new type of composite cementitious materials was prepared by using activated diatomite and converter slag grinded for 120 min as main raw materials,and adding some compound activators such as quicklime,desulfurization gypsum,sodium hydroxide and sodium silicate.Through single factor experiment and orthogonal experiment,the optimum proportion?mass percentage?is 80.75%?diatomite:steel slag=2:8?,10%quicklime,6%desulfurized gypsum,2%sodium hydroxide,0.75%sodium silicate and 0.5%polycarboxylic acid water reducer.The 28-day flexural strength and compressive strength of composite cementitious material mortar are 7.91MPa and 23.94 MPa respectively.?3?The cement paste test of 20%composite cementitious material?replacing 20%cement equally?shows that the initial setting time is 109 min,the final setting time is 223 min,and the water requirement of stability and standard consistency is qualified.The flexural and compressive strength of the cementitious sand blocks in 28d reaches 8.9 MPa and 53.1 MPa respectively,which meet the strength requirements of 42.5 ordinary Portland cement.The hydration exothermic rate and total exothermic heat of composite cementitious materials?20%cement replaced by equal amount?and pure cement were measured by isothermal calorimetry.When hydration lasted 96hours,the total exothermic heat of composite cementitious materials paste decreased by 17.65%compared with pure cement,meeting the minimum requirement of exothermic heat of Portland cement.?4?The hydration products of diatomite-steel slag based composite cementitious materials at different hydration ages were analyzed by XRD and SEM.The hydration products of the system were calcium silicate hydrate?C-S-H?,ettringite?AFt?,Ca?OH?₂ and the residues of the raw material system after hydration.Diatomite-steel slag based composite cementitious system can be roughly divided into three stages during the whole hydration and hardening process:the hydration of diatomite and steel slag,the formation of hydration products and the cementation of unhydrated parts.In the whole hydration process,there is a synergistic effect in the system.