Experimental Study On The Influence Of Ages And Water-binder Ratio Of Circulating Fluidized Bed Combustion Desulfurization Slag Cement-soil On Its Strength

Circulating fluidized bed combustion（CFBC）desulfurization slag is a solid waste produced by coal gangue power plant circulating fluidized bed boiler combustion and desulfurization.Cement-soil is a common material for road pavement base,slope protection construction,lining perfusion,foundation reinforcement,foundation rammed soil and bedding engineering.Its advantages are economic durability,local materials,construction convenience and so on.CFBC desulfurization slag is applied to cement-soil after mechanical grinding,which is used to replace part of cement.It provides a new way for resource utilization of CFBC desulfurization slag,which is conducive to protecting the environment and saving engineering costs.In this paper,the effects of different dosages of the mechanical grinding CFBC desulfurization slag and water-binder ratio on the strength of cement-soil are discussed.Through particle size distribution analysis,unconfined compressive strength test,expansive performance test of cement-soil mixed with the mechanical grinding CFBC desulfurization slag,scanning electron microscopy（SEM）and X-ray diffraction（XRD）test,the following conclusions are obtained.（1）Control grinding material and ball material ratio at the same time,with the increase of the mechanical grinding time of the ball mill,the grinding particles of the raw CFBC desulfurization slag gradually becomes finer and finer.When the milling time exceeds 55 min,the specific surface area of the particles begins to decrease when the milling time reaches 75 min,because the particles are too thin to produce static electricity and cause the particles to reintegrate into large particles,so it is not the longer the milling time is,the better.According to the grinding test results,the grinding time of the raw CFBC desulfurization slag used in cement-soil should be about 55 min.The incorporation of CFBC desulfurization slag after grinding into cement-soil is conducive to the better participation of active substances in desulphurization slag in hydration reaction.（2）The strength of cement-soil can be improved to some extent by adding the CFBC desulfurization slag after grinding.When the cement/CFBC desulfurization slag = 2:1,the unconfined compressive strength of cement-soil with 20 %,25 % and 30 % total cementing materials is higher than that of pure cement-soil with the same total content after 7 d age.（3）When the cement/CFBC desulfurization slag = 2:1,with the increase of water-cement ratio,the peak unconfined compressive strength of cement-soil with certain total content of cementing materials increases first and then decreases.The water-binder ratios corresponding to the peak compressive strength of cement-soil with 20 %,25 % and 30 % of total cementing materials are 1.6,1.3 and 1.0.The water-binder ratio is gradually decreasing,and the corresponding peak value of unconfined compressive strength increases with the increase of the total content of cementitious materials.Moreover,by the age of 60 d,the strength of cementsoil test blocks with desulfurization slag of 20 %,25 % and 30 % of the total content of cementitious materials increased by 4.4 %,4.6 % and 5.0 % compared with that of pure cement soil.（4）Due to the hydration reaction of cement before 28 days of age and the secondary hydration reaction of active components in CFBC desulfurization slag particles and cement hydration product calcium hydroxide has been largely completed,so with the increase of curing age,the unconfined compressive strength of cement soil mixed with CFBC desulfurization slag increases rapidly before 28 days,and the increase is relatively slow after 28 days.（5）The cement-soil test block with the mechanical grinding CFBC desulfurization slag shows certain expansion.The more the content of desulfurization slag is,the greater the expansion performance of cement-soil is.（6）The results of SEM and XRD tests show that compared with the pure cement-soil,the cement-soil with CFBC desulfurization slag has a more compact connection between particles,and the pores between particles are reduced.The C-S-H gel and ettringite（AFT）generated between cement-soil structures are more than those of pure cement-soil,which greatly improves the microstructure characteristics of cement-soil,makes the structure more compact,and then shows a higher compressive strength value at the macro level.