| Steel slag is the slag discharged in the steelmaking process.It has the characteristics of low activity and high content of free alkaline earth metal oxides(CaO,MgO).As a cementing material admixture,its utilization rate is low,and it will cause problems such as poor volume stability.It is difficult to be used on a large scale in the cement and concrete industries.As a major producer of steel materials,China emits nearly 150 million tons of steel slag each year,and its utilization rate is only about 30%.Most of the steel slag is still stored in piles or landfills,occupying limited arable land resources and causing serious environmental problems.and it is also a huge waste of resources.How to efficiently and fully utilize the main components in steel slag to overcome the volume stability problem caused by free oxides has become a key technical problem to be solved in solving the resource utilization of steel slag.Based on this,this paper proposes to use the alkaline properties of steel slag and the rich calcium-iron phase substances to react with acid phosphate at room temperature to prepare fast-setting and early-strength multi-metal composite phosphate cement,which can realize the efficient resource utilization of steel slag.It can also greatly reduce the manufacturing cost of traditional phosphate cement and improve its operability.The main research contents and conclusions are as follows:First,the effects of the type and content of retarder and the mass ratio SSP/ADP of steel slag to ammonium dihydrogen phosphate on the setting characteristics and mechanical properties of steel slag-based phosphate cement are studied.The research shows that when the borax content is 3.0%and the SSP/ADP is 6/1,the initial setting time of the phosphate cement paste is 7.5min,and the compressive strength of natural curing 1d,3d,7d,28d reaches the highest of 13.5,21.9,27.3,30.4 MPa,respectively.Secondly,XRD,FTIR,SEM-EDS,DTG-TG and BSE are used to analyze the composition and structure of hydration products,and the reaction mechanism is inferred.The study concluded that FeO?Ca2(Al,Fe)2O5?CaMgSiO4?Ca2Fe2O5 and Ca2Si O4 in steel slag reacted with ammonium dihydrogen phosphate,and the hydration products formed were crystalline phase(NH4)2Ca(HPO4)2·H2O and amorphous phase(Fe(OH)3,Al(OH)3,H4SiO4,FeHPO4),etc.,as the reaction progresses,the hydration product wraps the steel slag particles,cements each other,and gradually forms a dense structure.Finally,the water resistance of steel slag-based composite phosphate cement is studied.The study shows that,unlike traditional magnesium phosphate cement,composite phosphate cement is cured in an aqueous environment,and its compressive strength retention rate is greater than 100%.The?-C2S contained in the steel slag,and its hydration reaction speed is slow.In the later water curing environment,it can undergo hydration reaction to form a gel phase product,fill the internal pores,and optimize the microstructure,improve its water resistance. |
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