Research And Development Of High Strength Steel Slag Brick By Carbonation Curing

Steel-slag is an industrial waste generated during the smelting of steel,and its mineral composition is very similar to that of cement.However,calcium aluminate and the solid solution of mafic-iron in the slag almost no water hardness,C₂S has low hydration activity,resulting in its cementing much lower than the cement.At present,about 70%of China's steel slag is used for storage and landfill,while the utilization rate of steel slag in developed countries reaches 100%.Slag carbonation technology is a hot topic in international research in recent years.The principle is that the calcium silicate in slag reacts with CO₂ under stable temperature and pressure to form stable carbonate.On the one hand,it can reduce CO₂ emission and relieve atmospheric pressure;On the other hand,the slag can be turned into treasure,not only solve the problem of a large number of steel slag piling up,reduce the burden on the environment,but also developed many new building materials products,accomplish three goals.In this paper,the steel slag as the research object,the use of carbonation curing method to study the characteristics of pure steel slag in different steaming conditions accelerated carbonation.XRD,FTIR,TG,N₂ absorption,BET specific surface area analysis and SEM-EDS were used to analyze the mineral and chemical compositions as well as the microstructure of steel slag pastes before and after carbonation.Their strengths were also determined.The results show that carbonation products with different morphologies were formed under different carbonation conditions.At carbonation temperature of 40?and 60?,the lime in steel slag was completely carbonated,whereas tricalcium silicate,calcium silicate and dicalcium silicate phases were partially carbonated.All the carbonated products were calcites.At carbonation temperature of 80?,tricalcium silicate was completely carbonated,whereas bredigite and magnesium rose pyroxene were partially carbonated to produce aragonite,magnesium calcium carbonate and spurrite products.The optimum temperature for the accelerated carbonation of steel slag was found to be90?,at which temperature the compressive strength of steel slag paste reached 32.8MPa.The BET specific surface area of the steel slag paste reduced after carbonation,macropores gradually disappeared,while the volume fraction of mesopores and micropores increased,indicating a higher density after carbonation.The influences of different carbonation modes,steel slag dosage and accelerator on the mechanical properties and microstructure of cement-slag test pieces were experimentally studied.The results show that carbonation has a significant effect on the early strength of the sample,and the effect on the strength of the latter is less.Carbonation should occur before the early hydration of the sample is completed.The earlier the carbonation is,the higher the strength of the sample.The strength of the test pieces with promoter were improved obviously.The compressive strength of the carbonized treatment was 12.0%higher than that of the carbonized treatment without promoter and 29.0%at 28 days.Promoter has a certain influence on the morphology of carbonized product CaCO₃ of cement-steel slag test pieces.The experiment also studied the preparation and properties of carbonized steel slag porous bricks,using XRD and SEM-EDS to analyze the products generated during the curing process of steel slag bricks.The results show that the steel slag porous bricks prepared with pure steel slag as the main raw material have a dry density of about 1000 kg/m³,and the compressive and flexural strengths can reach19.9 MPa and 5.3 MPa,respectively,reaching the JC/T 1062-2007 foam concrete block grade B10,A7.5.Adding Steel slag-powder slag is double-blended and a small amount of portland cement,desulfurized gypsum and additives steel slag porous bricks,the dry density is about 700 kg/m³,and the compressive and flexural strengths are up to 5.0 MPa and 2.5 MPa,respectively,reaching JC/T 1062-2007foamed concrete block grades B08,A5.0.The initial strength of the porous brick is mainly provided by the hydration reaction of the cementitious material,and the strength of the carbonized porous brick is better than that of the uncarbonized porous brick,it is because the dense CaCO₃ layer formed by carbonation is wrapped in the outer layer of the pore wall,increasing the support of the pore wall.The experiment further tried the carbonation curing preparation of stainless steel slag?also known as nickel slag?bricks.The change of nickel slag before and after carbonation and hydration products of nickel slag bricks.The results show that after the nickel slag is carbonized,the wearability is improved.The order of the wearability of uncarbonized nickel slag and carbide nickel slag is as follows:non-carbonated nickel slag<90?carbide nickel slag<120?carbide nickel slag<150?carbide nickel slag;75?m sieve residue:uncarbonized nickel slag>90?carbide nickel slag>120?carbide nickel slag>150?carbide nickel slag.Carbonized nickel slag has higher hydration reactivity than uncarbonized nickel slag.