Research On The Preparation And Applications Of Accelerated Carbonation Steel Slag Aggregate

Steel slag is a by-product of the steel manufacturing process.For every 1 t of steel produced,about 0.13⁰.2 t of slag is produced.The global production of steel slag is estimated to be between 170 million and 250 million t.Unlike slag,steel slag exhibits low hydration reactivity and poor hydraulic properties.The steel slag contains free calcium oxide and free magnesium oxide.Under the action of hydration,they will have a larger volume expansion,resulting in volume instability.In addition,the slag has poor grindability and high energy consumption for grinding.Due to the above reasons,the economic value of the utilization of steel slag is low,and the utilization path is very limited.China's steel slag utilization rate is only 10%.Nevertheless,countries around the world are still looking for ways to use steel slag efficiently.Steel slag has strong carbonization reactivity in an environment rich in CO₂,so it has broad prospects as a raw material for fixing CO₂.In this paper,using steel slag as raw material,the treatment,preparation and physical,chemical and mineral characteristics of the original and carbonated steel slag fine aggregate were studied.The carbonated steel slag fine aggregate was sprayed with phenolphthalein indicator for preliminary judgment,and combined with XRD and TG-DSC analysis.The changes of the main minerals in the steel slag were analyzed by MIP,SEM-EDS,and BSE.Steel slag mortar was prepared using carbonated steel slag fine aggregate,steel slag fine aggregate was pressed into steel slag brick and then carbonated and cured.In the above experiments,the methods of carbonization reshaping and molding recarbonization were used respectively.The work,mechanics and volume stability of steel slag aggregates,steel slag mortar specimens,steel slag bricks and other construction materials were analyzed.The main reasons for their different effects on performance were analyzed,which provided references for the preparation and application of steel slag fine aggregate The main conclusions of the study are as follows:?1?The presence of free calcium oxide and free magnesium oxide in the untreated steel slag fine aggregate results in poor volume stability.After carbonation,the quality of steel slag sand increased,and the weight gain rate of 0.08⁰.15 mm steel slag sand carbonated for 8 h was 3.3%.The steel slag crushing index and autoclaved pulverization rate decreased.After 8 hours of carbonation,the steel slag crushing index decreased from20.3%to 12.1%,and the 2.36⁴.75mm steel slag sand autoclaved powdering rate decreased from 2.91%To 1.85%.After the steel slag is carbonated,the expansion component free CaO in the steel slag reacts with CO₂ to form a stable carbonate,which fills the pores of the steel slag sand particles,and the pore diameter is reduced.The volume is reduced from 0.045 ml/g to 0.015 ml/g,which may be the main reason for its strength increase.?2?The strength of the steel slag mortar specimen prepared by the untreated steel slag fine aggregate is low,and the compressive strength at 28 d is only 30.5 MPa.The carbonated steel slag aggregate improves its mechanical properties.The 28-day compressive strength of the mortar specimen increased to 34.6 MPa.The 24 h carbonation group had the highest strength of the mortar specimens,and the 28-day compressive strength reached 39.2 MPa,which was due to the increase in the strength of the aggregate itself and the removal of the expansion component contained in the aggregate itself.In addition,as the amount of carbonated steel slag sand in the mortar specimen increases,the strength of the carbonated steel slag mortar specimen increases first and then decreases.This is because a certain amount of carbonated steel slag sand aggregate improves the mechanical properties of the mortar,but with the carbonated steel slag As the amount of sand added increases,the expansion components that are not fully carbonated will also increase,resulting in a decrease in the strength of the mortar specimen.The carbonated steel slag aggregates improved the stability of the steel slag mortar specimens.The mortar specimens of the uncarbonated group were cured at 80?to 14 d,which resulted in expansion cracking.The 4 h carbonation group was cured until 21 d.After curing for 24 h,the group showed slight cracks until 28 d.It can be seen that the longer the carbonation time,the better the stability of the carbonated steel slag mortar specimen.?3?Carbonated steel slag compacted bricks were prepared with ordinary steel,manganese steel,and chromium steel slag as the main raw materials.The 28-day compressive strength of ordinary steel,manganese steel,and chromium steel compacted bricks is 36.2 MPa,15.9 MPa,and 20.8 MPa,respectively,and after 24 h of carbonation,they are increased to 57.1 MPa,18.1 MPa,and 30.4 MPa,respectively.57.7%,13.8%,46.2%,reaching the Cc50,Cc15,Cc30 grade of GB 28635-2012 concrete pavement bricks.Carbon steel slag permeable brick was prepared by double-mixing steel slag and natural aggregate and adding a small amount of Portland cement.The 7th d compressive strength of ordinary steel,manganese steel and chromium steel permeable brick is 29.8 MPa,32.4MPa and 36.3 MPa respectively.After 24 h,they were increased to 41.1 MPa,40.3 MPa,and 40.2 MPa,respectively,and curing was continued until the 28-d compressive strength reached 53.0 MPa,52.4 MPa,and 55.0 MPa,respectively,and all reached the Cc50 level.The 28-d compressive strength of ordinary steel slag,manganese steel,and chromium steel permeable bricks is 35.6 MPa,39.9 MPa,and 37.8 MPa,respectively,and the carbonation reaches 43.1 MPa,49.3 MPa,and 49.4 MPa for 24 h.It is found by comparison that the three steel slag permeable bricks are carbonated in a short time after they are formed,which has a better effect on promoting their strength improvement.Figure 53 table 15 reference 123...