Steel Slag Aggregate To Prepare Permeable Concrete And Its Stabilization Studies

As a by-product of the steelmaking process,steel slag emits more than 100 million tons per year and has a historical stock of about 1.5 billion tons.A large amount of stored steel slag not only occupies valuable land resources,but also pollutes water bodies and endangers ecology and human health.On the other hand,with the acceleration of urbanization in China,a large number of pavements are made of dense concrete,which leads to frequent urban waterlogging in the rainy season.Studies have shown that steel slag has good physical properties and can be used as concrete aggregate to replace natural sandstone,but due to its poor volume stability,the application of steel slag in concrete is restricted.In this paper,the effects of steel slag aggregate particle size,water-adhesive ratio and ash collection ratio on compressive strength,water permeability coefficient and porosity of steel slag permeable concrete were explored by orthogonal test,and a stabilized steel slag was prepared by boiling-carbonization combined method,and the effects of boiling time,boiling temperature,carbonization time,carbonization temperature and carbonization pressure on the volume stability of steel slag were analyzed.Finally,the standard curing and carbonization curing of the prepared steel slag permeable concrete were carried out respectively,the influence of curing conditions on its hydration products and working performance was analyzed,and the sulfate erosion resistance of steel slag permeable concrete was studied by the method of alternating cycle erosion of dry and wet.The main conclusions of this study are as follows:(1)Through the orthogonal test,the optimal mixing ratio of permeable concrete prepared by steel slag as aggregate is: aggregate particle size 9.5-13.2mm,water-to-adhesive ratio 0.32,ash collection ratio 3.The 28 d compressive strength of steel slag permeable concrete under this ratio is 22.65 MPa,the water permeability coefficient is 5.13mm/s,and the porosity is 28.77%.(2)The boiling method has a certain effect on reducing the content of f-Ca O and Mg O in steel slag,and the influence of boiling time relative to boiling temperature is more obvious.Through orthogonal tests,the optimal preparation conditions for carbonized steel slag were carbonization temperature 60°C,carbonization pressure0.2MPa,and carbonization time of 8h.The F-Ca O content and Mg O content of the stabilized steel slag prepared under these conditions were 0.11%,and the Mg O content was 2.42%.(3)The analysis results of XRD,TG-DTG and SEM all showed that the steel slag reaction after boiling-carbonization treatment generated more stable calcium carbonate and magnesium carbonate,which improved the stability of steel slag aggregate.The compressive strength of steel slag permeable concrete with carbonization curing 28 d is 33.38 MPa,the water permeability coefficient is 3.25mm/s,and the porosity is 17.93%,which is 7.26 MPa higher than the compressive strength of the standard cured test block.XRD,FT-IR and SEM analysis showed that carbonization curing can accelerate the hydration reaction,generate more hydration products,make the structure more dense,and steel slag permeable concrete has higher compressive strength.(4)The dry and wet alternating method was used to simulate the erosion of permeable concrete by sulfate,and the test results showed that the sulfate erosion resistance grade of steel slag permeable concrete after carbonization curing reached KS120.