Research On Mechanical Properties And Microstructure Of Steel Slag Concrete

Steel slag is a waste by-product generated from steel industry.Each one ton of steel produced would generate 130-200 kg of steel slag.In mainland China,the utilization rate of steel slag is only 29.5% and more than 400 billion tons of steel slags were deposited,causing severe farmland occupation,water pollution and other environmental issues.On the other hand,granulated blast-furnace slag(GBFS)is another waste by-product from steel industry,the annual output of which is close to 1 billion tons per year.Previous research studies proved that steel slag and GBFS were not “waste” but “wealth”.Replacing natural coarse and fine aggregates with steel slag coarse and fine aggregates partially or totally or cement with GBFS to make concrete would improve its strength and durability.Therefore,steel slag and GBFS can be termed as new green material to make concrete to attain sustainability and mitigate the supplement of natural aggregate problem.This paper follows the principle of maximum utilization of steel slag,takes the stability test of steel slag as the premise,uses steel slag instead of natural fine aggregate in ordinary concrete,and GBFS instead of cement in concrete to produce "green" concrete.The mix proportion of 37 groups of medium and low strength steel slag concrete was designed by using steel slag and GBFS.Firstly,steel slag coarse aggregate was used to replace natural coarse aggregate to test the mechanical properties and microstructure of steel slag coarse aggregate concrete.Secondly,on the basis of steel slag coarse aggregate replacement,natural fine aggregate was replaced by steel slag fine aggregate to test the mechanical properties and microstructure of steel slag concrete;The optimal group of steel slag aggregate replacing natural aggregate would be obtained,in which the cement is replaced by steel slag to prepare concrete and test the compressive strength;Then,the influence of steel slag and granulated blast furnace slag on the compressive strength of concrete is analyzed by microstructure and bulk density.The results show that the best replacement rates of coarse aggregate,fine aggregate and granulated blast furnace slag are 40%,50% and 10% respectively;For medium strength steel slag concrete,the best replacement rates of coarse aggregate,fine aggregate and granulated blast furnace slag are 50%,30% and 5% respectively.Under the optimal replacement ratio of coarse steel slag aggregate,fine steel slag aggregate and granulated blast furnace slag,the compressive strength of low strength concrete at 7,28 and 44 0d is 13.42%,19.42% and 19.74%higher than that of ordinary concrete,respectively;The 7 d,28 d and 90 d compressive strength of medium strength concrete is 5.41%,16.81% and 19.26% higher than that of ordinary concrete respectively.The reason is that the surface of steel slag is porous and rough,and the water absorption is high,which leads to the decrease of water binder ratio,so as to improve the compressive strength;In addition,through the analysis of micro electron microscope experiment,it is found that due to the formation of C-S-H and surface roughness after the hydration reaction of steel slag,adding a certain amount of steel slag can significantly improve the transition interface zone of concrete;The addition of granulated blast furnace slag can also improve the transition interface area of concrete to a certain extent,and replacing cement with appropriate amount of granulated blast furnace slag has a good effect on the mechanical properties of concrete.Therefore,it can be concluded that the use of alkaline oxidation slag and granulated blast furnace slag in concrete is not only beneficial to environmental protection and green use of materials,but also improves the performance of concrete and provides a win-win solution.