| The annual output of iron and steel in Zhanjiang Baowu Steel Group is more than 8 million tons.At the same time,about 1 million tons of steel slag and 1.2 million tons of blast-furnace slag(BFS)are discharged each year.BFS have high hydration activity and are well used in cement and concrete production,while most of steel slags are used for roadbed filling and remelting as steel slags have poor grindability,hydration activity and unsoundness,which constrains its application in cement and concrete industry on a large scale.This thesis aimed to achieve comprehensive utilization of steel slag as resources in Zhanjiang.The main research contents and conclusions are as follows:(1)The effects of the granulate of steel slag and BFS on their performances were studied,and the steel slag and BFS with different granulates were compared with and Portland cement.With the particle sizes of steel slag and BFS granulates decrease,the water requirement for standard consistency increases,the setting time is shortened,the fluidity of mortar declines,and the hydration activity improves.The hot stuffy steel slag used in this study had a low f-Ca O content,less than 3%.The soundness of steel slag of various granulates was qualified,and was significantly improved by the refinement of the steel slag granulates.The particle size D50 of the three typical types of Portland cements in South China ranged from 10 to 20?m with a narrow distribution and there is little difference in their overall performances.The hydration degree and strength development of steel slag were much lower than that of the BFS with the same granulates and Portland cement.Among the steel slag studied,the coarsest one(D50=31.52?m)presented the worst reaction activity,the 28-day activity index was only 71%.The BFS exhibited excellent hydration activity.The hydration degree and strength development of the fine BFS(D50=6.94?m)were superior to those of Portland cement,the 28-day activity index was 111%.(2)The particle grades and hydration activitities of steel slag,BFS and Portland cement were matched.The admixture of BFS and steel slag with the fine particle size interval(<8?m)and coarse particle size interval(>32?m)was blended into cement according to the optimal proportion of BFS and steel slag,1:1.By changing the particle size and dosage of the admixture,the overall particle size distribution of the binder is controlled to be close to fuller grade distribution,so as to produce high-performance steel slag-BFS graded admixture.When the dosage of this admixture was 30%,the 3-day activity index is 96%and the 28-day activity index is up to 110%.Compared with the steel slag admixture,steel slag-BFS graded admixture had a much better soundness,even though in a large dosage.(3)The effects of steel slag-BFS graded admixture on the hydration heat,hydration products,Ca(OH)2 content and pore structure of cement paste were systematically studied.Compared to Portland cement paste,the addition of such admixture increased the late hydration rate of cement,and promoted the late hydration of cement,so the content of C3S and C2S at 28d was significantly reduced and there were more hydration products,but it significantly lower Ca(OH)2 content in the paste.Reasonable grade matching and the hydration reaction of the admixture have the paste structure significantly improved.Compared to Portland cement paste,the Ca(OH)2 content at 28d was reduced by 25%and the porosity decreased by 11%.When the dosage of the admixture added into the paste was 30%.(4)C40 concrete with a large flowability was prepared with steel slag-BFS graded admixture which can significantly improve the working performance and later mechanical performance in a dosage between 10 to 50%.It can also significantly improve the chlorine ion resistance of the concrete and the sulfur erosion resistance in the later stage.When the dosage of the mixture was 40%,the slump of fresh concrete increased by 10%,the 90-day compressive strength was increased by 11%,the 90-day electric flux was reduced by 36%,and the corrosion resistance coefficient of 60 wet-dry cycles was increased from 0.82 to 0.85,compared with blank concrete specimens. |
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