Study On The Effect Of High Temperature Reconstruction Of Steel Slag On Its Composition,Structure And Properties

Steel slag is an industrial by-product in the process of steel production.At present,steel slag is mainly used in:road construction,fertilizer,agriculture,cement and other products.The main mineral composition of steel slag is dicalcium silicate（C₂S）,tricalcium silicate（C₃S）,RO phase（solid solution of Ca O,Mg O,Fe O,Mn O）and a small amount of free calcium oxide（f-Ca O）.Due to the presence of cement phases such as C₂S and C₃S,steel slag can be used to prepare mineral admixtures for concrete.However,due to the problems of unstable volume,poor grindability and poor gelling activity,steel slag can not be applied on a large scale in cement and concrete building materials industry.This research takessteel slag as the main research object,uses adjusting materials to change the mineral composition of steel slag through high-temperature reconstruction,thereby improving the cementing activity of steel slag,and solving the problems in the application of steel slag.Draws the following research conclusions:（1）Analyze the main chemical composition and mineral composition of steel slag by XRF and XRD and other test methods:the main chemical composition of steel slag is Ca O,Fe₂O₃,Si O₂,Mg O,Al₂O₃.These steel slags have an alkalinity value of 3.55,which belongs to high alkali tricalcium silicate.The main components of the steel slag phase are minerals C₂S,C₃S,C₁₂A₇,C₂F,RO,Fe O,f-Ca O,pyroxene and olivine,and some amorphous substances.The 7d activity index of steel slag is 65.5%,and the 28d activity index is 70.2%.The content of f-Ca O in steel slag is 2.97%,and the content of f-Mg O is 2.26%.（2）The mineral phase composition of steel slag can be changed through high-temperature reconstruction.Reconstruction at high temperature can promote the reaction of Ca O and Si O₂ to generate cementitious minerals;when the temperature is too high,the content of cementitious minerals C₂S and C₃S in the reconstituted steel slag will decrease;the RO phase partly decomposes,and the content of the RO phase Fe O is transformed into Fe₃O₄.（3）The test of reconstituted steel slag shows that when the reconstitution temperature is 1250℃and the amount of fly ash is 10%,the activity index of 7d reaches70%,and the activity index of 28d reaches 86.8%;At 20%,the 7d activity index reached 74.2%,and the 28d activity index reached 82.4%.It meets the technical requirements of Grade I steel slag powder in GB/T20491-2017"Steel Slag Powder for Cement and Concrete".（4）The hydration mechanism of reconstructed steel slag shows that the whole hydration process of steel slag is similar to that of cement.The main hydration products of the reconstructed steel slag system are Ca（OH）₂,C-S-H gel and AFt.RO phase,Fe₃O₄,C₂F and Mg O are inert minerals there is no hydration reaction.When the curing age is 28 days,the C-S-H gel will overlap and grow to form a dense structure.The gap between the particles is filled by acicular AFt crystals.These hydration products overlap each other to form a network structure that is attached to the steel slag particles to form dense agglomerates,thereby increasing the strength of the system.