Preparation And Characterization Of Steel Slag/Desulphurized Ash-Based Green Cementitious Materials

Corresponding to that China has become the largest producer of steel production in the world,it also has brought a large amount of solid waste,such as steel slag and metallurgical desulfurization ash domestically.Because these solid wastes are complex and contain harmful substances,it is difficult to reuse them.Based o to prepare their green cementitious materials has become one of the main directions of solid waste recycling,such as recycles of desulfurization ash and steel slag.However,the calcium sulfite contained in the iron ore sintering process（IOSP）desulfurization ash and the free calcium oxide contained in the steel slag could harm the stability of their cementitious materials.Therefore,IOSP desulfurization ash and steel slag have not been widely used as raw materials in ordinary cement.In view of the above existing problems,this paper innovatively used expanded perlite（EP）and IOSP desulfurization ash to make out the granulated IOSP desulfurization ash with more rich specific area,and oxidized it at high temperature.The effect of the granulation method,the amount of EP adding and other factors on the oxidation rate of calcium sulfite in the granulated IOSP desulfurization ash were systematically investigated.Besides,a new type of supersulfate binder was prepared with oxidized IOSP desulfurization ash and P.O 42.5 cement as exciting agents,while the blast furnace slag（BFS）as raw materials.In addition,aiming at the frost damage of concrete with portland cement as binder,this paper also used the combination of both coking desulfurization ash（CDA）and polycarboxylic acid（PCA）water reducer as admixture to explore the improvement of the frost resistance of mortar of portland cement.In the end,the activated mechanism was studied for that of CDA and oxidized IOSP desulfurization ash used in steel slag-BFS based binder.Firstly,H₂O and EP were added into the IOSP desulfurization ash according to their respective designed proportions,and then to mix and granulate the mixture.The granulated IOSP desulfurization ash was been oxidized by high temperature air.The results showed that both the addition of 5 wt.%EP and the shape of columnar granulated IOSP desulfurization ash could promote the efficiency of oxidation of CaSO₃ in the later.After oxidizing reaction taking place at 500 ℃,the oxidation rate of CaSO₃ in IOSP desulfurization ash was as high as 94.5%.The supersulfate binder was prepared using oxidized IOSP desulfurization ash,the P.O 42.5 cement,and as well as the BFS as raw materials.It was found that the resulting mortar specimen with the composition had the promising mechanical properties,the composition was comprised of the oxidized IOSP desulfurization ash being 15 wt.%,P.O 42.5 cement being 15wt.%,and the BFS being 70 wt.%.This resulting mortar specimen had the 28d compressive and flexural strength being 37.2 MPa and 7.2 MPa,respectively.Secondly,the admixture with function of enhancement of early-strength and antifreeze for concrete was prepared,which was based on both CDA and PCA water reducer.It was found that the CDA could accelerate the early hydration process of P.O 42.5 cement and improve the early strength of its mortar.The resulting mortar specimen with 1wt.%CDA addition had the significant improvement of 3d compressive strength and 3d flexural strength（which being 1.8MPa and 1.3MPa,respectively）,as compared with that blank specimen（namely,without CDA addition）.The combination of CDA and PCA water reducer could improve the frost resistance of resulting mortar specimen of P.O 42.5 cement effectively,which was more than that of single-mixing of CDA or single-mixing of PCA.For the relative strength after and before 125 times of freeze-thaw cycle,the resulting mortar specimen excited by combination of CDA and PCA water reducer had improved 9.9% as compared with that of blank specimen.Finally,aimed at improvement of the low hydration activity and poor volume stability of steel slag,the promoted steel slag-BFS binder was prepared using metallurgical desulfurization ash and P.O 52.5 cement as activator,while the changing of proportion on the mechanical properties of mortar specimens of as prepared binder was investigated systematically.The results shown that with the increase of P.O 52.5 cement,the mechanical properties of resulting mortar specimens of steel slag-BFS based binder were increased at first and then decreased,and the best mechanics performance was achieved for the specimen with the adding content of P.O 52.5 cement being 24 wt.%（its 28d compressive and flexural strength being 36.8 MPa and 8.1 MPa,respectively）.Based on the above binder composition,the CDA and the oxidized IOSP desulfurization ash were separately used as admixtures for the steel slag-BFS based binder,and the stimulation effect of the later was better than that of the former at the same extra adding amount.With the increase of amount of oxidized IOSP desulfurization ash,the mechanical properties of resulting mortar specimens were increased at first and then decreased,and it had the highest strength value as the extra adding amount of oxidized IOSP desulfurization ash being 4wt.%.For this mortar specimen,the 28 d compressive and flexural strengths were 42.3 MPa and 8.6MPa,respectively,and it had the lowest water absorption rate（5.12%） and the highest softening coefficient（0.92） among all the resulting mortar specimens with oxidized IOSP desulfurization ash as admixture for steel slag-BFS based binder.