| Magnesium slag is a solid waste generated by the factory of magnesium smelting magnesium, because of magnesium slag take natural cooling way after baked, Which leads to the decrease of magnesium slag activity, and with the lag expansion phenomenon, this has been the key to restrict the application of magnesium slag. How to improve the activity of magnesium slag, and eliminate the lag expansion damage has important significance for the full and effective use of magnesium slag.In this paper, through the analysis of the conditions of magnesium slag and the mechanism of magnesium slag, first formulated by using self-made miniature cooling equipment for cooling magnesium slag after baked, and by controlling the airflow to produce different cooling rate of magnesium slag, respectively rapid cooling, semi-rapid cooling and natural cooling magnesium slag, after comparative analysis the physical and chemical properties of three kinds of cooling rate of magnesium slag, we can concluded that change from the cooling rate impact on physical and chemical properties of magnesium slag, and for the preparation of controllable dilatability of magnesium slag cementing materials provide for the suitable cooling rate of magnesium slag, and then use the suitable cooling rate of magnesium slag and cement mixed at different ratios were prepared by magnesium slag standard test block and magnesium slag expansion test block, then through the test of physical properties, expansion measurement,chemical analysis, XRD, SEM, mercury injection and other methods contrast research under the different ratio of magnesium slag cementitious materials physical and chemical properties and swelling, which for the application of magnesium slag in controllable expansion concrete provide a theoretical basis. Through the experimental analysis, we can obtained the following conclusions:(1)As the cooling rate is accelerated, the physical and chemical properties ofmagnesium slag are changed, After curing 3d, the natural cooling magnesium slag did not occur hydration behavior, the compressive strength is only 3.75 MPa, the hydration degree is still not obvious after curing to 28 d, and the compressive strength is 13MPa;however, rapid cooling curing after 3d, the compressive strength is 11.33 MPa, and it can be observed that most particles are covered with a thin layer of internet shape C-S-H gel on the SEM image, after curing to 28 d, he compressive strength is 21.7MPa,we can see the phenomenon of C-S-H gel cementation on the SEM image.(2)Changing the cooling rate can affect the grain size of MgO in the magnesium slag, the grain size of MgO is 98.32 nm in natural cooling magnesium slag; in semi-rapid cooling magnesium slag, the grain size of MgO is 10.534nm; in semi-rapid cooling magnesium slag, the grain size of MgO is 3.04 nm. Therefore, with the cooling rate, the grain size of MgO decreases rapidly, the activity of MgO increase, which is beneficial to early hydration. After curing 3d,the diffraction pattern of the cementitious materials which are prepared with semi-rapid cooling magnesium slag and cement can find the MgO peak, but after curing to 28 d, the diffraction diagram has been almost non-existent MgO peak.(3)Curing 3d to 28 d process, the natural cooling magnesium slag internal porosity increased from 48.92% to 67.72%, the volume of the small hole occupied by 55.95% to23.57%, The most probable pore size has almost no change, about 91μm; the semi-rapid cooling magnesium slag internal porosity decrease from 52.62% to 42.63%, the volume of the small hole increased from 44.55% to 67.53%, the most probable pore size by91.25μm fell to 60.70μm; the rapid cooling magnesium slag internal porosity decrease from 39.13% to 31.32%, the volume of the small hole increased from 69.51% to97.27%, the most probable pore size by 60.75μm fell to 0.83 μm.(4)The gelled material, which are preparation of rapid cooling magnesium slag and cement, with the increase of magnesium slag content, the degree of hydration of cementitious materials decreased, expansion performance enhancement. When the magnesium slag content is 30%, cementitious materials has shown the phenomenon of negative thermal expansion, and the negative expansion rate is stable at 1.08% within the curing 200 d, which suggests that the shrinkage behavior of gelled material was not be improved well; when the magnesium slag content is 40%, cementitious materials is shown the negative expansion first, then is postive expansion, and the expansion is stable at 0.12% finally within the curing 200 d, which indicates that the shrinkagebehavior of cementitious materials is completely offset, and the final cementitious material is in a micro expansion state; if the magnesium slag content continued to increase to 50%, the autoclave of cementitious materials unqualified.(5)The compressive strength, flexural properties and density of cementitious materials are decreased with the increase of magnesium slag content, and the porosity of cementitious material with the increase of curing time decreased gradually. Curing 3d to28 d process, the internal pore size of cementitious materials range in 0~120μm, among them, when the magnesium slag content is 50%, cementitious materials internal porosity decrease from 32.39% to 26.76%, the most probable pore size by 60.67μmμm fell to 1.3μm, the volume of the small hole increased from 66.51% to 94.82%; when the magnesium slag content is 40%, cementitious materials internal porosity decrease from28.48% to 16.08%, the most probable pore size by 45.37μm fell to 0.18μm, the volume of the small hole increased from 63.67% to 94.34%; when the magnesium slag content is 30%, the porosity of cementitious material after curing 3d is the smallest, is26.9837%, the most probable pore size is 45.45μm, the volume of the small hole is70.58%, after curing 28 d, the internal porosity decrease to 16.64%, the most probable pore size fell to 0.1831μm, the volume of the small hole increased to 93.85%. |
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