In this paper, the stripped steel slag of waste magnesia-alumina spinel bricks and waste magnesia-alumina spinel are used as the main raw materials, and cement is used to prepare unburned bricks. To obtain optimized process parameters, it can provide technical reference for the overall utilization of refractory materials after use.
test
1.1 Raw materials
Stripped steel slag and waste magnesia-aluminum spinel are obtained after being stripped, cut and sorted by tools such as hammers and cutting machines.
(1) Stripping steel slag: After crushing, ball milling and screening, three different specifications of 0-1, 1-3 and 3-5mm are obtained. Because the 1-3mm and 3-5mm stripped steel slag raw materials can act as the skeleton component in the unburned brick and play a supporting role, improve the strength of the unburned brick and reduce the cost of brick making, so natural sand is not added to the ratio. The chemical composition of the stripped steel slag is shown in Table 1. It can be seen that the raw materials of the stripped steel slag are high iron (Fe2O3) and high sand type (SiO2) type steel slag, and the main phases of the stripped steel slag are dicalcium silicate phase and free calcium oxide phase; The layered structure is porous and not dense, similar to the microstructure of clay, so it can replace clay to produce non-burning bricks. The EDS analysis shows that the main elements of the exfoliated steel slag are Si, Mg, Al, Ca, Fe and so on.
(2) Waste magnesia-aluminum spinel: pass through a 45-mesh sieve after ball milling to ensure that the raw material particle size of the sample is less than 0.5nm. The main components of waste magnesia-aluminum spinel are Al2O3 and MgO; after analysis, it can be concluded that the main phases of waste magnesia-aluminum spinel are periclase phase and magnesia-aluminum spinel phase; it can be observed that waste magnesia-aluminum spinel Stone is a layered structure. Through EDS energy spectrum analysis, it can be seen that the main elements of waste magnesia-alumina spinel are Al, Mg, Si, etc., and there are many aluminum elements, which can provide the necessary strength for unburned bricks.
(3) Cement: P·O42.5, the performance meets the requirements of GB175-2007 “General Portland Cement”. Cement is used as a cementitious component and activator in unburned bricks.
1.2 Sample Preparation
This test sample is prepared by the processes of batching, mixing, molding, and curing. The batching conditions are: stripped steel slag is 60%, 70% (divided into three specifications of 0-1, 1-3, 3-5mm), waste magnesia-aluminum spinel is 20%, 30%, cement and water are respectively fixed as 10%, 2%. The material is mixed by first dry mixing for 2 minutes, and then adding water and wet mixing for 2 minutes. After the raw materials are evenly mixed, the molding process is adopted. The diameter of the mold is 20 mm and the molding pressure is 15 MPa. After demoulding, the samples were cured at room temperature and pressure for 28 d, and water sprayed every 3 d to prevent the samples from cracking, so as to obtain unburned brick samples. In the molding process, the pressure of 10MPa was used for molding first, and it was found that the sample was not completely formed, and the powder fell off. And through comparison, it is found that the compressive strength of the samples formed under the pressure of 15MPa is higher than that of the samples formed under the pressure of 10MPa.
1.3 Structural characterization and performance testing
(1) Using the D/max-rA model X-ray diffractometer of Rigaku Company of Japan, the phase analysis of the raw materials of steel slag and magnesia-alumina spinel and the unburned bricks after forming and curing was carried out.
(2) The S-3000N scanning electron microscope of Hitachi, Japan was used to characterize the morphology, structure, shape and distribution of unburned bricks.
(3) Using an electronic universal testing machine (CTM4304, China MTS Company), the compressive and flexural strength tests of the unburned brick samples were carried out.
Results and Analysis
2.1 Bulk density and water absorption of unburned bricks
(1) The bulk density of unburned bricks shows an overall increasing trend with the increase of stripped steel slag content and the decrease of waste magnesia-alumina spinel content. When the gradation of the peeled steel slag particles is 0-1mm25%, 1-3mm25%, and 3-5mm20%, the bulk density of the unburned brick is the largest, which is 2863kg/m3. The reason may be that the content of exfoliated steel slag in the sample increases, and the density of exfoliated steel slag is higher than that of waste magnesia-alumina spinel, which leads to the increase of the overall bulk density of unburned bricks. (2) When the particle gradation of the peeled steel slag is 0~1mm15%, 1~3mm15%, 3~5mm30%, the water absorption rate of the unburned brick is the smallest, which is 6.07%, and the reason may be 30% waste magnesia-aluminum spinel. The powder and 0-1mm exfoliated steel slag fully filled the voids in the skeleton of the unburned brick, resulting in a decrease in the water absorption of the sample. And the water absorption of the samples are all in line with the requirements of the water absorption less than 18% in the JC/T422-2007 “Non-sintered Garbage Tailings Bricks” standard.
2.2 Dimensional deviation of unburned bricks
Since the active components such as C2S, C3S, and calcium ferric aluminate in the peeled steel slag are gelatinous, an activator that can stimulate the activity of the cement can be generated during the hydration process, and the activated cement will lead to the volume of non-burning bricks. Expansion, so it has a certain influence on the size of unburned bricks.
In this test, the amount of cement used is 10%, and the radial and axial dimensional changes of the workpiece are relatively small, and no cracks appear on the surface. In line with JC/T422-2007 “appearance and size deviation less than 2mm requirements.
in conclusion
(1) The forming pressure and the ratio of raw materials have an influence on the performance of unburned bricks. The optimized preparation process parameters obtained through research are: peeling steel slag 0-1mm25%, 1-3mm15%, 3-5mm20%, magnesium-aluminum spinel 30%, cement 10%, molding pressure 15MPa.
(2) In addition to the original magnesium oxide and calcium sulfate, the obtained unburned brick also generates a new phase of serpentine. Morphological analysis shows that the non-burning bricks have a cladding and inlaid structure, and the fine particles of magnesia-alumina spinel are embedded in the irregular exfoliated steel slag skeleton, which plays a filling role and makes the non-burning bricks dense.
(3) In this test, the minimum water absorption rate of the prepared non-burning bricks is 6.07%, and the maximum compressive strength is 9.57MPa, which meets the standard requirements of JC/T446-2000 “Concrete Pavement Bricks”. This experimental study is of great significance to the overall utilization of refractory materials after use.
