Search

Millimeter-scale magnesian refractory granules were found to be a unique magnesian-expansive component in steel slag. To systematically study the effects of these granular magnesian-expansive components on the volume stability of cement-based materials containing steel slag, an investigation of their existing forms and influence on the volume stability was conducted in this paper. The various-sizing waste–magnesium–chromate-based refractory brick (Mg-Cr brick) granules and different (FeO + MnO)/MgO ratios' synthetic MgO·xFeO·yMnO ternary solid solutions granules were adopted to simulate magnesian-expansive granules by partially replacing manufactured sand in mortar. The 100 °C–3 h boiling and 213 °C–2 MPa–3 h autoclaving treatments were adopted as volume stability testing methods. The results indicated that whether Mg-Cr brick or MgO·xFeO·yMnO solid solution, the concentration of expansive stress and the anisotropy expansion came with the granular size rising weakening the volume stability of cement-based materials which contained magnesian-expansive granules, significantly. Meanwhile, this phenomenon resulted in the ineffectiveness of the single linear expansion rate when assessing the qualification of volume stability. Furthermore, it also changed the mortars' failure mode from "muddy damage" to "break into blocks". Especially, there is no volume stability issue when the MgO·xFeO·yMnO satisfied (FeO + MnO)/MgO ≥ 1.00. Considering the significant effect of the granular magnesian-expansive components on the volume stability of cement-based materials containing steel slag, it is imperative to enhance the detection of both MgO content and mineral existing forms in steel slag in practical applications. For recommendation, the threshold value of conducting autoclaved volume stability testing on steel slag should be set at MgO ≥ 3%. Furthermore, the qualification cannot be judged by the single linear expansion rate; the specimens' appearance integrity and strength loss should also be noted. [ABSTRACT FROM AUTHOR]

In the whole process of cement production, the electricity consumption of a raw material mill accounts for about 24% of the total. Based on the statistics of the electricity consumption of the raw material mill system of 1005 production lines in China between 2014 and 2019, it is found that the average electricity consumption of the raw material preparation process of all clinker production lines between 2014 and 2019 was 25.2 kWh/t. The average electricity consumption of different-tonnage production lines varies with time. In comparison with high-tonnage ones, the electricity consumption of low-tonnage production lines has wider distribution. The average electricity consumption of raw material mill dropped from 30.88 kWh/t in 2014 to 16.13 kWh/t in 2019, with a drop of more than half. At present, the raw material preparation process of new drying-process cement production enterprises mainly includes middle unloading drying tube mill raw material preparation system, vertical mill raw material final grinding system, and roller press raw material final grinding system. This paper compares the characteristics of several grinding systems and summarizes their influence on the electricity consumption. [ABSTRACT FROM AUTHOR]