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Synthetic vanadium slags were melted at 1673 K and then cooled to a predetermined temperature at different cooling rates. The mineralogical phases and crystallisation behaviour were investigated based on optical microscopy, SEM, EDS and XRD analyses. The results show that spinels and silicates were the major phases in the complex vanadium slag samples, and V is enriched in the spinel phases, i.e. Fe x V 32x O 4 and Mg x (V,Ti) 32x O 4 . The apparent diameter of spinel crystal grains decreases with increasing cooling rate, e.g. from 14 to 5 mm at 1523 K. Crystal grain size increases significantly with increasing holding time. It is also found that the grain sizes of spinels at higher temperatures, 1573 and 1623 K, are considerably smaller than at lower temperatures, 1473 and 1523 K. At lower temperature, large blocked spinel crystals between grey silicate phases are formed, whereas there only a few smaller blocked spinels when performed at higher temperature. Better control of the process cooling parameters will benefit vanadium slag quality.

This paper studies experimentally the behaviour of circular FRP-steel confined concrete columns subjected to reversed cyclic loads. The influence of main structural factors on the cyclic behaviour of the columns is discussed. Test results show the outstanding seismic performance of FRP-steel confined reinforced concrete (RC) and steel-reinforced concrete (SRC) columns. The lateral confinement effectiveness of GFRP tube and GFRP-steel tube was verified and a simplified OpenSees-based finite element method (FEM) model was developed to simulate the experimental results of the test columns. Based on the proposed FEM model, a parametric analysis was conducted for investigating the effects of main factors on the reversed cyclic behaviour of GFRP-steel confined RC columns. Based on the test and numerical analyses, the study discussed the influence of variables such as the lateral confinement on the plastic hinge region (PHR) height and peak drift ratio of the columns under reversed cyclic loads. Results indicate that the lateral confinement significantly affects the PHR height of the circular confined RC columns. Based on the analyses of the data from this study and literature, a simple model was suggested to predict the peak drift ratio of the confined RC columns.

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