## 1 Introduction  
The blast furnace slag produced by Panzhihua Iron and Steel Group Co., Ltd. during steel-making is called high titanium blast furnace slag or high titanium slag for short, because it contains more than 20% TiO\({}_{2}\)[1]. Piling of high titanium slag not only occupies a large amount of land resource, but also brings great pollution to the environment. Therefore, how to consume and make full use of it is an urgent but difficult problem to solve [2]. It is found that the high titanium slag crushed into particles of different sizes can partially or completely replace the coarse or fine aggregate in concrete with a good mechanical performance [3; 4]. At present, high titanium slag concrete has been widely used in roads, bridges, and building structures in the Panzhihua-Xichang area. The research on the mechanical properties of high titanium slag concrete material has been very extensive [5; 6; 7], but the research on the stressed members or integral structure of high titanium slag concrete, especially in the field of steel-concrete composite structures, is limited [8; 9; 10; 11]. In China, studies on stressed members with high titanium slag concrete mainly focus on reinforced concrete (RC) beams and columns. For example, [PERSON], [PERSON], and other scholars carried out an experimental study on the seismic performance of high titanium slag RC columns [12; 13; 14; 15; 16], and the results showed that the seismic performance of high titanium slag concrete column was almost the same as that of normal concrete column. [PERSON], [PERSON], [PERSON], and other scholars carried out experimental study on the bending behavior of RC beams with high titanium slag [17; 18; 19; 20]. According to their report, the bending capacity and ductility of high titanium slag concrete beams were improved slightly compared with that of normal concrete beams. [PERSON], [PERSON], and other scholars carried out an experimental study on the shear behavior of RC beams with high titanium slag [21; 22], and the results showed that the high titanium slag RC beams had better shear strength than normal RC beams. The above researches indicated that the high titanium slag concrete used in RC structure had good mechanical properties. CFST columns, as a typical representative in the field of steel-concrete composite structures, have been extensively studied by scholars all over the world. However, no relevant literature has focused on the feasibility of applying high titanium slag concrete to steel-concrete composite structures. Therefore, it is necessary to carry out relevant experimental research on CFST columns filled with high titanium slag, which can provide the necessary theoretical basis for the application of high titanium slag concrete in steel-concrete composite structures. Under the action of axial pressure, both steel tubing and the core concrete of CFST columns are in the state of three-dimensional stress, as a special feature of CFST [23; 24]. The compressive strength and deformation capacity of concrete are greatly improved by means of the confinement effect of steel tubes in concrete, especially in the case of circular sections. Moreover, it transforms concrete from a brittle material to a plastic one. At present, each country has relatively complete design specifications of bearing capacity calculation for CFST columns, such as European EC4 (2004) [25], American AISC 360-10 (2010) [26], Japanese AIJ (1997) [27], German DIN18800-5:2007-03 [28], Chinese GB50936-2014 [29]. Except for Japan, which still adopts the allowable stress method, other countries adopt the limit state design method, and the strength and stiffness in the design formulas are basically calculated by the superposition method. Although the design specifications are relatively complete, CFST is still a research hotspot for scholars around the world.