# Effect of Fly Ash on the Properties of Ceramics Prepared from Steel Slag
## 1 Introduction  
Steel slag is a by-product of the steelmaking process that accounts for approximately 10-15% of the steel production [1]. In China, the steel production in 2015 reached 804 million tons, and steel slag production was about 100 million tons. However, the overall utilization rate is only about 22% [2]. If a large amount of steel slag is not used, it not only occupies land resources, but also causes the waste of available resources and significantly pollutes the environment. In general, some of the steel slag is used internally by steel companies as a flux and returned to the blast furnace for secondary smelting or as a raw material for ironmaking. In addition, many scholars have conducted numerous studies on topics such as the production of agrochemical fertilizers [3], the production of adsorbents for wastewater treatment [4; 5], the chemical leaching extraction of rare elements [6], and the production of cement [7]. Due to the huge output of steel slag, it is necessary to develop other ways to utilize steel slag. In addition to ceramic materials, the contribution of other materials to sustainability is also a topic of study, such as cement-based ones [8; 9; 10; 11], and in that way, the performance of several additions and wastes, such as steel slags, has been analyzed.  
Ceramic is an aluminosilicate material that can tolerate certain component fluctuations. The main raw materials include minerals such as clay, quartz, and feldspar. In 2016, the output of Chinesebuilding ceramics exceeded 10 billion m\({}^{2}\), and the consumption of raw materials was approximately 350 million tons. Thus, building ceramics can consume steel slag and other solid wastes in large quantities.  
In recent years, research on the use of solid waste to prepare ceramics has become popular. [PERSON] et al. [12] used blast furnace slag, fly ash, and traditional ceramic materials to prepare ceramics and studied the relationship between different solid waste contents and the ceramic mechanical properties. [PERSON] et al. [13] fabricated ceramic tiles by using fly ash as the main raw material and proposed an alumina-rich ceramic system. Moreover, they systematically investigated the influences of fly ash content on the macro properties and microscopic structures. [PERSON] et al. [14] produced ceramics from blast furnace slag, kaolin, and quartz, and studied the process of densification and the formation of crystal phases. [PERSON] et al. [15] used red mud to prepare ceramic bricks with a maximum red mud content of 50 wt %, and studied the fixation mechanism of Na\({}^{+}\) ions in ceramic tiles. Further, Beijing University of Science and Technology carried out a large number of studies on the use of steel slag to prepare ceramics [16; 17; 18]. They used steel slag and traditional ceramic materials to prepare steel slag ceramics with good performances by the sintering process of traditional ceramics. The amount of steel slag was about 35 wt %. The influence of the addition amount of steel slag on the performance, crystallization process, and densification process of steel slag ceramics was studied, and a SiO\({}_{2}\)-Al\({}_{2}\)O\({}_{3}\)-CaO-MgO (5 wt %) steel slag ceramic was proposed.  
Based on SiO\({}_{2}\)-Al\({}_{2}\)O\({}_{3}\)-CaO-MgO (5 wt %) steel slag ceramics, fly ash was used in this study to replace quartz and feldspar in steel slag ceramics. The effects of different addition amounts of fly ash on the sintering shrinkage, water absorption, flexural strength, and sintering temperature range of steel slag ceramics were investigated. XRD, Fourier transform infrared (FTIR), and SEM were used to evaluate the effect of fly ash on crystal phase and microstructure. In this study, not only steel slag, but also a certain amount of fly ash was consumed, which lays the foundation for the better utilization of steel slag and fly ash.