# Characterization of Slag Cement Mortar Containing Nonthermally Treated Dried Red Mud
## 1 Introduction  
Sustainable development of an industry depends on effective treatment of industrial wastes and conservation of natural resources. Therefore, it is important to transform industrial wastes into raw materials that can replace natural resources [1]. Red mud (RM) is an industrial byproduct generated from the Bayer process, which is used to produce alumina, and is one of the most commonly generated industrial byproducts in modern society [2]. Production of 1 ton of alumina generates 1.0-1.5 tons of RM [3]. Growth of the aluminum industry has increased the number of factories, and it is estimated that 1.2 million tons of RM is being generated every year, and 4 billion tons of RM has been generated worldwide as of 2015. RM discharged from the Bayer process is an insoluble solid that exhibits high alkalinity (pH 10-12.5) because of the influence of caustic soda, which is added in the course of extracting alumina from bauxite ores [4]. Dumping of RM in the sea or in open yards may cause various environmental problems, and landfills can reach their limits because of such dumping [1,3]. Therefore, new RM treatment methods are required for sustainable growth of the aluminum industry [3,5]  
Use of industrial byproducts as construction materials is one of the good methods to reuse such byproducts in large quantities [6,7]. Efforts have been made in various fields to use RM as a construction material. For example, [PERSON] et al. [8] produced cement through sintering at 1450 \({}^{\circ}\)C using RM as a raw material. [PERSON] et al. [7] examined the rheology and curing characteristics of cement mortar containing RM. [PERSON] et al. [9] attempted to produce ceramics by replacing clay with RM andproposed optimal conditions for the RM substitution rate, sintering temperature, and sintering time. [PERSON] et al. [10] examined a method of utilizing RM in the production of ordinary Portland cement (OPC) mortar, and they reported that the workability of mortar decreased because of the addition of RM, but the water absorption rate could decrease and the compressive strength could increase when the RM substitution rate was 20% or less. [PERSON] and [PERSON] [11] confirmed that the addition of RM into self-compacting mortar had various benefits such as an increase in compressive and tensile strengths and a decrease in drying shrinkage. Moreover, [PERSON] et al. [12] examined the production of geopolymers using RM. As described above, many researchers have made efforts to use RM as a construction material, but there are still several limitations in the production process used for such a material. In the production of ceramics using RM, an increase in the amount of RM leads to benefits such as an increase in the compressive strength of ceramics and a decrease in the water absorption rate because the presence of RM increases the vitreous phase in the ceramic matrix; however, the firing process used in production requires a high temperature of more than 900 \({}^{\circ}\)C [7]. In most studies that used RM as a base material for binders or geopolymers, dried RM powder was used. However, RM in the Bayer process is discharged in a slurry state with 40%-60% water content. Because water content in the RM sludge varies depending on the storage location or period, appropriate management of water content is necessary to use RM as a raw material [13]. Therefore, RM is turned into powder through a high-temperature drying process, which requires additional energy input. The cost increase resulting from this energy-intensive pretreatment process may act as another obstacle to the use of RM as a construction material [14]. Therefore, technology is required that can convert RM into a construction material using minimal energy input. This study attempted to develop a method of controlling the water content in RM sludge without heat treatment. The method of removing moisture without heating is based on the principle of using soil stabilizers to stabilize the soft ground.