# Frost Resistance of Coal Gangue Aggregate Concrete Modified by Steel Fiber and Slag Powder
## 1 Introduction  
Coal gangue, a main solid waste of the coal industry, accounts for almost a quarter of the coal output [1, 2]. According to the China National Coal Association (CNCA), the yearly coal output of China has exceeded 3 billion tons in recent years, and the annual increase of coal gangue is more than 400 million tons, resulting in at least 2000 coal gangue piles nationwide [3]. The accumulated coal gangue has been occupying a large amount of cultivated land and its leaching has been causing severe contamination of soil and groundwater [4, 5]. At the same time, the coal gangue dust floating in the air infiltrates into the ground with rainwater, which aggravates pollution and seriously affects the lives of residents nearby and the growth of surrounding plants [6, 7]. Although many investigations have been conducted on the application of coal gangue in recent years, the utilization of coal gangue is still limited [8, 9, 10, 11, 12]. If coal gangue can be made into ceramics and used as coarse and fine aggregate ofconcrete mixtures, the environmental impact caused by both coal gangue and over-exploitation of sand and gravel can be reduced.  
In addition, freezing/thawing (F-T) damage is a major cause of durability deterioration of concrete structures in cold regions [13; 14], which accounts for almost 60% of China's inland area, where most of the Chinese coal mines exist. However, the poor frost resistance of coal gangue aggregate concrete (CGAC) limits its wide application in cold regions. In recent years, the material properties of coal gangue and the working performance and mechanical failure mechanism of CGAC with aggregate partially or totally replaced by coal gangue have been studied [15; 16; 17]. As for the frost resistance of CGAC, the existing research mainly focused on the influences of the content of coal gangue and mineral admixture on frost resistance of concrete [18; 19]. However, as a lightweight aggregate, the properties of coal gangue mean that the mechanical properties and durability of CGAC are worse than those of ordinary concrete under the same conditions [20; 21; 22]. Since [PERSON] and [PERSON] applied the theory of composite mechanics to steel-fiber-reinforced concrete in 1970s [23], the theoretical research and engineering application of steel-fiber-reinforced concrete have developed rapidly [24]. For ordinary concrete, the fibers can significantly enhance the tensile strength, deformation capacity, crack resistance, and durability of concrete [24; 25; 26; 27; 28; 29]. Besides, due to the pozzolanic effect and microaggregate filling effect of mineral admixtures, the addition of proper mineral admixtures in concrete can not only save cement but also optimize its pore structure, improve its strength, impermeability, and durability to a certain extent [30; 31; 32; 33; 34]. However, there are few studies on CGAC modified by steel fiber and mineral admixture.  
This study attempted to replace ordinary crushed stone and river sand with coal gangue ceramsite, modify CGAC with fibers and slag powder, and carry out accelerated F-T testing of CGAC. The frost damage of CGAC was evaluated by compressive strength loss, splitting tensile strength loss, mass loss, and relative dynamic modulus of elasticity (RDME), and the effects of steel fibers and slag powder on the frost resistance of CGAC were studied.