*Article* **Experimental Study on the Characteristics of Activated Coal Gangue and Coal Gangue-Based Geopolymer**

**Weiqing Zhang 1,2, Chaowei Dong 1,2, Peng Huang 2,3,\*, Qiang Sun 2,3, Meng Li 1,2 and Jun Chai 1,2**


Received: 14 April 2020; Accepted: 14 May 2020; Published: 15 May 2020

**Abstract:** Coal gangue-based geopolymer (CGGP) is one of the hot spots existing in the recycling of coal gangue resources due to its good comprehensive mechanical properties. However, the coal gangue structure is stable and reactivity is poor, so the coal gangue needs to be activated before utilization. In this paper, the microstructure changes of activated coal gangue by different mechanical and thermal activation methods, as well as the mechanical properties and microstructure changes of the CGGP specimens were studied by experimental investigation. The results indicated that mechanical activation and thermal activation were two effective methods to change the reactivity of coal gangue, which consisted of destroying the stable kaolinite structure and improving the activity of coal gangue. Conversely, part of the amorphous structure in coal gangue was destroyed when the activation temperature reached 900 ◦C, which was not conducive to the further enhancement of coal gangue activity. For the CGGP prepared by thermally activated coal gangue and modified sodium silicate alkali solution, the uniaxial compressive strength of the CGGP specimens decreased with thermal activation temperatures of the raw coal gangue materials at 700 ◦C, 800 ◦C, and 900 ◦C. The main reason for this was the lower amount of the active metakaolin structure in coal gangue at 900 ◦C, which was not conducive to the geopolymerization process.

**Keywords:** coal gangue; geopolymer; mechanical activation; thermal activation; mechanical property; microstructure
