Coal gangue, a by-product produced during the process of coal mining and washing, has a serious impact on the environment. Using coal gangue as a concrete aggregate has been proven helpful in potentially improving its value and reducing its environmental impact to a certain extent. However, the high water absorption and low strength of coal gangue aggregate cause a poor frost resistance of coal gangue aggregate concrete (CGAC), and thus limits its application in cold areas. This study attempted to modify the CGAC with steel fibers (including hooked-end, undulated, and copper-plated steel fiber) and slag powder, and investigated its frost resistance. Moreover, the impact that steel fiber and slag powder had on air-void characteristics of CGAC was also analyzed. The results show that when steel fibers were incorporated into CGAC, the compressive strength and splitting tensile strength of CGAC reduced significantly after freezing/thawing and that they experienced the smallest reduction when the content of the steel fiber was 1 vol.% and the undulated steel fibers worked best. However, the effect of slag powder on frost resistance of CGAC at an early age was not obvious, which may be related to the slower pozzolanic reaction of slag powder. Incorporating steel fiber or slag powder into CGAC can optimize its mesostructure and make the air-voids of concrete smaller, which is beneficial to its frost resistance. The results provide a good way to improve the performance of CGAC, expand its application in cold regions, and reduce the pollution caused by coal gangue.
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