Mechanical property and microstructure of cemented tailings backfill containing fly ash activated by calcium formate

Cemented tailings backfill (CTB) is the most economical and environmental method to recycle tailings and fly ash (FA) for filling mining, but the high content of FA will weaken its strength property. This paper aims to use calcium formate (CF) as an activator to stimulate the activity of FA, thereby enhancing the mechanical property of CTB. The influence of FA and CF content on the stress-strain behavior, dilatancy deformation, and compressive strength of CTB was investigated using uniaxial compression test and scanning electron microscope. The coupling effect mechanism of FA and CF content on the compressive strength of CTB was revealed. The results show that increasing the content of FA and CF can enhance the bearing capacity of CTB during the dilatancy deformation stage, but the excessive content of FA and CF will lead to the attenuation of peak stress. The relations between FA content, CF content, and the compressive strength of CTB can be characterized by quadratic polynomial. Adding CF can stimulate the activity of insoluble FA, increasing the utilization of FA in CTB and producing rich hydration products to fill the internal defects of CTB. The microstructure of CTB is effectively improved by adding CF, including the size and distribution of microcracks and micropores, so that the strength property of CTB is optimized. However, too much CF will make the microstructure of CTB loose and porous, resulting in more microcracks and micropores. Microcracks propagate and connect with micropores to form defects, which deteriorate the microstructure of CTB, thus weakening the strength parameters of CTB. This study provides a method to increase the utilization of FA in CTB, which is of great significance for strengthening the mechanical properties of CTB and improving engineering economic benefits.