| Summary: | If the cemented paste backfill (CPB) does not contact the roof, it will cause mining safety problems such as roof collapse, and the passive roof contact technology cannot effectively solve the problem. Therefore, the active roof-contact technology based on expansion agent was developed. The orthogonal experiments were carried out to study the influence of mass concentration, tailings-to-cement ratio and expansion agent content on the expansion ratio and mechanical properties of CPB. Through the range analysis of the expansion ratio and unconfined compressive strength (UCS), the significance of influencing factors on the expansion ratio and UCS was obtained. The experimental results show that the tailings-to-cement ratio has the greatest influence on the UCS, and the expansion agent content influence the expansion ratio more. The multivariate nonlinear regression models can accurately predict the expansion ratio and UCS of CPB. It is found that the sensitivity of expansion agent content to the expansion ratio decreases with the increase of tailings-to-cement ratio. According to the requirement of the mine for the expansion ratio and UCS, the expansion ratio and UCS were optimized by multi-objective optimization, and the optimal proportioning schemes suitable for the CPB in mines were obtained. Finally, the expansion mechanism was revealed by scanning electron microscope (SEM), and the evolution of the expansion agent with hydration process was analyzed. This study is of great significance to realize the roof-connect of metal mines, and has important practical value for the safe mining.
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