Shear characteristics of the interface between rock and cemented tailings exposed to internal sulphate attack

A clear understanding and accurate assessment of the mechanical properties of the interface between backfill material and the adjacent rock mass is paramount to a safe and economical design of cemented paste backfill (CPB) structures. With the CPB being a cementitious material, sulphate compounds prevalent in the mining environment may affect the shear characteristics of rock-CPB interface. However, there are currently no research studies on the long-term shear behaviour of the CPB-rock interface exposed to sulphate attack, although CPB often contains a relatively large amount of sulphate ions. This paper presents and discusses the findings obtained through experimental investigation of the impact of the initial sulphate concentration in CPB on the shear characteristics of the interface between rock and CPB cured for advanced ages. The obtained results show that sulphate considerably influences the long-term shear strength and behaviour of the interface. Sulphate can either negatively or positively alter the shear properties of the mature CPB-rock interface due to the competition between the processes that reduce or increase the strength at the interface. The dominant process is a function of the initial sulphate content and the curing time.