Influence of Air Entraining Agent on Strength and Microstructure Properties of Cemented Paste Backfill

The conveying distance during the backfill operation has become extensively large with the advancement of mining work. It requires the immediate attention of academic and industrial communities. Adding air entraining agent (AEA) can improve the rheological properties of the filling slurry and facilitat the filling slurry transfer to the long-distance underground stope. The AEA can generate a large number of tiny bubbles, which acted as floating balls and reduced the friction between the particles. In addition, AEA acted as a dispersing and wetting agent. Herein, we have obtained filling material from the Sanning mine (Hubei, China) and utilized sodium abietate (SA) and triterpenoid saponins (SJ), as air entraining agents, to improve the fluidity of filling slurry. The influence of AEA content on mechanical properties, structure and morphology has been analyzed by uniaxial compressive strength (UCS) testing, nuclear magnetic resonance (NMR) and scanning electron microscopy (SEM). The results reveal that the addition of AEA increased the fluidity of filling slurry. Moreover, UCS of the AEA-free cemented paste backfill (CPB) sample, cured for 28 days, was found to be 2.23 MPa. However, the addition of 0.2% AEA (SA and SJ) increased the UCS to 2.31 MPa and 2.35 MPa, respectively. However, when SA and SJ amount was increased to 0.6%, UCS decreased to 2.19 MPa and 2.13 MPa, respectively. Hence, UCS of the CPB initially increased with the addition of AEA, followed by a gradual decrease, which can be ascribed to the pore structure inside CPB. One should note that the presence of AEA increased the number of small pores inside the CPB. The SEM results shows that pore structure of CPB can be optimized by adding an optimal proper amount of AEA.