Microscopic characteristics of the action of an air entraining agent on cemented paste backfill pores

Abstract Many factors affect pores in cemented paste backfill (CPB), and there are numerous species of admixtures which have complicated influences on CPB, such as the action of air entraining agents (AEAs). Previously, sodium abietate (SA) and triterpenoid saponins (SJ) have been used as AEAs. In this study, CPB was prepared by mixing different amounts (0%, 0.2%, 0.4% and 0.6%) of AEA with different compounds (tailings, cement etc.). The quantitative relationship of microscopic characterization between the action of AEAs on CPB pore structure was established using nuclear magnetic resonance (NMR), scanning electron microscope (SEM) and fractal theory. Our results indicate that: (1) T2 spectrums of CPB samples tested using NMR all have three peaks, where the proportion of main peaks characterizing micro-pores (the main pore type) was >88%. (2) The addition of AEAs increases CPB porosity, optimizes the pore structure in the CPB sample, and achieves uniform distribution. The proportion of main peaks characterizing micro-pores increased to >90%. (3) In the same period the degree of cement hydration reaction was found to differ when CPBs with or without AEAs were compared. The addition of AEAs has a certain delay hindering effect on the cement hydration reaction. (4) The fractal properties of CPB pores with the addition of AEA are very strong. The fractal dimension of pores is linearly directly proportional to AEA content and porosity, and the complexity of pores increases with the increase of fractal dimension.