Effects of superabsorbent polymer on mechanical properties of cemented paste backfill and its mechanism evolution

Cemented paste backfill (CPB) technology offers advantages in safety, efficiency, environmental protection, and economy, and it has been increasingly applied in mines worldwide. The mechanical properties of CPB are critical indicators of the quality of the backfill. Traditionally, cement is used as the primary binding material; however, its high cost and the resulting inconsistent strength of CPB present challenges. Superabsorbent polymer (SAP) has been extensively used in cement-based materials due to its beneficial effects on mechanical properties, shrinkage, and durability. In this study, SAP is incorporated as an additive, with the unclassified tailings from an iron ore mine used as the research material to prepare SAP-enhanced CPB. The study focuses on SAP content, the cementto-tailings ratio, and curing time as the main influencing factors. Uniaxial compressive strength (UCS) tests, thermogravimetric analysis (TGA), X-ray diffraction (XRD), and scanning electron microscopy (SEM) tests were conducted on CPB specimens to investigate the mechanical characteristics of SAP-enhanced CPB and to explore the influencing mechanisms of SAP on CPB. The results indicate that CPB strength initially increases and then decreases with rising SAP content, reaching a maximum UCS value at 0.2 % SAP content. XRD, TGA, and SEM results show that SAP affects the formation of hydration products and the pore structure of CPB. Specifically, when the SAP content is below 0.2 %, increasing SAP content leads to a denser pore structure and lower porosity, which correlates with higher UCS values. There is an exponential decrease in UCS with increasing porosity. Additionally, a quadratic relationship exists between UCS and the amount of calcium hydroxide, a key hydration product in CPB specimens. These findings provide valuable insights for improving the mechanical properties of CPB and serve as a reference for designing the strength of backfill in similar mining applications.