Polymer shape effect on damage evolution, internal defects and crack propagation of 3D-printed polymer-based cementitious backfill

The strength property and damage mode of cementitious tailings backfill (CTB) are governed by its structural characteristics in the presence of the microstructure/internal defect effects. However, this correlation is still unclear for 3D-printed polymer (3D-PPL) based CTB materials. Hence, the mechanical properties of microscopic damage and fracture evolution of 3D-PPL reinforced CTB were studied in this study. The fracture of CTBs with three shapes of polymer (cross, quarter, and EEP) were visualized and digitally characterized by the Brazilian splitting test, scanning electron microscopy (SEM) and industrial computed tomography. Experimental results indicate that CTB's failure mode mainly starts from the low-density pore area, gradually evolves to a crack, and finally expands to the main crack by the center of the specimen. 3D-PPL has a certain interface bonding and supporting effect on CTB specimens, and the 3D-PPL specimen's porosity is significantly below that of ordinary backfill. Incorporating 3D-PPL into CTBs effectively decrease the penetrated pore number, while enhancing the density of CTB's microstructure, which dominates the strength and integrity of specimens. 3D-PPL-based backfill specimens also indicate a complex and diverse damage pattern, with a negative link between crack volume and tensile strength. The 3D fractal dimension of cracks in 3D-PPL-based fills is greater than that of ordinary fills. Combined with SEM-EDS tests, CTB's hydration materials were mostly CSH gels, which interleaved as nucleating agents to inhibit crack growth. The findings of the present work will be beneficial for manufacturing and operational usage of 3P-PPL-based backfills.