Effect of polypropylene fiber on cement backfill based on tailings
Authors:   University of Science and Technology MISIS, Agafonov Valery , Oganesyan Armine ,   University of Science and Technology MISIS, Solovykh Danila ,   University of Science and Technology MISIS, Kozlova Olga ,   MIREA – Russian Technological University
Published: March 2024

Introduction. The advantages of technology with backfill in minerals extraction predetermined their widespread use despite the high cost of production. One of the ways to reduce the backfilling cost is the use of tailings. However, earlier studies did not consider the inhomogeneity of shapes, sizes and internal mutual arrangement of particles, as well as the inhomogeneity of phases and density, which is characterized by the presence of pores. Materials and methods. Comparative analysis of samples with different recipes was used to investigate the bending strength of polypropylene fiber-reinforced backfill. A high-frequency automatic laboratory setup with strength transducers (load cells) was used to measure the bending characteristics. Optical moving digital image correlation (3D-DIC) method was used to track and automatically store the obtained results. Microstructure of the prepared and cured backfill was studied to correlate the obtained values. Results. 1. Maximum bending strength was demonstrated by unreinforced samples with 1:4 cement/tailings combination compared to the rest of samples regardless of the presence or absence of reinforcing fiber in the composition; 2. Directly proportional dependence between the increase in bending strength of samples and increase in the cement/ tailings ratio in backfill was established; 3. Increase in bending strength of the samples is maximum at low cement/tailings ratio in backfill composite; 4. There is a linear increase in peak strength and deflection values as the cement/tailings ratio in reinforced backfill increases. Discussion. Compaction of the internal structure is observed when reinforcing the composite with polypropylene fiber. It is noticeable that the compaction occurs due to fiber bonding, which allows improving the bending characteristics of samples. Such compaction is observed in all the investigated reinforced composites with ratios of 1:4, 1:6, 1:8. In some cases a decrease in fiber diameter is observed, which can be explained by the factor of occurrence of yanking or torsional forces at the moment of fracture. All the changes in reinforcing fibers confirm the fact that they are prone to deformations. Conclusion. The following conclusions can be drawn from the research conducted: 1. Unreinforced samples with a cement/tailings combination of 1:4 have the maximum bending strength in comparison with other samples, regardless of the presence or absence of reinforcing fiber in the composition; 2. Reinforcement of backfill with polypropylene fiber changes the fracture behavior of samples and passes from brittle to ductile at maximum strain rate; 3. Reinforcing fibers in the cement backfill have an overlapping effect, which significantly slows the development of cracks and increases the ductility of the material. Resume. The results of the research can be useful in the creation of high-strength and resistant to increased bending stresses artificial mass where tailings are used as an aggregate. In the future there is a need to study the cement backfill with different types of reinforcing fibers.