Key Takeaways & Executive Findings
- •• Aggregate segregation in cemented coarse aggregate backfill is nonlinearly influenced by solid concentration and cement-to-aggregate ratio, with critical thresholds at 81–82 wt% SC and 10–12.5 wt% C/A. • Uniaxial compressive strength (1.75–12.65 MPa) correlates linearly with SC and C/A but not with segregation degree; however, lower segregation (standard deviation <1.63) indicates higher elastic modulus. • Segregation intensifies differential deformation and failure: top regions crack earlier, bottom regions are more compressible, and local strain differences reach 515–1693.70 με during stable deformation. • Extreme aggregate unevenness accelerates crack penetration, leading to premature macroscopic tensile failure, which is critical for backfill design and stability in mining operations.
Abstract
Utilizing coarse aggregates containing mining waste rock for backfilling addresses the strength requirements and reduces the expenses associated with binder and solid waste treatment. However, this type of material is prone to aggregate segregation, which can lead to uneven deformation and damage to the backfill. We employed an image-segmentation method that incorporated machine learning to analyze the distribution information of the aggregates on the splitting surface of the test blocks. The results revealed a nonlinear relationship between aggregate segregation and variations in solid concentration (SC) and cement/aggregate ratio (C/A). The SC of 81wt%–82wt% and C/A of 10.00wt%–12.50wt% reflect surges in fluid dynamics, friction effects, and shifts in their dominance. A uniaxial compression experiment, supplemented with additional strain gauges and digital image correlation technology, enabled us to analyze the mechanical properties and failure mechanism under the influence of aggregate segregation. It was found that the uniaxial compressive strength, ranging from 1.75 MPa to 12.65 MPa, is linearly related to both the SC and C/A, and exhibits no significant relationship with the degree of segregation in numerical terms. However, the degree of segregation affects the development trend of the elastic modulus to a certain extent, and a standard deviation of the aggregate area ratio of less than 1.63 clearly indicates a higher elastic modulus. In the pouring direction, the top area of the test block tended to form a macroscopic fracture surface earlier. By contrast, the compressibility of the bottom area was greater than that of the top area. The intensification of aggregate segregation widened the differences in the deformation and failure characteristics between the different areas. For samples with different uniformities, significant differences in local deformation ranging from 515.00 με to 1693.70 με were observed during the stable deformation stage. The extreme unevenness of the aggregate leads to rapid crack penetration in the sample, causing macroscopic tensile failure and resulting in premature structural failure.
1. Introduction
The mining industry is a fundamental industry that ensures economic development and national security and plays a crucial role [1‒3]. However, the mining industry is challenged by surface resource depletion, with global mining depths for metals and coal exceeding several kilometers. Deep mining causes engineering problems such as high ground stress [4‒6]. Additionally, the negative impacts on the natural environment hinder the development of the mining industry [7‒8]. In China, mining waste rock currently amounts to approximately 5.20 × 109 t, accounting for over 70wt% of the solid waste generated by mining operations [9]. The backfill mining method, which can fully utilize mining waste and significantly improve mining efficiency in high-stress environments, has received widespread attention in the industry [1‒2, 10‒15].
In the mining industry today, binder prices are high [16‒17]. To reduce costs, some mines use waste rock, coal gangue, and sand as primary backfilling aggregates. Backfill achieves higher strength with a lower binder content and a strong skeleton structure of coarse particles [18‒20]. This backfilling material resembles a high-flow self-compacting concrete (SCC) [21]. SCC is prone to aggregate segregation, which adversely affects its strength, permeability, and durability [22‒24]. The areas where segregation or insufficient compaction occur mostly arise when the failure process begins [25]. In mining operations, aggregate segregation leads to an uneven distribution of backfill strength. In severe cases, regional instability and damage can occur, posing a threat to the safety of underground workers [26].
Research on aggregate segregation has mainly focused on concrete, particularly SCC. Navarrete and Lopez [27] investigated the comprehensive effects of the size, shape, and density of aggregates on segregation, but the specific impact on cemented backfill remains underexplored.
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Aixiang Wu, Lei Wang, Zhuen Ruan, Jiandong Wang, Shaoyong Wang, Ruiming Guo, Jingyan Xu, Longjian Bai (2025). Impact of aggregate segregation on mechanical property and failure mechanism of cemented coarse aggregate backfill. Int. Journal of Minerals, Metallurgy and Materials (矿物冶金与材料学报). https://doi.org/10.1007/s12613-025-3109-7
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Frequently Asked Questions
What is the main objective of this study?
The study investigates how aggregate segregation affects the mechanical properties and failure mechanisms of cemented coarse aggregate backfill, using image segmentation and uniaxial compression tests.
How was aggregate segregation quantified?
Aggregate segregation was quantified using an image-segmentation method incorporating machine learning to analyze the distribution of aggregates on the splitting surface of test blocks.
What are the key findings regarding strength and segregation?
Uniaxial compressive strength (1.75–12.65 MPa) is linearly related to solid concentration and cement-to-aggregate ratio, but not significantly to segregation degree. However, lower segregation (standard deviation <1.63) indicates higher elastic modulus.
How does segregation affect failure behavior?
Segregation intensifies differential deformation and failure: top regions crack earlier, bottom regions are more compressible, and extreme unevenness accelerates crack penetration, leading to premature macroscopic tensile failure.
What are the practical implications for mining engineering?
The findings highlight the need to control aggregate segregation to ensure uniform backfill strength and stability, thereby enhancing safety and reducing costs in mining operations.
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