Engineering Verification and Quality Evaluation of Underground Concrete Slipform Paving with Accelerator- Incorporated Side Support
This study validates a novel composite slipform paving strategy for underground roadways that utilizes localized alkali-free accelerators on side strips to prevent edge collapse and deformation, achieving high surface flatness and mechanical strength through optimized operational parameters.
Original paper licensed under CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). This is an AI-generated explanation of the paper below. It is not written or endorsed by the authors. For technical accuracy, refer to the original paper. Read full disclaimer
Beneath the earth, in the narrow, dark corridors of coal mines, the floor is more than just ground; it is a critical piece of infrastructure. These roadways must support the immense weight of heavy machinery and the constant traffic of vehicles that move coal and supplies. For decades, building these floors relied on manual labor, a slow and physically demanding process where workers shaped the concrete by hand. The result was often uneven, and the quality depended heavily on the skill and stamina of the crew. To modernize this work, engineers have turned to slipform paving, a method where a machine moves forward, continuously pouring and shaping wet concrete into a smooth, solid path. However, this technique faces a stubborn problem in the tight, uneven spaces of a mine. As the machine pushes the wet concrete forward, the sides lose their support the moment the mold passes. Without a quick way to harden, the fresh edges of the concrete tend to slump, crack, or collapse inward, ruining the smooth surface and the structural integrity of the floor.
Researchers from a coal industry group and a university in China set out to solve this specific problem of collapsing edges without sacrificing the strength of the entire floor. They developed a clever, two-part strategy for the concrete mix. Instead of treating the entire floor the same way, they decided to treat the sides differently from the center. They proposed adding a special liquid chemical, known as an accelerator, only to the two narrow strips of concrete on the edges. This chemical acts like a fast-forward button for the concrete's setting time, causing those side strips to harden almost immediately after being poured. The wide, central section of the floor, which carries the most weight, remains a standard mix that hardens at a normal pace. This approach aims to give the edges the "standing performance" they need to hold their shape while preserving the long-term strength of the main roadway.
To test if this idea worked in the real world, the team took their equipment into an active underground coal mine. They calibrated their machinery with precise settings: the machine moved forward at a steady speed of 6.0 meters per minute, while a rotating screw inside the machine churned the concrete at 45 turns per minute. They applied the accelerator to the side strips, which were 14 centimeters wide, using a dosage of 9 percent. As the machine moved, it laid down a continuous path of concrete. The results were immediate and clear. Where the edges used to slump and fall apart, they now stood firm. The researchers measured the sides and found that the concrete barely moved at all; the average sideways deformation was just 1 millimeter, a distance so small it is barely noticeable. The width of the finished floor matched the machine's mold perfectly, proving that the sides held their ground against the pressure of the wet concrete in the middle.
The team also examined the quality of the surface. They ran a three-meter straightedge across the floor to check for bumps and dips, finding an average gap of 4.6 millimeters, which indicates a very smooth surface. To get an even more detailed look, they used a high-resolution 3D camera to scan the texture of the concrete. The center of the floor was exceptionally smooth, with a flatness of 2.8 millimeters, while the accelerator-treated sides were slightly rougher at 4.1 millimeters. This slight difference makes sense, as the rapid hardening of the sides locks in tiny surface irregularities before they can smooth out. Despite this, the sides were still considered to be of high quality. The researchers then tested the strength of the concrete by cutting out samples and crushing them. The center concrete was the strongest, with a compressive strength of 43.637 megapascals. The side concrete, having been treated with the accelerator, was slightly weaker at 33.925 megapascals. This reduction in strength is a known trade-off when using high doses of accelerators, but the side concrete remained strong enough to handle the loads of the mine.
The study confirms that this composite approach works effectively. By using the accelerator only where it is needed most—the unstable edges—the engineers managed to stop the collapse and deformation that usually plague underground paving. The central concrete retains its full strength to carry the heavy loads, while the reinforced sides provide a stable boundary. This method does not require a complete overhaul of existing mining equipment; it simply involves adjusting the mix and the speed of the machine. The findings suggest that this technique offers a reliable path forward for mechanizing mine floor construction, turning a difficult, manual task into a continuous, high-quality process that meets the rigorous demands of modern underground operations.
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