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Analysis of Wet-Spraying Trolley Technology for Low-Workability Concrete Spraying
Release time:
2026-07-27
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Summary:
In tunnel support, slope stabilization, and other engineering applications, the use of wet‑spraying rigs to place low‑slump concrete has become a core technique for enhancing spraying quality and construction efficiency. Compared with conventional spraying methods, employing a precisely controlled low‑slump concrete mix and applying it via modern wet‑spraying equipment can substantially improve the mechanical properties and durability of the support layer.
Technical Definition and Process Advantages of Low‑Slump Concrete
Engineering practice has shown that the optimal slump range for concrete sprayed by wet-mix shotcrete rigs is typically maintained within 80-150mm between. This range is significantly lower than the slump requirements for conventional pumped concrete, and its technical advantages are primarily manifested in three aspects:
1. Effective control of rebound loss: Concrete with a lower slump exhibits superior cohesiveness and structural integrity, reducing aggregate spalling upon impact with the rock surface and enabling the rebound rate to be kept within… 15% The following is significantly superior to conventional jetting processes, directly reducing material waste.
2. Enhancing the mechanical properties of shotcrete: A low water-to-cement ratio in the mix design enables shotcrete to achieve higher early- and late-age strengths, while reducing the occurrence of shrinkage cracks and resulting in a denser, more durable support structure.
3. Ensuring spray thickness and construction safety: An appropriate workability allows the concrete to build up layer by layer, enabling a single-pass spray thickness that meets design requirements while ensuring effective adhesion to the arch crown and other surfaces. overhead Location, to avoid the risk of flaking.
Technology for the Adaptability of Wet-Spraying Boom Trucks to Low-Workability Concrete
To successfully spray low‑slump concrete, modern wet‑spraying rigs integrate a number of key technologies:
1. Stable pumping system: Utilizing advanced hydraulically driven plunger pumps or screw pumps, it delivers smooth, continuous, high-pressure conveying power, effectively overcoming the significant frictional resistance encountered when low‑slump concrete flows through pipelines.
2. Precise accelerating‑agent dosing system: This is the key to the success of the process. The system uses flow meters and servo‑controlled valves to inject liquid accelerating agent in a precisely proportional manner based on the concrete pumping rate, with dosing errors typically not exceeding ±1% Precise dosing ensures that the concrete is instantly and uniformly mixed with the accelerating agent at the nozzle, achieving initial set within a few minutes after spraying—this is the foundation for minimizing rebound and producing thick spray layers.
3. Scientific nozzle design and operational techniques: The nozzle should be engineered to ensure thorough vortex‑induced mixing between the concrete and the accelerating agent. In addition, operators must undergo systematic training to master the optimal distance between the nozzle and the sprayed surface (typically…). 1-1.5 The material is conveyed at a specified distance (m) and angle (perpendicular to the sprayed surface), while performing a uniform helical motion; these operational techniques are essential for ensuring the quality of shotcrete with low slump.
Material and Mix Proportion Design for Low-Workability Concrete
To achieve good pumpability and sprayability, the mix design must adhere to specific principles:
1. Cementitious material system: Typically, cement is used in combination with high-quality fly ash, mineral admixtures, and other supplementary cementitious materials. These admixtures can enhance the rheological properties of concrete and reduce its hydration heat.
2. Aggregate selection and gradation: A stringent aggregate gradation is essential for ensuring pumpability. The maximum particle size generally does not exceed 15mm Moreover, a continuous gradation must be achieved to reduce the void ratio, thereby decreasing the paste demand and lowering flow resistance.
3. Application of high-efficiency water reducers: High-performance polycarboxylate-based water reducers must be used, even at extremely low water-to-cement ratios (typically…). 0.4-0.45 ) It can still provide concrete with sufficient fluidity and workability, enabling it to be pumped smoothly.
4. Fiber reinforcement: To enhance toughness and crack‑resistance, steel fibers or synthetic fibers are often incorporated. However, fiber addition can adversely affect workability, necessitating a low‑slump concrete mix design and relying on high‑range water reducers and an appropriately optimized sand ratio to ensure adequate passage through the fiber network.
Precise control of construction processes
Successful jetting operations depend on full-process control:
Preparation before spraying: Thoroughly remove loose rock fragments and dust from the sprayed surface, and pre‑wet the pipelines thoroughly.
Process Monitoring: Real-time monitoring of pumping pressure, accelerating agent dosage, and air pressure; the stability of these parameters is essential for ensuring consistent spraying quality.
Layered Spraying: For support structures with substantial design thicknesses, the principle of layered spraying must be strictly adhered to; the next layer may be sprayed only after the preceding concrete layer has fully set.
Summary
Wet‑spraying using a shotcrete carriage for low‑slump concrete is a modern construction technique that integrates materials science, mechanical automation, and operational expertise. By employing an optimized low‑slump mix design and leveraging the carriage’s precise metering, smooth conveying, and instantaneous mixing capabilities, this method effectively resolves the longstanding trade‑off in shotcrete applications between high strength and durability on the one hand, and low rebound and high productivity on the other. As a result, it has become the dominant technological trend in shotcrete support for tunnels and underground structures.
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