The wet-mix shotcrete machine is critical equipment in shotcrete construction. Its core function is to convey pre-mixed concrete (i.e., "wet-mix concrete")-prepared at a batching plant or mixer according to specified mix proportions-through a pipeline.
The machine uses compressed air or mechanical pumping to spray concrete continuously at high velocity onto rock surfaces or structural substrates, achieving immediate compaction and shaping.
It is a mechanical device specifically designed to convey and spray pre-mixed wet concrete. In contrast, a "dry-mix shotcrete machine" conveys the dry mix and water separately, mixing them only at the nozzle.
To ensure construction safety, quality, efficiency, and equipment longevity, the operation of a wet-mix shotcrete machine must strictly adhere to the following guidelines:
Pre-construction Preparation
1. Equipment Inspection and Commissioning
Comprehensive Inspection: Before startup, inspect all hydraulic, electrical, and pneumatic systems to ensure pipelines and connections are secure and free of leaks.
Lubrication and Cleaning: Ensure all lubrication points are filled with the specified grade of lubricant. The hopper and pipelines must be cleared of any hardened concrete residue from previous operations.
No-load Test Run: Start the equipment for a no-load test run. Check that the main motor, hydraulic pump, and accelerator pump are operating correctly and that all pressure gauge readings are within the normal range.
Air/Water Line Testing: Check that the compressed air pressure (typically required to be 0.5–0.7 MPa) and water supply are adequate and stable. Test the accelerator pump and calibrate its flow rate to match the concrete pumping speed.
2. Work Face Preparation
Substrate Surface Treatment: Remove loose rock, soil, oil stains, and other debris from the rock or structural surface to ensure a solid foundation. For areas with water seepage, drainage measures must be implemented first.
Measurement and Marking: Mark indicators for shotcrete thickness (e.g., by inserting rebar stakes) to facilitate thickness control. 3. Material Preparation
Concrete Quality Control: Ensure the slump of the ready-mixed concrete strictly meets equipment requirements (typically 12–18 cm for concrete pumps).
Excessively low slump can easily cause pipeline blockages, while excessively high slump compromises strength and increases rebound and sagging.
Aggregate Control: The maximum aggregate size must not exceed the equipment's permissible limit or two-thirds of the reinforcement spacing (typically ≤15 mm) to prevent pipeline blockages.
Accelerator Verification: Confirm the type of accelerator (alkali-free or low-alkali types are preferred) and its compatibility with the cement. Conduct setting time tests.