Components, systems and materials › Slope protection and rockfall › Shotcrete
Shotcrete
What it is
Shotcrete is concrete or mortar sprayed at high velocity onto a surface, where it compacts itself on impact. It needs no formwork.
Where it is used
Tunnel linings and primary support, soil-nail and rock-slope facings, repair of damaged concrete, swimming pools and thin shells.
How it works
The mix is pumped to a nozzle and projected with compressed air. Impact compacts the material and bonds it to the surface. In tunnels a thin layer applied soon after excavation, combined with rock bolts, lets the ground carry load and limits loosening. Accelerators make it set quickly so it can be built up overhead.
Types
- Wet-mix shotcrete
- dry-mix shotcrete (water added at nozzle)
- steel or synthetic fibre-reinforced shotcrete
- mesh-reinforced shotcrete
Materials
Cement, sand and small coarse aggregate (often up to about 10 mm), water, set accelerator, sometimes silica fume and fibres.
Thickness, strength class, early strength gain and fibre dosage or energy-absorption class are specified for the purpose. EN 14487 covers specification and execution in Europe. Thickness is checked against design and drainage behind the layer is provided to prevent water pressure.
Installation and QA steps
- Clean and wet the substrate and fix drainage strips
- Spray at right angles to the surface from a suitable distance in layers
- Control rebound and do not reuse it
- Check thickness with probes or pins
- Test early strength and take panels or cores for strength and toughness
- Cure
- Rebound and sand lenses trapped in the layer
- Delamination from a dusty or wet substrate
- Cracking from shrinkage
- Water pressure behind an undrained facing
Codes cited
- EN 14487 (series) (Europe): Sprayed concrete: definitions, specification and execution.
Cited by number only. We do not reproduce code text, tables or figures.
Related
Road tunnel through a mountain: drill, blast, NATM
Excavate in rounds and let the rock help support itself.
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