Shotcrete/Sprayed Concrete, structural finish (75mm, 100mm, 150mm, 200mm)
Shotcrete, also known as sprayed concrete, is pneumatically applied structural concrete delivered through a hose and nozzle at high velocity onto a prepared surface. Two distinct processes exist: the dry-mix process (gunite), where dry cement and aggregate are fed through the hose and water is added at the nozzle; and the wet-mix process, where a pre-batched concrete mix is pumped to the nozzle where compressed air propels it onto the surface. The wet-mix process dominates modern Australian practice due to better quality control, lower rebound waste (5-15% for walls vs 25-50% overhead for dry-mix), and reduced dust. Standard structural mixes use Portland cement (GP or HE), 10-14mm maximum aggregate, and a water-cement ratio of 0.40-0.50 per ACI 506R. Compressive strength ranges from 20 MPa (light retaining) to 48 MPa (primary tunnel lining), typically specified as 32-40 MPa for structural work. Accelerating admixtures allow near-vertical and overhead application. Standard structural thicknesses are 75mm, 100mm, 150mm, and 200mm, built up in layers of 50-75mm maximum per pass. Steel fibre reinforcement (25-60 kg/m3) or polypropylene fibres are commonly incorporated to control shrinkage cracking and improve toughness, per EFNARC European Specification for Sprayed Concrete.
- Tunnel primary lining
- Rock slope and embankment stabilisation
- Retaining walls
- Structural concrete repair
- Underground mining roadway support
- Swimming pool shells
- Dam face protection and repair
- Architectural feature walls
- Fire protection to steel structure
- Emergency ground support
Shotcrete was invented by American taxidermist Carl Akeley in 1910, who developed a pneumatic cement gun to repair the Field Museum of Natural History in Chicago. The dry-mix 'gunite' process was patented in 1911 and adopted for swimming pools and tunnel linings throughout the 1920s. The wet-mix process emerged in the 1950s, developed initially in Scandinavia for Norwegian Method of Tunnelling (NMT), which uses unsupported rock spans stabilised by rock bolts and shotcrete rather than steel ribs. By the 1970s, steel fibre reinforcement was introduced by researchers at the US Army Corps of Engineers, dramatically improving toughness and enabling shotcrete to serve as primary tunnel lining without secondary concrete. In Australia, shotcrete gained widespread adoption during the construction of the Sydney Underground Railway extensions in the 1970s (St James to Central). The tunnelling industry standardised on wet-mix fibre-reinforced shotcrete during the Lane Cove Tunnel (2007) and Airport Link (1999) projects. Australian mining adopted shotcrete for coal and metalliferous mine roadway support during the 1980s-90s, replacing timber and steel sets. Today Australia has a sophisticated shotcrete contracting sector with specialists such as Geotech (NSW), Ground Consolidation (QLD), and local aggregate-supplier premixed batches are available from Hanson, Holcim, and Boral in all capital cities.
DISCLAIMER: This specification document is generated from the CLAD Materials Atlas Database. Information is for general guidance only and does not constitute professional engineering advice. Values are typical and may vary by batch, manufacturer, and production run. Verify suitability for specific project applications independently.