SURFACE FINISHES

The final surface of shotcrete can have many types of finishes: Normal gun finish, screeded surface, wood float, sponge finish, steel trowels, patterned finish (blockwork, masonry), simulated “mock rock” and simulated pre-cast panels.

Overview of Shotcrete Spraying Techniques

1. Introduction to Shotcrete Spraying Techniques:

   • Definition of Shotcrete: Shotcrete is mortar or concrete conveyed through a hose and pneumatically projected at high velocity onto a surface or substrate​.

2. Types of Shotcrete Spraying Techniques:

   • Wet-Mix Shotcrete Process: Involves premixing cement, aggregate, and water before delivery to a pump. The mixture is conveyed through a hose to a nozzle where compressed air projects the material onto the surface​.
   • Dry-Mix Shotcrete Process: Cement and aggregates are mixed dry and pneumatically conveyed to a nozzle where water is introduced to wet the mixture before projection​.

Comparative Analysis and Applications

1. Comparison of Wet-Mix and Dry-Mix Processes:

   • Equipment: Wet-mix requires lower maintenance but has higher capital cost. Dry-mix has lower capital cost but higher maintenance​.
   • Mixing and Output: Wet-mix ensures accurate mixing and can handle wet aggregates. Dry-mix is more labor-intensive and less efficient with wet aggregates​.
   • Rebound and Dust: Wet-mix has lower rebound and generates less dust. Dry-mix has higher rebound and dust generation​.
   • Quality and Conveyance: Wet-mix offers consistent quality and is suited for shorter distances. Dry-mix can convey over longer distances but has potentially higher variability in quality​.
   • Applications: Wet-mix is better for high volume applications. Dry-mix is more suited for low volume and remote applications​.

2. Applications and Advantages:

   • Versatility in Application: Shotcrete is used in a wide range of ground-support applications, linings, and building structures.
   • Advantages: Provides rapid and efficient placement, excellent bond strength, and is ideal for restricted access areas​.

For the achievable surface finish of shotcrete is dependent on the skill of the labour and funds available to do the job, plus the mix design which is different for decorative shotcrete compared to structural shotcrete.

For a high value surface finish is usually applied in locations which are highly visible to the public and are usually implemented for aesthetic purposes.

The public generally does not recognize shotcrete that has been subjected to special surface finishing because it looks like commonly cast-concrete or other types of surface such as native rock.

Surface cracking and durability issues should be considered in the process of designing the shotcrete for surface finish.

LINK: Concrete Institute of Australia - Shotcreting in Australia