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Shotcrete

Shotcrete is used for repairing and strengthening various structures such as buildings, tunnels, bridges, reservoirs, viaducts, silos, dams, quays, water towers, tanks, pools etc. Also, it is used as ground support in tunnelling, mining and soil nailing. The term shotcrete is used to define both the material and the method. The material is concrete, mortar or grout and additives and the method is the application of this material by pneumatic pressure through a special hose. The terms gunite or sprayed concrete can also be used.

There are two types of shotcrete, wet and dry mix. For wet-mix shotcrete, all ingredients, including water, are premixed in a concrete plant and introduced into the application equipment. The wet material is pumped to the nozzle by compressed air in order to provide high velocity for placement and consolidation of the material onto the receiving surface. For dry-mix shotcrete, a premix of sand and cement is placed into the delivery system and, by means compressed air, it is conveyed, at high velocity, through a hose to the nozzle, where water is added. The material is consolidated on the receiving surface due to the high impact velocity.

Both wet and dry processes produce a material that exhibits, after hardening, superior properties than high quality conventional concrete (high strength, low permeability, good resistance to weathering and many types of chemical attack, excellent fireproofing qualities). These properties allow shotcrete to be used in most cases as a structural material.

Compared to the dry-mix process, the wet-mix process has the following benefits: improved quality, less dust/improved working environment, less rebound, and improved safety. However, the achieved advancements in both material and equipment technology make the two processes almost interchangeable. Usually, the process is adopted based on: economics, availability of material and equipment, site access and expertise of the contractor.

The experience of the contractor and equipment have a significant influence on the result, the consumption, and thus the resulting strength. Design requirements are verified in the field by using special metallic forms or by coring.

Highlights

  • Reduced time of execution;
  • Reduced cost;
  • High durability;
  • Excellent bond;
  • Instant or rapid capabilities - particularly on complex forms and shapes.