What is Shotcrete?

SHOTCRETE (wet mix or dry mix) is a mixture of sand, cement, and water. Dry mix is applied through a rubber hose from a cement gun. The materials are mixed in a relatively dry state and are hydrated at the nozzle in a special mixing nozzle.

Hydration begins as the material leaves the chamber and the resulting mixture is shot into place under air pressure.

The pressure application permits shotcrete to be applied to practically any surface at any angle and at a specified thickness.

When properly mixed and applied, Shotcrete has a wider range of applications and is less expensive than concrete that is applied by any other method. It is extremely strong, dense and is highly resistant to weathering and many forms of chemical attack. The ease and speed at which the material can be applied has resulted in the method's ever-increasing use in construction, maintenance, and refurbishment. It is used to resurface and rehabilitate damaged or deteriorated sewers, bridges, dams, water treatment plants, and many other types of masonry construction.

Specifications For Shotcrete

General

Shotcrete is a fine aggregate and cement that is mixed in a dry state in the specified proportions. Water is added to the mixture immediately before its expulsion from the nozzle. The Shotcrete is applied in layers of various thickness by pneumatic pressure with a machine known as a cement gun operated by skilled workers.

Cement

Cement used shall be any type of Portland cement and/ or Lumnite cement (calcium aluminate). This conforms to specification of the American Society of Testing Materials. Each bag of cement shall be deemed to be one cubic foot.

Fine Aggregate

When sand is used it shall be clean, sharp, and reasonably free from clay, loam, and slit. The term "dry" as applied to sand means that it shall have a normal moisture content of from 3 to 8 percent. It shall be well graded from coarse to fine, passing through a 3/8 inch sieve, and have a fineness modulus of 3.0 or less. Other fine aggregates, such as trap rock, lightweight expanded shale, crushed fire clay brick, and so forth, when required to meet specific job problems shall have a graduation as specified above for sand. Water used in mixing shall be fresh, clean, and free from injurious amounts of oil, acid, alkali, or organic matter.

Promotions & Mixing

Shotcrete material shall be mixed in the proportions of one part cement to three or four parts of fine aggregate by volume, depending on the strength desired, with allowance made for bulking. The material shall be thoroughly mixed in a dry state before placing in the hopper of the "Cement Gun." All lumps or particles over 3/8 inch in size shall be removed by screening before placing the mixture in the hopper of the "Cement Gun."

Shotcrete is superior because of its...

  • Strength
  • Density
  • Bonding & Adhesion
  • Weather Resistance
  • Low Water Absorption
  • Abrasion Resistance
  • Chemical Resistance
  • Heat Resistance
  • Ease of Application
  • Coefficient of Expansion