Guide to Shotcrete
|Publication Date:||1 June 2016|
Work specified (shotcreting processes)-The work should be classified as either structural or nonstructural. Shotcrete having a specified compressive strength of 4000 psi (28 MPa) or greater is considered structural shotcrete. Shotcreting can be applied by one of two processes: wet-mix or dry-mix. Shotcrete is further described according to the size of aggregate used (coarse or fine). Refer to Table 1.1.1 for fine-aggregate grading (No. 1) and coarse-aggregate grading (No. 2)
Dry-mix process-The dry-mix process consists of five steps and are as follows:
1. All dry ingredients, except water, are thoroughly mixed. Dry ingredients are predampened to contain approximately 6 percent moisture.
2. The cementitious aggregate mixture is fed into a special mechanical feeder or gun called the delivery equipment.
3. The mixture is usually introduced into the delivery hose by a metering device such as a feed wheel, rotor, or feed bowl. Some equipment uses air pressure alone (orifice feed) to deliver the material into the hoses.
4. The material is carried by compressed air through the delivery hose to a nozzle body. The nozzle body is fitted inside with a water ring through which water is introduced under pressure and thoroughly mixes with the other ingredients.
5. The material is jetted from the nozzle at high velocity onto the surface to be shotcreted.
Wet-mix process-The wet-mix process consists of five steps and are as follows:
1. All ingredients, including mixing water, are thoroughly mixed.
2. The shotcrete mixture is introduced into the chamber of the delivery equipment.
3. The mixture is metered into the delivery hose and moved by positive displacement.
4. Compressed air is injected at the nozzle to increase velocity and improve the shooting pattern.
5. The concrete is jetted from the nozzle at high velocity onto the surface to be shotcreted.