Features & Benefits
Shotcrete has often been described not as a material but as a process. Both wet and dry processes produce a material that exhibits superior hardened properties to high quality conventional concrete, such as high strength, low permeability and high durability.
Although the hardened properties of shotcrete are similar to conventional cast-in-place concrete, the nature of the shotcrete placement process provides additional benefits, such as excellent bond with most substrates and instant or rapid capabilities, particularly on complex forms or shapes.
The properties of both wet- and dry-process shotcrete can be further enhanced through the addition of many different additives or admixtures such as:
- Silica Fume — Provides reduced permeability, increased compressive and flexural strength, increased resistance to alkali and chemical attack, improved resistance to water washout, reduced rebound levels, and allows for thicker single pass applications;
- Air-Entraining Admixtures — Improve pumpability and adhesion in wet-process shotcrete and freeze-thaw durability in both wet and dry processes;
- Fibers — Control cracking, increase toughness values, improve impact resistance and energy absorption; and
- Accelerators — Improve placement characteristics in adverse conditions, allow for thicker single pass applications, increase production capabilities, and reduce the occurrence of fallouts on structures subjected to vibration.
The numerous advantages of the shotcrete process are especially evident when viewed from a sustainability point of view. Unlike many sustainability claims that are based on political or social ideals that are often difficult to quantify and substantiate, the sustainability advantages of the shotcrete process directly and positively impact the economic side of a project, falling in-line with traditional business decisions such as material, labor, and time savings as well as improved quality.
In addition to the following “top ten” sustainability advantages of shotcrete, ASA’s Sustainability page offers a wealth of information on the topic.
- Formwork savings of 50 to 100% over conventional cast-in-place construction;
- Formwork does not have to be designed for internal pressures;
- Complex shapes require very little, if any, formwork;
- Crane and other equipment savings or elimination;
- Labor savings of at least 50% in repair applications;
- New construction speed savings of 33 to 50%;
- Speed of repair reduces or eliminates downtime;
- Better bonding to the substrate, which enhances durability;
- Adaptability to repair surfaces that are not cost-effective with other processes; and
- Ability to access restricted space and difficult-to-reach areas, including overhead and underground.
Methods of Application – Dry Mix or Wet Mix Processes
Dry Mix (sometimes referred to as Gunite)
Wet or Dry?
Although both wet and dry shotcrete have specific benefits, advancements in both material and equipment technology make both processes almost interchangeable. In most applications, the preferred method is determined by:
- Availability of material and equipment;
- Site access; and
- The expertise and preference of the contractor.
Today, rebound levels, dust levels, and properties such as bond strength, compressive strength, and durability can be similar whether the wet or dry method is used.