What is Shotcrete? Are Shotcrete and Gunite the Same Things?

In the construction world, this method, known as concrete spraying, sprayed concrete, or technically shotcrete, is the process of projecting concrete onto a surface through a nozzle with the help of high-pressure air. Unlike traditional formwork methods, concrete compacts itself and adheres as soon as it hits the surface.

Before Shotcrete: What Was Done in the Past?

Before shotcrete technology, applying concrete on vertical surfaces or in tunnels was a complete engineering challenge. Workers had to set up complex and costly wood/steel forms, support these forms, and then wait for the concrete to be poured and set. This process caused both weeks of time loss and massive labor and material costs.

A revolution has occurred in construction processes with shotcrete:

• Time Savings: Since it eliminates the formwork installation process, projects started to be completed 30% to 50% faster than traditional methods.

• Cost Advantage: Labor expenses decreased and material waste (formwork timber, etc.) was minimized.

• Accessibility: It has become the only solution in narrow tunnels, steep slopes, and areas requiring slope stabilization where cranes or large forms cannot enter.

The basic principle is the delivery of the material to the surface by passing through a concrete hose at high speed. Two main methods are used today:

• Dry Mix System (Gunite): The method where the material enters dry and meets with water at the nozzle, increasing mobility.

• Wet Mix System: The method where pre-mixed concrete is pumped and dust is at a minimum.

The content of high-quality sprayed concrete consists of more than just cement and water. Depending on the purpose of the application, the following are used:

• Aggregate: Generally screened sand and gravel not exceeding 10-12 mm.

• Accelerators: Chemical additives that ensure the concrete sets as soon as it hits the surface.

• Fiber and Steel Mesh: Fiber-reinforced sprayed concrete or steel meshes are added to provide flexibility and tensile strength to the concrete.

Gunite, often heard in the industry, is actually the ancestor of shotcrete technology and the first commercial name for dry-mix sprayed concrete.

Differences:

• Mixture Structure: While Gunite consists only of sand and cement (fine aggregate), Shotcrete contains larger aggregates and modern additives.

• Application: Today, the term "Shotcrete" is a general name covering both wet and dry systems; "Gunite" is mostly used for thin-layer dry system applications (pool construction, repair works).

• Strength: Shotcrete offers higher strength in heavy structural projects (tunnels, dams) thanks to modern additives.