- What is Ferrocrete? -
Ferrocrete is derived from the root words ferrous and concrete. Ferrous refers to anything made from iron. And, we are all familiar with concrete, which is made from cement, sand, rocks, and water. Ferrocrete is sometimes referred to as ferrous concrete, and even more commonly as rebar-reinforced concrete.
The combination of iron/steel and concrete forms a building material that far surpasses any other. This is due to the complimentary properties of the two materials. Iron has a very high tensile strength that keeps the ferrocrete from being stretched or bent to the breaking point. Concrete has a very high compressive strength that protects the structure from crushing forces. That's why ferrocrete is used extensively in commercial buildings designed to last centuries.
The primary component of concrete is Portland cement. Cement is a combination of limestone and gypsum that has been ground to a very fine powder. When mixed with water, it forms a very strong adhesive which bonds together the other elements in concrete: sand and stone. The concrete for monolithic domes achieves a higher cured strength than typical driveway concrete because we use a mix that is richer in cement. Whereas your driveway uses a concrete mix that is designed to resist crushing forces of 3000 psi, the concrete in our domes is rated to 6000 psi. Because the dome structure only requires 500 psi to adequately support itself, the extra 5500 psi allows for both protection from the winds of an F5 tornado along with an additional safety factor.
In a monolithic dome, the rebar is tied together in a lattice framework. Concrete is then applied to the lattice using a process that blows the concrete onto it from a hose. Concrete applied in this manner is called shotcrete. It's similar to the process used for forming swimming pools. The force of blowing the concrete also contributes to increasing the strenth of shotcrete over conventionally poured concrete.