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Ferrocement is a thin-walled reinforced concrete formed by small-diameter wire meshes placed uniformly throughout the cross-section in cement mortar. Its tensile strength-to-weight ratio is very high compared to reinforced concrete, showing a superior cracking behavior.
Though ferrocement is not a sustainable material, it is cost-effective and highly efficient. It is fireproof, strong, economical, rust-free, earthquake resistant, and does not rot or blowdown in inclement environmental conditions.
Materials required for ferrocement construction
The conventional ferrocement has two main components- the reinforcing mesh and mortar mix. The commonly used material for ferrocement construction is described in detail below.
1. Cement mortar mix
The cement mortar is a mixture of cement, sand, admixtures, and water. Generally, the mix used in the construction of ferrocement has a cement-sand proportion of 1 part of cement to 1.5-2 parts of sand. The mix's water-cement ratio has to be as low as possible to have good workability and quality.
Usually, Ordinary Portland Cement is used in the cement mortar mix of ferrocement construction, whereas Rapid hardening Portland cement can be used in colder regions. In some cases, the sulfate-resistant portland cement is used either partly or completely to counter sulfate attack.
The recommended quantity of cement is 500 to 600 kg per cubic meter. Using a lesser quantity of cement will decrease the overall strength and increase permeability.
To attain a high-grade impervious mortar, it is necessary to have clean, good, and well-graded sand (ordinary river sand can be used). It should not contain pyrites, sulfates, or chemically active elements that could be harmful to the mixture. The sea sand could also be used after washing off its saline compositions. It is recommended to use sharp sand (also known as grit/river sand) without non-crystalline minerals. The maximum allowable grain size of the sand is 2.36mm, and the fineness modulus should lie within the range of 2.5 to 3.0.
Water is necessary to form a workable mix and facilitate the hardening of concrete through hydration. Utmost care should be taken that the water used for the mixture is potable and free from harmful salts. A pH of 7 or higher is preferred.
A wide range of admixtures are available in the market today. The admixture could be chosen after testing parameters such as its effect on reinforcement and increase/decrease of mortar strength after mixing.
Admixtures can improve the workability of the mortar and can reduce the water-cement ratio. Air-entraining agents should be avoided.
2. Skeleton steel
The skeleton steel forms the skeleton of the structure and consists of steel rods and staples and wire fabric. The basic function of the skeleton steel is to support the steel wire mesh that plays a major role in imparting structural strength, especially in boats, barges, etc.
The steel rods used are 3 to 8mm thick and their thickness varies according to its location from 6mm to 20mm. They are spaced at a distance of 7.5cm to 12cm from each other. Mostly, mild steel, Fe 415, or Fe 500 bars are used in the skeleton. The bars should be checked and must be free from rust, dust, and other impurities before use.
The staples and wire fabric helps retain the basic skeleton structure.
3. Steel mesh reinforcement or fiber-reinforced polymeric meshes
The steel mesh reinforcement is generally made of galvanized steel wires with diameters ranging from 0.5mm to 1.5mm and spaced out at a center to center distance of 6mm to 20mm. The wires are either woven using natural fibers or welded together to form a mesh. The woven mesh has a square opening, whereas the welded wire mesh has a rectangular or hexagonal openings.
Expanded metal lath is stiffer and provides better crack control and impact resistance. It cannot be used in structures having sharp curves.
Fiber-reinforced polymeric meshes can be used as a replacement to the steel mesh reinforcement. The use of polymeric fiber reduces the overall cost of materials and increases durability and wards off the threat of corrosion.
In addition to the above three components, short steel wires and other fibrous materials can also be added to the mortar mix to control cracking.
Ferrocement is a form of thin-wall reinforced concrete.
The basic materials required for ferrocement construction are cement mortar mix, skeleton steel, and mesh reinforcement.
The intrusion of moisture and air will facilitate corrosion and reduce the durability of the ferrocement.
READ MORE: Ferrocement Water Tank Construction and Uses