Appropriate Building Material Technology
Centre for Alternative Technology, Wales. July 2011
Ferrocement Septic Tank (abridged) from Julia King on Vimeo.
The above sequence shows the first construction stage of a model for a ferrocement septic tank. One chamber of two is shown here with a hole for an inlet and outlet into the second chamber. This is part of on-going research into appropriate building materials and technology for urban low cost sanitation which will be expanded upon throughout the year.
Ferrocement is a thin-shell reinforced concrete made of wire mesh, sand, water, and cement, which possesses unique qualities of strength and serviceability. It can be constructed with a minimum of skilled labour and utilizes readily available materials. Ferrocement is particularly suited to developing countries for the following reasons:
- its basic raw materials are available in most countries
- it can be fabricated into almost any shape to meet the needs of the user
- more durable than wood and cheaper than imported steel
- skills are quickly acquired, and include skills traditional in many developing countries
- does not need heavy plant machinery
- is labour-intensive as opposed to machine or factory based systems
The great advantage of wire-reinforced concrete (ferrocement) over conventional reinforced concrete is its ability to resist shrinkage cracking during curing, its resistance to severe cracking under tensile load, and the need for only one set of forms for construction when the concrete is applied by hand o one side. For smaller objects no formwork is needed. Un reinforced concrete is strong under compressive loads but very weak at resisting tensile or pulling loads. Conventional concrete is designed to overcome this characteristic by allowing the tensile loads to be taken completely on the reinforcing bars which results in think concrete sections. In ferrocement the dense distribution of wire mesh allows the loads to be taken throughout the complete layer and will prevent the concentration of critical stresses in planes of weakness.