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. (more photographs below)
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 difference between conventional concrete and ferrocement
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 to 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 thick 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.
The first known example of reinforced concrete was a ferrocement boat – Joseph-Louis Lambot’s original French patents on wire-reinforced boats were issued in 1847 not long after the development of portland cement. The technology of the period could not accommodate the time and effort needed to make mesh out of thousands of wires. Instead, large rods were used to make what is now called standard reinforced concrete, and the concept of ferrocement was almost forgotten for a hundred years. In the early 1940’s, Pier Luigi Nervi resurrected the original ferrocement concept when he observed that reinforcing concrete with layers of wire mesh produced a material possessing the mechanical characteristic of an approximately homogenous material and capable of resisting high impact.