Ferrocement

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Ferrocement is both a method and a material used in building or sculpture with cement, sand, water and wire or mesh material - often called the thin shell. Thin shell ferrocement offers strength and economy and has a broad range of applications which include home building, creating sculptures, or building boats and ships.

The building system was originated by the Italian architect Dr. Dante Bini (see www.itsa.info/bini.shtml) to construct 'blow-up' shells and it has been extrapolated by others into hyperbolic catenary structures that derive their rigitity from their complex shape.

To view photos of ferrocement structures from all over the world, check the photo section of http://www.ferrocement.com

Ferrocement.com also has other sections of interest for sculpture and building such as the use of biological organic substances rather than steel, for example. Within the broad concept of ferrocement, or thin shell, is the use of organic fibers and portland cement. The basic idea is as old as mud and wattle, which is mud smeared on a bamboo or some other readily available stick and fiber armature.

In the world of yacht designing, many designers, mostly in the 1970's, adapted their designs to the then very popular backyard building scheme of building a boat in the ferrocement medium. Its big attraction was that, for a minimum outlay and a reasonable application of skill, an amateur could construct a fair (no bumps) strong and substantial yacht hull.

Construction of earthquake resistant buildings

A few companies in India have been experimenting with Ferrocement technology to complement traditional construction materials and techniques. Ferrocement is being used to fabricate a variety of objects, such as water tanks, irrigation channels & drains, pre-fabricated houses, street furniture (bus stops, shelters, benches etc.) and temples.

Ferrocement technology is particularly suited to conditions in developing countries because it is cheaper, lighter and sturdier than brickwork, which has traditionally been the mainstay of most of the building and ancillary construction.

After the 2004 Indian Ocean earthquake and the 2005 Kashmir earthquake, there has been interest in the Indian subcontinent to explore earthquake resistant construction techniques suited to local conditions. Ferrocement is being proposed as a suitable alternative. Its proponents cite the following advantages when compared to brickwork masonry:

The weight of a Ferrocement building is about 25% of an equivalent structure built with conventional 23cm brickwork, and only 10% when compared to a building made out of stone.
The building is entirely a box construction with rigid frames along all three axes.
The building is resting on the ground and is not embedded in the ground, so there is no need for an excavation.
Thus, there is no mechanism to transfer the seismic loads or ground vibrations to the building. However, there is a frictional force between the base blocks and the ground, and assuming that the friction coefficient does not exceed 0.4, it can be very safely presumed that only 40% of the seismic loads are transferred to the building. Moreover, as the self load of the building is only 25% compared to the conventional brick masonry building, the seismic loading on ferrocement building would be only 10% of a conventional brick building.
The advantage conferred by the two factors cited above can be illustrated by examining the scenario if the building experiences a strong earthquake of intensity 7.5 on the Richter scale
# The effective seismic loading on the Ferrocement building is only 10%, therefore the effective intensity of the tremors would be comparable to an earthquake of 6.5 – a huge reduction.
# The building weighs only a quarter of a brick building, therefore the force experienced by the Ferrocement building for the same earthquake would be 25% of the conventional building. Thus the effective earthquake intensity would be reduced even further to 5.9.
Ferrocement buildings also have the advantage of ‘’Windscreen Effect’’ – i.e. the material does not disintegrate upon impact. Ferrocement walls and roofs, being reinforced with steel mesh, do not move and fall from their location, even when damaged by an earthquake. This factor nullifies the major cause of casualties in any earthquake.
Debris removal is a major task after an earthquake and often takes lot of time and hinders relief and rescue efforts. Ferrocement buildings are very easy to remove, even when damaged. Ferrocement walls and roofs are joined together by the steel mesh reinforcement as one large chunk, which can be easily moved by a crane or a tractor.
The material required for construction is lightweight and results in major savings on transportation costs. The major construction component is coarse sand, which can usually be sources locally.
The speed of construction is much faster than brickwork masonry.
It is claimed that Ferrocement is eco-friendly when compared to brickwork because bricks are usually made from topsoil baked in coal-fired kilns. However, it should be kept in mind that cement manufacturing is also known to cause high levels of industrial pollution.
Ferrocement walls can be made to insulate against widely varying temperatures in the tropical regions by employing a method of construction where a layer of Thermocol is sandwiched between two layers of Ferrocement. This provides a thermally and acoustically insulated interior.

Yacht hull construction

The hull shape is defined by a basic form-work of curved steel pipes and wooden battens, on which is laid a sandwich of fine wire mesh (chicken wire), steel rods, and more wire mesh, tied together with wire ties. This structure is plastered with a mixture of sand and cement, sometimes with an admixture added. The sand must first be graded so that the sand particles fill all voids in the matrix, and then washed to remove all clay or earth particles. The plaster mix must remain relatively dry during the process - too much water weakens the result - and is pushed by hand through the wire sandwich taking care to not leave any air voids. A mechanical vibrator is handy for persuading the mortar to move into difficult places. The result is smoothed off by long battens moved by hand after a few hours to achieve a fair hull, with care taken to ensure sufficient depth of mortar covering the outside layer of wire. Then the hull must be cured by keeping it damp for 30 days.

If built upside down the hull must be turned over with a crane, and the deck structure is then completed in a similar way.

When all is cured, paint or fibreglass finish the job. The supporting formwork is then stripped out and the fitout may commence.

[Pictures] and a [detailed description] of building here.

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