FERROCEMENT1. INTRODUCTIONThe term ferrocement is most commonly
applied to a mixture of Portland cement and sand reinforced with
layers of woven or expanded steel mesh and closely-spaced
small-diameter steel rods rebar. It can be used to form relatively
thin, compound curved sheets to make hulls for boats, shell roofs,
water tanks, etc. It has been used in a wide range of other
applications including sculpture and prefabricated building
components. The term has been applied by extension to other
materials including some containing no cement and no ferrous
material. These are better referred to by terms describing their
actual contents.The term "ferrocement" was given to this product by
its inventor in France, Joseph Monier. At the time, (1850's) he
wanted to create urns, planters, and cisterns without the expense
of kiln firing. In 1875 he created the first steel and concrete
bridge. The outer layer was sculpted in its wet state to mimic
rustic logs, thereby also introducing Faux Bois concrete into
practice. (Recent trends have "ferrocement" being referred to as
Ferro concrete or Reinforced concrete to better describe the end
product instead of its components. By understanding that aggregates
mixed with Portland cement form concrete, but many things can be
called cement, it is hoped this may avoid the confusion of many
compounds or techniques that are not Ferro concrete.)Ferro concrete
has relatively good strength and resistance to impact. When used in
house construction in developing countries, it can provide better
resistance to fire, earthquake, and corrosion than traditional
materials, such as wood, adobe and stone masonry. It has been
popular in developed countries for yacht building because the
technique can be learned relatively quickly, allowing people to cut
costs by supplying their own labor. In the 1930s through 1950's, it
became popular in the United States as a construction and sculpting
method for Novelty architecture, examples of which created
"dinosaurs in the desert", or a "giant pair of cowboy boots and
hat" for a service station.
1.1 CONSTRUCTIONThe desired shape may be built from a
multi-layered construction of mesh, supported by an armature or
grid, built with rebar and tied with wire. For optimum performance,
steel should be rust-treated, (galvanized) or stainless steel. (In
early practice, in the desert, or for exterior scenery
construction, "sound building practice" was not considered or
perhaps unknown as it grew in some cases, from a folk craft
tradition of masons collaborating with blacksmiths.) Over this
finished framework, an appropriate mixture (grout or mortar) of
Portland cement, sand and watered/or admixtures is applied to
penetrate the mesh. During hardening, the assembly may be kept
moist, to ensure that the concrete is able to set and harden slowly
and to avoid developing cracks that can weaken the system. Steps
should be taken to avoid trapped air in the internal structure
during the wet stage of construction as this can also create cracks
that will form as it dries. Trapped air will leave voids that allow
water to collect and degrade (rust) the steel. Modern practice
often includes spraying the mixture at pressure, (a technique
called Shotcrete,) or some other method of driving out trapped
air.Older structures that have failed offer clues to better
practices. In addition to eliminating air where it contacts steel,
modern concrete additives may include acrylic liquid "admixtures"
to slow moisture absorption and increase shock resistance to the
hardened product or to alter curing rates. These technologies,
borrowed from the commercial tile installation trade, have greatly
aided in the restoration of these structures. Chopped glass or poly
fiber can be added to reduce crack development in the outer skin.
(It should be noted that chopped fiber could inhibit good
penetration of the grout to steel mesh constructions. This should
be taken into consideration and mitigated, or limited to use on
outer subsequent layers. Chopped fibers may also alter or limit
some wet sculpting techniques.)1.2ECONOMICSThe economic advantage
of Ferro concrete structures is that they are stronger and more
durable than some traditional building methods Depending on the
quality of construction and the climate of its location, houses may
pay for themselves with almost zero maintenance and lower insurance
requirements. Water tanks could pay for themselves by not needing
periodic replacement, if properly constructed of Reinforced
concrete.Ferro concrete structures can be built quickly, which can
have economic advantages. In inclement weather conditions, the
ability to quickly erect and enclose the building allows workers to
shelter within and continue interior finishing.In India, Ferro
concrete is used often because the constructions made from it are
more resistant to earthquakes. Earthquake resistance is dependent
on good construction technique and additional reinforcement of the
concrete.In the 1970s, designers adapted their yacht designs to the
then very popular backyard building scheme of building a boat using
ferrocement. Its big attraction was that for minimum outlay and
costs, a reasonable application of skill, an amateur could
construct a smooth, strong and substantial yacht hull. A
ferrocement hull can prove to be of similar or lower weight than a
fiber (fiberglass), aluminum, or steelhull.New methods of
laminating layers of cement and steel mesh in a mold may bring new
life to ferrocement boat-building. A thorough examination of
Reinforced concrete and current practice would benefit the boat
builder.1.3 ADVANTAGESThe advantages of a well built Ferro concrete
construction are the low weight, maintenance costs and long
lifetime in comparison with purely steel constructions. However,
meticulous building precision is considered crucial here.
Especially with respect to the cementitiouscomposition and the way
in which it is applied in and on the framework, and how or if the
framework has been treated to resist corrosion.When a Ferro
concrete sheet is mechanically overloaded, it will tend to fold
instead of break or crumble like stone or pottery. So it is not
brittle. As a container, it may fail and leak but possibly hold
together. Much depends on techniques used in the construction.1.4
DISADVANTAGESThe disadvantage of Ferro concrete construction is the
labor intensive nature of it, which makes it expensive for
industrial application in the western world. In addition, threats
to degradation (rust) of the steel components is a possibility if
air voids are left in the original construction, due to too dry a
mixture of the concrete being applied, or not forcing the air out
of the structure while it is in its wet stage of construction,
through vibration, pressurized spraying techniques, or other means.
These air voids can turn to pools of water as the cured material
absorbs moisture. If the voids occur where there is untreated
steel, the steel will rust and expand, causing the system to
fail.In modern practice, the advent of liquid acrylic additives and
other advances to the grout mixture, create slower moisture
absorption over the older formulas, and also increase bonding
strength to mitigate these failures. Restoration steps should
include treatment to the steel to arrest rust, using practices for
treating old steel common in auto body repair2. APPLICATIONS OF
FERROCEMENT2.1 HOUSING APPLICATIONSFerrocement is considered as a
suitable housing technology for developing countries attested by
the increasing number of easily built and comfortable ferrocement
houses.Ferrocement houses utilizing local materials such as wood,
bamboo or bush sticks as equivalent steel replacement have been
constructed in Bangladesh, Indonesia and Papua New Guinea. Precast
ferrocement elements have been used in India, the Philippines,
Malaysia, Brazil, Papua New Guinea, Venezuela and the Pacific for
roofs, wall panels and fences. In Sri Lanka, a ferrocement house
resistant to cyclones has also been developed and constructed. A
pyramidal dome over a temple in India and numerous spherical domes
for mosques in Indonesia have been constructed with ferrocement.
The choice was dictated by low self-weight, avoidance of formwork
and availability of unskilled labor. In Israel, ferrocement is used
to improve existing houses. Precast corrugated roof units
reinforced with local fibers comparable to asbestos cement sheet
and galvanized iron sheet are in used in Singapore, India,
Indonesia, Peru and Zimbabwe.
Ferrocement Housing
Location:
Bombay, India
Usage:Residential house
Parts in Ferrocement:CASTONE panels (Structural wall panels)
Cost:US$30/m. sqr.
Year of Construction:1980
Additional Information:Prefabricated panels, joining with nuts
and bolts, stability of the structure is achieved by box type
configuration.
Name: Ferrocement Tenements
Location:Bombay, India
Usage:Low-cost housing
Parts in Ferrocement:CASTONE panels
Cost:US$32 - US$ 64 /m. sqr.
Year of Construction:1980
Additional Information:360 units of one storey and 9260 units of
two storey tenement houses built.
Name: Ferrocement Housing
Location:Israel
Usage:Residential house
Dimensions:Covered area of 52 sq. meter
Cost:US$310 per sq. meter (Composed to US$ 400 to US$ 500 per
sq. meter for concrete in 1982)
Additional Information:Temperature inside the house is cool and
pleasant.
2.2 MARINE APPLICATIONFerrocement has been adapted to
traditional boat designs in Bangladesh, China, India, Indonesia and
Thailand due to timber shortages.In China, 600 ferrocement boat
manufacturing units produce annual capacity of 600,000 to 700,000
tonnages. Ferrocement boats are divided into four categories
according to usage: farming boats, fishing boats, transport boats
and working boats. In countries like Hong Kong, Korea, India,
Malaysia, Philippines, Sri Lanka and Thailand, ferrocement boats
generally conform to western standards. In Hong Kong, India and Sri
Lanka, most of the ferrocement crafts constructed are used as
mechanized fishing trawlers In addition, the Southeast Asian
Fisheries Development Center, Philippines, has used ferrocement
tanks for prawn broodstock and ferrocement buoys for a floatation
system in the culture of green mussels. This is the first large
scale use of ferrocement for these purposes. In Africa, ferrocement
boatyards have been successfully established in Kenya, Sudan and
Malawi. The boatyards are now self supporting under the management
of local staff trained by the consultants. The objective of these
boatyards is to provide rural fisherman opportunities to explore
the fishable grounds to increase their income. Ferrocement vessels
have also been constructed for Guinea Bessau.
2.3 AGRICULTURE APPLICATIONAgriculture provides the necessary
resource bas for economic growth in developing countries. The use
of ferrocement technology can contribute towards solving some of
the production and storage problems of agricultural
produce.Ferrocement has been used for grain storage bins in
Thailand, India and Bangladesh to reduce losses from attack by
birds, insects, rodents and molds.Thailo, a conical ferrocement
bin; was designed and first constructed at the Asian Institute of
Technology (AIT), Bangkok, Thailand. Storage capacities range from
one to ten tons (1000 kg to 10000kg). This bin has proved to be
structurally sound and construction has provided adequate
protection to the produce against rodent, insect and bird attacks.
The bin costs well within the means of the farmers. In Nigeria, the
traditional timber thatch cub for food grain storage has been
improved with ferrocement. These bins are called "Ferrumbu".The bin
developed at the Structural Engineering Research Center (SERC),
Roorkee, India, is manufactured in the form of precast elements and
assembled on site. In Bangladesh, ferrocementsilos six to ten tons
(6000 kg to 10000 kg) capacity reinforced with bamboo and two
layers of no. 20 gage hexagonal mesh on both sides of the bamboo
have been proven satisfactory. In Ethiopia, traditional underground
pits are lined with ferrocement and provide with an improved
airtight lid, for a truly hermatic and waterproof storage chamber.
The use of ferrocement canal lining prevent seepage loss according
to the research on the construction techniques and behavior of
ferrocement canal linings undertaken at AIT. Ferrocement canal
linings and aqueducts are now in use in China, Indonesia and
Vietnam.
2.4 WATER AND SANITARY APPLICATIONFerrocement can be effectively
used for various water supply structures like well casings for
shallow wells, water tanks, sedimentation tanks, slow sand filters
and for sanitation facilities like septic tanks, service modules
and sanitary bowls. Ferrocement water tanks of 20 to 2000 gallon
capacity are mass produced in India. In Thailand and Indonesia,
ferrocement and bamboo-cement rainwater colloection tanks are being
built on a self help basis by villagers under the supervision of an
apprapriate technology group to provide clean drinking water.
Ferrocement water tanks over multistory buildings in Singapore,
Bangladesh and the Solomn Island. Bamboo-cement well casings have
been built in Indonesia to prevent contamination of the water.
Prefabricated service modules have been developed and
constructed in the Solomn Islands and India. A service module is a
unit which provides water supply for drinking and washing toghethe
with toilet facilities. Ferrocement septic tanks have been in used
in Thailand, India, Indonesia, Philippines and Papua New Guinea
while ferrocement toilet bowls have been developed and constructed
in Thailand and Bangladesh.2.5 RURAL ENERGY APPLICATIONBiogas and
solar energy are two alternate sources of energy for the rural
areas in which ferrocement can be of use in their production.
Biogas can be used for cooking, lighting and refrigeration. In
Thailand and India, biogas digesters and biogas holders have been
constructed with ferrocement which lead to a considerable cost
reduction. Ferrocement has also been used as digester lining when
bricks are not economically available. More ferrocement biogas
digesters will promote conservation of timberlands and it will
encourage farmers to raise livestock providing additional income to
the family.2.6 MISCELLANEOUS APPLICATIONFerrocement is proving to
be a technology that can respond to the diverse economic, social
and cultural needs of man.Ferrocement has been used to strengthen
older structures, a medium for sculpture and for many other types
of structures. Ferrocement as a medium for sculpture proves its
versatility and the unlimited dimension to which it can be used.
Ferrocement in art is an exciting development and it open new
horizons.
3. CONSTITUENT MATERIALS1. Cement2. Fine Aggregate3. Water4.
Admixture5. Mortar Mix6. Reinforcing mesh 7. Skeletal Steel8.
Coating
4. FERRO CEMENT JARS:
Ferrocement consists of a thin sheet of cement mortar which is
reinforced with a cage made of wire mesh and steel bars. Because
ferrocement is structurally more effectient than masonry, the
thickness of the walls of the container are as low as 10 to 15 mm.
Ferrocement components can be casted in any shape using suitable
moulds. The technology is extremely simple to implement, and even
semi-skilled workpersons can learn it with ease. Ferrocement
requires only a few easily available materials - cement, sand,
galvanized iron (GI) wire mesh, and mild steel (MS) bars - in small
amounts compared to masonry and RCC.
4.1 POT SHAPED CONTAINERThe process of construction of a pot
shaped Ferro cement container is quite simple. The only materials
required are hessian cloth, chaff (waste from agricultural
produce), GI wire mesh, MS bars, cement and sand.4.1.2Preparation
of mould: The hessian cloth is first stitched into a sack
resembling the shape of a container. It is then filled with chaff
that is compacted in layers. Dry leaves or dry grass can also be
used in place of chaff. Once the sack is filled with the filler
material, it is beaten into the required shape by a wooden bat.
Source: Catch water
4.1.3Laying of reinforcement:A GI wire mesh (22-26 gauge - see
table) is tied around the mould leaving sockets at suitable
locations for inlet, over flow and cleaning pipes. Tying 6 mm
diameter MS bars at wide intervals both horizontally and vertically
strengthens the reinforcement cage.4.1.4 Preparation of cement
mortar for plastering:Cement mortar of suitable proportion (see
table) is prepared, having water content equal to 0.45 times the
volume of cement.Capacity of containerLitresThickness of the
wallsRatio Cement: sandThickness of GI wire (guage)
400101:326
600101:324
900121:2:524
1500151:2:522
4.1.5 Plastering:The mortar is plastered in two layers along the
wall thickness, the second layer being applied 24 hours after the
first. The Ferro cement wall normally has a thickness of 10 to 15
mm, depending on the volume of the container. The cement mortar is
applied ensuring a minimum clearance (cover) 3 mm between the
reinforcement mesh and the outer surfaces of the wall.
4.1.6 Removal of mould:The mould of the container is removed 24
hours after casting of the wall is completed, by removing the
filler material. The container can be brought into use after 10
days of wet curing.
4.2 Ferrocement Tank using Skeletal Cage:
4.2.1 Phases of construction
i Selection of siteiiMarking for circular foundation:Choose the
diameter of foundation (Df) for required storage capacity from the
tableCapacity of storage tank (litres)5,000 and 6,0007,000 and
8,0009,000 and 10,000
Df2.40 m2.70 m3.00 m
iii Excavation for foundationiv Compacting the excavated pitv
Placing cement concrete in foundation:Prepare Plain Cement Concrete
of 1:4:8 mix ( 1 cement: 4 sand: 8 stone aggregate of 40mm size)vi
Erection of mould/ Preparation of elements of skeletal cage
a. Preparation of Elements of Skeletal Cage:
Source: Action for food Production and United Nations Children's
Fund, Rooftop rainwater harvesting systems
Skeletal cage is an assembly of 4 types of elements (of
different shapes) made from mild steel rods. They are 'U' shaped
elements 'L' shaped elements '' shaped elements 'O' shaped
elementsDimensions of elements for tank capacities 5,000 litres to
10,000 litresElementNo.DimensionsCapacity of Storage Tank (in
litres)
5,0006,0007,0008,0009,00010,000
U2H1.82.11.92.11.92.1
W12.052.052.352.352.652.65
4H1.82.11.92.11.92.1
LW20.820.820.950.951.051.05
8H1.82.11.92.11.92.1
LW30.50.50.60.60.650.65
D19Nos11Nos10Nos11Nos10Nos11Nos
2.052.052.352.352.652.65
1D21.251.251.411.411.601.60
1D30.620.620.710.710.840.80
b. Assembling the elements: Place the two 'U' shaped rods
vertically over the foundation, perpendicular to each other Place
the outer, middle and inner rings over the two 'U' shaped rods,
coinciding with the circular marking and tie the intersections with
binding wires Place and tie 4 'L' shaped elements on the center
marking of each quarter, each rod extending upto the inner most
ring Place and tie 8 '' shaped elements on the remaining markings,
each element extending to the middle ring Place and tie all the
rings of diameter 'D1" over the vertical reinforcement at a uniform
spacing of 20 cm For providing cylindrical shape to the skeletal
cage, fix cross bars at the top of skeletal cage and ie with ropes,
3-4 vertical rods to wooden pegs pegged to the ground.c. Tying of
mesh over skeletal cageSelect the reinforcement mesh that suits the
capacity of the tank from the table below: Capacity of Tank
(Lt)5,000 & 6,0007,000 & 8,0009,000 & 10,000
Specification of wire meshChicken wire mesh of 22 gauge and 12
mm (1/2") openingChicken wire mesh of 20 gauge and 25 mm (1")
openingChicken wire mesh of 20 gauge and 25 mm (1") opening
Source: Action for food Production and United Nations Children's
Fund, Rooftop rainwater harvesting system
Tie the mesh with binding wire to the skeletal cage at all
intersections of elementsProvide a tucking length of 30 cm (1 foot)
at the base Project the mesh 10 cm above the top of the skeletal
cage Cut the skeletal cage and insert pipe fixtures such as
overflow pipe, drain pipe and tap at appropriate places as given in
tableOver flow pipe10 cm below the top of cage
Drain pipe5 cm above the foundation
Tap10 cm above the foundation
viii. Plastering the tank's outside wall Prepare cement slurry
(cement mixed with water) and add anti-rust agent (chrometrioxide
tablets) Apply one coat of cement slurry (mix of cement and water)
over the mesh using a painting brush Prepare cement mortar of
depending on capacity of tank Apply the first coat of cement mortar
on the outer surface at a thickness of 1 cm. Care has to be taken
to fill the space between the two layers completely. This could be
done by using a GI sheet, slightly curved in shape to be held close
to the skeletal cage from inside by a person, while cement mortar
is applied by another from outside Leave 10 cm of mesh projected
above the cage unplastered in order to join the skeletal dome to
the tank After two hours, apply a second coat of mortar of a
thickness of 1 cm.ix. Plastering the tank's inside wall After two
hours of outside plastering, apply cement slurry to the inner
surface of the tank wall Prepare cement mortar of 1: 3 mix and add
waterproof compound in liquid form Apply first coat of cement
mortar of 1 cm thickness on the inner surface, starting from bottom
of the tank moving laterally and progressing towards the top After
two hours, apply second coat of mortar to attain a total wall
thickness of 2 cm Apply cement slurry as final coat on outer and
inner surfaces of tank and smoothen using coir brushx. Removal of
mouldxi. Casting of tank floor: Sprinkle cement slurry over the
foundation concrete Prepare plain cement concrete of 1:2:4 mix ( 1
cement: 2 sand: 4 stone aggregate of 12 mm size), pour it over the
base and compact to a thickness of 50 mm (2 inch) Finish the floor
base using cement mortar keeping the slope towards the drain pipe
Finish the wall and base joints (inner and outer) with cement
mortar Twelve hours after setting the tank floor, add waterproof
compound (liquid form) with cement slurry and apply it over inside
surface of the tank and smoothen with coir brush.xii. Curing the
tank Cure the tank for 14 days by pouring water thrice a day or
covering the tank with wet gunny bags In coastal areas, after
curing for 14 days, apply rust proof paint over the outer surface
of tank wallxiii. Construction of roof for the tank An assembly of
mild steel elements is prepared as a skeletal frame for the roof.
Chicken wire mesh is tied over it and plastered in cement mortar
The roof is provided with two openings. One is an opening of
diameter 35 cm for accommodating the filter container. Another is a
manhole with a 60 cm opening. The opening for the filter will be on
one side of the roof. The manhole is provided at the centre of
dome
5. COST EFFECTIVENESS OF FERRO-CEMENT STRUCTURES The type of
economic system. Type of applications.Relative cost of labor.
Capital and local tradition of construction procedure.Doesnt need
heavy plant or machinery. Low cost of construction material
LIST OF PICTURES
Fig1: Typical cross section of Ferro-cement structure
Fig2:REINFORCING MESH
Fig3: Residential and Public Buildings
Fig4: Industrial Structures
Fig5: Transportation Structures
CONCLUSIONFerro-cement come into wide spread use only in the
last two decades and still in its infancy. Sufficient design
information is available and adequate field experience has been
acquired to enable safe design and construction of many types of
Ferro-cement structures.Whether it can economically compete with
alternate materials depends on the type and location of
application. For industrially developed countries, Ferro-cement
seems economical for medium storage tank, roofshells, boat, tank
and the ease of forming complicated shapes and lighter weight of
Ferro-cement can be safely exploited.
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