Ferro Cement

FERROCEMENT 1. INTRODUCTION The 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.

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1.1 CONSTRUCTION The 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.)

1.2ECONOMICS The 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.

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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 ADVANTAGES The 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 DISADVANTAGES The 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 3

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 repair

2. APPLICATIONS OF FERROCEMENT 2.1 HOUSING APPLICATIONS Ferrocement 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

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Location: Usage: Parts in Ferrocement: Cost: Year of Construction: Additional Information:

Bombay, India Residential house CASTONE panels (Structural wall panels) US$30/m. sqr. 1980 Prefabricated panels, joining with nuts and bolts, stability of the structure is achieved by box type configuration.

Name: Location: Usage: Parts in Ferrocement: Cost: Year of Construction: Additional Information:

Name: Location: Usage:

Ferrocement Tenements Bombay, India Low-cost housing CASTONE panels US$32 - US$ 64 /m. sqr. 1980 360 units of one storey and 9260 units of two storey tenement houses built.

Ferrocement Housing Israel Residential house 5

Dimensions: Cost: Additional Information:

Covered area of 52 sq. meter US$310 per sq. meter (Composed to US$ 400 to US$ 500 per sq. meter for concrete in 1982) Temperature inside the house is cool and pleasant.

2.2 MARINE APPLICATION Ferrocement 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.

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2.3 AGRICULTURE APPLICATION Agriculture 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.

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2.4 WATER AND SANITARY APPLICATION Ferrocement 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 bamboocement 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. Bamboocement 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 APPLICATION Biogas 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 APPLICATION Ferrocement 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. 8

3. CONSTITUENT MATERIALS 1. 2. 3. 4. 5. 6. 7. 8.

Cement Fine Aggregate Water Admixture Mortar Mix Reinforcing mesh Skeletal Steel 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 CONTAINER The 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.

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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 containerLitres

Thickness of the walls

Ratio Cement: sand

Thickness of GI wire (guage)

400

10

1:3

26

600

10

1:3

24

900

12

1:2:5

24

1500

15

1:2:5

22

10

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 site iiMarking for circular foundation: Choose the diameter of foundation (Df) for required storage capacity from the table Capacity of storage tank (litres) Df

5,000 and 6,000

7,000 and 8,000

9,000 and 10,000

2.40 m

2.70 m

3.00 m

iii Excavation for foundation iv Compacting the excavated pit v 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

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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



'ë' shaped elements



'O' shaped elements

Dimensions of elements for tank capacities 5,000 litres to 10,000 litres Element U

No. 2 4

L 8 L

Dimensions

Capacity of Storage Tank (in litres) 5,000

6,000

7,000

8,000

9,000

10,000

H

1.8

2.1

1.9

2.1

1.9

2.1

W1

2.05

2.05

2.35

2.35

2.65

2.65

H

1.8

2.1

1.9

2.1

1.9

2.1

W2

0.82

0.82

0.95

0.95

1.05

1.05

H

1.8

2.1

1.9

2.1

1.9

2.1

W3

0.5

0.5

0.6

0.6

0.65

0.65

D1

9Nos

11Nos

10Nos

11Nos

10Nos

11Nos

2.05

2.05

2.35

2.35

2.65

2.65

1

D2

1.25

1.25

1.41

1.41

1.60

1.60

1

D3

0.62

0.62

0.71

0.71

0.84

0.80

b. Assembling the elements: 

Place the two 'U' shaped rods vertically over the foundation, perpendicular to each other

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

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 'ë' 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 cage

Select the reinforcement mesh that suits the capacity of the tank from the table below: Capacity of Tank (Lt)

Specification of wire mesh

5,000 & 6,000

7,000 & 8,000

9,000 & 10,000

Chicken wire mesh of Chicken wire mesh of Chicken wire mesh of 22 gauge and 12 mm 20 gauge and 25 mm 20 gauge and 25 mm (1/2") opening

(1") opening

(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 table Over flow pipe

10 cm below the top of cage

Drain pipe

5 cm above the foundation

Tap

10 cm above the foundation

viii. Plastering the tank's outside wall 13



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 brush

x. Removal of mould xi. 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. 14

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 wall

xiii. 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.

•

Doesn’t need heavy plant or machinery.

•

Low cost of construction material

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LIST OF PICTURES

Fig1: Typical cross section of Ferro-cement structure

Fig2:REINFORCING MESH

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Fig3: Residential and Public Buildings

Fig4: Industrial Structures

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Fig5: Transportation Structures

CONCLUSION Ferro-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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