FERROCEMENT

1Dept. of Civil Engineering, GEC Ajmer

Introduction In 1943 pier Luigi nervi tested and presented in his paper, a

new structural elements, an extremely thin plate of concrete

made of layers of small diameter wire mesh and cement mortar

with sand used as the binder.

WHAT IS FERRO CEMENT ?

“Ferro cement is a type of thin wall reinforced concrete,

commonly constructed of hydraulic cement mortar, reinforced

with closely spaced layers of continuous and relatively small

size wire mesh. The mesh may be made of metallic or other

suitable materials.”

2Dept. of Civil Engineering, GEC Ajmer

Typical section of ferrocement.

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Contd.

Mortar provides the mass and wire mesh imparts tensile strength

and ductility.

When building Ferro-cement structures the sand/cement mortar is

applied to the reinforcing wire with a trowel, never poured like

common concrete work. Often a form is used to provide the

desired shape.

Ferro cement is a super reinforced concrete. It differs from

conventional concrete in that there is a higher ratio of steel to

cement mortar. By altering the cement/steel ratio to make Ferro

cement we actually produce a material, which exhibits properties,

superior to either steel or cement separately. Ferro cement has

many of the properties of steel and yet it will not rust. Although it

looks and feels like concrete it can flex without cracking.

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Ferro-Cement

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TECHNIQUES OF MANUFACTURES

Hand plastering

Semi-mechanised process

Centrifuging and Guniting

MATERIALS USED IN FERRO CEMENT

Cement mortar mix

Skeleton steel

Steel mesh reinforcement or Fiber-reinforced polymeric meshes

• CEMENT MORTAR MIX

Ordinary Portland cement and fine aggregate matrix is used

The matrix constitutes 95% cement mortar & 5% wire mesh of the

composite.

FA (sand), occupies 60 to 75% of the volume of the mortar

Plasticizers and other admixtures are used

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o MIX PROPORTIONS

Sand: cement ratio (by mass) 1.5 to 2.5

Water: cement ratio (by mass) 0.35 to 0.60

o SAND

Free from impurities

o WATER

Free from salts and organic impurities

Minimum to achieve desired workability

PH equal or greater than 7.

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• SKELETON STEEL

It support the steel wire mesh

3 to 8 mm steel rods are used

Thickness varies from 6-20mm according to loading condition

Generally mild steel or Fe 415 or Fe 500 bars are used

Spacing 7.5cm to 12cm

Used to impart structural strength in case of boats, barges etc.

Reinforcement should be free from dust, rust and other impurities.

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• STEEL MESH REINFORCEMENT

Consists of galvanized steel wires of diameter 0.5 to 1.5 mm,

spaced at 6 to 20mm center to center.

Welded wire mesh has hexagonal or rectangular openings

Expanded-metal lath is also used Made from carbon, glass etc.

Chicken wire mesh

PROPERTIES OF FERRO CEMENT

It is very durable, cheap and versatile material.

Low w/c ratio produces impermeable structures.

Less shrinkage, and low weight.

High tensile strength and stiffness.

Better impact and punching shear resistance.

Undergo large deformation before cracking or high deflection.

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ADVANTAGES OF FERRO-CEMENT

It is highly versatile and can be formed into almost any shape for a

wide range of uses

20% savings on materials and cost

Suitability for pre-casting

Flexibility in cutting, drilling and jointing

Very appropriate for developing countries; labor intensive

Good fire resistance

Good impermeability

Low maintenance costs

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Contd.

Thin elements and light structures, reduction in self weight & Its

simple techniques require a minimum of skilled labor

Reduction in expensive form work so economy & speed can be

achieved

Only a few simple hand tools are needed to build any structures

Structures are highly waterproof & Higher strength to weight ratio

than R.C.C

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DISADVANTAGES OF FERRO-CEMENT

Low shear strength

Low ductility

Susceptibility to stress rupture failure

It can be punctured by collision with pointed objects.

Corrosion of the reinforcing material due to the incomplete

coverage of metal by mortar.

It is difficult to fasten to Ferro cement with bolt, screw, welding

and nail etc.

Large no of labours required

Tying rods and mesh together is especially tedious and time

consuming.Dept. of Civil Engineering, GEC Ajmer

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APPLICATIONS OF FERRO CEMENT

Marine Applications

Boats, fishing vessels, barges, flotation buoys

Key criteria for marine applications: light weight, impact

resistance, thickness and water tightness

Water supply and sanitation

Water tanks, sedimentation tanks, swimming pool linings, well

casings, septic tanks etc.

Agricultural

Grain storage bins, silos, canal linings, pipes, shells for fish and

poultry farms

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Cont.

Residential Buildings

Houses, community centers, precast housing elements, corrugated

roofing sheets, wall panels etc.

Rural Energy

Biogas digesters, biogas holders, incinerators, panels for solar

energy collectors etc.

Miscellaneous uses

Bus shelters, pedestrian bridges, Mobile homes, Kiosks, Wind

tunnel, Silos and bins, soil stabilization, chemical resistant

treatment, Precast Ferro cement structures etc.

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Fiber Glass Reinforced Polymer

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Definition:

Fiber-reinforced plastic FRP (also fiber-reinforced polymer) is a

composite made of high-strength fibers and a matrix for binding these

fibers. The fibers are usually glass, carbon, aramid, or basalt.

FRP systems have significant advantages over classical structural

materials including:

o Low weight

o Corrosion resistance

o Ease of application

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Usage:

• FRP is particularly suitable for structural repair and rehabilitation of

reinforced concrete structures.

• FRPs are commonly used in:

Aerospace

Automotive

Marine

Construction industries

Ballistic armor

• It is possible to increase the strength of structural members even

after they have been severely damaged due to loading conditions.

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Repair of concrete surface using FRP

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Installation Procedure:

Applying FRP wraps to structural concrete isn't difficult, but does

require experience. One hundred percent of the quality is due to

workmanship. All of the FRP strengthening system manufacturers

consulted require some level of expertise in an installer.

Step-1: Surface preparation, starting with simply cleaning the concrete

to remove any chemicals or dirt. For most applications, this is followed

by water blasting to achieve a roughened surface profile.

However, there are two types of applications to consider: bond critical

and contact critical.

Bond-critical applications rely completely on the bond of the material

to the surface of the concrete to transfer the stresses. Contact-critical

applications are where the FRP is bonded to itself and creates

confinement of the structural member. An example of a contact-critical

application is a column where the FRP wraps completely around onto

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Step-2: Any defects in the concrete are repaired—holes and cracks

filled with epoxy.

• Sharp edges, corners, and other form lines should be smoothed to

prevent stress concentrations.

Step-3: Placement of the saturated fiber fabrics.

• Fiber sheets come in rolls that are typically 24 or 48 inches wide.

Prior to application, it must be saturated with resin. Resins are color-

coded two-part materials that are premeasured to simplify mixing.

For a small job, you can make a temporary table and pour the

saturating resin over the fabric and work it in with a squeegee, while

for larger jobs saturating machines pass the fabric through a vat of

resin and run it between two steel wringer rollers to force the resin.

• The installer needs to be sure to apply the fabric in the correct

orientation, in the correct locations, and in the correct number of

layers or plies. The fabric can be placed in up to three layers.

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Step 4: A top coat is applied next that can handle PH 2 to 12.

• Fire protective coatings often are applied last and four-hour ratings

can be achieved.

• Curing takes about 24 hours, which can be accelerated with

temperature.

Step 5: Testing after installation often is required with the most

common tests being a tap test and a pull-off test to check the bond of

the epoxy to the concrete surface.

• Tap tests are just like hammer sounding for concrete delamination.

Pull-off tests usually specify a bond strength of 200 psi.

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Advantages and special properties of FRP:

The most important advantage is that:

FRP has a high s/w ratio.

FRP doesn’t show any yielding or plastic behavior.

FRP composites have tensile stiffness lower than that of steel

Resistance to corrosion so it can be utilized on interior and exterior

structural members in all almost all types of environments

They are devoid of any magnetic field and can offer considerable

resistance to electric sparks, then it is a very good option for the

power industry

FRP is characterized by the ease of application since heavy

equipment is not needed for the rehabilitation hence social effects

are witnessed.

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The other exclusive advantages of fiber reinforced plastics

include:

Commendable thermal insulation

Structural integrity, and fire hardness along with UV radiation

stability

Resistance to chemicals and other corrosive materials.

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