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.
Dept. of Civil Engineering, GEC Ajmer
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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
itself.Dept. of Civil Engineering, GEC Ajmer
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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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