Ferrocement Concrete- Construction, Applications and Advantages

Ferrocement Concrete-Construction, Applications and Advantages

Conventional RC members are too heavy, brittle, cannot be satisfactorily repaired if damaged, develop cracks and reinforcements are liable to be corroded. Ferrocement concrete consisting of wire meshes which are impregnated with rich cement mortar mix. The wire mesh is usually of 0.5 to 1mm dia wire at 5mm to 10mm spacing and cement mortar of cement-sand ratio of 1:2 or 1:3 with W/C ratio of 0.4 to 0.45.

The ferrocement elements are usually of the order of 2 to 3 cm in thickness with 2 to 3mm external cover to the reinforcement. Steel content in ferrocement concrete varies from 300kg to 500kg/m3of mortar.  The basic idea behind this material is that concrete can undergo large strains depends on the distribution and subdivision of reinforcement throughout of the mass of the concrete. The development of Ferrocement depends on the suitable casting techniques for the required shape

Ferrocement Concrete

Advantages of ferrocement concrete

o Simplicity of construction
o Lesser dead weight of the elements due to their small thickness
o High tensile strength
o Less crack width
o Easy repairability
o Non corrosive nature
o Easier mouldability to any shape
o Saving in basic materials: cement and steel.

Method of casting or construction of ferrocement concrete

Hand plastering(without any form work)

– A reinforced cage is made using small diameter steel rod reinforcement bent to the required shape, usually cylindrical
– This frame provides the rigidity for the whole structure before plastering
– Then the required number of wire mesh layers is securely tied to the reinforcement cage. The mortar is dashed from outside against a plain curved G. I. sheet held on the other side.
– The whole thickness is built up gradually in two or three consecutive dashing of mortar and then both inside and outside are rubbed smooth
– Hand plastering results in slightly increased thickness of ferrocement member which makes it uneconomical and makes it lose some of the technical advantages

– Use of chicken mesh in this type of construction may not be advisable as it is very flexible and plastering over chicken mesh (without inner mould)may not be satisfactory
– Woven mesh and welded mesh are preferred over chicken mesh
– Control of thickness is difficult- minimum 2cm
– Strength obtained is low compared to other methods
– Less pressure is required to be applied to prevent the distortion of the shape of the cage
– Used in situations where the facilities for other improved methods do not exist
– Can be used for pipes, storage structures and gas holder units
– This type of casting suits cylindrical units of size approximately 60cms in dia and above and also for other irregular shapes for which mould is difficult to make
– Hand plastering is unlikely to result in a water tight structure

 Semi- mechanised process(Using hand plastering)

– An inner cylindrical mould is provided over which one layer of wire mesh is wound
– Over this layer, 4mm wire is tied at a spacing of 15cm in both the directions
– Over this one more layer of chicken wire mesh is wound. This forms the complete wire mesh system of reinforcement.
– The cement plastering is done layer by layer
– As the mesh is tightly wound round the formwork the formwork thickness of formwork is reduced
– Units upto a thickness of 1cm can be produced(two layers of wire mesh)
– The system is termed as semi- mechanised because the mould can be rotated to facilitate dashing of mortar
– Better compaction and better uniformity of thickness than hand moulding
– The wire mesh can be tightly wound over the mould and can be tightened during the casting process. This avoids the looseness in the mesh and uneven thickness
– Advantages of semi mechanised process:
 Does not require any sophisticated equipment or electricity
 The skill can be easily acquired by local people
 Can be adopted at rural areas with ease
 Convenient for cylindrical units of size 1m and above

 

 

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