Building Materials, Third Edition

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As stated earlier, ferrocement specimens exhibit finer and more numerous cracks than
conventionally reinforced concrete. Research studies have shown that crack width in reinforced
concrete can be reduced by increasing the bond between reinforcement and concrete, by
increasing the distribution of reinforcement and by reducing the thickness of cover. All these
factors are favorable in ferrocement. Crack width is nearly zero at the interface between the
steel and mortar and increases from the interface towards the surface. Therefore the smaller
distance between the interface and the surface of structure, i.e., the cover, the smaller is the
crack width. Specific surface and volume fraction of the reinforcement are found to play a
significant role in the cracking behavior of ferrocement and their influences are described
below.

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The stress and strain at first crack increases with increasing specific surface, up to certain point.
This means that the total bond forces between the steel and the mortar play an important role
in influencing the cracking behavior of ferrocement. After the occurance of first crack, the
number of cracks increase with increasing load. The optimum value of specific surface,
considering stresses at first crack, seems to lie between 1.4 cm^2 /cm^3 to 2.0 cm^2 /cm^3.

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By increasing volume of reinforcement the stress at first crack increases. However, this increase
is different for each size of mesh employed. In addition, it not increases always that smaller the
dimension of the mesh, that is the smaller the spacing between longitudinal wires, the higher
the first crack stress for the same volume.

ApplicationsThe excellent crack control and impermeability characteristics of ferrocement
make it suitable for liquid retaining structures, boat building, gas containers, caissons, canal
lining, etc. Since it is cheaper than steel and R.C.C. and can be cast in thin sections it is most
suitable for low cost roofing, precast units, manhole covers, casings, etc. and is the most
appropriate building material for the construction of domes, vaults, shells, grid surfaces,
corrugated sheets and folded plates.

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Conventional cement concrete is a heavy building material. For structures such as multistorey
buildings it is desirable to reduce the dead loads. Light weight concrete (LWC) is most suitable
for such construction works. Lightweight aggregate concrete is particularly suitable for use
where low density, good thermal insulation or fire protection are required but not all of the
available aggregate are equally suitable for any particular application. It is best produced by
entraining air in the cement concrete and can be obtained by anyone of the following methods:

1. By making concrete with cement and coarse aggregate only. Sometimes such a concrete
   is referred to as no-fines concrete. Suitable aggregates are—natural aggregate, blast furnance
   slag, clinker, foamed slag, etc. Since fine aggregates are not used, voids will be created
   and the concrete produced will be light weight.