16-04-2013, 02:32 PM
Ferrocement Water Storage Tanks for Rain Water Harvesting in Hills & Islands
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INTRODUCTION
Rain water harvesting has a special
importance for hill areas and
islands as it can solve the
drinking water problem of population
living there. Since water recharging into
ground is difficult and an immediate
existing need for drinking water can be
met by storing it in suitable and safe
storage structures during rain. This
stored water is consumed during dry
spells. Families residing in these areas
(mostly in scattered locations) can
harvest Rain water using their roof tops
and court yards, easily and successfully.
What is Ferrocement?
Ferrocement is a durable long lasting
cement based composite material -
modified form of reinforced cement
concrete in which the reinforcement is
finely subdivided and dispersed in the
matrix in order to achieve a closely
spaced crack regime coupled with
excellent corrosion resistance and high
impermeability to ingress of water. The
matrix of the composite is modified
cement based microconcrete/mortar
prepared using ordinary portland cement
(33 & 43 gd), well graded medium silt free
coarse sand, specially formulated
admixtures containing bonding agents +
plasticizer + poresealent and water.
Techniques and equipment for vibrating
the thin ferrocement layers (including an
orbital vibrator and a medium frequency
surface vibration device) have been
developed by author for use in
ferrocement jobs. The orbital vibrator
developed is suitable for working over
vertical and horizontal surfaces. Fig. 1 (a)
& 1 (b) shows cross section of two
ferrocement units.
Durability
Many Structures constructed or treated
with ferrocement in India in 1973–74
period are still in excellent performing
condition. The development was
encouraged by the fact that there were
many very old ferrocement boats (Now
more than 120 year old) placed in
European museums. These cases can be
considered as examples of durability of
ferrocement construction.
Many large F.C. Dome structures
constructed in 1976 at B.M. Instt.
Ahmedabad by SERC & Sarabhai
Technology Dev. Syndicate faced the
Gujarat Earthquake without showing
even a single crack. A SHANKH of very
large size and large number of domes have
been constructed at Manan Dham
Ghaziabad using Ferrocement. Very large
number of structures have been treated
for Waterproofing 10 to 20 years ago and
are without any problem. Large number
of these are basements and water bodies.
Ferrocement Tanks
Ferrocement, a cement based composite
construction material - modified form of
reinforced cement concrete has been
found to be an effective & durable
construction materials. It has been very
widely used for construction of water
retaining structure such as tanks. The
technique is very suitable for use in
construction of Storage Tanks in Rain
Water Harvesting schemes in Hills, Plains
& Islands as it involves simple procedure
for construction and easy to find
materials.
Ferrocement tanks are being used all over
the world for domestic / industrial &
commercial purposes, In India SERC
(R/G) developed designs and
construction Techniques for Tanks of up
to 25000 litre capacities for NDWM,
Unicef, CSTE Shimla, CSTE Shillong
which could be constructed using local
masons after short span training. Design
packages were prepared and handed over
to these organisations and the
technology provided has been
extensively used.
The Casting Technology
F.C. tanks are produced using ‘skeletal
cage plastered by hand’ method in most
of the countries outside India. The
thickness for such units comes to about
30 mm even for smaller capacities and
casting speed is also slow. The author
and his group at SERC (R/G) improved
the casting system and bought the
minimum thickness to 20 mm for tanks
upto 2500 l. capacity. The time taken in
casting was also reduced to all most half.
For overcoming these problems, the
author at SERC (G) developed three
casting techniques for fabrication of walls
for cylindrical F.C. tanks upto 25,000 litre
capacity. Use of SERC techniques result
in reduction of wall thickness,
improvement in compactness of mortar,
improved performance, reduction of
construction time and cost when
compared to the traditional casting
system. Two of these processes (given
on sl. 1 & 2) are covered by Indian Patent
No 145250 and have been released to
more than 75 licencees through NRDC,
New Delhi.
SERC Precast Segmental Shell elements casting and assembling
process
Suitable for mass production, long distance transfers and erection
over multi storeyed bldgs or in hill areas and islands. Segments of
a cylinder with designed reinforcement meshes projecting on both
sides for subsequent field assembling, are cast (designed
thickness - 10mm) over permanent or temporary moulds.
The total circumference of the cylinder is divided into 3, 4, 6, 8, 12
or 16 segments. These units are cast separately and cured for
about 7 days and then transported to site. The precast units have
reference number marked over these. The base concrete is cast
using designed reinforcement and segmental units are placed
vertically over the premarked wall point & held in vertical position.
Wire mesh laps (as per design) for projections on both sides are
fixed. M-25 grade mortar/microconcrete is impregnated into the
cage and extra mesh layers are fixed over joint portion and mortar
applied over these meshes also. Fig 3(1) to 3(18) show different
stages of segmental casting process. Base and Roof for segmental
tanks can also be cast in segments and assembled jointed at site
Fig. 3 (19) & 3 (20) show Tank Roof cast in segments. Fig. 4 show
finished 10000 ltr. tanks cast using segmental technique.