2. What is Guniting
The guniting is the most effective process of
repairing concrete work which has been
damaged due to inferior work or other
reasons. It is also used for providing an
impervious layer.
The gunite is a mixture of cement and sand,
the usual proportion being 1:3. A cement gun
is used to deposit this mixture on the
concrete surface under a pressure of about
20 to 30 N/cm2.
3. Key points :-
Gunite is also known as shotcrete or
pneumatically applied mortar.
It can be used on vertical and
overhead, as well as on horizontal
surfaces and is particularly useful for
restoring surfaces spalled due to
corrosion of reinforcement.
Gunite is a mixture of Portland
cement, sand and water, shot into the
place by compressed air.
Guniting is basically used in swimming
pool, dams, tanks, etc.
5. Mixture:
A cement-sand mixture in the ratio of 1:2 or 1:3 depending upon the
requirement, is applied at high pressure over the surface with the help
of specialized equipment.
Guniting is extensively used to rehalibate concrete bridges, dams,
spillways, buildings, etc.
7. WHAT IS THE PROCEDURE OF GUNITING ?
The cement is mixed with slightly moist sand and
then necessary water is added as the mixture
comes out from the cement gun. A regulating valve
is provided to regulate the quantity of water.
The surface to be treated is cleaned and washed.
The nozzle of gun is generally kept at a distance of
about 750 mm to 850 mm from the surface to be
treated and the velocity of nozzle varies from 120
to 160 m/sec.
Sand and cement are mixed dry in a mixing chamber,
and the dry mixture along a pipe or hose to a nozzle,
where it is forcibly projected on to the surface to be
coated.
The flow of water at the nozzle can be controlled to
give a mix of desired stiffness, which will adhere to the
surface against which it is projected.
9. Spraying of concrete
There are two different methods of spraying:
- Dry process spraying
- Wet process spraying
Dry process spraying is the process in which the mixture of damp sand and cement
is passed through the delivery hose to the nozzle and the water is mixed at that
time.
Water cement ratio should be between 0.33 and 0.50
This process is often used for repair work.
It is because of its fast application process and restoration of structural strength
at early stage
The performance characteristics of dry sprayed concrete are they have good
density and high strength.
It has very good bond to a suitable substance.
These advantage make it more variable than conventional concrete abd wet process
sprayed concrete.
11. Quality finish
Distance of spraying should be about 0.6m to 1.5m from treatment surface.
Angle of spraying should as far as possible perpendicular to treatment
surface.
Formed in successively from top down without gaps or slumps.
Freshly gunite surface should be protected from rain or strong sunlight.
Wet slope surface should be allowed to dry by covering with tarpaulin for a
few days before guniting to ensure good bonding between gunite and
slope surface,
13. WHAT ARE THE ADVANTAGES OF GUNITING ?
Following are the advantages of guniting
The high compressive strength is obtained. Strength
of about 56 to 70 n/mm2 at 28 days is generally
obtained.
The high impermeability is achieved.
The repairs are carried out in any situation in a short
time
