Reinforced Concrete Cement
(RCC) structures are widely used in buildings, bridges, dams, and various
infrastructural projects due to their durability and load-bearing capacity.
They are strong enough mechanically, yet vulnerable to deterioration and damage
over time. This deterioration may be due to the weathering action, environmental
factors, overloading, abuses, fire, soil failure, defects in construction, and
also due to natural calamities like flood, tsunami, earthquake etc. Therefore,
it is essential to have a proper maintenance and repair strategy to ensure the
safety, functionality, and aesthetics of the concrete assets.
The need for repair and
protection of RCC structures has grown considerably in recent years. Different
techniques are utilised for repairing the RCC structures and structural
elements. While costs associated with repair of deteriorating concrete
structures can be substantial, costs resulting from poorly designed or executed
repairs may be even higher. Therefore it is essential to use proper repairing
technique with consideration for the anticipated or desired remaining service
life of the structure.
Shotcrete:
Shotcrete, or pneumatically
applied concrete, is a method for repairing RCC structures by spraying concrete
or mortar onto the surface at high velocity using compressed air. In situations
where large-scale repair of concrete is necessary and installation of formwork
is either cost prohibitive or difficult, shotcrete offers an economical and
effective solution. Shotcrete is comprised of cementitious products with
aggregates similar to concrete.
Shotcrete may be installed
on vertical or horizontal surfaces. Shotcrete may be used to protect exposed
reinforcing, replace deteriorated or damaged concrete, restore structural
integrity, or increase the structural capacity of existing concrete members.
Shotcrete is a very
versatile construction material that can be readily placed and successfully
used for a variety of concrete repair applications such as bridges, buildings,
tunnels and marine structures. It is primarily used for beam repairs of
variable depths, abutments, damage caused by fire or earthquakes.
There are two primary
application methods: the wet process pumps mixed concrete through a hose to the
nozzle where compressed air is added to provide high velocity for placement and
consolidation; the dry process, commonly known as unite, uses compressed air to
blow pre-blended dry materials through a hose at high velocity to the nozzle,
where water is added. The effects in most cases are almost identical.
Form
and Pump Technique:
The form and pump repair
method involves the injection of a specially-formulated concrete mixture into
the cavity confined by formwork and existing concrete in the structure using a
pressure pumping system. It is a two-step process for repairing concrete
structure.
The first step in the
process involves the creation of a form or a temporary casing around the
damaged area. The form helps to contain the concrete mixture and ensures that
it is distributed evenly throughout the damaged area. Next, the concrete
mixture is prepared and placed into a pressure pump. The mixture is then injected
into the damaged area through cavity in the form, filling any cracks or voids.
The pressure pump is used to control the flow of the mixture, ensuring that it
is evenly distributed throughout the damaged area.
In the form and pump repair
method, rodding or internal vibration is necessary to remove air and provide
intimate contact for placing concrete substrate. It is important to ensure that
no air pockets are trapped inside the injected repair material. Trapped air
pockets can weaken the repair, causing it to fail over time, and potentially
leading to further damage to the structure.
The form and pump repair
method is effective for repairing concrete structures that are under tension,
such as post-tensioned concrete bridges, buildings, and parking structures. It
is a fast, efficient, and cost-effective method of repairing concrete
structures that provides long-lasting results.
Jacketing:
Jacketing is a structural
strengthening and retrofitting technique. It's utilised to boost bearing load
capacity after a structural design change or to restore structural design
integrity after a structural member failure. This technique increases the
strength of existing structural members (e.g. Columns, Beams etc.) by providing
a “Jacket” of additional material around the existing member. This additional
material can be of several types e.g. concrete, steel or FRP etc. Around the
damaged portion, a steel reinforcement cage or composite material wrap can be
built, then shotcrete or cast-in-place concrete can be applied.
Jacketing is particularly
used for the repair of deteriorated columns, piers, and piles and may easily be
employed in underwater applications. The method is applicable for protecting
concrete, steel, and timber sections against further deterioration and for
strengthening. Jacketing improves axial and shear strength of columns and a
major strengthening of the foundation may be avoided.
Plate bonding:
Plate bonding is an
inexpensive, versatile and advanced technique for rehabilitation of concrete
structures by mechanically connecting steel plates by bolting and gluing to
their surfaces with high-strength adhesives, primarily epoxy.
Plate bonding can
substantially increase strength, stiffness, ductility and stability of the
reinforced concrete elements and can be used effectively for seismic
retrofitting. In this method the bolts, which are first used to hold the plates
in position during construction, act as permanent shear connectors and integral
restraints. The bolts are also designed to resist interface forces assuming the
epoxy glue used as non-existent assuming it as destroyed by fire, chemical
break down, rusting or simply bad workmanship.
The method has proven its
ability to provide durable and reliable repairs that meet design requirements
for strength and rigidity over long periods. The process is clean, requiring no
wet work, and does not significantly alter the structure's appearance,
maintaining architectural integrity.
Dry
Packing:
Dry packing is the hand
placement of a very dry mortar and the subsequent tamping of the mortar into
place, producing an intimate contact between the new and existing works. Dry
mortar consists of cement and clean sand with just enough water to be able to
form a ball by hand. Because of the low water-cement ratio of the material,
there is little shrinkage, and the patch remains tight. So it will be of good
quality with respect to durability, strength and water tightness. Dry packing
is used for filling small, relatively deep holes, such as those resulting from
the removal of form ties, and narrow slots cut for repair of cracks.
