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Grouting is one of the oldest
techniques used in repair and rehabilitation of
civil engineering structures. The technique has
been refined over the years on a account of the
availability of newer and better materials on
the one hand, and advancements in the equipment
used for grouting, on the other.
In the initial stages, cement based grouts were
used. However, their limitations were soon
realized. Newer materials and material
combinations were soon realized. Newer materials
and material combinations were tried. With a
large spectrum of new materials available today,
it is now possible to achieve better results of
grouting. However, it is important to choose the
right type of grout material. Factors like
workability, wetting capacity dimensional
stability, adhesion, strength, high elastic
modulus, chemicals resistance, long-term
integrity, resistance to corrosion and economics
play an important role.
TYPE OF GROUTS
Various types of grouting injection systems are
available in the market.
Cementitious grouts : These use high water
cement ratio, although in some cases powdered
plasticizers are added to reduce water demand.
Such grouts, due to the high water-cement ratio
end up as mere void filling materials and are
generally useful in providing temporary
solutions. The shrinkage loss of water is a
cause of worry too. However, where cost is a
major constraint and special structural or any
other requirements do not play a major role,
this type of grouting is generally adopted. The
shrinkage problem in this grout can be over come
with the use of shrinkage compensating cements.
EXPANSIVE CEMENTITIOUS GROUTS (NON SHRINK
GROUTS) :
These are modified cementitious grouts in that
the shrinkage effect is controlled by
incorporating either gas producing agents or
chemicals like lime or calcium sulpho aluminate,
which cause expansion in the mass. The grouts
produced from calcium sulpho aluminate give
better service and performance than those
produced from gas producing agents, which are
not so effective in terms of contact, good
adhesion, desired high elastic modulus, chemical
resistance and protection against corrosion.
This is because the expansion produced due to
hydrated calcium sulpho aluminate is more
uniform stable and controllable and is available
even in the hardened state. In the latter case
the dispersion of metallic powder in cement is
usually not uniform and while the expansion is
not steady, the same is available only during
the plastic stage. Moreover, there is a
possibility of corrosion of reinforcement due to
the generation of hydrogen gas.
LOW VISCOSITY EPOXIES AND
POLYURETHANES :
These are polymer grouts consisting of two or
three pack system in which one part is
necessarily a resin and others are accelerators
/ curing agents. Once the curing agent is added
to the resin, the setting process or cross
linking process starts irreversibly with visual
increase in viscosity as the time passes. Often,
this creates problems in the grouting
performance by adhering to any obstacle in the
passage as a result of increasing viscosity. At
such times, the remaining part of the passage /
capillary may never get filled. Hence, the very
purpose of grouting gets defeated. This also
creates problems in the cleaning operation of
the pressure device.
Sometimes these grouting materials are modified
by diluents to lower the viscosity of the grout
or the setting time. In such cases, the strength
parameters of the matrix are found to suffer.
However, for fast setting and underwater setting
wherein faster strength developments are
required, epoxy and PU systems are very useful.
Polyester resins are also used for grouts in
some parts of the world. These systems are quite
costly, because the resins themselves are costly
and these are generally to be grouted in the
pure resin form and a filler material cannot be
added into the system, which could reduce the
ocst of the system. The mechanical injection
pressure systems developed for this are costly
too, since high pressure producing pumps are
required due to the high viscosity of the
materials.
Generally, these systems give good adhesion to
dry surface but do not behave well in wet
conditions. Such systems are not quite desirable
since they are fire hazardous. Infact, PU
systems may create obnoxious gases like
isocynates under combustible conditions. Still,
these systems were quite popular due to the
dearth of better and more suitable materials.
However, water-based polymer systems are now
available and can be mixed with cement. These
co-matrices offer better convenience and
superior cumulative performance as compared to
other contemporary materials.
POLYMER LATEX CEMENT
COMATRIX :
Many polymers after their polymerization can be
converted into water based emulsion forms, which
are microfine solids, suspended in liquids.
After appropriate use and loss of water, the
same can be brought to a solid polymer state.
However, while they are in the aqueous phase,
they render many useful properties to cement
when mixed with it. Cement itself has good
compression properties but lacks flexural
properties, which can be very effectively
increased with polymers. The solvent-based
polymers cannot become compatible with
cementitious matrix , though the same polymers
when used in latex form can be totally
compatible with cement and offer improved
results. There are several such latexes used for
modifying cement properties.
The advantages of such polymer latex-cement
comatrix systems over pure solvent-based epoxy
polyurethane grouting system are as follows:
-› Polymer
latex cement comatrix being water based it is
quite compatible
with cement and can work in wet conditions.
-› Since
it is a polymer and cement together, it can
display the properties
of both cement and
polymer that is one can have the desirable
compression
properties from cement and flexural properties
from the
polymer.
-› It
is already a polymerized system hence on drying
there would not be a
volume change due to
shrinkage
-› Cement
is structurally a good material and if dispersed
properly with the
right water-cement
ratio it can give excellent results. However in
plain
cement injection the
water cement ratio has to be kept very high to
provide workability
and this adversely affects all structural
properties of
grouts. In case of
polymer latexes, water cement ratio can be
controlled
without loss in
workability. Hence grouted areas get an
additional
parameter of
compression along with mere filling of the
voids.
-› The
incorporation of polymer gives good adhesion to
the surface even if
the same is damp. On a smooth surface like polished granite or
marble
top also, these systems stick so well that the experimental results
on
axial pull out have
shown that the tiles break but the bond cannot
be
separated.
-› The
total comatrix has excellent flexural and
tensile parameters, which
will additionally
reinforce the grouted area.
-› Finally
as compared to any other grout with similar
parameters, these
systems are very
-› Economical
since they use cement as one of the components. |
