·
Cementitious grouts
These
grouts use high water-cement ratio, although in some cases powdered
plasticisers 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 are not playing a major role, this type of grouting
is generally adopted. The shrinkage problem in this grout can be overcome with
the use of shrinkage compensating cements.
·
Expansive cementitious grouts (Non-shrink grout)
This is
a modified cementitious grout in which 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 good 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, 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.
·
Inorganic liquid grouts
In many
cases cementitious grouts do not offer sizeable relief because these grouts
being insoluble powders do not disperse uniformly in water and do not reach the
various capillaries properly. The reach of a single grout is not substantial,
thus many grouts are needed to cover the entire periphery of a structure. In
the chemical grouting method a clear solution of a silicate-based chemical A is
injected first which reaches easily to all the capillaries being a watery
liquid and also spreads in the larger areas without any discontinuities. Almost
immediately afterwards, a solution of a precipitating agent chemical B is
injected which also spreads similarly. On coming in contact with chemical A, an
insoluble precipitation is immediately formed. Wherever these two materials
meet, including at the extreme ends of the capillary networks, voids and pores
are filled blocking the entire passage. Such a method is particularly useful in
arresting dampness in foundations and costs much less than other polymeric
grouting. These can totally discontinue the capillaries and hence effectively
bring down dampness of the structure. Several alternatives can be suggested for
such methods. However, care is to be taken that none of the resultant products
is a soluble sulphate, chloride or any other radical which will affect the
concrete or steel.
·
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, 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 amount of curing agent is adjusted so as to increase 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 have reduced the cost of the system. The mechanical
injection pressure systems developed for this are costly too, since high
pressure producing pumps are required due to 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.
In fact, 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.
