Many polymers after their
polymerization can be converted into a water-based emulsion form 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 effiectively
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 as given in table 1.
Generally, the polymer latexes
are copolymer systems of two or more different monomers and their total solid
contents vary between 40-50 percent by weight.
The commercial latexes widely
used in the world are styrenebutadiene rubber (SBR), Polychloroprene rubber
(PCR), Polyacrylic ester (PAE), Polyethylene-vinyl acetate (PEVA) and Poly
vinylidene chloride-vinyl chloride (PVDC) copolymers. However, acrylates and
SBRs are more popularly used.
There are many advantages of
such polymer latex-cement comatrix systems over pure solvent based
epoxy/polyurethane grouting systems. There 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 i.e. one can have the desirable compression properties
from cement and flexural properties from the polymer.
- It
is already polymerized system and 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
injections, 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.
Table 1 : Popularly used
polymer latexes:
SBR : Styrene butadiene
rubber
|
PAE : Polyacrylic ester
|
PCR : Polychlorprene rubber
|
PEVA : Poly Ethylene -
Vinylacetate
|
NBR : Acrylonitrile-Butadiene
rubber
|
PVDC : Polyvinylidene
chloride
|
RA : Rubberised asphalt
|
PVAC : Polyvinylacetate
|
Pa : Paraffins
|
PVP : Polyvinyl propionate
|
EP : Epoxy
|
PP : Polypropylene
|
