Saturday, September 12, 2015
Polymer Concrete, Test and its Applications
ABSTRACT:
In Concrete Technolgy
there are many types of Concretes here we are mainly discussing
about Polymer
Concrerte. Polymer concrete is a composite material. A graded mixture
coarse and fine
aggregates bound together by an appropriate organic resin system. Polymer
concrete is a
relatively low-cost composite material system that has been developed to be a
technically viable
alternative to porcelain for most high voltage electrical insulation
applications. Polymer
composites appear as useful materials for repair and protection of
building structures,
as well as for manufacturing pre-cast elements. In the case of pre-cast
elements as well as
repair materials, the usefulness and durability of polymer composites
depend on the
selection of the material composition for obtaining the composite with
controllable
properties Polymer Concrete consists of a polymer binder which may be a
thermoplastic but
more frequently is a thermosetting polymer, and a mineral filler such as
aggregate, gravel and
crushed stone. PC has higher strength, greater resistance to chemicals
and corrosive agents
lower water absorption and higher freeze-thaw stability than
conventional Portland
cement concrete.
Polymer modified
concrete may be divided into two classes; polymer impregnated
concrete and polymer
cement concrete. The first is produced by impregnation of pre-cast
hardened Portland
cement concrete with n monomer that is subsequently converted to solid
polymer. To produce
the second, part of the cement binder of the concrete mix is replaced by
polymer Both have
higher strength, lower water permeability, better resistance to chemical,
and greater
freeze-thaw stability than conventional concrete.
INTRODUCTION
Polymer concrete is
a composite material in which the binder consists entirely of a synthetic
organic polymer. It
is variously known as synthetic resin concrete, plastic resin concrete.
Because the use of
a polymer instead of Portland cement represents a substantial increase in
cost, polymers
should be used only in applications in which the higher cost can be justified
by superior
properties, low labor cost or low energy requirements during processing and
handling. It is
therefore important that architects and engineers have some knowledge of the
capabilities and
limitations of PC materials in order to select the most appropriate and
economic product
for a specific application. The first polymer concrete construction in the
worldis
Concrerte-Roman_colosseum_red.
NATURE AND GENERAL PROPERTIES:
Polymer concrete
consists of a mineral filler and a polymer binder (which may be a
thermoplastic, but
more frequently, it is a thermosetting polymer. When it is used as a filler,
the composite is
referred to as a polymer mortar. Other fillers include crushed stone, gravel,
limestone, chalk,
condensed silica fume, granite, quartz, clay, expanded glass, and metallic
fillers.
To produce PC, a
monomer, a hardener and a catalyst are mixed with the filler. Other
ingredients added
to the mix include plasticizers and fire retardants. To achieve the full
potential of
polymer concrete products for certain applications, various fiber
reinforcements
are used. These
include
glass
fiber,
glass
fiber-based mats,
fabrics
and
metal
fibers.
The amount polymer
binder used is generally small and is usually determined by the size of
the filler. Normal
the polymer content will range from 5 to 15 percent of the total weight, but
if the filler is
fine, up t 30 percent may be required.
Polymer concrete
composites have generally good resistance to attack by chemicals and other
corrosive agents
have very low water sorption properties. Portland cement concrete permits
the use of up to 50
percent less material. This puts polymer concrete on a competitive
basis
with cement concrete
in certain special applications. The chemical resistance and physical
properties are
generally determined by the nature of the polymer binder a greater extent than
by the type and the
amount of filler In turn, the properties of the matrix polymer are highly
dependent on time and
the temperature to which it is exposed.
The polymers most
frequently used are based on four types of monomers systems: methyl
methacryl , polyester
prepolymer-styrene, epoxide prepoiymer hardener and furfuryl alcohol.
MATERIALS
AND TESTING PROGRAM
Based on workability,
polymer content for GFRPC and CFRPC were determined to be 18%
and 20% respectively.
Fiber content for both the matrices was varied up to 6%. CIGMAT
standards (CIGMAT
PC1-01, CIGMAT PC2-01, CIGMAT PC3-01) were followed for
specimen
preparations, compression test and tension test. Destructive tests were
performed in
displacement-controlled
mode.
TEST
RESULTS AND CONCLUSIONS
Based on the
experimental study the following conclusions can be drawn:
Adding 6% glass
fibers required 18% polymer in the GFRPC system for good
workability. Glass
fibers increased the failure strain, peak strength and modulus in
compression and
tension.
Adding 6% PAN based
carbon fibers required 20% polymer to develop a workable
CFRPC. The addition
of carbon fibers increased the failure strain, but strength and
modulus decreased. In
tension, it increased the tensile strain, modulus and strength.
Carbon fibers also
increased the failure strain in compression, but reduced the
strength and modulus.
Tension
Test
Acrylic
Polymer Concrete:
The most common
acrylic polymer is poly, obtained by polymerization of methyl
methacrylate. PC made
with this acrylic polymer as a binder is versatile material,has
good
waterproofing properties
good
chemical resistance and
relatively
low setting shrinkage
its coefficient of
thermal expansion is equivalent to that of Portland cement concrete.
Because of its very
low tendency to absorb water, acrylic PC has a very high freeze-thaw
resistance.
Polyester
Polymer Concrete :
Because of low cost,
the most widely used polymer-binders are based on unsaturated
polyester polymer. In
most applications, the polyester binder is a general purpose,
unsaturated polyester
prepolymer formulation. The chemical reaction is called cross-linking,
the production
process associated with it is referred to as curing, and the resulting polymer
binder is a
thermosetting polymer.
Polyester PC has good
mechanical strength, relatively good adhesion to other materials, and
freeze-thaw
resistance. Polyester PC is used in various pre-cast and cast-in place
applications
in constructs works,
public and commercial buildings, floor tiles, sewer pipes and stairs.
Epoxy
Polymer Concrete :
Epoxy binder like
polyester, is a thermosetting polymer. The epoxy polymer can be hardened
with a variety of
curing agents, the most frequently used being polyamines. The use of
polyamine hardeners
results in PC products with the highest chemicals resistance. Other
curing agents are
polyamides and polysulfide polymers. Epoxy PC products cured with
polyamides give
greater flexibility.
Epoxy PC exhibits
high strength, low-setting and post-setting shrinkage, high chemical
resistance, good
fatigue and creep resistance. Because they are relatively expensive, epoxy
polymers have not
been used very widely as binders in PC products. Therefore, epoxy PC is
used for special
applications. Epoxy PC reinforced with glass, carbon or boron fiber is used
in the fabrication of
translucent panels, boat hulls and automobile bodies.
Furan
Polymer Concrete :
Furan polymers are
based on furfuryl alcohol, which is derived from agricultural residues
such a corn cobs,
rice hulls, oat hulls or sugar cane bagasse. The furan pre-polymer is usually
cross-linked with
furfuryl alcohol, furfuraldehyde to yield thermosetting polymers, high
resistant to most
aqueous acidic or basic solutions and strong solvents such as ketones,
aromatics, and
chlorinated compounds. The furan polymers are used as binders in mortars
and grouts to achieve
chemically resistant brick floors and linings. In addition to exhibiting
superior chemical
resistance, these floors have excellent resistance to elevated temperatures
and extreme thermal
shock.
Polymerization
:
Polymer- modified
cementitious materials date back more than 70 years. In the 194G's they
were developed for
use on ships' decks and bridges. Polymers arc made from simple organic
molecules that
combine to form more complex structures through a process called
polymerization. The
polymers are dispersed in water. These are added to hydraulic cement,
with or without
aggregate or admixtures, depending on trip desired result.
Advantages
of adding polymers to concrete :
In Polymer- Modified
Concrete, a report by the American Concrete Institute. Lists these
advantages to polymer
concrete:
• Increased bond
strength
• Freeze/thaw
resistance
• Abrasion resistance
• Flexural and
tensile strengths
• Reduced
permeability and elastic modulus
How
it works :
To the normal process
of cement hydration, polymer modifications add a process of
coalescence. As
cement hardens, there form small spaces between the aggregate particles.
These spaces arc what
allow water to penetrate, and do damage in freezing conditions.
Polymer particles
coalesce to fill these voids. Thai's why the concrete becomes less
permeable and better
protected against freeing. Interestingly, polymer concrete does not
produce bleed water.
It makes an excellent overlay because it needs very little finishing. It is
more accurate to say
that it dries, than to call it curing. For that reason that it is used to
resurface concrete.
Applications
& Advantages :
There are several
chemical systems for polymer concrete and mortar. Acrylic binders provide
excellent
environmental resistance and fast setting times. Epoxy resins exhibit high
strength
and low shrinkage
during curing. They also provide toughness and resistance to chemical and
environmental damage.
Furan resins are formed from the polymerization or poly
condensation of
furfural, furfural alcohol, or other compounds containing a furan ring. They
are commonly used in
foundry binders, grinding wheels, refractories and other high-
applications.
Polyurethane provides excellent flexibility, impact resistance and durability.
Other chemical
systems for polymer concrete and mortar include silicone, polyester, and
vinyl ester.
The subject of
polymer concrete has generated a lot of interest among researchers during the
past decade. This is
due to the many advantages that polymer concrete pavement offers
compared to regular
portland cement concrete. The advantages of polymer concrete, when
compared to portland
cement concrete include, quick curing and setting, reduced moisture
sensitivity and
permeability and improved mechanical properties resulting in reduced
pavement thickness to
support the same load. These advantages will lead to attractive life
cycle cost benefits.
Material properties and mix designs for PC with epoxy,
methylmethacrylate
and Polyester as the binder material have been investigated. It has been
shown in this study
that increased material cost of PC can be offset by the reduced thickness
of the pavement. In
order to develop life cycle cost information, it is necessary to obtain field
performance data of
PC pavement, especially in the composite design mode.
Applicaton of Polymer
Impregnated Concrerte:
Keeping in view the
numerous beneficial properties of PIC it is found useful in a
large no of
applications some of which have been listed &discussed below
a) Prefabricated
structural elements
b) Prestressed
Concrete
c) Marine works
d) Desalination
plants
e) Sewage works –
Pipe & Disposal Works
a) Prefabricated
structural elements:
For solving the
tremendous problems of Urban housing shortage,
maintaining , quality
econmy and speed ,builders had to fall back on prefabricated
techniques of
construction. At present due to the low strength of conventional concrete, the
prefabricated
sections are large and heavy ,resulting in costly handling and erection. These
reasons have
prevented wide adoption of prefabrication in many countries.
At present, the
technique of polymer impregnation is ideally suited for precast concrete .It
will find
unquestionable use in industrialization if building components .Owning to
strength ,
much thinner
&lighter sections could be used which enables easy handling and erection.
b) Prestressed
Concrete :
Further development
in prestressed concrete inability to produse high strength
concrete, compatible
with the high tensile steel available for prestressing .Since PIC provides
a high compressive
strength of the order of 100 to 140 Mpa will be possible to use it for
larger spans and for
heavier loads.Low creep properties of PIC willl also make it good
material for
prestressed concrerte
c) Marine Works :
Aggressive nature of
sea water ,abrasive and leaching action of waves and
inherent porosity
,impair the durability of conventional concrerte in marine works. PIC,
possessing high
surface hardness ,very low permiabilty and greatly increased resistance to
chemical attack is a
suitable material for marine works.
d) Deslination Plants
:
Deslination if sea
water is being resorted augment the shortage of surface and
ground water in many
countries .The material used in the construction of flash distillation
vessels in such works
has to withstand the corrosive effects of distilled water ,brine and
vapour upto a temp of
143 C. Carbon steel vessels which are currently in use are
comparatively costly
.
e) Sewage Disposal
Works :
It is common
experience that concrete sewer pipes deteriorate due to attack of
effluents and when
buried in sulphated infested soils. Further, in the sewage treatment plant,
concrete structures
are subjected to severe attack from corrosive gases particularly in sludge
digestion tanks.
f) Impregnation of
Ferrocement Products :
The Ferrrocement
techniques of construction is being extensively used in
manufacture of boats,
fishing trawlers , domestic water tanks .Application of Polymerimpregate
concrete due to its
high sulphate and high resistance will prove to suitable
material in the
ssituations .
References
:
1. A. Blaga and J.J.
Beaudoin. "Polymer Modified Concrete", Division of Building
Research, National
Research Council Canada, Canadian Building Digest 241, Ottawa,
2. A. Blaga.
"Plastics", Division of Building Research, National Research Council
Canada,
Canadian Building
Digest 154. Ottawa, 1973
3. A. Blaga.
"Thermoplastics" , Division of Building Research, National Research
Council
Canada, Canadian Building Digest 158,
Ottawa, 1974.
