POLYMER CONCRETE

Continuous research by concrete technologists to understand, improve and develop the

properties of concrete has resulted in a new type of concrete known as, “Polymer Concrete”.

It is referred time and again in the earlier chapters that the concrete is porous. The porosity

is due to air-voids, water voids or due to the inherent porosity of gel structure itself. On

account of the porosity, the strength of concrete is naturally reduced. It is conceived by many

research workers that reduction of porosity results in increase of strength of concrete.Therefore, process like vibration, pressure application spinning etc., have been practised mainly

to reduce porosity. All these methods have been found to be helpful to a great extent, but

none of these methods could really help to reduce the water voids and the inherent porosity

of gel, which is estimated to be about 28%. The impregnation of monomer and subsequent

polymerisation is the latest technique adopted to reduce the inherent porosity of the concrete,

to improve the strength and other properties of concrete.

The pioneering work for the development of polymer concrete was taken up by United

States Bureau of Reclamation (USBR). The initial exploratory works carried out at the

Brookhaven National Laboratory (BNL) in cooperation with USBR and US in Atomic Energy

Commission (AEC) revealed great improvement in compressive strength, permeability, impact

resistance and abrasion resistance.

The development of concrete-polymer composite material is directed at producing a new

material by combining the ancient technology of cement concrete with the modern

technology of polymer chemistry.

Type of Polymer Concrete

Four types of polymer concrete materials are being developed presently. They are:

(a) Polymer Impregnated Concrete (PIC).

(b) Polymer Cement Concrete (PCC).

(c) Polymer Concrete (PC).

(d) Partially Impregnated and surface coated polymer concrete.

Polymer Impregnated Concrete (PIC)

Polymer impregnated concrete is one of the widely used polymer composite. It is nothing

but a precast conventional concrete, cured and dried in oven, or by dielectric heating from

which the air in the open cell is removed by vacuum. Then a low viscosity monomer is diffused

through the open cell and polymerised by using radiation, application of heat or by chemical

initiation.

Mainly the following types of monomer are used:

(a) Methylmethacrylate (MMA),

(b) Styrene,

(c) Acrylonitrile,

(d) t-butyl styrene,

(e) Other thermoplastic monomers.

The amount of monomer that can be loaded into a concrete specimen is limited by the

amount of water and air that has occupied the total void space. It is necessary to know the

concentration of water and air void in the system to determine the rate of monomer

penetration. However, the main research effort has been towards obtaining a maximum

monomer loading in concrete by the removal of water and air from the concrete by vacuum

or thermal drying, the latter being more practicable for water removal because of its rapidity.

Another parameter to consider is evacuation of the specimen prior to soaking in

monomer. This eliminates the entrapment of air towards the centre of the specimen during

soaking which might otherwise prevent total or maximum monomer loading. The application

of pressure is another technique to reduce monomer loading time.Polymer Cement Concrete (PCC)

Polymer cement concrete is made by mixing cement, aggregates, water and monomer.

Such plastic mixture is cast in moulds, cured, dried and polymerised. The monomers that are

used in PCC are:

(a) Polyster-styrene.

(b) Epoxy-styrene.

(c) Furans.

(d) Vinylidene Chloride.

However, the results obtained by the production of PCC in this way have been

disappointing and have shown relatively modest improvement of strength and durability. In

many cases, materials poorer than ordinary concrete are obtained. This behaviour is explained

by the fact that organic materials (monomers) are incompatible with aqueous systems and

sometimes interfere with the alkaline cement hydration process.

Recently Russian authors have reported the production of a superior Polymer cement

concrete by the incorporation of furfuryl alcohol and aniline hydrochloride in the wet mix. This

material is claimed to be specially dense and non-shrinking and to have high corrosion

resistance, low permeability and high resistance to vibrations and axial extension.

Washington State University in cooperation with Bureau of Reclamation tested the

incorporation of several monomers into wet concrete for preparing PCC for fabrication of

distillation units for water disalination plants. However, it is reported that only epoxy resin

produced a concrete that showed some superior characteristics over ordinary concrete.

Polymer Concrete (PC)

Polymer concrete is an aggregate bound with a polymer binder instead of Portland

cement as in conventional concrete.

The main technique in producing PC is to minimise void volume in the aggregate mass

so as to reduce the quantity of polymer needed for binding the aggregates. This is achieved

by properly grading and mixing the aggregates to attain the maximum density and minimum

void volume. The graded aggregates are prepacked and vibrated in a mould. Monomer is

then diffused up through the aggregates and polymerisation is initiated by radiation or

chemical means. A silane coupling agent is added to the monomer to improve the bond

strength between the polymer and the aggregate. In case polyester resins are used no

polymerisation is required.

An important reason for the development of this material is the advantage it offers over

conventional concrete where the alkaline Portland cement on curing, forms internal voids.

Water can be entrapped in these voids which on freezing can readily crack the concrete. Also

the alkaline Portland cement is easily attacked by chemically aggressive materials which results

in rapid deterioration, whereas polymers can be made compact with minimum voids and are

hydrophobic and resistant to chemical attack. The strength obtained with PC can be as high

as 140 MPa with a short curing period.

However, such polymer concretes tend to be brittle and it is reported that dispersion of

fibre reinforcement would improve the toughness and tensile strength of the material.