Use
of Plastics
Waste
in Construction of Tar Road
The
use of waste plastics on the road has helped to provide better place
for burying the plastic waste without causing disposal problem. At
the same time, a better road is also constructed.
Dr. R. Vasudevan
Professor & Head Dept. of Chemistry,
Thiagarajar College of Engineering,
Madurai
(Excerpts from the paper submitted for Seminar on Integrated Development
of Rural and Arterial Road Network for Socio-Economic Growth.) (This
project was co-sponsored by Indian Centre for Plastics in the Environment,
Mumbai.)
Introduction
Bitumen
is a useful binder for road construction. Different grades of bitumen
like 30/40, 60/70 and 80/100 are available on the basis of their penetration
values. The steady increase of high traffic intensity in terms of
commercial vehicles, and the significant variation in daily and seasonal
temperature demand improved road characteristics. Any improvement
in the property of the binder is the need of the hour. Elastometers
like natural rubber, crumb rubber, SBR, etc. as well as plastomeric
substances like polyethylene, ethylene vinyl acetate and ethylene
butyl acrylates are mixed with bitumen to modify the properties.
Modified bitumen possesses better quality. Today, the availability
of waste plastics is enormous, as the plastic materials have become
part and parcel of daily life. They either get mixed with Municipal
Solid Waster and/or thrown over land area. If not recycled, their
present disposal is either by land filling or by incineration.
Both the processes have certain impact on the environment. Under these
circumstances, an alternate use for the waste plastics is also the
need of the hour.
Thinner polythene carry bags are most abundantly disposed of wastes,
which do not attract the attending rag pickers for collection for
onward recycling, for lesser value.
These polythene/polypropylene bags are easily compatible with bitumen
at specified conditions. The waste polymer bitumen blend can be prepared
and a study of the properties can throw more light on their use of
road laying.
Modified Bitumen
Addition of natural or synthetic polymers to bitumen
is known to impart enhanced service properties. By adding small amounts
of polymers to bitumen, the life span of the road pavement may be
considerably increased. The purpose of bitumen modification using
polymers is to achieve desired engineering properties such as increased
sheer modulus and reduced plastic flow at high temperatures and/or
increased resistance to thermal fracture at low temperatures.
Homopolymers like high and low density polyethylene and polypropylene,
as well as random and block copolymers, like ethylene-vinyl acetate,
ethylene/propylene, styerenebutadine copolymer have been used as bitumen
modifiers.
However, the major obstacle to the usage of polymer-modified bitumen
in paving practice has been their tendency towards gross phase separation
under quiescent conditions at elevated temperatures.
A precise study on processing conditions of binders and polymeric
additives selection are, thus required. Moreover, incompatibility,
unstabilisation of emulsions, higher cost of polymer and cumbersome
procedure of the preparation of the mix add to the complexity of the
process.
Reuse of Waste Plastics:
Plastics as Binder and Modifier
Waste plastics (polythene carry bags, etc.) on heating
soften at around 130°C. A study using thermo-gravimetric analysis
has shown that there is no gas evolution in the temperature range
of 130-180°C. Moreover, the softened plastics have a binding property.
Hence, the molten plastic materials can be used as a binder and/or
they can be mixed with a binder like bitumen to enhance their binding
property. This may be a good modifier for the bitumen used for road
construction. Study on waste plastics for road is highlighted here.
Determination of Solubility
of Polymer in Bitumen
The waste polymers such as polyethylene (as sheets),
polypropylene (sheets, film) and polystyrene (thermocole) are soluble
to the extent of 1 to 2% of the ...
....contd.
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