FUNCTIONS OF
PAVEMENT COMPONENETS
[1] Soil Sub grade: - The soil sub grade is a layer of
natural soil prepared to receive the layers of pavement materials placed over
it. The loads on the pavement are ultimately received by the soil sub grade for
dispersion to the
earth mass. Therefore it is desirable that at least top 50cm layer of the sub
grade soil is well compacted under controlled conditions of optimum moisture
content and maximum dry density.
[2] Sub base: - These layers are made of broken
stones, bound or unbound aggregate. Sometimes in sub base course a layer of
stabilized soil or selected granular soil is also used. In some places boulder
stones or bricks are also used as a sub base or soiling course. Base course and
sub base courses are used under flexible primarily to improve the load
supporting capacity by distributing the load through a finite thickness.
[3] Wearing course: - The purpose of the wearing course
is to give smooth riding surface that it dense. It resists pressure exerted by
tyres and takes up wear and tear due to traffic. Wearing course also offers a
water tight layer against the surface water infiltration. In flexible pavement,
normally a bituminous surfacing is used as a wearing course.
SOIL STABILIZATION:-Soil stabilization is a
technique aimed at increasing or maintaining the stability of a soil mass or
otherwise improving its engineering properties. Soil stabilization is used in
the varieties of engineering works, e.g – for the construction of earth road or
other roads.
Purpose
of stabilization: - [1] To
increase Compressive strength irrespective of moisture content. [2] To increase resistance to softening
action of water. [3] To reduce
shrinkage due to withdrawal of moisture, and swelling due to wetting. [4] To increase flexibility to take the
wheel load without deformation and cracking. [5] To increase shear strength and resistance to punching.
TYPES OF SOIL STABILIZATION
[1]
Mechanical Stabilization: - This
is the simplest method of stabilization. It has been observed that if a soil
consists of coarse grains and fine grains in the ratio of two and one or if a
soil consists of two parts of sand and one part of clay, and is compacted at
optimum moisture content (O.M.C), it will have better wearing qualities and
will not deform easily under normal wheel load.
[2]
Cement Stabilization: - Cement
is a binding material. When mixed with soil, it forms a sort of low strength
concrete in which the soil acts as aggregate and cement as matrix. The soil is
excavated to a depth of nearly 15cm and 8 to 12% of cement is mixed. Sufficient
quantity of water is then added and the soil cement mixture is compacted
properly by road stabilizers. The cement binds particles of clay and forms a
flexible dustless and durable road surface. The cement stabilized roads are
water tight, require less maintenance and are very suitable for light traffic.
It is suitable for sand predominant soils.
[3]
Lime Stabilization: - In
this case the process of stabilization is similar to that of cement
stabilization. The soil is loosened, pulverized, sieved and mixed with 5 to 10%
by weight of hydrated lime. It is suitable for predominant soils.
[4]
Fly Ash Stabilization: - Fly ash has been used
successfully in many projects to improve the strength characteristics of soils.
Fly ash can be used to stabilize bases or subgrades, to stabilize backfill to
reduce lateral earth pressures and to stabilize embankments to improve slope
stability. Typical stabilized soil depths are 15 to 46 centimeters (6 to 18 inches).
The primary reason fly ash is used in soil stabilization applications is to
improve the compressive and shearing strength of soils.
SURFACE DRESSING: -Surface dressing is a process that provides
added protection to the carriageway surface, sealing it from the ingress of
water while also enhancing its skid resistance. This added protection can
extend the life of the carriageway surface by up to 10 years. The process
entails spraying the road with bitumen and covering it with stone chippings.
The dressing is then rolled, which together with the actions of slow
moving traffic, embeds the stone chips into the surface.
PREMIX CARPET:-
Premix carpet (PC) is the oldest hot
mix in India. It is a good, economical, bituminous wearing course mix to be
placed directly on water bound macadam (WBM) of low-volume rural roads. Since
such roads are not constructed by mechanical means,
the quality of WBM may not be consistent.
TACK COAT: -A
tack coat is sprayed on the surface of an existing asphalt or concrete pavement
by a distributor truck immediately prior to placing an overlay. Tack coat is a thin layer of asphalt that
ensures the bonding between old and new asphalt layers. It is also used in
construction or for renovation of roads to achieve better strength.
SEAL COAT:-
Seal coat is a final coat of bituminous material applied during
construction to a bituminous macadam or concrete for sealing the surface of the pavement by a
single layer of uniform size aggregate. It treats the surface to help prevent
surface water from penetrating old, weathered or crack pavements. The asphalt
seals the old surface and the aggregate carries the traffic. This reduces pot
holes and slows deterioration
of old asphalt pavement surfaces.
ASPHALT CONCRETE:
- Asphalt concrete is a composite material commonly used to surface roads,
parking lots, and airports. It consists of mineral aggregate bound together
with asphalt, laid in layers, and compacted.
