Road pavement construction has
experienced many significant problems mainly in sub-base and base design and
construction over the years in this country (Nigeria).
Roads in Osun State have a very
high volume of traffic which comprises of many type of commercial vehicles,
cars and trucks. Roads have been constructed for more than 2000years. Even the
earliest engineers practiced drainage of the pavement’s sub-surface layers in
order to keep the highway functioning. Nowadays, many billions of Naira are
spent on road construction and maintenance each year, and road transport in the
primary method of mobility for Nigeria people or goods, Transport constitutes
about 10% of the gross national product of the Nigerian union and more than 80%
of the total transport of people and goods is provided y the infrastructure.
Investment in road construction and maintenance in Nigeria is therefore at a
very high level and any improvement can have a significant effect on the
Nigeria economy. Not only will well maintained roads and highway contribute
economically, for they are also essential for social development of Nigeria. On
the other, the deterioration of roads can have serious consequence for the
safety and comfort of roads user.
In many countries premature
break-down especially of low volume asphalt roads, is an accelerating problem
increasing traffic and traffic roads demand higher performance levels from
pavement if premature rutting and cracking is to be avoided. At the same time
climate change means that highway are likely to be exposed to more rain and to
greater thermally induced cracking that can lead the run-off into the
structure. Once in the pavement or embankment, plays a primary role in giving
shorter service life and in increasing the needs of rehabilitation measures. A
further problem that is becoming of more and more concern 1is the possibility
that the road is a source of contaminants that are having an undesirable effect
on the hydro1ological environment. Two sources are possible.
(i) Contaminant in runoff from rainwater or snowmelt
that flows over the top `of the
pavement and than soaks into the ground.
(ii) Leaching of contaminant from
the roads construction materials and earthworks.
According to E.J Yoder and M. w
Witczak (1975), the foundation of the roads which comprises of both sub-base
and base courses should be well compacted and to make them free from water.
Most design techniques strength test made on sub-grade samples that is in
soaked or nearly saturated condition. This has been saturated practice for many
years since it is assumed that the saturated case is the controlling one. On
the other hand, it is known that even under certain desert condition water
accumulate in sub-base and base course under a pavement and the moisture content
of the soil can become high.
in – place moisture content or ground water in sub-base and base course under
flexible pavement is influenced by amount of rainfall and high-rise of water
roads, two type of pavement are considered for use in roads construction.
A flexible pavement : As defined by AASHO is a pavement structure
which distributes loads to the sub- grade that is, the foundation of the roads
and this relies on the bituminous aggregate
interlock, particle friction and collation for stability, the strength
of the supporting foundation, the quality materials and the construction
Rigid pavement: it can be as a pavement structure which distributes
loads evenly to the sub- grade i. e foundation having one course, a Portland
cement concrete slab of relatively high binding resistance. The foundation of
the roads which comprises of the structure of a concrete pavement slab should
be designed for the loads, in order to render year of service. The factors
below should be considered
1. The amount,
type and weight of present anticipated traffics
depth o ground water should be considered.
strength and quality of concrete to be used.
4. Supporting power and character of the sub-
5. The climate of the region (Osun State) in which
the pavement is to construct.
for a road to be constructed for this purpose, certain criteria have to be
Traffic density and the vehicle pattern.
The economic importance of the roads.
of the area.
1.1 SCOPE OF THE STUDY
The study focus on various source
by which base and sub- base cause of road pavement get in contact with water
and proffer solution to curtail the ingress of water in to the road pavement
structure so that the road pavement structure at Iree – Ibokun in Osun state as
a case study well serve beneficial community up to the expected optional level.
1.2 AIMS AND OBJECTIVE
The primary aim of the project is
to investigate the primary cause of roads pavement failure on the structural
stability of sub- base and base course of typical flexible pavement at Iree-
Ibokun road in Osun state.
primary objectives of the project are basically on
To identify, investigate and control contaminants
leaching from soils natural aggregate and by- productivity and moisture
To examine the geotechnical properties of the materials
2.2.1 LIMITATION OF THE STUDY
The limitation to this research
work is due to.
1. Economic situation of the country which lead to inadequate
2. Time there is limitation period of time to carry out the