overview of road construction and maintenance

8/3/2019 Overview of Road Construction and Maintenance

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Introduction

Road construction is one of the oldest arts known to man. The earliestroads developed from trails made by man or animals which became

footpaths. They naturally followed the lines of least resistance, avoiding

steep grades, marshland, and circumventing natural obstacles. If a river had

to be crossed, the trail either detoured to affordable location or fallen trees

used as bridges across the river.

The invention of the wheel at about 3500 BC constituted a significanttechnical advancement and greatly accelerated the development of road

construction. The possibility of carrying greater loads on wheel called for

corresponding improvement in carriageway development

The period after the world War of 1914-1918 was marked by quick growthof automobile transportation and an increase in the speed and carrying

capacity of automobiles. It was then that parallel with construction of

highways for mixed traffic (automobile traffic and horse traffic), highways

were constructed which were intended exclusively for high-speed

automobile traffic on large scale. This period might well be called the

automobile age for during this period highway transportation assumed a

dominant role in most part of the worlds.


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ROAD DEVELOPMENT IN NIGERIA

Road transportation has played a vital role in every aspect of Nigerias

development. Before the advent of British rule, movement of people and goods

naturally took place between the various communities. Social requirements such

as traditional festivals, where people had to travel from one village to another

gave rise to communal footpaths. These paths eventually developed into

commercial routes for trading, and from these roads the genesis of highway

development in Nigeria started.

Highway construction however started in the real sense at the beginning ofthe twentieth century.

The first efforts were made with: Roads from Calabar to Obubra and from Oron to Onitsha in the East; Ibadan to Oyo, Oshogbo to Ilesha and Ogbomosho in the West, and Zungeru-Zaria cart road in the North.

Progress was slow because of the First World War, but the tempo increasedsomewhat after the war as Lagos was linked to Ibadan, Benin to Sapele,

Ijebu-Ode to Ibadan and Abeokuta, Enugu to Port Harcourt, Sokoto to Zaria

and Kano to Katsina.

These roads were first developed as feeders to the railway, but by themiddle of the twentieth century, road development had overtaken the railin importance.

The total length of road (federal, state and local governments) has grown asfollows:

45,128km (with 1,648km bituminous surfaced and 43,480km oflaterite/gravel surface) in 1950

66,086km (with 8,745km bituminous surfaced) in 1960, 116,421km (with 30,285km bituminous surfaced) in 1980. According to the Federal Ministry of Works and Housing Road Vision

2000 report, the total length of roads in Nigeria as at Year 2000 was

about 191,250km as shown in Table 1.


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Components of a road

A road is composed of the following elements: Pavement Shoulders Kerbs Sidewalks Drainage channels and side slopes Medians Right of way

The Pavement A road pavement is a structure consisting of superimposed layers of

processed materials above the natural soil sub-grade,

Its primary function is to distribute the applied vehicle loads to thesub-grade.

The pavement structure should be able to provide: a surface of acceptable riding quality, adequate skid resistance, favorable light reflecting characteristics, and low noise pollution.

The ultimate aim is to ensure that the transmitted stresses due to wheelload are sufficiently reduced, so that they will not exceed bearing capacity

of the sub-grade.

Two types of pavements are generally used as serving this purpose, namely: flexible pavements and rigid pavements.

This section will present an overview of pavement of the two pavementtypes, layers, and their functions, and pavement failures.

Improper design of pavements leads to early failure of pavements affectingthe riding quality.


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Requirements of a Pavement

An ideal pavement should meet the following requirements: Sufficient thickness to distribute the wheel load stresses to a safe

value on the sub-grade soil,

Structurally strong to withstand all types of stresses imposed upon it, Adequate coefficient of friction to prevent skidding of vehicles, Smooth surface to provide comfort to road users even at high speed, Produce least noise from moving vehicles, Dust proof surface so that traffic safety is not impaired by reducing

visibility,

Impervious surface, so that sub-grade soil is well protected, and Long design life with low maintenance cost.

Flexible and Rigid Pavements

Classification of pavements into flexible and rigid is based on the structuralperformance, that is the behavior of the pavement under traffic loads:

In flexible pavements, wheel loads are transferred by grain-to-grain contactof the aggregate through the granular structure. The flexible pavement,

having less flexural strength, acts like a flexible sheet (e.g. bituminous

road). On the contrary, in rigid pavements, wheel loads are transferred to sub-

grade soil by flexural strength of the pavement and the pavement acts like

a rigid plate (e.g. cement concrete roads).

In addition to these, composite pavements are also available. A thin layer of

flexible pavement over rigid pavement is an ideal pavement with most

desirable characteristics. However, such pavements are rarely used in new

construction because of high cost and complex analysis required.

Flexible Pavements

Flexible pavements will transmit wheel load stresses to the lower layers by

grain-to-grain transfer through the points of contact in the granular structure

(see Figure 1).


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Figure 1: Load transfer in granular structure

The wheel load acting on the pavement will be distributed to a wider area,and the stress decreases with the depth. Taking advantage of this stress

distribution characteristic, flexible pavements normally has many layers.

Hence, the design of flexible pavement uses the concept of layered system. Based on this, flexible pavement is constructed in a number of layers and

the top layer has to be of best quality to sustain maximum compressive

stress, in addition to wear and tear.

The lower layers will experience lesser magnitude of stress and low qualitymaterial can be used.

Flexible pavements are constructed using bituminous materials. These canbe either in the form of surface treatments (such as bituminous surface

treatments generally found on low volume roads) or, asphalt concrete

surface courses (generally used on high volume roads such as national

highways).

Flexible pavement layers reflect the deformation of the lower layers on tothe surface layer (e.g., if there is any undulation in sub-grade then it will be

transferred to the surface layer).

In the case of flexible pavement, the design is based on overallperformance of flexible pavement, and the stresses produced should be

kept well below the allowable stresses of each pavement layer.


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Components of Flexible Pavements

Flexible pavements: Are layered systems with high quality expensive materials placed in

the top where stresses are high, and low quality cheap materials are

placed in lower layers.

Flexible pavements has the following components: Wearing course of bituminous treatment or asphalt concrete Binder course of asphalt concrete Base course of crushed stone (stone base) or good laterite Sub-base course of good laterite or stabilized poor materials Service life is about 10 to 15 years Service life refers to period of use with routine maintenance

and no periodic maintenance.

Typical layers of a flexible pavement

Figure 2: Typical cross section of a flexible pavement

Wearing Course

Wearing course is the layer directly in contact with traffic loads andgenerally contains superior quality materials. They are usually constructed

with dense graded asphalt concrete(AC).

The functions and requirements of this layer are: It provides characteristics such as friction, smoothness, drainage, etc. Also it will prevent the entrance of excessive quantities of surface

water into the underlying base, sub-base and sub-grade,


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It must be tough to resist the distortion under traffic and provide asmooth and skid- resistant riding surface,

It must be water proof to protect the entire base and sub-grade fromthe weakening effect of water.

Binder Course

This layer provides the bulk of the asphalt concrete structure. It's chief purpose is to distribute load to the base course The binder course generally consists of aggregates having less asphalt and

doesn't require quality as high as the surface course, so replacing a part of

the surface course by the binder course results in more economical design.

Base Course

The base course is the layer of material immediately beneath the surface ofbinder course and it provides additional load distribution and contributes to

the sub-surface drainage

It may be composed of crushed stone, good laterite, and other untreated orstabilized materials.

Sub-Base Course The sub-base course is the layer of material beneath the base course and

the primary functions are:

To provide structural support, improve drainage, and reduce the intrusion of fines from the sub-grade in the pavement structure A sub-base course is not always needed or used. For example, a pavement

constructed over a high quality, stiff sub-grade may not need the additional

features offered by a sub-base course. In such situations, sub-base coursemay not be provided.

Sub-grade

The top soil or sub-grade is a layer of natural soil prepared to receive thestresses from the layers above.


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It is essential that at no time soil sub-grade is overstressed. It should becompacted to the desirable density, near the optimum moisture content.

Kerbs

Use of kerbs is generally confined to urban and sub-urban areas. Notusually used for rural roads.

Functions of Kerbs

To control surface drainage To act as deterrents to vehicles leaving the pavement at haphazard

locations

To delineate the edge of the pavement To present a more finished appearance To assist in orderly development of the road side

Shoulders

Shoulders are strips provided on both sides of the carriageway. Theirprimary function is to serve as parking place for vehicles which have

developed some defects and need parking. If shoulders are not provided,

vehicles going out of order shall have to be parked on the carriageway andthus efficiency of the road is affected and may even become the source of

serious accidents.

Functions of Shoulders

They provide space for emergency and occasional stopping of vehicles dueto motor troubles, such as breakdown, flat tyres, etc.

They provide space for escaping potential accidents or reducing theirseverity

They improve sight distance especially in hilly and cut sections and bendsthus reducing hazards

They provide space for road maintenance operations They make the discharge of storm water farther away from the pavement They provide lateral support to the pavement structure


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Types of Road Maintenance

Road Maintenance Proper road maintenance contributes to reliable transport at

reduced cost, as there is a direct link between road condition and

vehicle operating costs (VOC). An improperly maintained road can

also represent an increased safety hazard to the user, leading to

more accidents, with their associated human and property costs.

Routine maintenance works.

These are works that are undertaken continuously in order topreserve the road. Activities can be grouped into cyclic and reactive

works types. Cyclic works are those undertaken where the

maintenance standard indicates the frequency at which activities

should be undertaken. Examples are verge cutting and culvert

cleaning, both of which are dependent on environmental effects

rather than on traffic levels. Reactive works are those where

intervention levels, defined in the maintenance standard, are used to

determine when maintenance is needed. An example is patching,

which is carried out in response to the appearance of cracks or pot-

holes.

Periodic maintenance works. These include activities undertaken at intervals of several years to

preserve the structural integrity of the road, or to enable the road to

carry increased axle loadings. The category normally excludes those

works that change the geometry of a road by widening or

realignment. Works can be grouped into the works types of

preventive, resurfacing, overlay and pavement reconstruction.Examples are resealing and overlay works, which are carried out in

response to measured deterioration in road conditions. Periodic

works are expected at regular, but relatively long, intervals.


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Special maintenance works. These are activities whose need cannot be estimated with any

certainty in advance. The activities include emergency works to

repair landslides and washouts that result in the road being cut or

made impassable. These works are also referred to as emergency

maintenance

Road and Highway Maintenance

Definition: Preserving and keeping each type of roadway, roadside, structures as

nearly as possible in its original condition as constructed or as

subsequently improved and the operation of highway facilities and

services to provide satisfactory and safe transportation, is called

maintenance of Highways.

The various maintenance function includes; Surface maintenance Roadside and drainage maintenance Shoulder and approaches maintenance Snow and ice control Bridges maintenance Traffic service Highway maintenance is closely related to the quality of constructionof original road.

Insufficient pavement or base thickness or improper construction ofthese elements soon results in expensive patching or surface repair.

Shoulder care becomes a serious problem where narrow lanes forceheavy vehicle to travel with one set of wheels off the pavement.

Improperly designed drainage facilities, mean erosion or depositionof material and costly cleaning operation or other corrective

measures.

Sharp ditches and steep slopes require manual maintenance ascompare to cheap maintenance of flatter ditch and soil by machine.


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In snowy country, improper location extremely low fills and narrow

cuts leave no room for snow storage, creating extremely difficult

snow removal problems.

Surface maintenance of Roads Pavement maintenance and rehabilitation programs, restore riding

quality and maintain the structural integrity of the pavement over its

full design life.

Asphalt concrete pavements are subjected to various types ofpavement distress or Failure these include.

Alligator Cracking: A series of interconnecting or interlaced cracks caused by fatigue of

the asphalt concrete surface under repeated traffic leading. [Cracking

is due to foundation movement at subgrade

Block Cracking: Cracks forming large interconnected polygon usually with sharp

corners or angles. These cracks are generated by hardening or

shrinking e.g. asphalt or reflection cracking for underlying layers suchas cement treated base.

Transverse Cracking: Cracks approximately at right angle to the pavement center line.

These may be caused by hardness and shrinkage of asphalt or

differential thermal stresses of asphalt concrete or may be reflection

cracking.

Longitudinal Cracking: Cracks approximately parallel to the pavement centerline. These are

caused by poorly constructed construction joints and shrinkage of

the asphalt concrete surface. They may also be reflection cracks.


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Raveling: Wearing away the pavement surface caused by dislodging of

aggregate particles and binders. This is usually a result of insufficient

asphalt binder in the mix or stripping of asphalt from particles of

aggregate.

Drip Track Raveling: Progressive disintegration of the surface between wheel paths

caused by dripping of gasoline oil from vehicle.

Longitudinal Cracking: Cracks approximately parallel to the pavement centerline. These are

caused by poorly constructed construction joints and shrinkage of

the asphalt concrete surface. They may also be reflection cracks.

Raveling: Wearing away the pavement surface caused by dislodging of

aggregate particles and binders. This is usually a result of insufficient

asphalt binder in the mix or stripping of asphalt from particles of

aggregate.

Drip Track Raveling: Progressive disintegration of the surface between wheel paths

caused by dripping of gasoline oil from vehicle.

Bleeding or Flushing (Fatting Up): The exuding of bitumen on to the pavement surface causing

reduction in skid resistance. Bleeding is generally caused by excessiveamount of asphalt in the mix or low air void content. It occurs in the

mix in hot weather.


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Corrugations: Due to instability of base or poor original riding surface (plastic

movement of pavement)

Pot Holes: When cracks become deep.

Ruts: Depressions formed under the wheel due to heavy load, this causes

consolidation, deformation or plastic flow.

General surface maintenance: For maintenance of gravel roads blading and occasional resurfacing is

required.

For surface treatments of low type bituminous surface inmaintenance of roads; Patching, seal coating or possible loosening

oiling, re mixing and relaying are involved.

For high type bituminous concrete and Portland cement concrete,the Removal and replacement of failure areas and resurfacing are

approximate treatment methods for highway maintenance.

Use same material and methods for road surface maintenance as fasas possible. Highway Maintenance must be planned for rapid performance and to

cause least possible disruption or hazard to traffic.

Roadside and Highway Drainage maintenance

Depends on the characters of road side where the roadside is grassy it mustbe mowed; cutting, ploughing or spraying with weed killer must be done.

If there is dry grass fire hazard burning, plowing must be done. When back slope is covered with bush, trimming must be done to

increase the sight distance and clearance of road.

Control of side slope erosion by mulching, seeding etc. Picking up litter, thrown or blown along roadside or wayside area a

Routine work.


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Drainage of Highway Maintenance: Keeping ditch, culvert and otherdrainage structure, clean and ready to carry next flow water.

Sediments deposited during period of heavy flow must be removed

badly eroded channel and dikes properly protected to prevent

recurrence.

Shoulders

Depend on the surface character of these areas SOD shoulders must be moved and occasionally bladed down to the

level of the roadway so that water is not trapped in the traveled way.

Gross must be kept in good condition.

Shoulders protected by bituminous blankets or surface treatmentssame as for roadway surface.

Gravel and earth shoulders that leaves a drop off at the pavementedges creates a serious accident hazard, hence, should be corrected

by reconstruction, resurfacing or other appropriate means.

Due to continuous wetting and drying of shoulder, edge joints resultbetween lane and shoulder which may cause settlement of

pavement due to entrance of water in sub grade soil. It can Repaired

by filling the joint with sand and asphalt concrete

CONCLUSION

This paper has discussed an overview of road construction on maintenanceas well as the importance of road infrastructure.

I believe you have stick one or two things from the paper Thank you for listening.

overview of road construction and maintenance

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