Nurela Abera (MSc)
address: nuralaabera@gmail.com
Road Cross-Section Elements
Flexible Pavement Structure
Rigid Pavement Structure
1. Road Construction
 Earthwork Operations & Equipment
 Construction of Subbases, Bases & Low-cost Surfaces
and Bituminous Pavements
1.1 Earthwork Operations & Equipment
 Preparation of Right-of-Way (ROW)
 The initial operation in the construction of a highway facility
 All obstructions & Objectionable Materials like trees, undergrowth, abandoned




utilities, drainage structures etc.. , are to be removed and disposed of in accordance
with the governing specifications
The Contractor is responsible for the protection and the preservation of all
property, both in and adjacent to the right-of-way.
The boundaries of all areas in which the project work is to be performed should be
clearly marked
A careful investigation should be made to determine the location of all underground
facilities within the right-of-way
Clearing & Grubbing:



All trees, undergrowth, stumps, shrubs, etc… not designated to remain in place shall be cleared & grubbed
Trees & shrubs which will not interfere with the use of a highway & its drainage system are often selected to
remain in place for their scenic, historical, and other values
All holes, ruts, etc… remaining after clearing & grubbing, should be backfilled and compacted to prevent
ponding of water
 Disposal of Materials obtained from clearing & grubbing
 Removing Structures & Obstructions
 Remove, salvage, or dispose of materials promptly. Backfill basements or cavities to




the surrounding ground level
Remove Bridges, Culverts & Other drainage structures. Dismantle designated
Agency-retained material without damage
Dispose of designated concrete pavement, base course, sidewalks, curbs, gutters,
foundations, gravel, bituminous material, etc..
Store salvageable ballast, gravel, bituminous material, and other pavement materials
at designated locations
Ensure stored material is free from dust and other foreign matter
 PREPARATION OF ROADBED AND PROTECTION OF EARTHWORKS
 covers all work in connection with the preparation of the road bed, prior to the
construction of the embankments or capping layers, and the preparation of the subgrade prior to the construction of the pavement layers
 The existing ground beneath embankments or the bottoms of cuttings classified as
suitable material which has a density of less then 95% of the maximum dry density
be scarified to a minimum depth of 150mm, watered and re-compacted in
accordance with the requirements
Con't

After areas of the existing ground that are to be covered by fill have been cleared and grubbed, or
after excavation in cut has reached the top of road bed, the existing ground in fill sections, or the
roadbed materials in cut sections should be treated as hereunder:
 Removal of Unsuitable Material
 Three-pass roller Compaction
 Preparation and compaction of existing ground in fill sections and of roadbed material in cut
sections
 Draining of existing ground and road bed
 In-situ treatment of roadbed
 Widening the roadbed
 Excavation & Embankment
 The construction of a graded roadbed, upon which the subbase, base and wearing courses
will be built, is called earthwork. Excavation is that part of the earthwork that is dug up,
hauled, and then used to form the embankment section of the roadbed.
 Roadway excavation, which is that material obtained from within the right-of-way,
exclusive of channel and structural excavation, may be composed of common earth, solid
rock, loose rock, or any combination of these materials
 When there is not enough suitable roadway excavation , together with suitable excess
channel and structural excavation, to complete the embankment to the required line and
grade, then borrow excavation must be imported to make up the difference
Con't
 Excavation involves the loosening, digging, loading, hauling, disposal of material




obtained from roadway cuts, channel changes, ditches, structure foundations, and/or
borrow pits.
Disposal of the materials is accomplished by incorporating it into an embankment or
wasting the surplus amount or material of unsuitable nature
Excavation includes the constructing, shaping, and finishing of all earth work for the
entire length of the roadway, and its approaches in conformity to the required lines,
grades, typical sections, and pertinent specifications
Excavate, haul, dispose of, place, and compact specified materials necessary to
construct the project
Different types of Excavation:




Common Excavation: Excavate and use or dispose of all material encountered. Clear, grub, and remove
topsoil before beginning excavation, grading and embankment operations. Dispose of surplus or unsuitable
excavated material
Rock Excavation: includes all masses of material, which cannot be removed without blasting or ripping, and
all detached stones or boulders having a volume of 2 m3 or more
Borrow Excavation: that material coming from approved sources normally outside the limits of the project
Unsuitable Excavation: used to provide the removal and disposal of saturated or unsaturated mixtures of
soil and organic matter not suitable for foundation material.
 Unsuitable Materials: such materials are unstable in their natural state because of
excessive moisture content. Such materials should be wasted, or used to flatten
slopes, unless an economical method of treatment is available to make them
satisfactory
Con't
 Surplus Material: the one obtained when the required excavation yields more






material than the proposed embankment construction requires. This surplus
material is normally classified as waste
Embankment Construction: construction methods which ensure, to the extent
economically feasible, uniformity of material, layer thickness, moisture content, and
compactive effort are vital in the accomplishment of proper embankment
construction
The proper breakdown of clods and blending of materials using disc plows, blade
graders, or similar equipment ordinarily will accomplish the desired result in most
soils. When feasible, poorer materials should be used in the lower portion of the
embankment
Hauling, Spreading and Shaping
More uniformity of compaction is ordinarily obtained when earth embankment
layers are relatively thin
The success of compaction operation is dependent to a large extent on proper
moisture control
Usually it is better to begin compaction with the moisture content slightly high;
however, in humid areas it may be better to begin with the moisture content at
optimum
Con't
 Embankment solids must be compacted to densities which will provide adequate






stability under the conditions to which the finished highway will be subjected
Density Tests for Control of Compaction
Control of Compaction by Ordinary Methods: Particular attention should be given
towards maintaining proper loose layer thickness, proper moisture content, and
adequate coverage with the specified rollers
When feasible the finished earthwork should have a pleasing contour and be
reasonable smooth in all respects
The work of finishing earth work can be held to a minimum and better construction
will result if every reasonable effort is made during excavation of cuts and
construction of embankments to maintain slopes, shoulders, and ditches as this
work progresses
Subgrade Preparation: consists of scarifying at least the top 15cm of the subgrade,
mixing until uniform in color and texture, compacting to a higher density than
normal embnkment layers at a specified moisture content, and shaping to the
required typical section within specified tolerances
It is essential that every possible measure is taken to control erosion during highway
construction. The effective way to control erosion and siltation is early treatment of
slopes-both cut and fill. Early treatment means treating cut slopes as excavation
progresses and fill slopes as embankment construction proceeds. Slope treatment
generally consists of seeding and mulching
Con't
 Protection of Earthworks
 Earthworks shall be protected from the weather at all times.
 The compacted layers of fill and the bottom of excavations shall be adequately





drained and shaped to prevent free water standing on or scouring the completed
layer or the in-situ material.
Any windrows or ridges, which will impede the free drainage of water, shall be
removed from the surface.
No fill material for a succeeding layer has been shall be placed if the underlying
layer has been softened by excessive moisture.
All permanent drains, plus additional necessary temporary drains, shall be
constructed as soon as possible to protect the earthworks.
Ruts, potholes and other damaged sections of earthworks and slopes shall
be reinstated.
Drains shall be so constructed as to avoid damage, caused by erosion, to
embankments.
1.2 Construction of Subbases, Bases &
Low-cost Surfaces
 Subbases:
 The materials used for the construction of subbases could be either:
Natural Gravel
 Scoria (Cinder Gravel)
 Weathered Rock
 Crushed Gravel
 Crushed Rock or Crushed Boulders
 Recycled Pavement Material
And any other granular material complying with the requirements of subbases

 Material requirements for Gravel Subbase could be obtained from approved sources
in borrow areas, cuts or existing pavement layers
 The complete subbase should contain no material having a maximum dimension
exceeding two-thirds of the completed layer thickness
 Gravel Subbase materials should conform to the following requirements



Grading Limits: the material should have a smooth continuous grading within the limits of
grading
Grading Modulus (GM)
Plasticity Index (PI)
Con't




California Bearing Ratio (CBR)
Compaction Requirements
Los Angeles Abrasion (LAA)
Particle Shape; Flakiness Index (for crushed stone sub-base)
 Construction Requirements for Sub-bases using Recycled Pavement Material

Milling/Scarifying


Before scarification or milling is commenced, the surface of the existing pavement should be
clean and free from soil and other deleterious matter
The existing pavement should be broken up to the required depth either by scarifying or by the
use of an approved milling machine
Placing, Spreading and Compacting


Any material which is required to be added, to either supplement or modify the scarified milled
material, should be evenly spread and thoroughly mixed into the scarified/milled material to
form a homogenous material prior to compaction
Construction Requirements




Sub-base material should be spread on the approved subgrade by mechanical means without
segregation. The material should be loosely spread in layers to give a compacted thickness not
exceeding 200mm and not less than 100mm. The final compacted layer should be free from
concentrations of coarse or fine materials.
The surface of each completed layer should be moistened prior to the construction of the succeeding
layer. Spread and shape the mixture on the prepared surface in a uniform layer
The material should be compacted by the use of rollers progressing gradually from the outside
towards the center of the layer, except on super elevated curves, where the rolling should begin at the
low side and progress to the high side.
Rolling should continue until the entire thickness of each layer is thoroughly and uniformly
compacted to the specified density
Con't
 Subbase as a filter or separating layer

This may be required to protect a drainage layer from blockage by a finer material or to
prevent migration of fines and the mixing of two layers.
 Road Bases:
 The materials used for the construction of road base layers could be one of
the following:



Crushed Rock or Stone
Naturally Occurring Granular Materials, Boulders, Weathered Rock
Dense Bitumen Macadam
 Graded Crushed Stone Base (GB1)




This material is produced by crushing fresh, quarried rock and may be a crusher-run or the
material may be separated by screening and recombined to produce a desired particle size
distribution
The material should be clean and free from organic matter, lumps of clays or other
deleterious substances.
The material should be in such a nature that it can be readily transported, spread and
compacted without segregation
Crushed Stone Base materials should conform to the following requirements




Grading
Plastic Index
California Bearing Ratio (CBR)
ACV ( Aggregate Crushing Value)
Con't

Mechanical Strength Requirements (TFVT)



Limits on the maximum loss in strength following a period of 24 hours of soaking in water. The
likely moisture condition in the pavement are taken into account in broad terms based on annual
rainfall
Flakiness Index
Graded Natural Gravel (GB2, GB3)



Lateritic, calcareous and quartzite gravels, river gravels, boulders and other transported
gravels, or granular materials resulting from the weathering of rocks can be used
successfully as base course materials.
These materials should be of such a nature that it can be readily transported, spread and
compacted without segreggation
Graded Natural Gravel Base materials should conform to the following requirements:
 Grading
 Plasticity Index
 CBR
 ACV
 Abrasion
 Flakiness Index
 Crushed Ratio
 Grading Modulus

Dense Bitumen Macadam


Bitumen macadam in which the aggregates and filler are so graded as to
form a close textured mixture, of low permeability, when spread and
compacted.
Material Requirements:






Coarse aggregates: should consists of hard durable particles produced by crushing
rock or boulders
 ACV
 LAA
 Soundness
 Flakiness Index
 Crushed Ratio
 Water Absorption
 Coating of Chippings
Fine Aggregates
Filler: where necessary to improve the combined grading or other properties of the
mix, a filler of either hydrated lime, cement or crushed rock or crushed boulder
dust may be added
Binder: 60/70 penetration grade bitumen
Mix Design Parameters for Dense Bitumen Macadam
Construction Requirements
 The material should be laid either by a self propelled paving machine or by
means of a grader
 The equipment should be of adequate rated capacity & in good working
order









The mixing plant could be either a batch type or continuous type and
equipped with means of accurately controlling the proportions of all
constituent material
Compaction should be carried out using 8-10 smooth wheel rollers or multi
wheeled pneumatic tyred rollers
Road base material should be spread by mechanical means without
segreggation
The material should loosely be spread in layers to give a compacted
thickness within 10-20cm.
The surface of each completed layer should be moistened prior to the
construction of the succeeding layer
Prior to compaction the moisture content of the spread material should be
adjusted either by the uniform application of water or drying out to achieve
the OMC
The surface of the completed layer should be tightly bound, free from
movement under the compaction plant, and free from laminations, ridges,
cracks, or loose or segregated materials
The in-situ density of the completed layer should achieve the desired MDD
The completed road base layer should not be used by construction or
public traffic prior to the application of prime coat

Vehicles used for transporting dense bitumen macadam base should have
tipping bodies capable of discharging directly into the paving machine

Dense Bitumen Macadam material should be laid by spreading/finishing
machine capable of laying to the required widths, thicknesses & cross-sectional
profiles without causing segregation or other surface defects

The maximum temperature of material during mixing should not exceed 165°c.

On discharge from the mixer plant the aggregate should be completely coated
with binder and the fine aggregate should be evenly distributed throughout the
mix

During transport the material should be insulated against heat loss and
protected from the ingress of moisture by the use of covers

The temperature of the spread material at the time of compaction commences
should not be less than 135°c. the compaction should be completed before the
temperature of the laid material falls below 105°c.

The density achieved in the completed layer should not be less than 97% of the
Marshal Density


Dense Bitumen Macadam Road Base and priming should not be carried out
in the following adverse weather conditions
 During foggy or wet conditions
 When rain is imminent
 when wind is sufficiently strong to cause uneven spraying;
 When the surface on which the layer is to be constructed is wet
 When the temperature of the surface on which the layer is to be
constructed is less than 10°c
Construction Tolerances
 Level & Grade
 Width
 Thickness
 Cross-Section
 Prime Coat
 Material


The material used for priming could be MC-30, MC-70, or MC-250
cutback bitumen
The aggregate used for blinding the primed surface should consist
of fine crushed rock or river sand
 Safety
 The handling and application of bituminous binders are hazardous
operations. Attention is drawn to the risk of fire and toxic fumes,
which may cause extensive damage to the equipment and injury
to the equipment operators.
 Crewmen should wear heat-resistant gauntlet gloves. Facemasks
should be worn when a spray lance is used because of possible
rupture of the armored hose.

Equipment

Bitumen Distributer
 The distributor should be free from binder or fuel leaks;
 The distributor should be fitted with an accurate means of measuring
and indicating the roads peed of the vehicle at operational speeds.
Pipes shall be provided with suitable couplings to ensure the safe
transfer of binder to and from the distributor for loading and unloading.
 The bitumen tank shall have an inspection manhole and a calibrated
dipstick registering the volume of the binder in the tank.
 The type of spray nozzles, the spacing of the nozzles along the spray bar
and the height of the spray bar above the road surface should be such
that the distribution of the binder over the sprayed width of the road is
of the required uniformity
 Before each separate application of binder, the spray bar shall be reset to
the height required to ensure the necessary uniformity of nozzle spray
overlap (double or triple) and distribution is maintained.


Air Blower/Compressor

Used to assist in the removal of loose or deleterious material from the
surface of pavement layers

Preparation of the layer to be primed




the layer to be primed shall be broomed and cleaned of all loose or
deleterious material by means of a rotary broom and hand brooms.
Brooming and cleaning shall be done carefully so as to avoid any damage to
the layer.
A light spray of water, sufficient to dampen the surface, shall be applied
uniformly to the layer immediately before the application of the prime.
Application of the Prime Coat





In general, the rate of application of prime shall be in the range of 0.6 – 1.0
litre/m2 residual bitumen
Wherever feasible, the prime shall be applied in one or more lanes evenly
over the full width of the road and allowed to penetrate and cure until
traffic can pass over the surface without the wheels picking up the prime.
All traffic shall be kept off the surface until this condition is obtained.
If prime is applied in more than one lane, allowance shall be made for
overlapping the lanes by 100 mm.
Care shall be taken to protect any kerbing, guardrails, channeling, and
gutters from the prime by covering with a suitable protective material when
spraying.
After the prime has penetrated sufficiently, surplus prime shall be
covered with damp crusher sand, which shall be worked into it by
means of hand brooms in order to absorb the surplus prime.
 Tack Coat

Material




RC-70 cutback bitumen
Bitumen emulsion
safety, equipment, preparation of the surface are similar to the prime coat
Application of the tack coat

In general, the rate of application of tack coat shall be in the range of 0.1 to 0.2 kg/m2
of residual bitumen
 Surface Treatments

Material
 Bituminous Binders

Conventional Bituminous Binders





Non-homogeneous (heterogeneous) Modified Bituminous Binders (Bitumen Rubber
Binders)




Penetration-grade bitumens
Cutback bitumens
Anionic bitumen emulsions
Cationic bitumen emulsions
Base bitumen: 60/70, 80/100 or 150/200 penetration-grade bitumen
Rubber: obtained by processing and recycling pneumatic tyres. The rubber crumbs shall be
produced by a mechanical comminuting process
Water for the production of bitumen emulsion
Chippings for surface treatements



Grading
Hardness
Shape


Aggregate for slurry seal
Plant & Equipment


Bitumen Distributor
Chip Spreaders

spreading the stone uniformly, both transversely and longitudinally, over widths from
1.5m to 4.0m;

adjustment to permit variation of the rate of application
stopping and starting without forming a joint line
keeping pace with the binder distributor.



Rollers

Brooms:






enable the chippings to be distributed evenly over the surface without
dislodging chippings from the binder
Trucks for transportation of chippings
Mixer for Slurry Seal
Spreader Box for Slurry Seal
Pre-coating plant
Weighing devices
•
 Bituminous Surfacings

Materials
 Bituminous binders
 Aggregates
 Resistance to crushing (ACV)
 Shape of the aggregate (flakiness index)
 Polishing
 Adhesion
 Absorbtion
 Sand equivalent
 Design requirements
 Grading
 Rolled-in chippings
 Fillers

If the grading of the combined aggregates for asphalt surfacing mixes
shows a deficiency in fines, an approved filler may be used to improve
the grading

Plant & Equipment
Mixing Plant
 Spreading equipment

• Paver
• Chip spreader
Rollers
 Binder distributors
 Trucks


General Limitations
Weather conditions
• Asphaltic mixes may be mixed and placed only under
favorable weather conditions, and should not be mixed or
placed when rain is imminent or during misty or wet
conditions
 Moisture
• The mixing and placing of asphaltic mixes will not be
allowed if:

• (i) the moisture content of the aggregate affects the uniformity
of temperature;
• (ii) free water is present on the working surface;

Surface Requirements
Correction of roadbase
 Cleaning of Surface
 Tack Coat
 Preparation for placing the overlays

Storage
Production & Transport
 Using batch plants



Heating the aggregate


Batching


The aggregate shall be dried and heated to the required temperature
Each fraction of the aggregate and binder shall be measured
separately and accurately in the proportions by mass in which they are
to be mixed
Mixing

The aggregate, filler and binder shall be mixed until a homogeneous
mixture is obtained in which all particles are uniformly coated

Using drum type mixer plants
The aggregate and filler shall be accurately proportioned and conveyed into
the drum mixing unit.
 The calibrated amount of binder shall be sprayed onto the aggregates at the
correct position so that no hardening of the binder shall take place.
 A homogeneous mixture and uniform coating of binder must be achieved


Transporting the mixture




Loads shall be covered by waterproof canvas or insulated metal sheets when
the haul exceeds 10 km or during cold, windy or rainy weather
Any asphalt which has become wet due to rain or any other cause shall be
rejected.
Hauling over freshly laid material is not permitted.
Spreading the mixture



The mixture shall be delivered to the paver in such a manner that the paver
will never be forced to stop for lack of asphalt
The temperature of the mixture shall be controlled by measuring in a
random pattern in the truck immediately before emptying and shall not be
more than 10° C below the minimum temperature specified for mixing
The addition and removal of material behind the paver shall normally
not be allowed and the paver shall be capable of spreading the mixture
to the correct amounts that will provide the required compacted
thickness
the paver shall be equipped to provide automatic control of levels and
cross section
 The mixer capacity and the operating speed of the paver are to be so
co-ordinated as to ensure continuous laying and to avoid intermittent
stopping of the paver.


Compaction
The material shall not be excessively displaced in a longitudinal or
transverse direction especially when changing gears, stopping or
starting rollers.
 No cracks or hair cracks shall be formed and the bond with the
underlying layer shall not be broken.
 Rollers shall not be left standing on the asphalt layer before it has
been fully compacted and before the layer surface temperature has
dropped below 60cc
 The mix shall be rolled as soon as possible after it has been laid by a
combination of vibratory and non-vibratory steel-tired flat rollers and
pneumatic-tyred rollers in a sequence predetermined and approved
during the laying of trial sections

 Final words and Questions?