What is Road /Pavement?

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Introduction

An open, generally public way for the passage of vehicles, people, and animals. 

Purpose :Many rely on paved roads to move themselves and their products rapidly and reliably

Finish with a hard smooth surface (pavement) helped make them durable and able to withstand traffic and the environment. 

Road pavements deteriorate over time due to the impact of traffic, particularly heavy vehicles, and environmental factors.

Roads have a life expectancy of between 20 - 30 years.

Functions : One of the primary functions of a pavement is load

distribution which can be characterized by the tire loads; tire configurations; repetition of loads; distribution of traffic across the pavement; and vehicle speed.

Pavement material and geometric design can affect quick and efficient drainage thus eliminating moisture problems such as mud and ponding (puddles). Consist of: i) Surface drainage : Removing all water present on the pavement surface, sloping, chambers, and kerbs. ii) Subsurface drainage : Removing water that seep into or is contained in the underlying sub-grade.

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Several elements make up the roadway.

Each layer represents one of the elements of the pavement system. 

All these elements work together to provide a quality durable pavement.

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Typical Components

Typical Components

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EMBANKMENT

SUB-DRAIN

SUB-GRADE

PAVEMENTBASE

Embankment When roads are built higher than the

surrounding ground, a structure of compacted earth called an embankment is built. 

The embankment is built to support the other three layers of the pavement system.

The construction of embankments for roadways can take up a large part of the total cost.

Embankments can be made from almost any common type of deposit except topsoil.

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Sub-grade The sub-grade is made of soils that have been

specially prepared to meet the requirements to support the other two layers.

The sub-grade is a selected soil material that is carefully compacted to provide uniform support to the pavement.

The sub-grade lies directly on either the embankment or the native soil.

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Base The base is a mixture of crushed rock. The base layer provides uniform support to

the pavement and allows water that penetrates any joints or cracks in the pavement to move quickly to the sub-drain without saturating and softening the sub-grade.

The base layer lies directly on top of the sub-grade and is built of clean sand or rock.

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Pavement The top layer is the pavement. The pavement materials can either be Hot

Mix Asphalt (HMA) and Portland Cement Concrete (PCC).

The pavement itself resists bending, and distributes vehicle weights over a large area.

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Sub-Drain The sub-drain collects water from the base and the sub-

grade and drains that water into the ditch. The sub-drain sits alongside the pavement, base and sub-

grade. The sub-drain is basically a trench with a perforated pipe

near the bottom, surrounded by clean coarse-size rock which allows rapid transportation of water.

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Sub-Drain

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Flexible pavements are those which are surfaced with bituminous (or asphalt) materials. 

Its "flexible" since the total pavement structure "bends" or "deflects" due to traffic loads. 

Generally this type of pavement requires some sort of maintenance or rehabilitation every 10 to 15 years.

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Each layer receives the loads from the above layer, spreads them out, and then passes on these loads to the next layer below. 

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Material layers are usually arranged in order of descending load bearing capacity with the highest load bearing capacity material (and most expensive) on the top and the lowest load bearing capacity material (and least expensive) on the bottom

Thus, the further down in the pavement structure a particular layer is, the less load (in terms of force per area) it must carry

This is the layer (or layers) under the base layer.  A sub-base is not always needed. A proper sub-base consists of various sizes of

crushed stone aggregate, commonly known as crusher run.

Depending on the sub soils on your site you may need 8-12 inches of various sizes of sub-base.

With well drained sub soils, without movement, added sub-base materials may be sufficient, along with proper pitch & grade.

If the sub-base is knowingly sufficient, grading & compaction with vibratory roller or plate compactor in small areas, may be all that is necessary.

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3.1 Sub-base Course

It functions primarily as structural support but it can also help:a) Minimize the intrusion of fines from the sub-grade into the pavement structure. b) Improve drainage. c) Minimize frost action damage. d) Provide a working platform for construction. 

The subbase generally consists of lower quality materials than the base course but better than the sub-grade soils. 

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3.1 Sub-base Course

The first coat to be placed, on top of your proper sub-base, is the base course .

It provides additional load distribution and contributes to drainage and frost resistance. 

The base is built of clean sand or rock. The base layer provides uniform support to the

pavement and allows water that penetrates any joints or cracks in the pavement to move quickly to the sub-drain without saturating and softening the sub-grade.

This coat is put in place for strength, plus it works as a true-leveler course, to take out any small imperfections in the grade.

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3.2 Base Course

After the binder is put into place with paver, it is compacted with a vibratory roller for tighter density and added strength.

Base courses are usually constructed out of:i) Aggregate: Base courses are most typically constructed from durable aggregates that will not be damaged by

moisture or frost action such as dense bitumin macadam (dbm)ii) HMA: In certain situations where high base stiffness is desired, base courses can be constructed using a

variety of HMA mixes. 

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3.2 Base Course

This is the top layer which comes in contact with traffic.  It normally contains the highest quality materials.  It serves to prevent the entrance of excessive quantities of

surface water into the underlying base & sub-grade. It is sometimes subdivided into two layers:

i) Wearing Course: A layer in direct contact with traffic loads.  It is meant to take the impact of traffic wear and can be removed and replaced as it becomes worn.  ii) Intermediate/Binder Course: This layer provides the bulk of the HMA structure.  It's main purpose is to distribute load. It may compose of one or several HMA sublayers.

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3.3 Surface Course

Hot mix asphalt (HMA) is "the black stuff" used as a pavement material.

Its a combination of aggregate and asphalt binder mixed together at elevated temperatures that forms a hard, strong construction material when cooled to suitable temperatures.  

Also known as "asphalt concrete" (AC or ACP), "asphalt", "blacktop" or "bitumin“

They must be mixed very well to make sure that the rocks are evenly distributed in the mix.

Each rock piece must be completely coated by the asphalt.

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3.3 Surface Course

Once it is well mixed, it is laid down on the roadway as pavement.

The pavement must then be compacted to achieve uniform density.

If this is not done properly,  it can reduce the lifetime of the pavement and increase the costs of maintaining the road.

It usually costs less. The life expectancy of an asphalt pavement

is between 15 to 20 years.

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3.3 Surface Course

Rigid pavement composed of a PCC surface course. Such pavements are substantially "stiffer" than

flexible pavements due to the high modulus of elasticity of the PCC material. 

Further, these pavements can have reinforcing steel, which is generally used to reduce or eliminate joints. 

Because of its relative rigidity, the pavement structure distributes loads over a wide area with only one, or at most two, structural layers.

This type of pavement can serve 20 to 40 years with little or no maintenance or rehabilitation and often used in urban and high traffic areas.

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This is the layer (or layers) under the base layer. 

The properties and function of this layer are similar to those under flexible roads/pavements.

A sub-base is not always needed and therefore may often be omitted.

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4.1 Sub-base Course

This is the layer directly below the PCC layer and generally consists of aggregate or stabilized sub-grade.

It provides additional load distribution, contributes to drainage, uniform support to the pavement and a stable platform for construction equipment.

Bases also help prevent sub grade soil movement due to slab pumping.

Base courses are usually constructed out of:a) Aggregate base. b) Stabilized aggregate or soil.c) Dense-graded HMA. d) Lean concrete

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4.2 Base Course

The surface course is the layer in contact with traffic loads.

It consists of the PCC slab which is the stiffest layer and provides the majority of strength.

The surface course can vary in thickness but is usually between 150 mm (for light loading) and 300mm (for heavy loads and high traffic). 

Portland cement concrete is the "white stuff" used as pavement material.

Portland cement is made by heating shale, limestone and small amounts of iron-ore to very high temperatures.

It is then cooled and ground into a fine powder.

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4.3 Surface Course

Gypsum is added to the powder to keep the powder from hardening instantly when water is added.

Portland cement concrete is made by mixing portland cement with water, and coarse- and fine-size rocks.

All the materials, including the right amount of air bubbles, must be in the correct proportions in order for the mixture to harden properly.

A properly mixed concrete has all the rock pieces completely coated all the way around each piece.

It initially can be more expensive. The life expectancy of portland  cement pavement

varies, as little as 20 years or more than 40 years.

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4.3 Surface Course

Combination of flexible and rigid pavements to give riding quality.

The layers for a composite road is similar to the layers consist in rigid road.

However, there is another bituminous layer on the surfaces of concrete slab.

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There are several factors that affect pavement life:

Traffic volume Quality of materials used Construction practices, and How well the other layers of the road

perform. All of these things function  together — and

any one of them can add to or detract from the pavement’s lifetime.

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Hard Shoulder Continuous strips alongside pavements, which

vehicles may drive during emergencies. Normally 3 m wide to fulfilled the functions of

the slow lane.

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Kerbs To define the limits of carriageway.

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Drainage- Surface and Subsurface Road Chamber – Cross falls. To cope with heavy water run-off during a storm.

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Street lamps Street lamps are

designed to illuminate the surrounding area at night, not only as a deterrent to criminals but also to allow people to see where they're going.

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Road Markings This furniture is any kind

of device or material that is used on a road surface in order to convey official information.

They provide guidance and information to drivers and pedestrians.

They can be used to delineate traffic lanes or serve as noise generators when run across a road.

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Traffic Signs They warn drivers of upcoming

road conditions such as a "blind curve", speed limits, etc.

Direction signs tell the reader the way to a location.

Direction signs are usually mounted on poles.

Illumination is added in order to aid nighttime users.

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Street Barriers and Railings

These keep vehicles within their roadway and prevent vehicles from colliding with dangerous obstacles.

Traffic barriers installed at the road side also prevent errant vehicles from falling off to deep slopes

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An interchange is a road junction that typically uses grade separation, and one or more ramps, to permit traffic on at least one road to pass through the junction without crossing any other traffic stream.

It differs from an intersection, at which roads cross at grade.

Interchanges are almost always used when at least one of the roads is a limited-access divided highway (expressway or freeway), though they may occasionally be used at junctions between two surface streets.

The type of road interchanges commonly used in road construction are cloverleaf, stacked, diamond, and trumpet.

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