c3010 highway engineering unit5

7/29/2019 C3010 Highway Engineering UNIT5

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ROADS CONSTRUCTIONMATERIALS & TESTING

Highway Engineering C3010 / UNIT5

ROAD CONSTRUCTION MATERIALS AND TESTING

OBJECTIVES

General Objective

To understand general elements in road construction materials and testing

Specific Objectives

At the end of the unit you should be able to:-

identify the material used in road construction.

describe the function of road materials and testing.

explain the purpose of road materials usage and testing.

perform the material testing.

analyze result of the road materials test.

UNIT 5


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5.0INTRODUCTION

Bituminous materials as described hereafter refer to hydrocarbons of

variable colour, hardness and volatility, sometimes associated with the mineral

matter. Their consistencies at normal temperatures range from something slightly

thicker than water to hard and brittle materials that will shatter under a blow from

a hammer, but even the hardest of them will flow if subjected to long continuous

loading. The non-materials and non-carbonaceous matter is largely soluble in

carbon disulphide (CS2).

5.1 FUNCTIONS OF BITUMINOUS MATERIALS

Bituminous materials, usually called binders, when used in combination

with the mineral aggregate have a number of functions to perform. The various

objectives achieved by using a bitumen binder in road construction may be

summed up as follows:

a. It acts as a cushion for the surface material and absorbs the kneading

action of traffic. The abrasive action of the wheels of a vehicle is also

resisted. This enhances the life of the pavement.

b. It seals the surface of the road against ingress of water, provided the

granular material used is dense-graded.

c. It binds the surface particles together and loss of material from the

surface by suction under the body of the moving vehicle, is thus

checked.

INPUT

BITUMINOUS MATERIAL


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d. If a properly selected bituminous material is used, it resists the action

of weathering agencies, like the wind and the sun and ensures a long

life for the pavement.

5.2 DEFINITIONS

The terms bitumen and asphalt are often confused. They actually refer to

the same material and different agencies use either of the two names. Some

standard definitions, almost universally accepted are given below :

5.2.1 Bituminous or Asphalt.

Mixtures of hydrocarbons of natural or pyrogenous origin, or

combinations of both, frequently accompanied by their non-metallic

derivatives, which may be gasesous, liquid, semi-solid or solid and which

are completely soluble in carbon disulphide.

5.2.2 Liquid Bituminous Materials.

Materials having a penetration at 25oC (77oF) under a load of 50

grams applied for one second, of more than 350.

5.2.3 Semi-solid Bituminous Materials.

Materials having penetration at 25oC (77oF) under a load of 100

grams applied for five seconds, of more than 10 and a penetration at 25 oC

(77oF), under a load of 50 grams applied for one second, of not more than

350.


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5.2.4 Solid Bituminous Materials.


grams applied for five seconds of not more than 10.

Emulsions, cut-backs and road oils are liquids, asphalt cements are semi-

solids and powdered asphalts are solids. Tars are both liquids and semi-solids,

depending upon the particular grade.

5.3 SOURCES OF BITUMINOUS BINDERS

Bituminous binders (including tars) represent combinations of hydrogen

and carbon. Some of the hydrocarbons used in road construction occur naturally

but most of them are obtained as by products from the manufacture of gas, liquid

fuels, lubricants, coal-gas and coke. Principal sources of bituminous materials for

pavements are given below :

5.3.1 Natural Asphalt.

Crude petroleum sometimes works its way up through cracks in the

earths crust to the surface, where the rays of sun and the wind drive away

the lighter oils, leaving behind a black and plastics material called asphalt.

These materials, which occur naturally, are usually found in combination

with a fairly high percentage of clay or fine sand which they pick up as

they travel up through the cracks. Natural asphalts are sometimes called

native asphalts also.

5.3.2 Rock Asphalt.

Deposits of lime-stone or sand-stone are sometimes found

impregnated with bituminous materials. Such deposits generally form


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good road construction materials. Experience in United States of America,

France and other foreign countries has shown that road surfaces

constructed with these materials are extremely durable and stable. The

percentage of bituminous material in these stones varies from 4.5 to 18 %.

5.3.3 Petroleum Asphalt.

Most widely used asphaltic or bituminous materials are those which

are derived by the distillation process from crude petroleum. Steam or Air

Distillation is employed for the purpose. Steam distillation produces

excellent asphaltic materials, whereas products obtained by air distillation

usually called blown or oxidized asphalts, find very little use as paving

materials. They are however put to other diversified uses.

5.4PAVING ASPHALT : CLASSIFICATIONS

The various Paving Asphalt Classifications are:

a. Road oils or Slow-Curing Liquid Asphalts (SC).b. Cut-Back Asphalt :

Medium Curing Liquid Asphalts (MC)

Rapid-Curing Liquid Asphalts (RC)

c. Asphalt Cements (AC)

d. Emulsified Asphalts.

e. Powdered Asphalts.

5.4.1 Road Oils

Road oils or slow-curing liquid asphalts may be described as the

petroleum distillates from which volatile and light fractions are largely

removed. They may range from liquid road oil having poor binding


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characteristics to a very viscous material having excellent binding

characteristics and requiring heat to become workable. These oils set very

slowly and are employed where the same consistency of binder is desired

both at the time of processing and after the curing period has elapsed.

They are designated by the letters SC, and range from light liquid SC-0 to

semisolid SC-5 consistencies. It may be noted here that higher the

number following the letters SC, the higher is the asphalt content with a

corresponding decrease in the quantity of fluxing oil. The application

temperatures may range from 500C to 3750F.

5.4.2 Cut-Back Asphalts Medium Curing Type

Medium curing cut-back asphalts are produced by cutting back

asphalt cement with heavier oils like kerosene or light diesel oil. The

addition of these oils increases the fluidity of the asphalt cement. These

oils evaporated slowly when exposed to heat or air. The presence of these

oils makes the asphalt workable at relatively low temperatures, gives it

good wetting properties and ensures a satisfactory coating of the fine-

graded and dusty aggregates. They are designated by the letters MC andrange from light MC-0 to almost semi-solid MC-5. The higher the number,

the higher is the quantity of asphalt in the cut-back. The application

temperature ranges from 500C to 2750F.

5.4.3 Cut-back Asphalt Rapid Curing Type

Rapid curing cut-back asphalts are produced by cutting back

asphalt cement with light oils like naphtha or gasoline. These products are

more volatile than kerosene and diesel oil, and since the distillates

evaporate more rapidly than kerosene. The cutbacks are known as rapid

curing. Lower penetration asphalt-cements are usually mixed with these

oils to prepare rapid-curing cut back asphalt. They are designated by the


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letters RC and range from RC-0 to RC-5 consistencies. Here also, the

higher the number, the higher is the quantity of asphaltic cement. Rapid

curing products are employed when a quick change from liquid state of

application back to original asphaltic cement is desired.

5.4.5 Asphalt Cements

Asphalt cement is a heavy binder usually used in the hot-process of

preparing asphaltic mixtures. They are the residues left after the

lubricating oils as well as fuel oils have been removed from petroleum.

They are designated by the penetration range or degree of hardness

suitable for the type of construction, climatic conditions volume and nature

of traffic to which the pavement is to be subjected. The actual degree of

penetration is controlled by the amount of fluxing oils permitted to remain

at the end of the process. Steam is used to refine the materials so that the

heavier volatiles can de driven off without much increasing the

temperature. Excessively high temperatures reduce ductility, lower

penetration and cause cracking which results in a less homogeneous

product.

The softest grade commonly employed for paving is of 200-300

penetration and the hardest grade commonly employed for the purpose is

of 30-40 penetration. All asphaltic cements are so viscous that both the

aggregate and the binder must be heated before mixing. Working

temperatures range from 22250F to 3500F.

5.4.6 Emulsified Asphalts

An emulsion is a mixture of two normally immiscible liquids, in this

case, the asphaltic cement and water. They are mixed in the presence of

an emulsifying agent such as resin or soap. The emulsifying agents helps


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in the mixing of the two materials, resulting in a liquid end-product. The

process of mixing consists in dispersing minute globules of asphalt in

water in the presence of the emulsifier.

An emulsion makes available the asphalt in the liquid form for

application at normal temperatures. Water separates out after coming in

contact with the aggregates. This process is called the breaking of

emulsion. Asphalt cement is, thus, left behind as a binder. These products

are superior with wet aggregates as the water medium carries the asphalt

into intimate contact with the particle surface.

The asphaltic Institute (U.S.A) classified the emulsions as Rapid

Setting (RS), Medium Setting (MS) and Slow Setting (SS), these products

having fast, medium and slow breaking times respectively. They are

suitable for a variety of purposes. They carry an asphalt content of about

55 to 65 percent by weight. Asphaltic cement of 150-200 penetration is

normally employed for preparing these emulsions. Care is needed to

handle these emulsions since due to excessive pressure, heat or cold,

they are liable to break down.

5.4.7 Powdered Asphalt.

Hard solid asphalts with penetration of 10 or less are designated as

powdered asphalts. For use, they are pulverized to a very fine state of

sub-division with 100 % passing No. 10 A.S.T.M. (2mm) sieve and at least

50 % passing No. 100 A.S.T.M (0.15mm) sieve.

Powdered asphalts are usually employed for low cost road

construction in conjunction with a fluxing medium such as SC-2, SC-3 or

SC-4 liquid asphalts. They are also , sometimes, used in the preparation


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of patented mixes. The principal advantage in using powdered asphalts is

that it is in effect, using asphalt cement in a cold mix.


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Lets test your understanding with these fun activities

to improve your knowledge

5.1State down the four (4) functions of bituminous materials in chart below.

5.2Give a definitions of the following :

a. Bituminous / Asphalt

b. Liquid Bituminous Materials

c. Semi-solid Bituminous Materials

d. Solid Bituminous Materials

Functions Of

BituminousMaterials

It acts___________________________________________________________

It seals__________________________________________________________

It binds__________________________________________________________

ACTIVITY 5

It resists_________________________________________________________


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5.3Match these paving asphalt with its their categories.

EMULSION

ROAD OILS

CUT-BACKS

TARS

POWDERED ASPHALT

ASPHALT CEMENTLIQUID

BITUMINOUSMATERIALS

SEMI-SOLIDBITUMINOUSMATERIALS

SOLIDBITUMINOUSMATERIALS


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Well, how did you find the activities? Lets

check out the answers!!!

5.1

5.2 The definitions are:

a. Bituminous / Asphalt - Mixtures of hydrocarbons of natural or

pyrogenous origin, or combinations of both.

b. Liquid Bituminous Materials - Materials having a penetration at

25oC (77oF) under a load of 50 grams applied for one second, of

more than 350.

c. Semi-solid Bituminous Materials - Materials having penetration

at 25oC (77oF) under a load of 100 grams applied for five seconds,

of more than 10 and a penetration at 25oC (77oF), under a load of

50 grams applied for one second, of not more than 350.

d. Solid Bituminous Materials - Materials having penetration at 25oC

(77oF) under a load of 100 grams applied for five seconds of not

more than 10.

It binds the surface particles together and loss of material from thesurface by suction under the body of moving vehicle.

It resists the action of weathering agencies and ensures a long life forpavement.

It seals the surface of the road against ingress of water.

FEEDBACK ONACTIVITY 5

It acts as a cushion for the surface material and absorbs the kneadingaction of traffic.


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5.3

EMULSION

ROAD OILS

CUT-BACKS

TARS

POWDERED ASPHALT

ASPHALT CEMENTLIQUID

BITUMINOUSMATERIALS

SEMI-SOLIDBITUMINOUSMATERIALS

SOLIDBITUMINOUSMATERIALS


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Did you have everything

right? Well, we have

finished unit 4 and to

improve your understanding

proceed to self assessment

on the next page.

BYE - BYE

Question


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1. Describe the purpose of using a bitumen binder in road

construction.

2. Describe the definition of following aspects: -

i. Liquid Bituminous Materials.

ii. Solid Bituminous Materials

3. State the classification of paving asphalt.

1. By using a bitumen binder in road construction may be summed up as

follows:

Answer


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a. It acts as a cushion for the surface material and absorbs the

kneading action of traffic. The abrasive action of the wheels of a

vehicle is also resisted. This enhances the life of the pavement

b. It seals the surface of the road against ingress of water,

provided the granular material used is dense-graded.

c. It binds the surface particles together and loss of material from

the surface by suction under the body of the moving vehicle, is

thus checked.

d. If a properly selected bituminous material is used, it resists the

action of weathering agencies, like the wind and the sun and

ensures a long life for the pavement.

2.

1. Liquid Bituminous Materials.

Materials having a penetration at 25oC (77oF) under a load of 50

grams applied for one second, of more than 350.

2. Solid Bituminous Materials.


grams applied for five seconds of not more than 10.

3. The Paving Asphalt classifications are:

a. Road oils or Slow-Curing Liquid Asphalts (SC).

b. Cut-Back Asphalt :

Medium Curing Liquid Asphalts (MC)

Rapid-Curing Liquid Asphalts (RC)


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c. Asphalt Cements (AC)

d. Emulsified Asphalts.

e. Powdered Asphalts.

c3010 highway engineering unit5

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