c3010 highway engineering unit5
TRANSCRIPT
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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.
Materials having penetration at 25oC (77oF) under a load of 100
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.
Materials having penetration at 25oC (77oF) under a load of 100
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.