05 - bituminous materials

Bituminous Materials


1.0 Introduction

a) The term bitumen is a generic name applied to various mixtures of

hydrocarbons.

b) According to ASTM D8, bitumen is a class of black or dark-coloured solid or

viscous, cementitious substances composed chiefly of high molecular weight

hydrocarbons.

c) Most common bituminous materials are tars, pitches and asphalts.

d) Destructive distillation is carried out on natural materials produces tar.

e) Partial evaporation or fractional distillation of tar produces the solid or semi-

solid residue of pitch.

f) Asphalts are dark brown or black solids or semi solids which are found in the

natural state and are also produced by the refining of petroleum. A great

majority of asphalts used nowadays are residues from refinery of crude oils.

g) Some natural deposits of asphalts are found in Kentucky, Utah, Colorado and

California.

h) 95% of asphalt materials used in North America are derived from the refining

of petroleum.

i) Asphalts are more resistant to weathering and less susceptible to temperature

than tars.

j) Asphalts will be dissolved in petroleum oils whereas tars will not.

k) Asphalts are black in colour whereas tars are usually brown-black in colour.

l) Now, tars are not used widely as binders for highway pavements.

m) Asphalts are used extensively for roadway construction, primarily because of

their excellent binding or cementing power and their waterproofing properties

as well as their relatively low cost.

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2.0 Types of Bitumen

Asphalt

A large percentage of the asphalt used results from the refining of crude oils.

There are three main groups of asphalt products produced from straight run

asphalts.

a) Hot mix asphalts – those soften by heat

Hot mix asphalts can be used directly or it can be processed further to produce

a harder material.

Hot mix asphalts have good resistance to the transmission of water and water

vapor when they are applied to dry surfaces and the heating process is

controlled.

Hot mix asphalts bond poorly to damp or wet surfaces, have relatively poor

flexibility, oxidize under the sun’s rays and are brittle at low temperatures.

b) Cutback asphalts – those dissolved in mineral solvents

Cutback asphalts are in liquid.

Cutback asphalts are of three types:

i) Straight run asphalt and solvent

ii) Heavily filled cutback made by adding a large amount of filler and fiber to

asphalt cut with solvent

iii) Primer type cutback asphalt in solution with no filler or fiber

Cutback asphalts are produced by dissolving the asphalt cement into a lighter

molecular weight hydrocarbon solvent.

Cutback asphalts are convenient to use because they can be applied without

heating.

However, the quality of cutback asphalts are not as good as hot mix asphalts.

Cutback asphalts are used as wearing coats on top of the pavement. They are

sprayed on pavement or mixed with aggregates. The solvent will then

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evaporate (or known as curing) leaving the asphalts residue as the bituminous

binders.

Cutback asphalts have been widely used for highway construction due to the

effectiveness and easy application on field.

The disadvantages of cutback asphalts are:

i) Cost of solvents. Due to the petroleum price is escalating, the use of

mineral solvents as carrying agents are no longer cost effective.

ii) Hazardous materials. Due to the volatility, the solvents are hazardous.

iii) Environmental pollution. Cutback asphalts release environmental

unacceptable hydrocarbon into the atmosphere.

c) Emulsified asphalts – those dispensed or suspended in a water base

Emulsified asphalts are of three types:

i) Soap type in which soap is used as the emulsifier

ii) Clay modified soap type – clay and soap are used as emulsifier

iii) Clay based type

The advantages of emulsified asphalts are:

i) Easy to handle.

ii) Only addition of water is necessary to decrease viscosity.

iii) Drying involves the loss of water by evaporation.

iv) No heating is required.

v) Good bonding to damp or wet surfaces.

3.0 Bituminous Tests

A large number of different tests are performed on bituminous materials for the

purpose of checking compliance with the specifications that are being used. A list

of most commonly tests is compiled in Table 1 to show the corresponding

AASHTO and ASTM designations as well as indicating the applicability of the

bituminous tests.

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Table 1: Tests of Bituminous Materials Used In Road Construction

Name of TestsAASHTO

Designation

ASTM

Designation

Applicable

to

General Tests

Specific gravity

Flash point (open cup)

Flash point (“Tag” open cup)

Water in petroleum products, etc.

Solubility Tests

Solubility of bituminous materials

Spot test

Consistency Tests

Specific viscosity (Engler)

Kinematic viscosity

Absolute viscosity

Float test

Penetration test

Softening point (ring-and-ball)

Ductility Test

Ductility

Volatility Tests and Aging Tests

Distillation

Cutback asphaltic products

Tar products

Loss on heating

Thin-film oven test

Tests for emulsions

T 228

T48

T79

T55

T44

T102

T54

T201

T202

T50

T49

T53

T51

T78

T52

T47

T179

T59

D70–D76

D92

–

D95

D2042

–

D1665

D2170

D2171

D139

D5

D113

D402

D20

D6

D1754

D244

A & T

A

A

A & T

A & T

A

T

A & T

A

A & T

A

A & T

A

A

T

A

A

A

Legends: A – Asphaltic materials, T – Tar products.

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4.0 Classification of Bituminous Materials

Bituminous materials are commonly grouped in various classes or grades based

on consistency. The classification of these materials facilitates the development of

specifications and provides the framework for the establishment of product testing

and quality controls. Until about 1970, the consistencies of asphalt cements were

based on the penetration test. As such, the specifications were commonly written

in those terms. The penetration grades of asphalt cement are as follows:

Table 2: Asphalt Cement Grading by Penetration

Asphalt Cement Grade Penetration Range (100 g, 5 sec)

AC 40 – 50

AC 60 – 70

AC 85 – 100

AC 120 – 150

AC 200 – 300

40 – 50

60 – 70

85 – 100

120 – 150

200 – 300

The grades of asphalt cements are now more commonly based on standard

capillary viscometer test, AASHTO Designation T202 (2). The grades and

corresponding viscosity ranges are as follows:

Table 3: Asphalt Cement Grading by Viscosity

Asphalt Cement Grade Viscosity, 60oC (140oF)

AC 2.5

AC 5

AC 10

AC 20

AC 30

AC 40

250 ± 50

500 ± 100

1000 ± 200

2000 ± 400

3000 ± 600

4000 ± 800

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05 - bituminous materials

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