11/3/2023

Highway Materials

Lecture # 1

An Introduction to Asphalt

Lecturer: Asst. Prof. Dr. Hardy Kamal Karim

Ph.D in Highway Engineering
University of Sulaimani 1

History of Asphalt
• Asphalt is one of the oldest materials used in construction.

• It is used since 6000 BC as a waterproofing and binder

material of great quality.

• A prominent example of bitumen use is cited in the Old

Testament, since it was used as coating for Noah’s Ark.

• The Sumerians used to use it in the prosperous shipbuilding

industry, whereas the Babylonians used it as a binder in the
mixture production for castle construction (Babel Tower).

• Asphalt was also used by the Egyptians both to mummify the

dead bodies and to waterproof tanks.
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• Around 3000 BC, the Persians also used bitumen for road
construction.

• Before the mid-1850s, asphalt came from natural pools found

in various locations throughout the world, such as the Trinidad
Lake asphalt.

• Natural asphalt also exists in the form of rocks, which is mainly

limestone or sandstones enriched with bitumen.

• However, with the discovery and refining of petroleum in

Pennsylvania, use of asphalt cement became widespread.

• By 1907, more asphalt cement came from refineries than came

from natural deposits.

• Today, practically all asphalt cement is from refined petroleum.

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Natural Asphalt

natural asphalt is a relatively hard bitumen found in natural

deposits, often mixed with fine or very fine mineral matter, which is
virtually solid at 25°C but which is a viscous fluid at 175°C.

1) Lake asphalt:

a) Trinidad Island
• approximately 15 million tones of asphalt.
• It is largest deposits of very good quality natural asphalt in the
world.
• Its composition: 54% asphalt, 36% mineral matter and 10%
organic matter.

b) Venezuela natural asphalts (pitch lake asphalts)

• asphalt content is approximately 64%.
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2) Rock asphalt

• It is natural asphalt found in solid form.

• Nowadays it is used only as an additive to petroleum bitumen.
• Since it is a very hard material, its use is to harden petroleum
bitumen.
• They are found in Utah in the United States and Kermanshah in
Iran.

3) Gilsonite

• The rock asphalt in the Uintah Basin in Utah has the trade name
gilsonite, from S.H. Gilson, the founder of a mining company in
1888.
• Gilsonite today is a well-known additive for hardening
petroleum bitumen.

Bituminous Materials

• Bituminous materials are classified as asphalts and tars.

• Asphalt is used mostly in pavement construction, but is also

used as sealing and waterproofing agents.

• Tars are produced by the destructive distillation of bituminous

coal or by cracking petroleum vapors.

• Tar is used primarily for waterproofing membranes, such as

roofs. It may also be used for pavement treatments,
particularly where fuel spills may dissolve asphalt cement,
such as on parking lots and airport aprons.

• Tar differs in chemical composition and odor to bitumen.

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• Over the last years, the usage of tar has been minimized
mainly for environmental and health reasons.

• Nowadays, tar is used almost exclusively for the production of

specific bituminous mixtures, not affected by petrol or oils,
known as fuel-resistant mixtures.

• It may also mix with petroleum bitumen to produce better-

quality binder for surface dressing works.

• Better coating of aggregates, as well as better adhesion of

bitumen to aggregate, is achieved with the use of tar/bitumen
binder.

• On the contrary, it is more sensitive to temperature variations,

and as a result, it softens easier and it hardens and becomes
brittle quicker than bitumen of similar viscosity.
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The fractional distillation process of crude petroleum

• Different products are separated

at different temperatures.

• Figure shows the main products,

such as gasoline, kerosene, diesel
oil, and asphalt residue (asphalt
cement).

• The quantity and quality of the

asphalt depends on the crude
petroleum source and the refining
method. Some crude sources,
such as the Nigerian oils, produce
little asphalt, while others, such
as many of the Middle Eastern
oils, have a high asphalt content.
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No. of carbon
Boiling point
Fraction Product type atoms (in
range C ͦ
molecule)
Light distillate Gasoline 4 - 12 40 - 200
Medium distillate Kerosene 12 - 15 175 – 300
Heavy distillate Diesel oil 15 – 20 220 - 370
Very heavy
Lubricating oil 20 - 35 ˃ 345
distillate
Residue Asphalt ˃ 35

When distillation process is controlled, without over heating and any

chemical changes, the asphalt is straight run asphalt
Distillation process
• Higher the temperature ⇾ Harden the asphalt
• Higher the vacuum ⇾ Harden the asphalt
• Larger the steam content ⇾ Harden the asphalt
• By controlling these three variables – we can get asphalt cement for
the required quality 30/40 – 180/200 …… 300 grade 11

Oxidized bitumen
• Oxidized bitumen is mainly used in roofing, waterproofing, adhesives
and insulations.

• The oxidation process is conducted after bitumen production and

consists of blowing air through heated bitumen (temperatures between
240°C and 320°C).

• O2 from air combines with H2 of asphalt molecule to form water which

is emitted as steam.

• Oxidation ‘dehydrates’ and ‘polymerizes’ bitumen. As a consequence,

the molecular weight of asphaltenes is increased, additional asphaltenes
are created from the continuous oil phase (maltenes) and thus bitumen
with a higher molecular weight is produced.

• Because of these changes, bitumen becomes harder and it becomes less

susceptible to temperature changes (the penetration index increased).
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Chemical composition of bitumen

• Bitumen (asphalt) is a complex chemical compound composed
predominately of carbon and hydrogen (hydrocarbon), with a small
amount of heterocyclic compounds containing sulfur, nitrogen and
oxygen.

• Bitumen also contains traces of metals including nickel, magnesium,

iron, vanadium and calcium in the form of inorganic salts and oxides.

• Elementary analysis of bitumen's produced from a variety of crude

oil showed that most bitumen contains carbon (82%–88%);
hydrogen (8%–11%); oxygen (0%–1.5%); and nitrogen (0%–1%).

• The exact composition of bitumen differs, and it depends on both the

source of the crude oil and the modification during its fractional
distillation. It also depends on the oncoming ageing in service.

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• Despite the complexity of bitumen’s chemical composition, it is possible

to be separated into two broad chemical groups, the asphaltenes and the
maltenes.

• Maltenes can be further subdivided into saturated hydrocarbons,

aromatic hydrocarbons and resins.

a) Asphaltenes

• Asphaltenes are complex polar aromatic compounds, black or dark

brown solids, insoluble in n-heptane, of high molecular weight,
containing in addition to carbon and hydrogen some nitrogen, sulfur
and oxygen.

• The asphaltene content directly affects the rheological properties of the

bitumen. When asphaltene content increases, the bitumen is harder and
more viscous.

• The percentage of asphaltenes in bitumen usually ranges from 5% to

28%. 15

b) Maltenes

1) Resins

• Resins have similar components to asphaltenes but they are soluble in

n-heptane.
• They are solid or semi-solid, dark brown in color and strongly adhesive.
• Resins are dispersing agents to asphaltenes and their proportion to
asphaltenes control the gel/sol type of character of bitumen.
• Their molecular weight is lower than asphaltenes.

2) Aromatics

• Aromatics are naphthenic aromatic hydrocarbons, have the lowest

molecular weight of the compounds in the bitumen and represent the
main dispersion medium of asphaltenes.

• They are viscous fluids of dark brown color and they can be found at
40% to 65% in bitumen.
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3) Saturates

• Saturates are aliphatic hydrocarbons together with alkyl naphthenes

and alkyl aromatics.
• Their molecular weight is similar to the molecular weight of aromatics
and their components contain both waxy and non-waxy saturates.
• Saturates are light yellow to white in color and its content ranges from
5% to 20% in bitumen.

• Bitumen is generally considered to be a colloidal system consisting of

high-molecular weight micelles dispersed or dissolved in a dispersed oil
medium of lower molecular weight, namely, maltenes.

• Any fluctuation in the percentage of asphaltenes and maltenes,

particularly of resins and saturates, influences the viscosity and the
temperature sensitivity of bitumen.

• The fluctuation of the abovementioned substances takes place mainly

during production of bitumen.
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• Chemical hardening of the bitumen with time in service is also known as

ageing of the bitumen.

• It occurs because of the oxidation of organic compounds and because of

further volatilization of volatile ingredients of the bitumen. This stage is
also called bitumen oxidation.

• Oxidation or ageing of the bitumen affects the mechanical behavior of

the bitumen and usually reduces the pavement’s service life.

• Oxidation and ageing can be decelerated with the use of chemical

additives.

• Oxidation and, consequently, ageing of bitumen after construction are

affected by climatic conditions and voids in the bituminous mixture.

• Greater oxidation of bitumen is expected in geographical locations

where ambient temperatures are high and sunshine periods are longer
in a year.
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• A similar result is expected between open and dense graded bituminous

mixtures.

• Finally, it should be mentioned that bitumen oxidation is more intense

at the surface (surface layer) than within the bituminous mixture
(layers beneath).

• The hardening of the bitumen during mixing, laying and compaction can
be simulated in the laboratory by either the rolling thin film oven test
(RTFOT) or the thin film oven test (TFOT), and its ageing can be
simulated by the pressurized ageing vessel test.

• Bitumen also hardens during hot storage; hence, prolonged storage

should be avoided.

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Photo showing asphalt cement, aggregate, and asphalt concrete. 21

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