UEMX 3813 Highway

and Transportation
Lecture 7
Highway Materials

Ir. Dr. Khoo Hooi Ling

Bituminous Materials
 Bituminous paving materials refers to any mixture of aggregate
and bituminous binder used in road construction
 Bituminous binders are natural or manufactured hydrocarbon
materials which are cementitious in character or from which a
residue of this nature will develop
 Bitumen:
 a viscous liquid, or a solid, consisting essentially of hydrocarbon
and their derivatives.
 substantially non-volatile and softens gradually when heated.
 Black or brown in colour
 Posses waterproofing and adhesive properties
 Obtained by refinery processes from petroleum or found as a
natural deposit or as a component of naturally occurring asphalt
Bituminous Materials (cont’d)
 Two types of bituminous materials are used in road and airfield
construction are asphalt and tar.
 Asphalt:
 A natural or mechanical mixture of bitumen with solid mineral matter
 Black to dark brown semi-solid to solid cementitious material that
gradually liquefies when heated
 Tar:
 A black of dark brown bituminous material obtained by the
destructive distillation of coal, wood, shale or other organic materials
 Advantages of asphalts over tars:
 no odor
 more resistant to weathering
 less susceptible to temperature
 Tars commonly used to seat asphalt concrete surfaces, to improve oil
resistance of asphalt surfaces
Classification of Asphalts
1. Asphalt cement
 Obtained as residue in refining petroleum
 By controlling the refining process, very high consistency or low
consistency asphalt cement can be produced
 4 methods to classify asphalt cements:
1. Performance grading
 PG 52-28 (Performance Grade; would meet the specification for a design
high pavement temperature up to 52oC, and a design low temperature
warmer than -28oC.)
 These temperatures are calculated 20mm below the pavement surface
 The binder is selected to satisfy the maximum and minimum design
pavement temperature requirements
 The average seven-day maximum pavement temperature is used to
determine the design maximum, whereas the design minimum pavement
temperature is the lowest pavement temperature
 The pavement temperatures vary from one year to another, so, the reliability
level is considered
 Classification of Asphalts
(cont’d)
2. Penetration grading
 Nine penetration grades (Pen Grade) or AP number
Pen 40/50 50/60 60/70 70/85 85/100 100/120 120/150 150/200 200/300

AP 7 6 5 4 3 2 1 0 00

Relative Hard Hard Hard Hard Medium Medium Medium Soft Soft
consistency

3. Viscosity grading (in 102 poise (1g/cm.s))

 AC-2.5; AC-5; AC-10; AC-20;AC-30;AC-40
4. Viscosity of aged residue grading
 After treated with rolling thin film oven test
 AR-1000; AR-2000; AR-4000; AR-8000
Classification of Asphalts
(cont’d)
2. Asphalt cutback
 Produced by dissolving asphalt cement in a lighter molecular
weight hydrocarbon solvent
 Examples of solvents: naphtha, gasoline, kerosene, jet fuels,
diesel oil or fuel oil
 When it is sprayed on a pavement or mixed aggregates, the
solvent evaporates, leaving the asphalt residue as the binder
 3 types:
1. Rapid curing cutback (RC): asphalt cement + high volatility
solvent, gasoline
2. Medium curing cutback (MC): solvent: kerosene or jet fuels
3. Slow curing cutback (SC): solvent: diesel oil or fuel oil
 Disadvantages:
 Expensive
 Hazardous materials due to volatility of the solvents
 Releases environmentally unacceptable hydrocarbons into the
atmosphere
Classification of Asphalts
(cont’d)
3. Asphalt emulsion
 By dispersing the asphalt in water as emulsion
 =asphalt cement + water + emulsifying agent
 Asphalt cement is physically broken down into micron-sized
globules that are mixed into water containing an emulsifying
agent
 Hence, it is a heterogeneous system containing 2 immiscible
phases (asphalt and water). Water forms the continuous
phase, and minute globules of asphalt form the discontinuous
phase. When exposed to atmosphere after application, water
evaporates and the asphalt droplets fuse into a continuous film
 Anionic: asphalt globules are electro-negatively charged
 Cationic: asphalt globules are electro-positively charged
 Nonionic: asphalt globules are neutral
Aggregate
 Term used to describe any hard, inert mineral material used for mixing in
graduated particles or fragments for road making
 Include sand, gravel, crushed stones, slag, rock dust, silt, clay or powder
 Gravel and sand are naturally occurring aggregates, seldom used, due to
little interlocking
 Crushed gravel and crushed gravel sand produced by artificial crushing of
natural gravel
 Crushed stone and crushed-stone sand
 aggregates produced by artificial crushing of quarried rock
 Usually used due to better interlocking characteristic
 All-in aggregate: containing different sizes as obtained from the pit, river
bed, foreshore, quarry or crushing plant
 Processed aggregate: natural gravel or stone that has been crushed and
screened
 Synthetic or artificial aggregate: resulting from manmade modification of
materials, involving physical and chemical changes
Classification of Aggregates
 By sources:
 Natural aggregate
 Processed aggregate
 Synthetic or artificial aggregate
 By origin:
 Sedimentary rocks
 Igneous rocks
 Metamorphic rocks
 By petrological characteristics
Aggregate Gradation Analysis
 Is an analysis used to determine how to select the sizes for
aggregates
 Aggregate gradation is the distribution of particle sizes expressed
as a percent of the total weight of aggregate
 Aim to mix material to produce comfortable and structure strong
enough highways, ex: increase individual aggregate size, the
strength of interlocking increase, but reduce riding effort
 Gradation is determined by passing the material through a series
of sieves stacked with progressively smaller openings, and
weighing the material retained on each sieve
 2 definitions:
 Maximum aggregate size: the smallest sieve size through which
100% of the aggregates sample particle pass
 Nominal maximum aggregate size: the largest sieve that retains
any of the aggregate particles, but generally not more than 10%
Aggregate Gradation Analysis
(cont’d)
 Methods of determining aggregate gradation:
1. Dry sieve analysis (ASTM C136)
 Dry sample to constant weight
 Sieve by hand or mechanical shaker
 Weigh aggregate retained on each sieve
2. Washed sieve analysis (ASTM C117)
 Dry sample to constant weight
 Immerse sample in water
 Agitate vigorously and pour over nested sieves. Pour more
water until wash water is clear
 Dry material retained on each sieve and weigh
 Loss in weight= weight of material finer than 75 micro
meter
Important Aspects of Road
Aggregate Properties
1. Strength: should be sufficiently strong to withstand
traffic wheel loads
2. Hardness: resistant to rubbing or abrasion due to
moving traffic
3. Toughness: resistant to impact loads
4. Durability: resistant to weathering action
5. Polish-resistance: resistant to polishing action of
traffic
6. Shape: angular and cubical aggregates are
preferred, flak, elongated or rounded particles to be
avoided
7. Adhesion with bitumen: should have less affinity
with water when compared with bituminous binder
Bituminous Mix Design
 Objective: to select and proportion
aggregates and asphalt to yield a mix with
satisfactory durability, stability, workability,
flexibility and safety characteristics
 Durability:
 Sufficient asphalt to coat aggregate against
weathering
 Sufficient asphalt to make surface water tight
 Aggregate resistant to abrasion
Bituminous Mix Design
(cont’d)
 Stability:
 Sufficient frictional and interlocking resistance
from aggregate
 Sufficient asphalt in voids to provide cohesion
 Workability:
 Aggregate gradation for compactability
 Sufficient asphalt for placement
 Sufficient asphalt to prevent segregation
 However, with more binder to serve this purpose,
the stability will be reduce balance
Bituminous Mix Design
(cont’d)
 Flexibility:
 Sufficient air voids to allow further compaction or
volume change
 Sufficient asphalt to prevent cracking upon
deflection
 Safety:
 Sufficient air voids to prevent bleeding
 Aggregate with high polishing resistance
 Coarse surface texture
Bituminous Mix Design
(cont’d)
 Factors affecting properties of Bituminous Mix
 Type & viscosity of binder
 High viscosity, low workability,
 Low viscosity, low stability
 Type of mineral aggregate
 Proportion of binder
 Grading of aggregate
 3 common design methods adopted:
1. Marshall (ASTM D1559)
2. Hveem (ASTM D1560)
3. Superpave mix design method
Steps in Bituminous Mix
Design
1. Selecting the aggregates
 Aggregates to be of good quality for durability
 Hard, hydrophobic, rough-textured and have a grading
satisfying workability, permeability, economy and skid
resistance requirements
2. Selecting the binder
 To match the selected aggregates and with properties
providing good workability, durability, stability
requirements
3. Mix proportioning
 To provide an acceptable safety margin against various
modes of ‘damage’ for the design traffic level
Recycling of Asphalt Concrete
 Advantages:
 Economic saving of about 25% of the price of materials
 Energy saving in manufacturing and transporting raw
materials
 Environmental saving by reducing the amount of required
new materials and by eliminating the problem of discarding
old materials
 Eliminating the problem of reconstruction of utility
structures, curbs, and gutters associated with overlays
 Reducing the dead load on bridges due to overlays
 Maintaining the tunnel clearance, compared with overlays
Recycling of Asphalt Concrete
(cont’d)
 3 types of recycling:
1. Surface recycling
 Heating machine heats the pavement surface and repair minor
cracks and roughness
 A rejuvenating agent is added after heating, followed by slight
scratching of the surface and compaction
2. Central plant recycling
 The old pavement is milled and sent to central concrete plant to mix
with aggregates to produce hot-mixed asphalt concrete
3. In-place recycling
 Rip and pulverize the old pavement surface and add new
aggregate, water, and asphalt emulsion
 The old and new materials are mixed together in place, graded, and
compacted
 Usually for the use of low-volume roads or as the base layer
Additives
 Is mixed in the asphalt concrete to improve
the properties of asphalt
 Laboratory tests are performed and field
performance is observed in order to evaluate
the effect of the additives and to justify their
cost
 The effects of using additives should be
carefully evaluated, or premature pavement
failure might result
Additives (cont’d)
 Types of additives:
 Fillers
 Ex: crushed fines, portland cement, lime, fly ash, and carbon black
 To increase stability, to improve bond between aggregates and asphalt,
or to fill the voids and thus reduce the required asphalt
 Extenders
 Sulfur and lignin are used to reduce asphalt requirement, cutting cost
 Rubber
 Natural rubber, SBR, SBS, or recycled tire rubber
 Increase elasticity and stiffness of the mix
 Increase bond between asphalt and aggregate
 Plastics
 Polyethylene, polypropylene, EVA, and PVC
 Increase the stiffness of the mix, thus reduce rutting potential
 Reduce temperature susceptibility of asphalt and improve its
performance at low temperature
 Antistripping agents
 Lime, portland cement
 To improve bond between asphalt cement and aggregates
References
 Chapter 9, and 5, Materials for Civil and
Construction Engineers, 2nd Ed, Mamlouk,
M.S., Zaniewski, J.P.