Asphalt and Asphalt Concrete
Dr. Kimberly Kurtis
School of Civil Engineering
Georgia Institute of Technology
Atlanta, Georgia
Some Ancient Asphalt History
Asphalt materials have been used since 3500BC
Waterproofing: boats, vessels for carrying liquids
Adhesive and mortar
Roads (1st evidence of Asphalt paving, Bablyon ~600BC)
Trinidad Lake Asphalt
Basket boats
http://www.ancientroute.com/resource/Asphalt.htm
Asphaltic mortar in
walls at Babylon
Native Asphalt Sources
144 acre -Trinidad Lake
Lake Maricaibo in Venezuela (formerly)
La Brea tar pits in California
Underground Athabascan tar sands in Canada
La Brea
Asphalt History
1852 - French place 1st modern natural asphalt pavement
1816 - Scottish engineer John MacAdam introduces paving method using large stones
bound with tar or asphalt
1868 - 1st hot mix pavement (with tar binder) placed in US designed by NB Abbott
1876 - Pennsylvania Avenue is paved using TLA
1885 - Automobile is invented
http://www.asphaltinstitute.org/faq/lakeasph.htm
Asphalt Stats
US produces 30-35M tons asphalt/year
500-550M tons asphalt pavement placed per year
70% used for paving
22% used for roofing
Other uses include coatings, tiles
Sustainability
Of the 100M tons of AC pavement removed annually in the US,
80% is recycled.
Terminology
Bitumen (ASTM D8) - a class of black or dark colored
cementitious substances, natural or manufactured, composed
primarily of high molecular weight hydrocarbons; completely
insoluble in carbon disulfide (CS2).
Includes both tar and asphalt
Asphalt - A viscous cementitious material composed principally of
high molecular weight hydrocarbons (typically 300-2000 g/mol)
Asphalt Concrete - A complex (composite) material consisting of a
mixture of asphalt cement and mineral aggregates
Terminology
Terminology
Tar
Product of destructive
distillation of coal,
petroleum, wood,
sugar
Odor
Does not dissolve in
petroleum products
Asphalt
Product of fractional
distillation of petroleum
No odor
Will dissolve in petroleum
products
Fractional
Distillation
Lower MW,
Lower viscosity
Higher MW,
Higher viscosity
Properties of Asphalt Cement
Composition is variable,
depending on source
C
80-87%
H
9-11%
O
2-8%
N
0-1%
S
0.5-7%
Trace metals 0-0.5%
CnH2n+bXd
where n ranges from 25-150
X may be S,N,O, trace metals
d is usually small
b may be negative
C84H97S3.2O2.5 for n=84, b=-71, d=5.7
One asphalt cement may contain many different kinds of
molecules of varying size, chemistry, and geometry
Properties of Asphalt Cement
Composition of the asphalt influences binder behavior and
performance of the asphalt concrete
Asphaltenes - larger, discrete solid (black)
inclusions; high viscosity component
Resins - solid or semisolid at room temp;
fluid when heated, brittle when cold
Oils - colorless liquid; low viscosity component
Aging
Substantial changes occur in the structure,composition, and
mechanical behavior of asphalt due to:
Volatilization of light HC fractions
Oxidation
Physical hardening
These processes can increase the asphalt viscosity and
decrease ductility of asphalt and asphalt concrete.
“VISCOSITY”, in simplest sense, is the resistance to flow
Aging
Aging can occur during mixing, placing, and service.
Volatilization - prevalent during hot mixing
Oxidation
- slow process generally; occurs over time
occurs more readily in warmer environments
and in poorly compacted pavements
Physical Hardening - most pronounced at T<0C
Temperature/Viscosity Relationships
Viscosity - “resistance to flow”
- a fundamental material property relating the
rate of shear strain (γ or dγ/dt) in a fluid to
the applied shear stress (τ)
τ = η(dγ/dt) for an ideally viscous material (Newtonian fluid)
η given in units of Poise (P)
1P = 1x10-1 Pascal sec (Pa s)
= 1 (g/cm) s
Chapter 7 Young book
Viscosity
Water
Motor oil
Asphalt
Lava
η= 1x10-3 Pa s, at room temp
= 1
= 105 to 107, at service temps
= 1, when heated
= 1011-1012
LOW
HIGH
Viscosity: Newtonian Fluids
Newtonian fluid - linear relationship
between shear stress and shear strain
rate at a given T.
(e.g., air, ethanol, water is close)
τ
η
The slope is the viscosity
dγ/dt
Viscosity: Non-Newtonian Fluids
τ
Shear-thinning or “pseudoplastic” fluid -
Viscosity decreases with increasing dγ/dt
(e.g., polymer melts, paints)
Apparent
viscosity
dγ/dt
dγ/dt
Viscosity: Non-Newtonian Fluids
τ
Shear-thickening fluid -
Viscosity increases with increasing dγ/dt
(e.g., clay slurries, cornstarch in water)
dγ/dt
Apparent
viscosity
Shear-thinning fluids are more common than
shear-thickening fluids.
dγ/dt
Viscosity: Non-Newtonian Fluids
Viscoplastic or “yield stress” fluid Does not flow until a critical or yield stress
is applied; below the critical stress,
it behaves like a solid
(e.g., toothpaste, fresh concrete)
τ
Bingham fluid
το
dγ/dt
Viscosity
Asphalt cements exhibit Newtonian and Non-Newtonian
behavior
Asphalt Viscosity
HMA
Asphalt Viscosity
330-340oF
275-310oF
Asphalt Viscoelasticity
At low temp or low loading duration, elastic behavior
At higher temp or long loading duration, viscous behavior
dominates
At most service temps, viscoelastic behavior is observed
True fluid - flows when it is
subjected to a shear field and
stress, and ceases as soon as
the stress is removed. viscous
Ideal solid - when subjected to
a stress recovers its original
state as soon as the stress is
removed. elastic
Viscoelastic materials - have
some characteristics of both a
solid and a liquid.
Temperature/Viscosity Relationships
More viscous/more stiff
@ lower T
Less viscous/more flowable
@ higher T
Rutting
Rutting - channelized
deformation under traffic
loading
Shoving - pushing of
mixture under loading,
stopping
Cracking - brittle failure
due to fatigure, aging, or
temperature
Shoving
Fatigue Cracking
Low Temperature Cracking
Extended transverse cracking, initiating at the pavement surface, is
typical of low temperature cracking. This type of cracking is due to:
• Contraction of asphalt concrete at lower temperatures
• Restraint to this shrinkage
• Tensile stress generated greater
than pavement tensile strength
CTE of asphalt is greater than that of aggregate => binder selection
important in resisting this form of cracking
Measuring Physical Properties
•
•
•
•
Asphalt cements have traditionally been graded according to:
Penetration (PEN) on AC and AR
Viscosity on asphalt cement (AC)
Viscosity on aged residue (AR)
Performance Grading
Penetration Test
Penetration of 100g weight in 5s at 25C (77F) is measured in
units of 0.1mm (e.g., 70 PEN=7mm penetration)
100 g
After 5 seconds
Initial
+ Fast, simple, low cost test
- Empirical; not related to property; similar PEN values can yield
wide range of behavior; effect of T not considered
Penetration Grades
Specifications for Asphalt Cement by Penetration Graded
Test
40-50
60-70
85-100
120-150 200-300
Penetration, 25 oC, 100 g, 5 sec.
Ductility, 25 oC, 5 cm/min, cm
Flash point, COC, oC
Soluibility in trichloroethylene, %
40-50
100 min
232
99.0
60-70
100 min
232
99.0
85-100
100 min
232
99.0
120-150
100 min
219
99.0
200-300
-----177
99.0
0.5
50
50
1.0
50
75
1.5
46
100
1.5
40
100
Test on residue from Thin-Film Oven Test:
Loss on heating, % maximum
0.5
Penetration, % of original, min
50
Ductility, 25 oC, 5 cm/min, min
Viscosity Grades
AC grades are based on measurements of absolute viscosity of
asphalt tested at 140 oF
AR grades are based on the absolute viscosity tested at 140oF of
asphalt after being aged in a rolling thin-film oven
The RTFO test (ASTM D2872) is made by
placing a 50cm3 asphalt cement sample in a
cylindrical flat-bottomed pan 5.5” of inside
diameter and 3/8” depth. The asphalt layer is
about 1/8” deep. The sample and container
are placed on a shelf, which rotates
approximately 5 to 6 revolutions per minute, in
a ventilated oven maintained at 325oF for 5 hr.
The asphalt cement is then poured into a
standard container used for the penetration
test or the viscosity test.
Viscosity Tests
•
•
•
•
The viscosity test utilizes a gravity-flow capillary
viscometer. This viscometer is mounted in a
thermostatically controlled, constant-temperature bath;
for kinematic viscosity: 135C or 275F
for absolute viscosity: at 60C or 140F
With the viscometer mounted in the bath, asphalt is
poured into the large opening of the viscometer until it
reaches the filling line. The filled tube remains in the
bath at test temperature for a specified period of time to
make sure that the tube and asphalt are at the same
temperature.
A slight pressure is applied to the large opening of the
tube, or a slight vacuum to the small opening, thus
causing the asphalt to start flowing over the siphon
section just above the filling line. Gravity causes the
asphalt to flow downward in the vertical section of
capillary tubing.
A timer is started when the asphalt reaches the first
timing mark and is stopped when it reaches the second
mark. The time interval, multiplied by a calibration factor
for the tube, determines viscosity of the asphalt cement
in units of centistokes (Kinematic) or poises (Pa s)
(Absolute)
AC Grades
Specifications for Asphalt Cement by Viscosity Grade
Test
Viscosity, 60 oC (140 oF), poises
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
Viscosity, 135 oC, Cs minimum
Penetration, 25 oC, 100 g, 5 sec.
Flash point, COC, oC minimum
Soluibility in trichloroethylene, %
125
220
162
99.0
Test on residue from Thin-Film Oven Test:
Loss on heating, % maximum
Viscosity, 60 oC, poises
1000
100
Ductility, 25 oC, 5 cm/min, min
175
140
177
99.0
250
80
219
99.0
300
60
232
99.0
350
50
232
99.0
1.0
2000
100
0.5
4000
75
0.5
8000
50
0.5
12000
40
400
40
232
99.0
0.5
16000
25
1 Poise = 1 Pa s = 0.672 lb./(ft.s) = 1g/(cm s)
1 Centistoke (Cs) = 1 mm2/s
AC Grading
+ Established test method
+ Measures a fundamental material property
+ Can be performed at maximum pavement service temperature
+ No effects of aging
- More expensive equipment than for PEN
- More technician skill required
- Not applicable for non-Newtonian fluids
- Wide range in behavior for same AC grade
AR Grades
Specifications for Asphalt Cement by AR Grades
Test
Viscosity, 60 oC (140 oF), poises
AR-1000 AR-2000 AR-4000 AR-8000 AR-16000
1000±250 2000±500 4000±1000 8000±2000 16000±4000
Viscosity, 135 oC, Cs minimum
Penetration, 25 oC, 100 g, 5 sec.
% of original penetration
Ductility, 25 oC, 5 cm/min, min
Flash point, COC, oC minimum
Soluibility in trichloroethylene, %
140
65
100
205
99.0
200
40
40
100
219
99.0
275
25
45
75
227
99.0
AR Grades
+ Established test method
+ Measures a fundamental material property
+ Represents asphalt properties after hot mixing
+ Limited, controlled aging
- More expensive equipment than for PEN, AC
- More technician skill required than for PEN
- Not applicable for non-Newtonian fluids
- Wide range in behavior for same AR grade
400
20
50
75
232
99.0
550
20
52
75
238
99.0
Comparison of Grading Schemes
Performance Grade
Research under the Strategic
Highway Research Program (SHRP)’s
Superpave program lead to the
introduction of Performance Grades in
1993. Addresses concerns with
earlier grading schemes:
• PEN value does not correlate to a
material property
• AC, AR grades rely on tests
performed at T higher than service T;
do not reliably predict performance
• PEN and viscosity are measured at 2
different temperatures
Summary of PG Tests
Procedure/Equipment
Purpose
Dynamic shear rheometer (DSR)
Measure properties at high and intermediate
service temperatures
Rotational viscometer (RV)
Measure properties at high construction
temperature
Bending beam rheometer (BBR)
Direct tension tester (DTT)
Measure properties at low service
temperature
Rolling thin film oven (RTFO)
Simulate hardening at construction
Pressure aging vessel (PAV)
Simulate aging under long-term service
Performance Grade
PG XX YY
XX = 7-day maximum pavement temperature, C
52-70C in 6C increments
YY = minimum expected pavement temperature, C
in 6C increments
Example: PG 64-16
Average 7-day maximum pavement temperature in summer near
64C, and minimum pavement temperature in winter near -16C.
Considers rutting at high T and cracking at low T
Modifications to Asphalt Cement
• Cutbacks - allow easy placement without high T
• Emulsions - allow easy placement without high T, lower
toxicity/fire hazard
• Air-blown asphalt - less susceptible to T
Cutbacks
Volatile components are mixed with asphalt cement to make a liquid
product. After volatilization, asphalt binder remains.
Slow Curing (SC): Asphalt cement mixed with a low volatile oil/fuel.
SC-70, SC-250, SC-800, SC-3000
Medium Curing (MC): Asphalt cement mixed with a solvent of
intermediate volatility, such as kerosene. Uses
a softer asphalt base than RC cutbacks.
MC-30, MC-70, MC-250, MC-800, MC-3000
Rapid Curing (RC): Asphalt cement mixed with a volatile solvent,
such as gasoline or naphtha. Uses a harder
asphalt base than MC cutbacks.
RC-70, RC-250, RC-800, RC-3000
Gradation based kinematic viscosity measured at 140F.
Ex. Viscosity of MC-250 is 250+20% centistokes
Cutbacks
RC cutback asphalt is used primarily for
surface treatments and tack coat.
MC cutbacks asphalt is typically used for
prime coat, surface treatments, and
stockpile patching mixes.
SC cutbacks may be used as surface
spray for dust control (least common).
Cutbacks
Asphalt Emulsions
Asphalt emulsions = water + asphalt + emulsifying agent
= suspension of asphalt in water or water in
asphalt; may be cationic, anionic, nonionic
Asphalt Emulsions
Some advantages:
• Like cutbacks, asphalt emulsions can be use with hot or cold
aggregate
• Unlike asphalt cements, an be used on dry, damp, or wet
aggregate
• Avoids fire and toxicity issues associated with cutbacks
Applications include: cold in-place recycling, cold mixing, tack
coats, surface treatment, patching
Air Blown Asphalt
Air is blown through asphalt at 400-500F; Oxygen in air reacts with
HC chains to form water (steam); chains repolymerize forming
heavier,harder, more temperature-resistant materials.
H
…-C-C-H
H
…-C-C-H
H
O
H
…-C-C-C=C + H2O
H
longer chains
Grading of air blown asphalt is based on the softening point of the
material. ASTM D-2398 defines 4 grades, Type I (57-66 C), Type II
(70-80C), Type III (85-96) and Type (99-107 C).
Asphalt Concrete
Asphalt Concrete
VMA
VMA = voids in the mineral aggregate
= Vsample-Vagg
VMA(%) = (Vsample-Vagg)/Vsample x 100%
VMA filled with asphalt = (Va/VMA)x100%
Where Va is the volume of absorbed asphalt
VMA Calcs (Example)
Calculate the percent voids and VMA in a compacted mixture with a 144 lb/ft3
unit weight with:
Ingredients
% total aggregate
Effective SG
Coarse agg
70%
2.70
Fine agg
25%
2.65
Filler
5%
2.60
Percent asphalt =5% with SGasphalt=1
VMA Calcs (Example)
MASS
0
0.05x144lb/ft3=7.2lb/ft3
0.05(0.95)x144=6.8lb/ft3
0.25(0.95)x144=34.2lb/ft3
0.70(0.95)x144=95.8lb/ft3
Σ 144lb/ft3
VOLUME
Air
1-(0.12+0.04+0.21+0.57) = .06
Asphalt
7.2lb/ft3/(1x62.4lb/ft3)=0.12
Filler
6.8/(2.60x62.4)
=0.04
Fine Agg
34.2/(2.65x62.4)
=0.21
Coarse Agg 95.8/(2.70x62.4)
=0.57
Σ 1
ANS. 6% Air
VMA = 1-(.04+.21+.57)=0.18 or 18%
Another Example
EXAMPLE Certain distresses are appeared on a newly constructed asphalt pavement
and an engineering evaluation is commissioned to assess the problem. The following
data are obtained based on the laboratory testing of the asphalt concrete cores removed
from the pavement.
a. The bulk specific gravity of the cores is determined (2.584) by measuring the weight of
the core in air and in water.
b. The core is then heated to soften the asphalt mix and the core is broken into small
pieces. The voidless specific gravity of the asphalt mix is determined (2.677)
c. After that, the asphalt mix is burned in a high temperature oven and the asphalt content
(4.5% of the total mass) is determined based on the weight loss from the testing
d. The bulk specific gravity of aggregate (2.885) is determined from the aggregate after the
asphalt is burned out.
e. The gravity of the asphalt cement (1.022) used in the mix is provided.
Determine the air void content, VMA and percent asphalt absorbed of the asphalt mix.
Example
Vma = Volume of voids in mineral aggregate
Vmb = Bulk volume of compacted mix
Vmm = Voidless volume of mix
Va = Volume of air
Vb = Volume of asphalt
Vba = Volume of absorbed asphalt
Vsb = Volume of mineral aggregate
Vse = Volume of mineral aggregate (by effective specific gravity)
Solution: Air Content
Assume 1000 gram asphalt mix (total mass)
Asphalt content by wt. of mix = 4.5% = 45 g
Aggregate by weight of mix = 1000 – 45 = 955g
Determine air voids
Va/Vmb.
Vmb =Bulk volume of compacted mix =1000/2.584 = 387.00cm3
Vmm=Voidless volume of mix
=1000/2.677 = 373.55cm3
13.45 cm3
AIR VOID CONTENT = (Vmb- Vmm)/ Vmb = 13.45/387 = 3.5%
Solution: Asphalt Absorption
Asphalt Absorption: ( Wt. of Asphalt Absorbed)/ (Wt. of Agg.)
Volume of absorbed asphalt=Volume of mineral aggregate Volume of mineral aggregate (by
effective specific gravity)
Vba = Vsb - Vse
Vsb = Volume of mineral aggregate = 955/2.885 = 331.02cm3
Vse = Vmm - Vb = Voidless volume of mix - Volume of asphalt
= 373.55 - 45/1.022 = 373.55 - 44.02 = 329.52cm3
Vba = 331.02 - 329.52 = 1.5cm3
(1.5cm3 x 1.022 g/cm3)/955g x 100% = 0.16%
= Asphalt Absorption
Solution: VMA
VMA = (Vmb – Vsb) / Vmb x 100%
= (Bulk volume of compacted mix- Vol Agg)/Bulk Vol x100%
= (387.00 – 331.02) / 387.00 x 100 = 14.46%
or VMA can be determined by
VMA = (Va + Vb - Vba)/Vmb x 100%
= (Vol of air + Vol of asphalt - Vol asphalt absorbed)/Bulk Vol x100%
= (13.45 + 44.02 - 1.5)/387 = 14.46%
Aggregate Properties affecting Stability
Gradation - want to maximize point-to-point contact for stability
-> dense gradation
-> some applications for one-size
or gap-graded aggregate
Aggregate Properties affecting Stability
Surface Texture - much of the strength of the asphalt concrete is
derived from mechanical interlock between aggregate particles;
crushed rock with much angularity is preferred for strength and
stability
Aggregate Properties affecting Wetting
Wetting - adsorption of asphalt molecules on the aggregate
surface
• Surface Texture- rougher surface more difficult to wet initially,
but once wetted, asphalt adheres more strongly
• Moisture Content- polar water molecules can replace longer
asphalt chains at aggregate surface
• Porosity - want 0.5% minimum porosity for good adhesion
• Surface Chemistry - hydrophobic aggregate (ex. Dolomites) are
more easily wetted by asphalt than water; converse is true for
hydrophilic aggregate (ex. Siliceous aggregate)
Proportioning Asphalt Concrete Mixtures
OBJECTIVE: to proportion an economical mixture which is stable,
flexible, durable, impermeable, fatigue resistant, skid resistant,
and workable.
However, it is not always possible to optimize all of these
properties. Thus, compromises must be made.
Proportioning Asphalt Concrete Mixtures
However, it is not always possible
to optimize all of these properties.
Thus, compromises must be
made.
Proportioning Asphalt Concrete
Mixtures
Definitions of Desirable Properties
Stability: ability of pavement to resist
deformation under applied loads
• Affected ability of aggregate to distribute
loads through point to point contact
• Stability improved with an angular, rough
textured, strong aggregate with a dense
grading
• Want just enough asphalt to coat
aggregate to provide adhesion. If asphalt
content is too high, it will act as a lubricant
and reduce particle-to-particle contact
between the aggregate.
Definitions of Desirable Properties
Flexibilty: ability of pavement to withstand deflections and
bending (caused by long-term settlement of the base or
subgrade layers) without cracking.
• Flexibility is maximized with an open-graded aggregate
• Flexibility increasing with a higher asphalt content
Conflict, then, between requirements for stability and flexibility!
Definitions of Desirable Properties
Durability: ability to resist disintegration due to weathering
(oxidation and stripping) and the abrasive action of traffic.
• Durability is maximized when aggregate particles are completely
covered with asphalt and no air voids exist which would facilitate
the entry of water, air, or light.
Because of durability considerations, air content is limited to 5%
maximum, and typically ranges from 3-5%.
Definitions of Desirable Properties
Impermeability: resistance to passage of air and water into the
pavement or through it is dependent on the content and
interconnectivity of the voids in the mixture.
• Impermeability is maximized at a higher asphalt content, with
dense aggregate gradations, and good compaction
Definitions of Desirable Properties
Fatigue Resistance: ability of the mixture to resist failure or
fracture under repeated traffic loading.
• Mixtures with higher asphalt
content and densely graded
aggregate generally have greater
fatigue resistance than those with
lower cement contents and open
graded aggregate.
Definitions of Desirable Properties
Skid Resistance:
• Skid Resistance is maximized at lower asphalt contents
• Vehicles are more likely to skid when excess asphalt is present
on the pavement surface
• ‘flushing’ - migration of asphalt to wearing surface; can occur
when air content is too low, such that when additional
compaction of the pavement occurs during loading, asphalt
cement has no voids left to fill and flows to surface.
Definitions of Desirable Properties
Workability: the ease with which a paving mixture can be placed
and compacted
• Workability is maximized with a higher binder content and
rounder aggregate
Those features that improve workability may decrease stability and
skid resistance.
Mixture Design
Three commonly accepted methods:
• Marshall method (ASTM D1559)
• Hveem method (ASTM D1560)
• Superpave method
In addition, some states have their own methods.
Marshall Method
Select Agg
Select Asphalt
Select Asphalt
Content
Test
End
1. Select aggregate blend to meet gradation
and other requirements (ASTM D3515).
2. Select and evaluate asphalt cement.
3. Estimate desired asphalt content to meet
requirements for:
stability
durability
flexibility
skid resistance
workability
4. Prepare 3 samples each
at estimated asphalt
content and at +0.5% and
+1%.
• Calculate unit weight
(density), % air voids, and
VMA
• Measure Marshall
stability and flow
Marshall Stability and Flow
The "stability" value
represents the maximum
load in lbs. the sample can
bear under this loading
condition, while the "flow"
value represents the
deformation, in 0.01 in., of
the sample at the
maximum load.
• High stability => high
shear strength
• Small flow => more brittle
• Large flow => more ductile
Marshall Method
4. (Cont.)
• Analyze results by plotting % asphalt vs. density, stability, flow,
air void content, and VMA
• Determine % asphalt by weight by taking average % asphalt for
these values:
- Highest Marshall stability
- Highest unit weight
- Air content at middle of allowable range (~4%)
Marshall Method
(4.75+5.25+4.25)/3=4.75
Marshall Method
5. Determine the stability, flow, air voids content, VMA of the mix at
the optimum asphalt content from the graphs and compare with
the Marshall mix acceptance criteria specified established by
highway and government agencies according to the local
service conditions.
Iterate, if necessary.
Superpave Mix Design
• One outcome of SHRP’s Superpave (Superior Performing
Pavement) research
• Developed to connect mix design parameters to predicted
performance of the asphalt concrete mixture
• Mixtures designed to resist or control 3 primary forms of distress
in asphalt pavements:
permanent deformation or “rutting” (PD)
fatigue cracking
low temperature or themal cracking
• Hence, this is a more mechanistic approach to mix design
Superpave Mix Design
Advantages:
• Mixture properties and performance are connected (Steps 2&3)
• Basic material properties are measured, rather than relying on
empirical measures (Steps 2&3)
• Seasonal variations are considered (Step 3)
• Achieve improved understanding of which mixture parameters
influence which mixture properties and which performance
measures (Steps 2&3)