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Pavement Engineering ECG 524 TOPIC 2.0 Asphaltic Concrete Pavement Design
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Pavement Engineering
ECG 524TOPIC 2.0
Asphaltic Concrete Pavement Design
2.1 Hot Mix Asphalt Mixture Design Methodology
2.2 Marshall mixture design method
2.3 Superpave mix design method
2.4 Design of Flexible Pavement
2.5 Overlay design and surface dressing
Topic Outlines
3
At the end of the lecture, students should be
able to:
Perform design mix according to either Marshall
or Superpave Method .(CO2-PO3, CO2-PO4)
To understand the element of thickness design,
material requirements, mixture requirements,
traffic loading and JKR Design Method.(C02-
PO4)
Learning Outcomes
4
Topic 2.1
Hot Mix Asphalt Mixture Design Methodology
Introduction
History of asphalt mix design dated backfrom 1860s (Crawford)
First binder used was TAR (1868 and1873)
Aggregate proportioning not understood,hence no proper mixing processedmechanized
Introduction
Clifford Richardson, an asphalt technologistdiscovered that material selection is important,especially the role of aggregate fractions
His documentations include the importantprinciples of HMA design including voids inmineral aggregate (VMA) and air void content
The first test to determine OBC of HMA mix is the “Pat Test”
Still used till early 1920s – visual assessments
Hubbard-Field method in the middle of 1920s
Marshall and Hveem mix design methodswere used between 1940s and mid 1990s
In 1939, Bruce Marshall developed theearliest version of Marshall mix designmethod
Controlling factor is the correspondence betweendensity achieved in field under traffic and thatproduced in the lab with specified compactive effort,hence only by knowing field conditions can properadjustments be made in the lab to replicate fieldconditions
Introduction
Hveem mix design method – FrancisHveem
Hveem developed stabilometer in 1959,a procedure to measure cohesivestrength of compacted specimen
Developed simple portable apparatusfor designing asphalt mixtures forairfield pavements
Introduction
Hot Mix Asphalt Design
History
Binder
HMA
Specimen
Aggregates
Hot Mix Asphalt Concrete (HMA)
Mix Designs
Objective:
– Develop an economical blend of aggregates and
asphalt binder that meets design requirements
Historical mix design methods
– Hubbard-Field, Hveem, Marshall (1920 – 1940)
New
– Superpave Mix Design Method (1995 - present)
– Srategic Highway Research Programme (SHRP)
No matter which design procedure is going to be usedthe HMA mixture that is placed on the roadway mustmeet certain requirements.
Sufficient asphalt binder to ensure a durable pavement
- To ensure durable, compacted pavement by thoroughly coating, bonding and waterproofing the aggregate
Sufficient stability under traffic loads
- To satisfy the demands of traffic without displacement or distortion (rutting)
Requirements in Common
Sufficient air voids
-to prevent excessive environmental damage
should be low enough to keep out harmful air and moisture
-to allow room for initial densification due to traffic
should have sufficient voids to allow compaction under
traffic
loading without bleeding and loss of stability
Sufficient workability
-Enough workability to permit placement and proper
compaction without segregation
Requirements in Common
Resistance to Permanent DeformationMix should not distort or displace when subjected to traffic. The
resistance to permanent deformation (rutting) becomes critical
at elevated temperatures during hot weather when the viscosity
of the bitumen is low and traffic load is primarily carried by
aggregate structure. Hence, selecting quality aggregate is
important with proper gradation.
Fatigue Resistance
Mix should not crack when subjected to repeated loads over a
period of time.
Objectives and Elements of Mix Design
DurabilityMix must contain sufficient bitumen to ensure adequate film
thickness around aggregate particles, thus minimizing binder
hardening or aging during production and in service.
Resistance to Moisture Induced Damage
Some HMA mix when subjected to moisture or water lose
adhesion between aggregate surface and binder. Aggregate
properties are primarily responsible for this phenomenon,
although some binder ar more prone to moisture damage
(stripping) than others. Antistripping agent should be use if a
HMA mix is prone to stripping to minimize problems or making
the mix impermeable
Objectives and Elements of Mix Design
Skid Resistance
This requirement is only applicable to surface mixes which must
be designed to provide sufficient resistance to skidding to permit
normal turning and braking movements to occur. Aggregate
characteristics such as texture, shape, size and resistance to
polish are primarily responsible for skid resistance. Mix should
not also contain too much binder that may cause mix to flush
and create slippery surface.
Workability
Mix must be capable of being placed and compacted with
reasonable effort. Workability problems are most frequently
discovered during the paving operations.
Objectives and Elements of Mix Design
16
Topic 2.2
Marshall Mix Design Method
MARSHALL
MIX
DESIGN
Marshall Mix Design
Developed by Bruce Marshall for the Mississippi Highway Department in the late 30’s
In 1943 for WWII – Developed simple portable apparatus for designing asphalt mixtures for airfield pavements
– Evaluated compaction effort
• No. of blows, foot design, etc.
• Decided on 10 lb.. Hammer, 50 blows/side
• 4% voids after traffic
Initial criteria were established and upgraded for increased tyre pressures and loads
Automatic Marshall Hammer
Mixtures designed in laboratory
using a variety of compactive
efforts in an attempt to produce
densities similar to field
One goal of lab compaction
study was to adopt a sample
preparation procedure that
would involve minimum effort
and time but would provide a
basis for selecting the proper
optimum binder content
Development and evolution of the Marshall method
concluded that two variables stand out in the design and
performance of HMA:
•Asphalt content
•Density
In the field, it is the highest satisfactory asphalt content at
a density achieved under traffic that is significant.
In laboratory, the important feature is selecting a
compaction procedure that represents traffic-induced
density and then selecting response properties that can be
averaged to yield as asphalt content that will produce
satisfactory performance.
Marshall Design Method
Advantages
– Attention on voids, strength, durability
– Inexpensive equipment
– Easy to use in process control/acceptance
Disadvantages
– Impact method of compaction
– Does not consider shear strength
– Load perpendicular to compaction axis
Marshall Mix Design Method
(ASTM D1559)
Steps:
– Step A: Aggregate Evaluation
– Step B: Binder/Bitumen Evaluation
– Step C: Preparation of Marshall Specimens
– Step D: Density-Voids Analysis
– Step E: Marshall Stability and Flow Test
– Step F: Tabulating & Plotting Test Results
– Step G: Determine Optimum Binder
Content (OBC)
Step A: Aggregate Evaluation
A-1:
Determine acceptability of aggregate for use in HMA, construction;
tests often performed include LA abrasion, sulfate soundness, sand
equivalent, presence of deleterious substances, polishing, crushed
face count and flat & elongated particle
A-2:
If material is acceptable in A-1, then perform other required
aggregate tests: gradation, specific gravity and absorption
A-3:
Perform blending calculations, plot mid range gradation on FHWA
0.45 power gradation chart
A-4:
Prepare a specimen weigh-out table by multiplying the percent
aggregate retained between sieves times an aggregate weight of
approximately 1150g, then determine the cummualtive weights
starting with the material passing the 0.075 mm sieve
Step A: Basic Aggregate Testing
Mix Type Wearing
Course
Wearing
Course
Binder Course
Mix
Designation
AC10 AC14 AC28
BS Sieve Size Percentage Passing by Weight
28.0
20.0
14.0
10.0
5.0
3.35
1.18
0.425
0.150
0.075
100
90-100
58-72
48-64
22-40
12-26
6-14
4-8
100
90-100
76-86
50-62
40-54
18-34
12-24
6-14
4-8
100
72-90
58-76
48-64
30-46
24-40
14-28
8-20
4-10
3-7
JKR Gradation Limits
Aggregate Blending
How many percentage from each stockpile to
achieve a blend that conform to PWD mid-gradation,
example ACW 14?
Blending of Aggregates
Agg. BAgg. A
Blend Target
Material
%
Passing
%
Passing
% Used
Sieve (mm)%
Batch
%
Batch
10
5
3.35
1.18
0.425
0.15
0.075
14
90
30
7
3
1
0
0
100
100
100
88
47
32
24
10
100
Blending of Aggregates
Agg. BAgg. A
Blend Target
Material
%
Passing
%
Passing
% Used
Sieve (mm)%
Batch
%
Batch
10
5
3.35
1.18
0.425
0.150
0.075
14
45
15
3.5
1.5
0.5
0
0
100
100
100
88
47
32
24
10
100
50 %50 %
First Try
(remember trial & error)
90
30
7
3
1
0
0
50
90 * 0.5 = 45
30 * 0.5 = 15
7 * 0.5 = 3.5
3 * 0.5 = 1.5
1 * 0.5 = 0.5
0 * 0.5 = 0
0 * 0.5 = 0
100 * 0.5 = 50
80 - 100
65 - 100
40 - 80
20 - 65
7 - 40
3 - 20
2 - 10
100
Blending of Aggregates
Agg. BAgg. A
Blend Target
Material
%
Passing
%
Passing
% Used
Sieve (mm)%
Batch
%
Batch
10
5
3.35
1.18
0.425
0.150
0.075
14
80 - 100
65 - 100
40 - 80
20 - 65
7 - 40
3 - 20
2 - 10
100
45
15
3.5
1.5
0.5
0
0
100
50
50
44
23.5
16
12
5
50
50 %50 %
90
30
7
3
1
0
0
50
95
65
47.5
25
16.5
12
5
100
100
100
88
47
32
24
10
100
Let’s Try
and get
a little closer
to the middle of
the target values.
Blending of Aggregates
Agg. BAgg. A
Blend Target
Material
%
Passing
%
Passing
% Used
Sieve (mm)%
Batch
%
Batch
10
5
3.35
1.18
0.425
0.150
0.075
14
80 - 100
65 - 100
40 - 80
20 - 65
7 - 40
3 - 20
2 - 10
100
27
9
2.1
0.9
0.3
0
0
100
70
70
61.6
32.9
22.4
16.8
7
70
70 %30 %
90
30
7
3
1
0
0
30
97
79
63.7
33.8
22.7
16.8
7
100
100
100
88
47
32
24
10
100
Aggregate Blending to Meet Specifications Given the gradation of aggregates A, B and C, determine the required percent of
each to result in a blend meeting the required specification requirements
Sieve Size
Aggregate
Specifications
Median of
SpecificationsA B C
1 inch 100 100 100 94-100 97
½ inch 63 100 100 70-85 78
No.4 (4.75 mm or 3/8 inch) 19 100 100 40-55 48
No.8 (2.36 mm) 8 93 100 30-42 36
No.30 (0.6 mm) 5 55 100 20-30 25
No.100 (0.150 mm) 3 36 97 12-22 17
No.200 (0.075 mm) 2 3 88 5-11 8
Desired
material
larger than
4.75mm
sieve is 52%
must come
from Agg. A
Desired
material
larger than
0.6 mm sieve
is 75% must
come from
Agg. A and B
percent of A = = 64 %81
52percent of B = 75 – 0.64(95) = 14 %
Sieve Size
Aggregate
Specification
s
Median of
SpecificationsA B C
1 inch 100 100 100 94-100 97
½ inch 63 100 100 70-85 78
No.4 (4.75 mm or 3/8 inch) 19 100 100 40-55 48
No.8 (2.36 mm) 8 93 100 30-42 36
No.30 (0.6 mm) 5 55 100 20-30 25
No.100 (0.150 mm) 3 36 97 12-22 17
No.200 (0.075 mm) 2 3 88 5-11 8
Desired
material
larger than
4.75mm
sieve is 52%
must come
from Agg. A
Desired
material
larger than
0.6 mm sieve
is 75% must
come from
Agg. A and B
percent of A = = 64 %81
52percent of B = 75 – 0.64(95) = 14 %
Based on these calculations, first estimate is :
Aggregate A : 64 %
Aggregate B : 14 %
Aggregate C : 22 %
Aggregate %
Used
Sieve Size
1 inch ½ inch No.4 No.8 No.30 No.100 No.200
A 64 64 40.3 12.2 5.1 3.2 1.9 1.3
B 14 14 8.8 2.6 1.1 0.7 0.4 0.3
C 22 22 13.8 4.2 1.7 1.1 0.7 0.4
Blend 100 100 62.9 19 7.9 5 3 2
Desired 97 78 48 36 25 17 8
Specification 94-100 70-85 40-55 30-42 20-30 12-22 5-11
FIRST TRIAL
A 71 71 44.7 13.5 5.7 3.6 2.1 1.4
B 21 21 21 21 19.5 11.6 7.6 0.6
C 8 8 8 8 8 8 7.8 7
Blend 100 100 73.7 42.5 23.2 23.2 17.5 9.0
SECOND TRIAL
A 66
B 28
C 6
Blend 100
Source : HMA Asphalt Materials, Mixture Design & Construction, NAPA
Step B: Basic Asphalt Testing
B-1:
Determine appropriate binder grade for type and geographic
location of mixture being designed
B-2:
Verify specification properties are acceptable
B-3:
Determine binder specific gravity and plot viscosity data on a
temperature-viscosity plot
B-4:
Determine the ranges of mixing and compaction temperatures from
the temperature-viscosity plot:
– Mixing temperature should be selected to provide viscosity of 170 ±
20 centistokes
– Compaction temperature should be selected to provide a viscosity
of 280 ± 30 centistokes
Step B: Basic Asphalt TestingAsphalt Properties Required by JKR Malaysia
Standard Tests Penetration Grades
60-80 80-100
Penetration @ 25oC 60-80 80-100
Loss on heating (%) <0.2 <0.5
Drop in penetration after heating (%) <20 <20
Retained penetration after thin-film
oven test (%)
>52 >47
Solubility in Carbon Disulphide or
Trichloroethylene (%)
>99 >99
Flash and fire point test (oC) >250 >225
Ductility test at 25oC >100 >100
Ring and Ball Softening Point test >48, <56 >45,<52
.1
.2
.3
.5
1
10
5
100 110 120 130 140 150 160 170 180 190 200
Temperature, C
Viscosity, Pa s
Compaction Range
Mixing Range
Mixing/Compaction Temperatures
To establish mixing and compaction temperatures it is necessary to develop a temperature viscosity chart.
Determining the viscosity at two different temperatures - generally 135 C and 165 C. These two
viscosities are then plotted on the graph above and a straight line is drawn between the two points.
The desired viscosity range for mixing is between 0.15 and 0.19 Pa-s and 0.25 and 0.31 Pa-s for
compaction. Appropriate mixing and compaction temperatures are selected as the temperature where these
viscosity requirements are met. This information can be obtained from the suppliers.
If using modified binders - it is recommended that you should contact the supplier to determine the mixing
and compaction temperatures.
Step C: Preparation of Marshall Specimens
C-1:
Dry and sieve aggregates into sizes (preferably individual sizes) and
store in clean sealable containers. Separate enough material to make
18 specimens of approximately 1150 g each.
C-2:
Weigh out aggregate for 18 specimens placing each in a separate
container and heat to mixing temperature determined in Step B-4.
However, the total aggregate weight should be determined as
discussed in C-3.
C-3:
It is generally desirable to prepare a trial specimen prior to preparing all
aggregate batches. Measure the height of the trial specimen (h1) and
check against height requirement for Marshall specimens (63.5 mm). If
the specimen is outside this range, adjust quantity of aggregate
included in a specimen using the following formula:
Q = 63.5/h1 x 1150 g
Step C: Preparation of Marshall Specimens
C-4:
Heat sufficient binder to prepare a total of 18 specimens. Three
compacted specimens each should be prepared at five different binder
content. Binder contents should be selected at 0.5% increments with at
least two asphalt contents above “optimum” and at least two below
“optimum”. See appropriate specifications for a guide on approximate
“optimum” binder content or the estimate of optimum can be based on
experience. Three loose mixture specimens should be made near the
optimum binder content to measure Rice specific gravity or theoretical
max density (TMD).
Table 4.3.4 : Design Bitumen Contents (JKR/SPJ/2008-S4)
AC 10 – wearing course
AC 14 – wearing course
AC 28 – binder course
5.0-7.0%
4.0-6.0%
3.5-5.5%
Step C: Preparation of Marshall Specimens
C-5:
Review appropriate specifications to determine number of blows/side
and type of compaction equipment required for compaction of Marshall
specimen
C-6:
Remove the hot aggregate, place it on a scale and add the proper
weight of binder to obtain the desired binder content
C-7:
Mix binder and aggregate until all the aggregate is coated. It is helpful
to work on a heated table. Mixing can be by hand, but a mechanical
mixer is preferred
Step C: Preparation of Marshall Specimens
C-8:
Check temperature of freshly mixed material; if it is above the
compaction temperature, allow it to cool to compaction temperature; if it
is below compaction temperature, discard the material and make a new
mix. (The mix can be placed back in the oven to be reheated which is
considered as curing time to better simulate what happens to the HMA
mix in the field. This curing time is especially important for aggregates
with high absorption since the asphalt absorbed into the aggregate
increases with time).
C-9:
Place a paper disc into an assembled, preheated Marshall mould and
pour in loose HMA. Check the temperature. Spade the mixture with a
heated spatula or trowel 15 times around the perimeter and 10 times
over the interior.
Step C: Preparation of Marshall Specimens
C-10:
Remove the collar and mound materials inside the mould so that the
middle is slightly higher than the edges. Attach the mould and base
plate to the pedestal. Place the preheated hammer into the mould, and
apply the appropriate number of blows to the top side of the specimen
C-11:
Remove the mould from the base plate. Place a paper disc on top of
the specimen and rotate the mould 180o so that the top surface is on
bottom. Replace the mould collar and attach the mould and base plate
to the pedestal. Place the hammer in the mould and apply the same
number of blows to the opposite side of the specimen
C-12:
Remove the paper filters from the top and bottom of the specimens.
Cool the specimens and extrude from the mould using a hydraulic jack.
Place identification marks on each specimen and allow specimens to sit
at room temperature overnight before further testing
Step C: Preparation of Marshall Specimens
C-13:
Determine the bulk specific gravity for each specimen by weighing in air.
Submerge the samples in water and allow to saturate prior to getting submerged
weigh in SSD condition. Remove the sample and weigh in air in saturated
surface dry condition. This test is conducted in accordance with AASHTO T166
C-14:
Measure the Rice specific gravity on the loose HMA mix samples in accordance
with AASHTO T209 (ASTM D2041). This specific gravity is required for voids
analysis. If the mix contains absorptive aggregate it is recommended to place
the loose mix in an oven (maintained at the mix temp) for 4 hours so that the
asphalt binder is completely absorbed by the aggregate prior to testing. Keep
the mix in a covered container while in the oven. If the test is run in triplicate on
the mix containing near optimum binder content, average the three results,
calculate the effective specific gravity of the aggregate, and then calculate the
Rice specific gravity or TMD for the remaining mixes with different binder
content. If one TMD test is conducted on each mix containing a different binder
content, then calculate the effective specific gravity of aggregate in each case.
Calculate the average effective specific gravity and then calculate the TMD
values using the average for all five mixes.
Mixing
Place pre-heated aggregate in bowl & add hot bitumen
Place bowl on mixer & mix until aggregate is well-coated (1minute mixing time)
Place funnel on top of mould & place mix in mould. Take carenot to allow the mix to segregate
Place another paper on top of mix. Tamp along circumference ¢re. Wait for specimen to cool down to compactiontemperature. Begin compaction.
Compaction
Marshall Hammer (impact) @50 or 75 blows each face
Step D: Density and Voids Analysis
D-1:
For each specimen, use the bulk specific Gravity (Gmb) from
Step C-13 and Rice Specific gravity (Gmm) from C-14 to
calculate the percent voids or VTM
D-2:
Calculate the density of each Marshall specimen as follows:
Density (g/ml) = Bulk Specific Gravity (Gmb) x δw
1001
mm
mb
G
GVTM
Step D: Density and Voids Analysis
D-3:
Calculate the VMA for each Marshall specimen using the bulk
specific gravity of the aggregate (Gsb) from Step A-2, the bulk
SG of the compacted mix (Gmb) from Step C-13, and the binder
content by weight of total mix (Pb)
D-4:
Calculate the VFA (voids filled with asphalt) for each Marshall
specimen using the VTM and VMA as follows :
VMA
VTMVMAVFA 100
sb
bmb
G
PGVMA
)1(1100
Step E: Marshall Stability and Flow Test
E-1:
Heat the water bath to 60oC and place specimens to be tested in the
bath for at least 30 but not more than 40 minutes. Place specimens in
the bath in a staggered manner to ensure that all specimens have been
heated for the same length of time before testing. Use waterbath large
enough to hold all specimens prepared for the mixture design
E-2:
After heating for the required amount fo time, remove a specimen from
the bath, pat with towel to remove excess water, and quickly place in
the Marshall testing head
E-3:
Bring the loading ram into contact with the testing head. Zero the pens
if using a load-deformation recorder or zero flow gauge, and place the
gauge on the rod of the testing head. Apply the load
Marshall Stability and Flow
Step E: Marshall Stability and Flow
Tests
test for Marshall Stability & flow at 60OC
The applied load must be corrected when thickness of
specimen is other than (2½ in.) or 63.5mm by using the
proper multiplying factor from Table below
Stability correlation ratio (ASTM D1559)
Lab Mix – Marshall Form
Step F: Tabulating and Plotting Test
Results
F-1:
Tabulate the results from testing, correct the stability values for
specimen height (ASTM D1559), and calculate the average of each set
of 3 specimens
F-2:
Prepare the following plots:
Asphalt Content versus density (or unit weight)
Asphalt content versus Marshall stability
Asphalt content versus air voids (or VTM)
Asphalt content versus VMA
Asphalt content versus VFA
Step F: Tabulating and Plotting Test
Results
F-3:
Review the plots for the following trends:
Stability versus asphalt content can follow two trends:
(a)Stability increases with increasing asphalt content, reaches a peak and
then decreases
(b)Stability decreases with increasing asphalt content and does not show
a peak. This curve is common for some recycled HMA mixtures
Flow should increase with increasing asphalt content
Density increases with increasing asphalt content, reaches a peak, and then
decreases. Peak density usually occurs at a higher asphalt content than
peak stability
Percent air voids should decrease with increasing asphalt content
Percent VMA decreases with increasing asphalt content, reaches a
minimum and then increases
Percent VFA increases with increasing asphalt content
OBC is the mean of bitumen contents that give an optimum value of density, stability
and 4% air voids
Peak curve taken from stability graph
Flow equals to 3mm from the flow graph
Peak curve taken from bulk specific graph
VFB equals to 75% for wearing course and 70% for binder course from the VFB
graph
VIM equals to 4% for wearing course and 5% for binder course from the VIM graph
The individual test values at the mean OBC shall then be read from the plotted smooth
curves and shall comply with the design parameters given in Table 4.3.5
The individual test values at the mean OBC shall then be read from the plotted
smooth curves and shall comply with the design parameters given in Table 4.3.5
Step G: Optimum Binder Content
Determination (JKR)
1. Determine the binder content which corresponds to the specification’s
median air void content (4 % typically). This is the optimum binder content.
2. Determine the following properties at this optimum binder content by
referring to the plots: Marshall Stability
Flow
VMA and
VFA
3. Compare each of these values against the specification values and if all are
within the specification, then the preceding optimum binder content is
satisfactory. If any of these properties is outside the specification range, the
mixture should be redesigned
Step G: Optimum Binder Content
Determination NAPA Procedure
1. Determine :(a) Binder content a maximum stability
(b) Binder content at maximum density
(c) Binder content at mid point of specified air void range (4% typically)
2. Average the three asphalt contents selected above.
3. For the binder content, go to the plotted curves and determine the following
properties: Stability
Flow
Air voids
VMA
4. Compare values from Step 3 with criteria for acceptability given in
specifications
Step G: Optimum Binder Content
Determination Asphalt Institute Method
Table 4.3.5 : Test and Analysis Parameters
(JKR/SPJ/2008-S4)
Parameter Wearing
Course
Binder
Course
Stability, S
Flow, F
Stiffness, S/F
Air voids in mix (VIM)
Voids in aggregate filled with bitumen
(VFB)
>8000 N
2.0-4.0 mm
>2000 N/mm
3.0-5.0 %
70-80%
>8000 N
2.0-4.0 mm
>2000 N/mm
3.0-7.0 %
65-75%
Lab Mix – OBC Determination
2.320
2.330
2.340
2.350
2.360
2.370
4.0 4.5 5.0 5.5 6.0 6.5 7.0
Bit. Content (%)
Density (
g/c
u.c
m)
800
900
1000
1100
1200
1300
1400
4.0 4.5 5.0 5.5 6.0 6.5 7.0
Bit. Content (%)
Sta
bili
ty (
kg)
2.0
3.0
4.0
5.0
6.0
7.0
8.0
4.0 4.5 5.0 5.5 6.0 6.5 7.0
Bit. Content (%)
VTM
(%
)
55.0
60.0
65.0
70.0
75.0
80.0
85.0
4.0 4.5 5.0 5.5 6.0 6.5 7.0
Bit. Content (%)
VF
B (
%)
c
a
d
b
OBC =(a + b + c + d)/4 = e
Check parameters @ OBC
3.00
3.50
4.00
4.50
5.00
5.50
6.00
4.0 4.5 5.0 5.5 6.0 6.5 7.0
Bit. Content (%)
Flo
w (
mm
)
100
150
200
250
300
350
400
4.0 4.5 5.0 5.5 6.0 6.5 7.0
Bit. Content (%)
Stiffn
ess (
kg/m
m)
Lab Mix – OBC Determination
Lab Mix – Value @ OBC
2.320
2.330
2.340
2.350
2.360
2.370
4.0 4.5 5.0 5.5 6.0 6.5 7.0
Bit. Content (%)
Density (
g/c
u.c
m)
800
900
1000
1100
1200
1300
1400
4.0 4.5 5.0 5.5 6.0 6.5 7.0
Bit. Content (%)
Sta
bili
ty (
kg)
2.0
3.0
4.0
5.0
6.0
7.0
8.0
4.0 4.5 5.0 5.5 6.0 6.5 7.0
Bit. Content (%)
VTM
(%
)
55.0
60.0
65.0
70.0
75.0
80.0
85.0
4.0 4.5 5.0 5.5 6.0 6.5 7.0
Bit. Content (%)
VF
B (
%)
e e
e e
Lab Mix – Value @ OBC
3.00
3.50
4.00
4.50
5.00
5.50
6.00
4.0 4.5 5.0 5.5 6.0 6.5 7.0
Bit. Content (%)
Flo
w (
mm
)
100
150
200
250
300
350
400
4.0 4.5 5.0 5.5 6.0 6.5 7.0
Bit. Content (%)
Stiffn
ess (
kg/m
m)
Compare parameters with JKR/SPJ/2008-S4 Specifications
Pass? @ OBC = e
If FAIL, then redesign
e e
Why are the Marshall criteria important?
Voids in the Mineral Aggregate (VMA)
VMA is the total volume of voids within the mass of the compacted aggregate.
This total amount of voids significantly affects the performance of mixture
If the VMA is too small, the mix may suffer durability problems, and if the VMA is
too large, the mix may show stability problems and be uneconomical to produce
VMA components divided into two : volume of voids filled with binder and volume
of voids remaining after compaction available for thermal expansion of the binder
during hot weather
The binder volume and aggregate gradation determines the thickness of binder
film around each aggregate particle
Without adequate film thickness, binder will oxidized faster, water easily penetrate
and tensile strength of mixture is adversely affected
The VMA of a mix must be sufficiently high to ensure there is room for binder plus
required air voids
Why are the Marshall criteria important?
Voids in Total Mix (VTM)
Suggested to range between 3 – 5 percent
However, air void content is for lab compacted samples and should not be
confused with field compacted samples
Void content must be approached during construction through the
application of compactive effort and not by adding binder to fill up the voids
High shear resistance must be developed in the HMA layers if adequate
performance is to be achieved
This high resistance must be present to prevent additional compaction
under traffic which could result in rutting in the wheel paths or flushing and
bleeding of the binder at the surface
Low air void contents minimize the aging of the binder films within the
aggregate mass and also minimize the possibility that water can get into
the mix, penetrate the thin binder film
The in-place air void content should initially be slightly higher than 3 to 5
percent to allow for some additional compaction
Why are the Marshall criteria important?
Density
The magnitude of the density achieved during compaction in the laboratory is
not so important. What is important is how close the density achieved in the
laboratory is to the density achieved in the field after several years of traffic
Density can be achieved by increasing compaction, increased binder content,
increased filler content or any method that reduces voids
Void content must be approached during construction through the application of
compactive effort and not by adding binder to fill up the voids
Density varies with binder content. Density increases as binder content
increases because the hot binder lubricates the particles allowing the
compactive effort to force them closer together.
The density reaches a peak and then begins to decrease because additional
binder produces thicker films around the individual aggregates, thereby pushing
the aggregate particles further apart and resulting in lower density
Why are the Marshall criteria important?
Stability
Marshall stability is defined as the maximum load carried by a compacted
specimen tested at 60oC
Generally a measure of the mass viscosity of the aggregate-binder mixture and
is affected significantly by the angle of internal friction of the aggregate and the
viscosity of the binder at 60oC
One of the easiest way to increase stability of aggregate mixture is to change to
higher viscosity grade of binder, also by selecting a more angular aggregate
Anything that increases the viscosity of binder increases Marshall stability
Marshall stability and field stability are not necessarily related. Stability in the
field is affected by the ambient temperature, types of loading, tyre contact
pressure and numerous mixture properties.
Primary use of stability is to aid selection of OBC and also useful in measuring
the consistency of a plant produced HMA
Why are the Marshall criteria important?
Flow
Flow is measured at the same time as the Marshall stability
Flow is equal to vertical deformation of the sample (measured from start
of loading to the point at which stability begins to decrease)
High flow values generally indicate a plastic mix that will experience
permanent deformation under traffic, whereas low flow value may indicate
a mix with higher than normal voids and insufficient asphalt for durability
and one that may experience premature cracking due to mixture
brittleness during the life of the pavement
Questions?
