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Mix Design & Link with Asphalt Pavement Design South African Asphalt Mix Design Workshop Tuesday, 18 November 2014, CSIR ICC, Pretoria Joseph Anochie-Boateng
Mix Design & Link with
Asphalt Pavement Design
South African Asphalt Mix Design
Workshop
Tuesday, 18 November 2014, CSIR ICC, Pretoria
Joseph Anochie-Boateng
Outline
• Mix design levels
• PAQs
• Overview of the mix design procedure
• Link with asphalt pavement design
Mix design levels
• Low risk of structural damage (rutting, cracking and layer stiffness disregarded)
• up to 3 million E80s • Recommended control points for
aggregate grading selection • Volumetric design with mechanical
properties testing
Level I: Low to medium volume roads
• Medium to high risk of structural damage (moderate to severe rutting and cracking expected), layer stiffness considered
• 3 to 30 million E80s • Involves Level I volumetric design • Performance related laboratory
testing to select optimum mix design
Level II : Performance-related for medium to high volume roads
• High risk of structural damage (where rutting, fatigue cracking could be severe), layer stiffness considered
• ≥ 30 million E80s • Involves Level I volumetric design,
and full scale laboratory testing • Establishes full scale laboratory
data for advanced pavement design and analysis
Level III : Performance-related for very high volume roads
What are the highlights of Level I design?
• Not completely new
• Mainly volumetric design for low to medium volume roads
• A mix design is usually tendered for each contract and client /consultant approval is obtained for each design
• The optimum mix is defined in terms of: – Binder content and grading;
– OBC is determined for VIM (VMA, VFB, are checked against criteria)
– TSR, ITS, dynamic creep, SCB, & permeability must conform to criteria
What are the highlights of Levels II & III
designs?
• Performance-related mix designs; new
• Designs are dependent on performance-related lab testing
• Not practical to repeat such designs on a contractual basis
What are the highlights of Levels II & III
designs?
• Individual suppliers would have a number of performance-related mixes certified for specific applications and performance expectations
• Certification would be valid for a period of two years if there were no significant changes to the raw materials used in such a certified mix
How is this mix design method different
from previous ones ?
• Involves performance testing (lab) for mixes designed for 3 million E80s or more
• Grading control points are guideline
• Link with modern asphalt pavement design
• More reliable
What are the new requirements for
aggregate grading?
• Control points are guideline
• This will make it easier to meet VMA and other requirements
What are the acceptable performance-
related lab tests?
• Five different tests are required
– Workability (Superpave gyratory compaction)
– Durability (Modified Lottman test)
– Stiffness/ dynamic modulus (Compression test; Asphalt Mixture Performance Test -AMPT)
– Permanent deformation / Flow number (Repeated load triaxial test, AMPT)
– Fatigue (4PB test)
What are the required values for the
performance tests?
• Typical values are given in the Manual
• Values are interim, require Lab validation tests
• Values were obtained from one Lab although repeatability was ensured
• Reproducibility tests will be required to set criteria / specifications
Will we have to redesign all mixes?
• No & Yes
• Many mixes will meet most or all of the requirements in the Manual for Level I
• Mixes for higher traffic levels (> 3 million E80s) will need to be evaluated for rut resistance, and check fatigue resistance
• Mixes that must be redesigned should require some adjustments
Will there be a training?
• Yes
• Sabita / SARF / CSIR
• Training materials will be developed
• Testing laboratories – training and development
Overview of asphalt
mix design
• Select the mix type based on design objective and situation
• The Nominal Maximum Particle Size (NMPS) is usually specified by the agency, and depends on the layer thickness to be used in the paving project
Step 1: Selection of mix type
• A binder type meeting the PG grading requirements (climate & traffic) as specified in Manual is selected
Step 2: Selection of binder
Step 3: Selection of aggregates
• Aggregates must meet all specification requirements of the project
• Procedures and acceptance requirements described in the Manual should be followed to select all aggregate fractions
Step 4: Develop 3 trial gradings
• Determine min binder content for each trial aggregate grading using richness modulus (K)
– Similar to the film thickness calculation in the TRH 8
Mix type Minimum K
Sand skeleton ≥ 2.9
Stone skeleton ≥ 3.4
Guideline
• Evaluate the three trial aggregate gradings
• Marshall or Superpave gyratory compactions are optional choices for volumetrics (Level I)
– SANS 3001-AS1 or AASHTO T 312
Marshall Superpave
# of blows Ndesign
75/45 75
Step 4: Develop 3 trial gradings
Criteria
• Compact specimens after short-term oven ageing to the recommended compaction levels
– 3 duplicate specimens with 1 binder content for each trail grading (9 briquettes)
• Prepare loose mixes for MVD tests
– 2 duplicates x 3 BC= 6 Tests
• Determine densities (BD, MVD)
– Determine volumetrics (VIM, VMA, VFB)
Step 4: Develop 3 trial gradings
Step 5: Select optimum design
• Select design aggregate grading and corresponding min binder content
• The selected design grading is used to determine the optimum mix
• Select four trial binder contents based on:
– minimum binder content,
– minimum binder content +0.5%,
– minimum binder content +1.0%, and
– minimum binder content +1.5%
• Produce laboratory trial mixes for each trial binder content
Step 5: Select optimum design
Trial
binder content
BRD
specimens (Marshall /
Superpave)
MTRD
specimens
Trial binder 1 3 specimens 2 tests
Trial binder 2 3 specimens 2 tests
Trial binder 3 3 specimens 2 tests
Trial binder 4 3 specimens 2 tests
Total 12 Briquettes 8 Tests
• Determine volumetrics (VIM, VMA, VFB)
• Use the volumetric data to generate graphs of VIM, VMA and VFB versus the four binder contents
Step 5: Select optimum design
Step 5: Select optimum design
NMPS (mm) Minimum VMA for design voids
3% 4% 5%
25 11 12 13
20 12 13 14
14 13 14 15
10 14 15 16
Minimum VFB Maximum VFB
65 75
• The design (optimum) binder content is established at 4 percent air voids
Criteria
Step 5: Select optimum design
• The optimum mix is assessed in accordance with the following properties and criteria
Property Test Method Criteria
Durability/TSR Modified Lottman ASTM D 4867 M Table 23 (Manual)
Stiffness Indirect tensile
strength ASTM D 6931-07
900 kPa- 1 650 kPa @
25°C
Creep modulus Dynamic creep CSIR RMT 004 10 MPa min. @ 40°C
Fatigue/tensile
strength
Semi-circular
bending (SCB) ---
@ 10°C (Criteria to be
finalised)
Permeability Air permeability EN 12697-19¹ 0.1mm/s - 4 mm/s
Criteria
Step 6: Mix acceptance
• If one or more of the mix design criteria cannot be met, then consider adjustments to be made in aggregate type, grading, or binder type in the design process
Mix design Level II & Level III
• The volumetric design of Level I is the starting point for Level II & Level III designs
• Superpave gyratory procedure is used for volumetric design
• Compaction levels for Level II and Level III are different
Step 1: Select optimum mix
• Sample preparation and determination of volumetrics; same as Level I except that the only option is Superpave gyratory
• Compaction levels:
• VIM, VMA, VFB criteria, same as Level I
Design traffic [E80s] Ndesign
3 to 30 million 100
> 30 million 125
Step 2: Evaluate workability
• Workability test is conducted on a short-term oven aged gyratory compacted specimens of dimensions 150 mm diameter by 170 mm high as per AASHTO PP 60
Mix type Number of
gyrations Voids
Sand skeleton 25 0 < V25 – Vdes < 2
Stone skeleton 25 0 < V25 – Vdes < 2
Criteria is interim, requiring lab validation test
Step 3: Evaluate durability
• Durability of the mix is assessed by using the Modified Lottman procedures (ASTM D4867M)
Climate Permeability
Low Medium High
Dry 0.60 0.65 0.70
Medium 0.65 0.70 0.75
Wet 0.70 0.75 0.80
Criteria
Step 4: Evaluate stiffness
• Stiffness (expressed as dynamic modulus) is assessed by using the AMPT procedures in AASHTO TP 79
Mix type Binder type Temperature (°C )
-5 5 20 40 55
Sand
skeleton
50/70 24 200 19 800 10 000 1 700 450
AP-1 26 200 21 700 11 200 1 900 700
AE-2 19 850 15 500 6 800 1 100 500
Stone
skeleton
35/50 24 750 19 800 10 150 2 300 600
AE-2 22 150 18 000 7 950 1 200 500
AP-1 25 000 21 250 12 500 3 000 950
AP-1 13 000 9 000 3 600 850 350
AR-1 9 200 5 750 2 250 500 NA
Typical values
Step 5: Select optimum mix based on
performance
• Permanent deformation
– Evaluated using repeated triaxial load flow number test (AASHTO TP79)
– Test is conducted in AMPT
• Three binder content levels are used to evaluate permanent deformation
– Optimum (b.c. @ 4% voids)
– Optimum minus 0.5%
– Optimum plus 0.5%
Step 5: Select optimum mix based on
performance
• Prepare three duplicate sets of gyratory compacted specimens in accordance with AASHTO PP60 (150 mm diameter by 170 mm high)
• Specimens for testing are cored and cut to 100 mm diameter by 150 mm high
• Total of 9 specimens are required to evaluate the mix at the three binder contents
• The binder content that provides highest flow number is selected as the performance-based design binder content
Mix type Binder type Temperature (°C )
40 55
Sand skeleton
50/70 850 120
AP-1 8 100 1 000
AE-2 900 80
Stone skeleton
35/50 1 900 250
AE-2 1 300 150
AP-1 4 000 – 6 500 ---
AR-1 700 50
Step 5: Select optimum mix based on
performance
Typical values
Step 5: Select optimum mix based on
performance
• Fatigue life
– The design binder content obtained from permanent deformation evaluation is used
– Is evaluated in a 4PBT (AASHTO T 321)
Mix type Binder type 200με 400με 600με
Sand skeleton
50/70 1.2 0.03 0.004
AP-1 4.9 0.04 0.002
AE-2 14.0 0.35 0.040
Stone skeleton
35/50 0.9 0.02 0.002
AE-2 10.2 0.15 0.013
AP-1 1.0 0.03 0.004
AP-1 (SMA) 6.8 0.19 0.023
AR-1 --- --- 0.313
AR-1 9.5 0.40 0.063
Typical values
Performance-related tests
Property Test conditions No. of
specimens
Test
method
Workability Superpave gyratory compactor 3 AASHTO PP60
Durability Modified Lottman test conditions 6 ASTM D 4867M
Stiffness/
(dynamic
modulus)
AMPT dynamic modulus at six loading
frequencies and five temperatures 5 AASHTO TP 79
Permanent
deformation
AMPT permanent deformation at max three
stress levels and three temperatures 3 AASHTO TP 79
Fatigue Four-point beam fatigue test at max three
strain levels and three temperatures 9 AASHTO T 321
Performance testing conditions
Design
Level Stiffness
Permanent
Deformation
Fatigue
Cracking
Level II
Dynamic modulus
testing at 20°C, 10Hz
Repeated load triaxial test
at 55°C, a deviator stress of
483 kPa & confining stress
of 69 kPa
4PB fatigue testing
at 10°C & three
strain levels
Level III
Six loading
frequencies (0.1, 0.5,
1, 5, 10 & 25Hz), five
test temperatures (-5,
5, 20, 40, 55°C)
Repeated load triaxial test
at three temps (25, 40 &
55°C), three deviator stress
levels (138, 276 & 483 kPa)
& confining stress of 69 kPa
4PB fatigue testing
at three test temps
(5, 10, 20°C) &
three strain levels
Performance testing equipment
Performance testing equipment
Step 6: Check permeability
• Conduct water permeability test on the design mix in accordance with EN 12697-19 procedures and check results against the criteria
Step 7: Mix acceptance
• The final mix design will be accepted when it meets all requirements /criteria presented in the design process
– If any of the requirements /criteria cannot be met, then consider adjustments to be made in aggregate or binder type, and aggregate grading in the mix design procedures
Special mixes
• Cold mixes – Sabita Manuals 14, 21 & TG2
• Porous asphalt – Sabita Man 17
• WMA – Sabita Manual 32
• EME – Sabita Manual 33
• SMA – Appendix of the design manual
Link with pavement design
• Not finalised …
• Only overview is presented
Link with pavement design
• The goal is to describe how the test results obtained in the performance related mix design process can be used to predict the structural performance of the material in the field
• The methodology will allow the designer to assess how the changes to a mix design will affect the performance of the material in the field
Link with pavement design
• SARDS requires response and damage models
– Dynamic modulus models
– Damage models
• Temperature models
– Max surface temperature
– Min surface temperature
– Temperature at depth
Dynamic modulus models
• Empirical method (Witczak model)
– Binder properties
– Mix volumetrics
– Grading
ηlog.flog..
abeff
beff
a
*
e
P.P.P.P..
VV
V.
V.P.P.P..E log
393532031335106033130
34
2
38384
4
2
200200
1
005470000017000395800021087197738022080
05809700028410001767002923207500633
Dynamic modulus models
• Laboratory method
– Deriving master curve
10
100
1000
10000
100000
0.000001 0.0001 0.01 1 100 10000 1000000
Dynam
ic m
od
ulu
s (M
Pa)
Reduced f requency (Hz)
Model (Master curve)
-5-deg C
5-deg C
20-deg C (Tref)
40-deg C
55-deg C
).(logVTSATlogVTSAc(f)logγβe
αδE* log
6752710101
Damage models
• Permanent deformation
– Linkage to AMPT required
• Fatigue cracking
– Based on 4PBT
32
111
kk
t
fE
kN
Summary - Link with Pavement Design
Performance Prediction Testing
Results
Dynamic Modulus |E*|
Performance Prediction Models
South Africa Road Design System
(SARDS) software
32
111
kk
t
fE
kN
854.0291.3
'
1
1100432.0
ECkN f
332211
rrrr aarr
r
pNTa
Summary - Link with Pavement Design
Vertical plane parallel to Y-Z at X = 0
Shear Strain YZ
0.000010
-0.000056
-0.000122
-0.000188
-0.000254
-0.000320
-0.000386
-0.000452
-0.000517
-0.000583
-0.000649
-0.000715
-0.000781
-0.000847
-0.000913
-0.000979
-0.001045
-0.001111
-0.001177
-0.001243
Pavement analysis
Property value
E* [GPa] > 5
Fatigue [με to 106] > 300
Perm. def. [εp] < 2%
Structural requirements
Property value
E* [GPa] > 5
Fatigue [με to 106] > 300
Perm. def. [εp] < 2%
Workability [voids] < 6%
Durability [TSR] > 80%
Tender specificationMix selection
Property Mix 1 Mix 2 Mix 3
E* [GPa] 14 6 3
Fatigue [με to 106] 220 370 280
Perm. def. [εp] 0.8 % 1.5 % 4.2 %
Workability [voids] 5.0 4.5 5.2
Durability [TSR] 90 85 75
Nf
Nf
• For a new asphalt pavement layer designers will have the option to pick a mix from the list of certified mixes to provide all input parameters for pavement design
Link with Asphalt Pavement Design
Thank You…
End of presentation
