balanced mix design approach - texas a&m university › conferences › tsc17 › presentations...
TRANSCRIPT
Initial Thoughts
Dry mixes are prevalent in our industry.
Restrictive specifications
and general notes are not
long term solutions.Lowering N-design
and raising lab molded
densities will only
help so much.
Continuing to increase binder
replacement without addressing mix
performance is not sustainable.
We need to increase our
understanding of the factors
which drive mix performance to
help us better optimize our mixes
2
We prescribe material qualities and characteristics, but don’t always get
the performance we are after
Current State of Affairs
3
“Recipe” driven volumetric designs are
based on history and what we think works
What constitutes a good cake? Is it the individual steps to make it, or is it the end product?
What defines a good cake? It Tastes Good
What defines a good mix? Lasting Performance
LET’S STOP USING THE RECIPE TO DETERMINE IF THE CAKE IS GOOD
What’s more important; cracking resistance or rutting resistance?
Can I have both?
Economics or performance?
Have we placed too many restrictions trying to prescribe what “good hot mix” should look like on paper?
Why not specify performance?
Current State of Affairs
4
Eliminate the restrictions and focus on
PERFORMANCE
What is a Balanced Mix Design?
Optimize
o Make the best or most effective use of
(a situation, opportunity, or resource)
Balance
o Being in proper arrangement or
adjustment, proportion
Balanced Mix Design
o Optimize the mix to provide needed performance and balance
between stability and durability.
5
Optimized Mix Design Approach – Framework
Material Selection
Aggregates
Binder, Modifiers & Additives
Recycled Materials
Optimize JMF
Gradation
Binder Content
Volumetrics
Mix Performance Evaluation
Stability
Durability
Adjustments
Workability
Mixing
Compaction
Segregation
6
Optimized Mix Design Approach – Framework
Mix Performance Evaluation
Stability
Durability
Indicator of cracking resistance Indicator of
rutting resistance
7
Balanced Mix Design Approach - PG 64-22
y = 2E-07x12.635
R2 = 0.9829
y = 698467x-2.4408
R2 = 0.9505
0
5000
10000
15000
20000
25000
4.0 4.5 5.0 5.5 6.0 6.5 7.0
Asphalt Content (%)
Nu
mb
er
of
Pa
ss
es
(1
2.5
mm
Ru
t D
ep
th)
0
500
1000
1500
2000
2500
3000
3500
4000
4500
OT
Nu
mb
er o
f Cy
cle
s
HWT
OT
5.3
5.4
300
5.7
5.4
8
OT Data Analysis
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0
0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0
Cri
tic
al F
rac
ture
En
erg
y l
b-i
n/i
n^
2
Crack Progression Rate
Averages
PFC (6)
SMA-C (16)
SMA-D (45)
SMA-F (5)
SMAR-F (9)
SP-C (36)
SP-D (6)
TOM-C (53)
TOM-F (3)
Type D (15)
9
Example
10
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0
0 0.25 0.5 0.75
Cri
tica
l F
ract
ure
En
ergy, lb
s-in
./in
.2
Crack Progression Rate
• SuperPave Type D
• PG 70-22
• Limestone Aggregate
SAC B
Stripping Inflection Point
Mix Performance Space Diagram
From: Dr. Bill Buttlar, University of Illinois
0
2
4
6
8
10
12
14
0 200 400 600 800 1000 1200
Ham
bu
rg R
ut
Dep
th (
mm
)
DC(T) Fracture Energy (J/m2)
SOFT MIX
(reflective crack
control)
SUPER MIX
(SMA, high
traffic surface
mixes)
POOR MIX
(non-surface, low
traffic or temporary
use only)
STIFF MIX
(bottom layers of
full depth
pavements)
11
Balanced Mix Design Approach – Limestone Rock Asphalt
12
0
2
4
6
8
10
12
14
16
18
20
22
24
26
30 35 40 45 50 55
Can
tab
ro L
oss
, %
Hveem StabilityType I D Fine
Specification Development
13
There is a lot of work at the national
level already in progress towards
utilizing this type of approach
Some form of a balanced mix design framework is probably in our future
Specification Goals:• Relax constraints
• Design by specifying end performance
HWT OT
Skid
IFI
MSCR
ΔTc
VMA