1. Dr. Randy West, P.E. Director / Research Professor
Update on the MnROAD-NCAT Cracking Group Experiments
Dr. Randy West, P.E. Director / Research Professor
Thank you Don for the invitation to speak to the OLLI.
OK, so I’m sure that some of you are thinking “what a great way to get a week started off. Have some engineer come talk about asphalt. How exciting!”

2. we have no way of knowing if these materials help or hurt
With the current
volumetric mix design system…
Recycled Shingles
WMA additives
Fractionated RAP
Recycling agents
we have no way of knowing if these materials help or hurt
Aramid & Polyolefin fibers
Recycled Tire Rubber

3. Balanced Mix Design
Cracking Resistance
Rutting Resistance

4. Validation of Performance Tests
Researchers typically develop methods independently
Most tests lack a regional or national validation effort with field pavements
Most have unknown precision statistics
Laboratory aging protocols are still being researched

5. MnROAD + NCAT Partnership
Working together on national need research projects
Validating cracking tests for balanced mix design
Documenting the life cycle benefits of Pavement Preservation

6. Modes of Cracking Fatigue Thermal Top-Down Reflection Block
Load Related
Environment Related

7. Scope of Experiments MnROAD NCAT Test Track Low-temperature cracking
Top-down cracking

8. Top-Down Cracking Sections on the NCAT Test Track
Surface Layer
1.5”
Intermediate Layer
2.25”
Base Layer
Granular base 6”
Stiff track subgrade
infinite
Cracking Group sections
7 200-ft. sections
each section instrumented
HiMA mix

9. CG Performance through
1 cycle, 10 MESALs
Section
Description
Rutting (mm)
Δ IRI
(in/mi.)
Δ MTD (mm)
Cracking
(% of lane) N1
20% RAP (Control)
1.7 3
0.4
21.5 N2
Control w/ High Density
2.2 7
0.5
6.2 N5
Low AC, Low Density
1.2 5
5.0 N8
20% RAP 5% RAS 13
0.7
16.9 S5
35% RAP PG 58-28
1.5 1 S6
Control w HiMA
1.4 10
0.6
S13
AZ Rubber Mix
2.8
0.1

10. Progression of Cracking

11. Selected Top-Down (Intermediate Temp. Fracture) Cracking Tests
Added early summer 2017
Energy Ratio
SCB-LA
IFIT
OT-TX
OT-NCAT
IDEAL-CT
We need to find a cracking test that we can count on to indicate performance. Actually, it may be different tests for different forms of cracking. But this webinar is not going to get into the pros and cons of the different tests.
These tests are being conducted on both lab mix and plant mix samples that are aged and unaged.
Also conducting cyclic fatigue (SVECD) with FlexPave analysis

12. Lab Mixed Lab Compacted Plant Mixed Lab Compacted
Status of Lab Work
Test
Lab Mixed Lab Compacted
Plant Mixed Lab Compacted
4 hrs. at Comp. Temp.
8 hrs. at 135°C
Reheated
Energy Ratio X
IFIT
SCB-Jc OT
OT-NCAT
Ideal CT
8 hrs at 135°C = “critically aged” which corresponds to 70,000 CDD

13. MnROAD Cracking Group Test Section Update

14. MnROAD Test Sections Test sections constructed August 201617 23 22 21 20 19 18
Cracking Group Cells 16-23
Test sections constructed August 2016

15. Asphalt Mixtures CELL NO BINDER GRADE ABR % RAS 16 64S-22 30-40 Yes 17
20-30 18
15-25 No 19 20
52S-34
25-35 21
58H-34
221 23
64E-342
10-20
All mixes are 12.5 mm NMAS
All mixes are Ndes = 80 and target air voids = 4.0% except cell 19 which has Ndes = 100 and target air voids = 3.0%
1 Cell 22 limestone aggregate in mix
2 Highly modified asphalt binder

17. Cracking Modes and Testing
Types of cracking investigated
Low temperature
Top-down or bottom-up fatigue possible
PMLC testing
Low temp: DCT-MN and IDT Creep
Intermediate temp: IFIT, OT, BBF
E*, TSR, Hamburg
Critically-aged PMLC now in planned
Samples provided to other research studies

18. Performance Tests Research is ongoing
select best test(s)
set mix aging protocol(s)
establish criteria
determine precision statistics
Numerous agencies and contractors are testing the waters to understand how BMD will change mix designs