1. Jerry Peterson, Construction Division
ΔTC and You
Jerry Peterson, Construction Division

2. Stiffness and m-value
Parameters from Bending Beam (BBR)
Creep Stiffness (“S” or “S-value”)
m-value (relaxation parameter)

3. Using S and m-value
Spec limits
S < 300 MPa
m > 0.300
Temperature depends on grade
Test at grade temperature +10°C
(example PG64-22 at -12°C)

4. Using S and m-value
Easiest: verifying a grade
Test at required temperature
Pass/fail
Unknown Grade
Run test at grade increments of 6°C
Lowest temperature where BOTH pass
Subtract 10°C from test temperature
Don’t care about values of S and m are, only pass or fail

5. Critical Temperature
Also known as “TC” “Exact Grade” or “Truegrade”
Find temperatures where S and m are equal the spec limits
Highest (worst) one determines grade
(Remember: negative temperatures so smallest number is highest)
“m-controlled” vs “S-controlled”
Other parameter is thrown out

6. Critical Temperature m = 0.3 m-value log S S = 300MPa Temperature
TC for S
m = 0.3
TC for m
m-value

7. Critical Temperature
Notes on spec development (SHRP)
TC about equal for S and m-value
BBR originally aimed at thermal cracking
Later Observations
Bigger differences is TC
Related to performance?

8. In comes ΔTC
ΔTC = TC,m – TC,S
Negative number means m-controlled
Research on the subject
ΔTC is very negative in recycled binders (Reinke)
ΔTC gets more negative with aging (Reinke)
ΔTC seems to be related to other things
REOBS (Zhou)
Overlay Tester (Zhou)
SARA Fractions (Zhou)

9. Will we use it?
ΔTC seems to help identify some things that may be important
“Incompatible” asphalt
REOBS, and other extenders (when overused)
Aged and poorly aging asphalt
Poor blends with recycled material
All of these issues without requiring or banning particular materials
It’s got our attention

10. How to Implement?
National recommendation (Reinke)
ΔTC after 40 hr PAV > -5°C
Problems
Maybe not realistic for out asphalt supply
Lots of extra time and tests

11. How to Implement?
Replace BBR with 4 mm DSR
Testing takes less material and is faster
Problems
Still need to development to figure out 4mm DSR
Still takes 40 hr

12. How to implement?
Aging correlation
Find a fudge factor to convert ΔTC from unaged
Eliminates long term aging
Can maybe use regular DSR instead of BBR
Needs lots of work!

13. How to Implement?
Estimate TC from one point
Still needs development and might not work well
Put a minimum on S
No extra testing
Easy to understand

14. Soft Implementation
You can already see this a little bit:

15. Conclusions
ΔTC looks promising
Don’t know what limits should be yet
Evaluate binder supply
Settle on testing methodology
Additional research needed
Time frame?
Can’t say yet
Likely not this year, unless it’s the Beetle