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

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

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)

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

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

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

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?

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)

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

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

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

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!

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

Soft Implementation You can already see this a little bit:

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