Heritage Research Group Innovation - Quality - Service 7th Asphalt Shingle Recycling Forum Program Chicago, Illinois Update on Latest Research October 29, 2015
Research on RAS Heritage has been conducting research on pavements for 35 years
Shingles Heritage has been using shingles for the last 6 years with good success
Recent Events DOT s have been expressing concern about early cracking in pavements. It is described as non-load related cracking
Possible Causes Many causes have been discussed including the following REOB Bio-softening agents (natural oils) Too much RAP Too much RAS Asphalts from Oil Sands in Canada The Polar Vortex
Cracking Cracking is complicated because it can be caused in so many ways There is however significant research currently underway nationally to better measure and characterize cracking
Binder Rheology Superpave under SHRP looked at cracking around two parameters using the Bending Beam Rheometer (BBR)
BBR A small beam of aged binder is tested for cold weather properties using two parameters Stiffness (S) S < 300,000 Mpa m-value (m) M >0.3
Stiffness vs. Relaxation Stiffness is simply how stiff the aged binder is at the low temperature of the test m-value is the rate that the asphalt can relax or flow at low temperature This is what separates asphalt from concrete (flexible vs. rigid)
Rheology To date under Superpave as long as both parameters are not exceeded at the low temperature required for use the binder is acceptable.
PG 58-28 In Illinois for example when using RAP or RAS to replace some of the binder in a pavement the final blended binder should meet the local climate as if no RAP or RAS is in the pavement mixture. In this case a 25% binder replacement with RAP or RAS should produce a combined binder in the road of PG 64-22
T critical Recently researchers have recently found that cracking is more complicated than originally determined using the BBR. Actually the ideal aged asphalt may be one in which the temperature at which Stiffness reaches 300,00 Mpa should be where m reaches 0.3
T critical The further apart these two low temperatures parameters get the greater risk for cracking The AASHTO Committee on Materials is currently considering characterizing binders using T critical Some researchers are recommending a maximum of -5 0 C difference between S and m failure temperature
ΔT CRITICAL Bending Beam Results PG 58-28 Straight Run PG 58-28 with 25% RAS Binder Replacement PG 58-28 with 40% RAS Binder Replacement Creep Stiffness (S) Failure Temperature, C S = 300,000 Mpa -28.6-23.1-16.5 m-value (m) Relaxation Failure Temperature, C m =0.3-28.4-17.0-4.7 ΔT CRITICAL Difference -0.2-6.1-11.8
Impact of Research As binder from RAS increases in the pavement in this test the ability of the pavement to relax went down The asphalts we use to soften RAP and RAS need to be better matched to bring the final binder properties back into the correct low temperature properties. This is especially true of higher RAP and RAS binder replacement levels.
ΔT CRITICAL Bending Beam Results PG 58-28 with 25% RAS Binder Replacement PG 58-28 (modified) with 25% RAS Binder Replacement PG 58-28 with 40% RAS Binder Replacement PG 52-28 (modified) with 40% RAS Binder Replacement Creep Stiffness (S) Failure Temperature, C -23.1-26.0-16.5-22.3 m-value (m) Relaxation Failure Temperature, C -17.0-22.5-4.7-18.2 ΔT CRITICAL Difference -6.1-3.5-11.8-4.1
Conclusions DOT s are very concerned about pavement cracking which has lead to a great deal of research to better understand it. They want answers. More validation of these new measures need to be performed between lab and actual field performance. We need to be aware of these concerns and look for solutions now.
Thank You!