Mix Characterization and Performance Testing at UMASS and Michigan State University
Liberty’s SmartMIXTM reduces cracking, resists rutting, minimizes moisture damage
and helps prolong the life of asphalt mixes.
Cracks Take Longer To Propagate Through SmartMIXTM (PSCR)
Standard Dense Graded Mixes – SmartMIXTM is PSCR (Pre-Swelled Crumb Rubber) The Disk‐Shaped Compact Tension Test (DC(T)) is generally used to obtain the fracture energy of asphalt mixture. The strength of SmartMIXTM PSCR mixtures were almost the same as control mixtures, which means that the load required to initiate cracks in both mixtures are about the same. However, the required energy for propagating the crack has increased in SMartMIXTM modified mixtures. So, the resistance against cracking has been improved in the new SmartMIXTM. The rubber particles don’t crack, filling the space between the rocks with rubber impedes the propagation of cracking, providing more endurance in the mix.
Hamburg Wheel Tracking Device testing conducted in accordance with AASHTO T324
SmartMIXTM reduces and helps resist rutting. Tire rubber is resilient and bounces back after loading, providing resistance to permanent deformation. Additionally, the SmartMIXTM additives and formulation provides greater resistance to moisture damage and helps the asphalt stick to the aggregates as shown by the stripping inflection point.
Water temperature of 50ºC (122ºF)
Test duration of 20,000 cycles
HWTD 9.5mm Dense Grade test result – Hamburg Test
|Test Samples||Test results|
|Control + 10%|
|Control + 10% |
|Control + 10%
|9.5 mm Dense ||Rut Depth at 10,000 Passes (mm)||>20||0.70||1.53||1.6
|Rut Depth at 20,000 Passes (mm)||>20||0.85||2.63||2.76
|Stripping Inflection Point from HWTD||5300||None*||None*||None*
The Overlay Tester is used to determine the susceptibility of a mix to reflective cracking coming from the mix underneath. SmartMIXTM outperforms other rubber mixes, over 10 times better resistance to reflective cracking.
Overlay Results for
Dense Graded mixtures
|Test Result||Control 58-28||Control + 10% Wet Process Rubber||Control + 10% GTR Dry Mix||Control + 10% SmartMIX™ Rubber
|Average Overlay Test (OT) Cycles to Failure||1004||20||10||289*
- The Overlay Tester predicts cracking
- No other rubber or polymer modifier provides this elevated level of performance while simultaneously performing well in the Hamburg Test. Typically we see a trade off when using rubber between rut and crack resistance (although the control mix performed well in OT, it failed the Hamburg test and is disqualified for use)
- SmartMIX™ material yields favorable results in both tests
- SmartMIX™ Rubber outperforms all other rubber modifiers by a factor of 15X
Thermal Stress Restrained Specimen Test Results
Dense Graded Mixtures
The thermal stress restrained specimen test (TSRST) has been developed to evaluate the thermal cracking resistance of asphalt concrete mixtures. SmartMIXTM improves the resistance to cold weather cracking.
|Binder||Control||Control + 10% Wet|
|Control + 10%
|TSRST Cracking Temperature (°C)||-24.75||-28.70||-29.30
- Goal is a minimum of -28ºC. Results outside of 3ºC are significant
- The control fails this test
- Comparative TSRST results, indicates that SmartMIXTM improved low temperature cracking in the Dense Graded mix
Standard Dense Graded Mixes Dynamic Modulus –
SmartMIXTM is PSCR (Pre-Swelled Crumb Rubber)
SmartMIXTM additives can reduce stiffness and improve aging resistance.