Multiple Stress Creep and Recovery and Time Sweep Fatigue Tests

Abstract

Crumb rubber modification (CRM) is an effective means of improving neat asphalt performance. Numerous studies have investigated the effects of CRM using the current Superpave® laboratory tests. Recent studies have shown that the assumption of linear viscoelastic behavior or employing insufficient stress or strain levels makes current tests inadequate for properly assessing the performance of binders, especially when modified. This problem has resulted in the development of improved test methods such as the time sweep binder fatigue test and the multiple stress creep and recovery (MSCR) test for permanent deformation. The present study assesses the performance of binders modified with a wide range of crumb rubber content using these newly developed test methods. Additional binder and mixture performance tests were used to compare and validate the results. The results showed that the new tests performed well in predicting performance. Current Superpave criteria also showed good conformance with mixture test results for CRM binders. Tests results suggest that the MSCR can complement current rutting prediction testing. Also, the time sweep test produces results similar in accuracy to current Superpave tests, but it requires longer testing time and is thus not recommended for performance grading.

A study on rutting susceptibility of asphalt binders at high stresses using MSCR test

“…Similar trend was observed for crumb rubber modified asphalt binders by Wasage et al [21]. Higher dosage of crumb rubber could be used to enhance rut resistance of asphalt binder [20]. Considering extreme conditions (25.6 kPa stress and 76°C), VG 30 showed highest J nr (16.9 kPa -1 ) followed by PMB 40 (8.3 kPa -1 ) and CRMB 60 (6.1 kPa -1 ).…”

“…Several studies observed better correlation between J nr estimated at 3.2 kPa and rutting performance of asphalt mixes in field and laboratory [10,12,20,21]. However, other studies argued and reported a good correlation between J nr estimated at high stresses and rutting performances of unmodified, SBS modified and/or crumb rubber modified asphalt binders.…”

“…Similarly, at 76°C increase in stress from 3.2 to 25.6 kPa showed increase in J nr by 135%. It may be concluded that with increase in temperature, base asphalt binder softens [20] and fails to maintain crumb rubber-base asphalt binder structure, hence showing sudden increase in J nr values. Similar trend was observed for crumb rubber modified asphalt binders by Wasage et al [21].…”

Comparison of different rheological parameters for rutting susceptibility of SBS + WMA modified binders

“…This test captures recovery and permanent deformation behavior of binders. Researchers have reported better correlation of non-recoverable creep compliance (J nr ) with rutting performance of asphalt mixes in laboratory as well as in the field [7,8,12]. The J nr is considered to have a better correlation with rutting performance of asphalt mixes compared to G*/sinδ [6,22].…”

“…A binder with high G*/sinδ will have lesser dissipated energy, and thus higher rut resistant. The G*/sinδ showed satisfactory results for unmodified binders [6][7][8]. However, this parameter showed unconvincing trend for polymer modified binders due to its inability to capture delayed elastic recovery [6,[9][10][11][12][13][14].…”