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Given the fact that fracture is a primary distress causing pavement failure, it is important to identify and characterize the fracture/cracking properties of asphalt concrete mixtures and to include them in pavement design processes. This study examined the testing variables for a reliable and practical semicircular bending (SCB) fracture test to evaluate the fracture characteristics of asphalt concrete mixtures at intermediate service temperatures. An integrated experimental-statistical approach was employed to identify testing variables by which repeatable SCB test results can be achieved. Using a typical Nebraska asphalt mixture, five critical testing variables (i.e., the number of testing specimens, specimen thickness, notch length, loading rate, and testing temperature) of the SCB test were investigated due to their significant effects on mixture fracture characteristics. Statistical analysis of test results indicated that approximately six specimens/replicates were a reasonable sample size that could properly represent asphalt concrete fracture behavior of a typical dense-graded mixture. Then, the coefficient of variation (COV) of the mixture fracture energy for six specimens was used to evaluate the effects of other remaining test variables. A range of a specimen thickness of 40 to 60 mm, a notch length from 5 to 40 mm, and a testing temperature between 15 and 40 C showed the reasonably low COV value of fracture energy at around or less than 10 %. The loading rates (0.1 to 10 mm/min.) attempted in this study did not show any significant differences in the testing repeatability.

Proper use of rejuvenators can improve the properties and performance of aged asphalt mixtures; however, there is currently a lack of understanding on how rejuvenator treatment details, such as type-dosage of rejuvenators and blending-curing of rejuvenation, affect properties and performance characteristics. This study aims to investigate the effects of type, dosage, and treatment methods of rejuvenators when added into aged bituminous materials. To meet the goal, three rejuvenators, categorized by their production technology, were selected to improve a high-recycled asphalt pavement mixture by conducting various binder-level and mixture-level tests. For the binder-level testing, the performance grading (PG) method was used to primarily determine proper dosages targeting desired binder grades, and two chemical tests (Fourier-transform infrared spectroscopy and Saturate, Aromatic, Resin and Asphaltene) were conducted to examine chemical characteristics altered by rejuvenation and the further aging process. The selected dosage levels from the binder testing were then applied to mixture-level performance evaluation by conducting two tests: flow number for rutting and semicircular bending fracture for cracking. Test-analysis results indicated that although it can successfully determine the proper dosage range of rejuvenators, PG binder testing is limited to only assessing the effects of rejuvenators on mechanical properties; this can be better aided by integrating chemical characterization that provides a more in-depth material-specific rejuvenation process. Moreover, it appears that rejuvenation methods can alter the performance of aged mixtures. Therefore, the selection of rejuvenators and their implementation into practice should be carried out considering multiple aspects, not only its PG recovery.

No abstract

The semi-circular bending (SCB) test is a simple, efficient, and easily applicable method in the pavement community to characterize fracture behavior. This makes it widely used as a quality control (QC) and quality assurance (QA) approach at several transportation agencies. However, public–private testing laboratories have implemented SCB test methods using different load-support fixture conditions with an insufficient understanding of how the conditions affect the results and testing variability. This could be particularly problematic when using SCB test results obtained from different load-support fixtures as QC–QA (or pass/fail) purposes. This study investigated the effect of SCB testing configurations on test results and their variability by conducting tests using six different load-support fixtures. Several fracture-related indicators such as fracture energy, flexibility index, peak load, and the coefficient of the cracking index resulting from the six different load-support fixtures were compared. Test results and statistical analyses showed that SCB tests generally showed repeatable results, whereas load-support fixtures can affect test results and their repeatability, thus care should be taken when choosing a testing fixture. The addition of roller springs generally increased the variability of the test results. It appears that the mid-span jig was detrimental to testing repeatability, and friction at the support should be avoided because it can erroneously increase fracture resistance with a higher variability.