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This study investigated the effect of the distribution of aged binder from reclaimed asphalt pavement (RAP) on the fracture tolerance of recycled asphalt mixtures. Two RAP sources (one coarse, one fine), one virgin polymer-modified asphalt binder, and four RAP contents (0 %, 20 %, 30 %, and 40 %) were used to produce a total of seven mixtures. Fracture tolerance was assessed in terms of fracture energy density (FED) at three levels: binder, interstitial component (IC) (composed of effective binder and fine aggregate fraction), and mixture. Binder fracture energy tests were conducted to measure the FED of blends of virgin and recovered RAP binder. IC direct tension tests were employed to determine the IC FED. Finally, Superpave indirect tensile fracture tests were performed to obtain the FED of RAP mixtures. FED decreased with increasing RAP content at the three levels (binder, IC, and mixture). More importantly, IC and mixture exhibited almost identical FED reductions in relative terms, while the reduction was less significant at binder level. This finding indicates that the full blending scenario artificially created at the binder level did not occur at IC and mixture levels. Furthermore, the coarse RAP yielded greater FED than the fine RAP, which substantiates that RAP gradation controls the distribution of RAP binder in recycled mixtures. Consequently, the lower content of aged RAP binder in the IC portion for mixtures with the coarser RAP resulted in better fracture tolerance. The application of a newly developed guideline for determining the maximum allowable RAP content in recycled mixtures confirmed that the coarser RAP used in this study allows for a greater RAP content than the finer RAP despite the stiffer RAP binder. [ABSTRACT FROM AUTHOR]

Fracture energy density (FED), which is defined as the energy per unit volume required to initiate fracture, is a key property governing the resistance to fracture of asphalt binders. This study evaluated the effect of reclaimed asphalt pavement (RAP) and recycled asphalt shingles (RAS) on virgin binder FED using the binder fracture energy (BFE) test. The objective was to determine whether RAP and RAS can be used with soft virgin binders to achieve satisfactory fracture tolerance. Experimental factors included two RAP sources, two RAS sources (manufacture waste (MW) shingles and tear-off (TO) shingles), and four virgin binders. BFE tests were conducted on blends of virgin and recovered RAP/RAS binders at two binder replacement rates of 15 % and 30 %. Moreover, the Superpave true grade of RAP/RAS binder blends was determined using the dynamic shear rheometer and bending beam rheometer. Results showed that the use of soft virgin binders effectively compensated for the stiffening effect of RAP/RAS in terms of true grade. The addition of RAP binder and MW shingle binder increased the FED of unmodified binders, whereas the opposite trend was observed for TO shingle binder. Furthermore, great caution should be exercised when using virgin polymer-modified binders because significant reductions in FED were observed when RAP and RAS binder was introduced, possibly because of the dilution of polymer modification in addition to stiffening and embrittlement effects. This study indicated that both RAP and RAS are recyclable, according to the Superpave true grade requirements. However, further research is needed to evaluate the effect of the reduction in binder FED caused by TO shingles on mixture fracture performance before its acceptance in asphalt mixtures. [ABSTRACT FROM AUTHOR]

Pavement top-down cracking performance not only depends on pavement layer material characteristics, but also on layer interface conditions. Interface conditions involve both the shear resistance along the interface and the cracking resistance across the interface provided by the interface bonding agents. Regarding hot-mix asphalt (HMA), currently available tests are mainly focused on pavement layer material properties. When thick polymer modified asphalt emulsion (PMAE) was applied at the interface between an open-graded friction course (OGFC) and a dense graded structural layer, a bonded interface was formed by the migration of PMAE up into the OGFC air voids. Shear strength tests, which can well characterize the adhesive film effect of interface bonding agents, cannot fully capture the effect of bonded interface on pavement cracking performance. To simulate the crack initiation and propagation process and evaluate the effect of bonded interface conditions on top-down cracking performance, a composite specimen interface cracking (CSIC) test was developed. The developed system involves repeated tensile loading and monitoring of the rate of damage development (reduction in stiffness) on composite specimens specifically designed for this purpose. Number of loading cycles to failure and damage rate results from the proposed test on three different interface conditions clearly indicate that this test method can be used to optimize bonding agents and application rates for enhanced cracking performance. This method may also provide a suitable specification test for evaluation of interface conditions on reflective cracking performance. [ABSTRACT FROM AUTHOR]

The article focuses on a device, the Creep Testing Apparatus (CRETA), developed for use in determining the viscoelastic properties of joint sealant. Creep tests were performed on two kinds of silicone sealant, self-leveling (SL) and non-self-leveling (NS). Results suggest the silicone sealant tested is a linear viscoelastic material and its creep response seem insensitive to temperature variations. Hot water aging seems to cause both SL and NS sealant to become softer and more ductile.

There are several issues of concern regarding indirect tension testing systems to evaluate and characterize tensile properties of open graded friction course (OGFC) mixture. It is necessary to evaluate the Superpave Indirect Tension Test (IDT) in terms of its ability to accurately determine tensile properties of OGFC mixture with an independent testing system. For this purpose, Superpave IDT and Dog-Bone Direct Tension Test (DBDT/were performed in resilient and creep loading modes to determine tensile properties of dense graded and OGFC mixture. It is also necessary to further verify with asphalt mixture, previously established correction factors based on three-dimensional finite element analysis to determine mixture properties accurately from the DBDT testing system. Prior verification was based only on polymer specimen of known properties. The tensile properties of dense graded and OGFC mixtures were successfully obtained with both testing systems employed in this study. Both Superpave IDT and DBDT provided reasonable and consistent test results with respect to test temperature, aging, and binder modification. Observed differences in creep response between the two were explained by well known phenomena involving effects of stress state on mixture properties (lower creep rate were obtained in Superpave IDT where die mixture is subjected to greater confinement). Thus, continued use of the Superpave IDT is recommended because it provides reasonable properties and is much more practical than DBDT. However, relationships to account for stress state effects need to be considered for mechanisms involving uniaxial stress states. DBDT creep compliance is more appropriate for uniaxial stress states (surface tension away from tires), while Superpave IDT creep compliance is more appropriate for stress states involving confinement (bottom or near-surface tension between tires). [ABSTRACT FROM AUTHOR]