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The process of reclaimed asphalt pavement (RAP) recycling may occur multiple times during the life of the pavement. This study investigates the effect of multiple recycling on binder properties by employing a virgin 3045 PEN grade binder that was aged in the laboratory intended to simulate aging of binders in RAP. The aged binder was rejuvenated using two bio-oils and one softer binder. The doses of the bio-oils and softer binder were determined by matching the continuous high-temperature performance grade (PGH) of the rejuvenated RAP binder to that of the virgin binder. This aging and rejuvenation cycle was repeated three times. Finally, fatigue and rutting performance of the binder was evaluated for the three reuse levels. Results indicate that the material can be reused up to three cycles keeping good performance on fatigue or rutting. However, care should be taken regarding the cumulative effect of bio-oils causing an over-softening effect on the of the RAP. [ABSTRACT FROM AUTHOR]

Porous friction courses (PFC) are thin layers of asphalt mixtures with open gradations and high air void contents, which are placed over conventional flexible pavements. Although they improve various safety and environmental issues, their main difficulty is their short service life. A common practice to enhance PFC durability is the use of modified asphalt binders (e.g. regular polymer-modified asphalt (PMA) or asphalt rubber). However, this approach has not been enough to achieve life-spans close or equal to those of dense-graded hot mix asphalt. The use of highly polymer-modified asphalts (HiMA), which are binders modified at polymer doses near 7–8% by total weight of the binder, constitutes an alternative to overcome this challenge. This work evaluates the mechanical performance of four PFC mixtures fabricated with a regular polymer modified (PMA) and a HiMA binder, and two aggregate sources. The experimental plan included the semicircular bending (SCB), IDEAL-CT, Cantabro abrasion loss and Tensile Strength Ratio (TSR) tests at intermediate temperatures and various ageing conditions. Results indicate an enhanced cracking and degradation resistance for PFC mixtures containing HiMA and suggest that the use of this type of asphalt binder could increase the service life of these mixtures. [ABSTRACT FROM AUTHOR]

The use of reclaimed asphalt pavement (RAP) in road construction has become a common practice in the asphalt industry due to environmental and economic benefits. However, since RAP is an aged material, recycling agents are typically used to reduce the stiffness of the recycled asphalt mixture and make it less prone to cracking at high RAP contents. This study evaluates the effect of ageing and the use of recycling agents on the rheological, microstructural, and micromechanical properties of binder blends with high RAP contents. A total of 27 binder blends were prepared with different recycled binder ratios (0.22, 0.31 and 0.5), recycling agent doses (0%, 1.2%, 5.5% and 9%), virgin binder performance grades (PG 58-28 and PG 52-34) and ageing conditions. The microscopic properties of the binder blends were characterised using atomic force microscopy (AFM). AFM results provided an evaluation of the microstructural homogeneity of the blends, with a good correlation with the binder blends macroscopic rheological properties. The addition of recycling agents improved the homogeneity of the binder blends by reducing the variation in modulus among the different phases in the microstructure. AFM proved to be a useful tool to evaluate rejuvenated binder blends at the microscale level. [ABSTRACT FROM AUTHOR]

Warm mix asphalt (WMA) is increasingly recognised as a green paving technology in terms of energy saving and emission reduction. The reduction in mix production temperature associated with the WMA additives is very desirable from the environmental aspect. However, researchers and practitioners desire a comparable performance with hot mix asphalt (HMA). The major issue with WMA is their moisture susceptibility especially in the pavement early life. Therefore, this study aims at investigating moisture susceptibility of WMA using both laboratory characterisation and field performance compared to HMA. Three mixtures were investigated, namely; HMA mixture, foaming and Evotherm WMA mixture. The laboratory tests included; resilient modulus (MR), Indirect Tensile test, and Hamburg wheel tracking test. Test sections on Farm to Market FM 973 Highway near Austin, Texas, were constructed using these three mixtures. The results of field performance monitoring for five years are represented in this paper. Laboratory test results revealed small differences between measured dry and wet tensile strength and MR of HMA and WMA which shows some improvements using antistripping agents. The field performance evaluation showed that the Evotherm WMA mixture had the least transverse and reflected cracks while the HMA performed better in both ravelling and longitudinal cracking. [ABSTRACT FROM AUTHOR]

Recycled asphalt mixtures with high amounts of reclaimed asphalt pavement (RAP) and recycled asphalt shingles (RAS) can be excessively stiff, brittle, and prone to cracking. The use of recycling agents, or rejuvenators, can significantly reduce mixture stiffness and improve performance, specifically cracking resistance. In this study, the performance of recycled and rejuvenated asphalt mixtures from several field projects, located in different environmental zones across the United States, was evaluated considering various recycling agent dosages determined by the contractors. Field core test results and the visual distress surveys of the field projects demonstrated that using the field recycling agent dosages yielded poor mixture performance. Laboratory test results demonstrated that adding the recycling agent at the dosage to match the continuous high-temperature performance grade (PGH) of the rejuvenated binder blend (virgin/base binder, recycled binder, and recycling agent) to that of the target binder PGH specified based on climate and traffic requirements yielded improved mixture performance. The rejuvenated mixtures at this recycling agent dosage showed significant reduction in stiffness and improved cracking resistance, and facilitated the use of higher quantities of recycled materials, regardless of aging level, while maintaining rutting resistance after short-term aging. [ABSTRACT FROM AUTHOR]

In the United States, mechanical foaming is the most popular method for producing warm mix asphalt, which is the latest technology implemented to reduce the production temperature and/or enhance the compactability of asphalt mixtures. Three commonly used commercially available laboratory foamers to produce asphalt foams include the Wirtgen WLB 10S (Wirtgen foamer), the InstroTek Accufoamer (InstroTek foamer) and the Pavement Technology Inc. Foamer (PTI foamer). Though these foamers have been widely used in research studies and construction practice, it is still unknown whether they produce asphalt foams with the same quality and quantity. In this study, asphalt foaming characteristics produced by these three laboratory foamers were measured using a non-contact test set-up consisting of a laser device and a digital camera, and compared in terms of instantaneous volume expansion, foam stability and surface area evolution of foam bubbles. Additionally, the workability, coatability and mechanical performance of foamed mixtures prepared using these same laboratory foamers were compared against the conventional hot mix asphalt (HMA). Test results indicated that foamed asphalts produced by the Wirtgen foamer had the largest volume expansion and greatest foam stability, followed by those produced by the InstroTek foamer and the PTI foamer. The optimum foaming water content (Wopt) was determined for each laboratory foamer based on the workability and coatability results of the corresponding foamed mixtures. In addition, the performance evaluation of the foamed mixtures produced atWoptvalues indicated equivalent mixture stiffness but greater moisture susceptibility as compared to the conventional HMA. [ABSTRACT FROM AUTHOR]