Influence of Bio-Additives on Recycled Asphalt Pavements.

The construction and maintenance of asphalt pavements is a resource-consuming sector, where the continuous rehabilitation of the superficial layers demands large volumes of non-renewable resources. The present work focuses on the design and characterization of asphalt mixtures for the binder layer of an asphalt pavement containing 50% reclaimed asphalt (RAP), in which seven different bio-based additives, identified as R1A, R1C, R2A, R2B, R2C, R3A, and R3B, were added to improve the workability, strength, and stiffness properties. The experimental program envisioned the hot mixing of aggregates and RAP with either a 50/70 or a 70/100 bitumen and, in turn, each of the seven bio-additives. The asphalt mixtures underwent the characterization of their densification properties; air voids; indirect tensile strength (ITS); indirect tensile stiffness modulus at 10, 20, 40, and 60 °C; and rutting resistance at 60 °C. The results highlighted that the performance in terms of workability and ITS of the resulting mixtures depends on the type of bio-additive and largely on the fresh bitumen type, while the stiffness at high temperature is not significantly affected by the presence of the bio-additives.

Technological advances and challenges of reclaimed asphalt pavement (RAP) application in road engineering-a bibliometric analysis from 2000 to 2022.

Reclaimed asphalt pavement (RAP) is a valuable material that can be recycled and reused in road engineering to reduce environmental impact, resource utilization, and economic costs. However, the application of RAP in road engineering presents both opportunities and challenges. This study visually analyzes the knowledge background, research status, and latest knowledge structure of literature related to RAP using scientific metric methods such as VOSviewer and Citespace. The Web of Science (WoS) core collection database identified 2963 research publications from 2000 to 2022. Collaborative networks between highly cited references, journals, authors, academic institutions, countries, and funding organizations are analyzed in this study, along with a co-occurrence analysis of keywords for the RAP research publications. Results showed that the USA has long been a leader in RAP research, China surpassed the USA in annual publication output in 2019, increasing from 2 publications in 2002 to 177 publications in 2022, and has made significant investments in technological aspects. Chang'an University ranked first in total publication output (131 publications, 4.4%). Current major research themes include road performance, recycling technology, regeneration mechanisms, and the life cycle assessment of RAP. In addition, based on cluster analysis of keywords, text content analysis, and SWOT analysis, this study also discusses RAP's challenges and future development directions in road engineering. These findings provide scholars with valuable information to gain insight into technological advances and challenges in the field of RAP.

Waste Cooking Oil as Eco-Friendly Rejuvenator for Reclaimed Asphalt Pavement.

Over 50 MioT of Waste Cooking Oil (WCO) was collected worldwide in 2020 from domestic and industrial activities, constituting a potential hazard for both water and land environments, and requiring appropriate disposal management strategies. In line with the principles of circular economy and eco-design, in this paper an innovative methodology for the valorisation of WCO as a rejuvenating agent for bitumen 50/70 coming from Reclaimed Asphalt Pavement (RAP) is reported. In particular, WCO or hydrolysed WCO (HWCO) was modified by transesterification or amidation reactions to achieve various WCO esters and amides. All samples were characterised by nuclear magnetic resonance, melting, and boiling point. Since rejuvenating agents for RAP Cold Mix Asphalt require a melting point ≤0 °C, only WCO esters could further be tested. Efficiency of WCO esters was assessed by means of the Asphaltenes Dispersant Test and the Heithaus Parameter. In particular, bitumen blends containing 25 wt% of WCO modified with 2-phenylethyl alcohol, showed high dispersing capacity in n-heptane even after a week, compared to bitumen alone (1 h). Additionally, the Heithaus Parameter of this bitumen blend was almost three times higher than bitumen alone, further demonstrating beneficial effects deriving from the use of WCO esters as rejuvenating agents.

Valorization of recycled wastes in pavement preventive maintenance: A review on reclaimed asphalt pavement and recycled waste tire.

Pavement preventive maintenance (PPM) is critical to ensuring traffic efficiency, road user experience, and safety. However, it imposes significant costs in annual road infrastructure budgets because it requires high-quality and natural material resources. This study provides a systematic and comprehensive review on the use of recycled wastes as an alternative for the natural materials used in PPM mixes. Specifically, the use of recycled waste tires (RWT) and reclaimed asphalt pavement (RAP) in chip seals, microsurfacing, slurry seals, and thin asphalt overlays were discussed. The current state-of-practice in terms of material specification and mix design were comprehensively investigated for PPM mixes containing RAP (RAP-PPM) and PPM with RWT (RWT-PPM). Laboratory and field performances of waste-treated PPM mixes were elaborated and compared with conventional PPM treatments to determine the feasibility of the RAP-PPM and RWT-PPM technologies. Furthermore, current research gaps were identified, and prospects for future investigations were discussed. It is envisaged that this study can provide a sufficient theoretical basis for the widespread practical application and beneficial use of this valuable technology, towards promoting sustainability in pavement maintenance practice.

Utilization of wollastonite, jarosite, and their blends for the sustainable development of concrete paver block mixes containing reclaimed asphalt pavement aggregates.

While several research studies considered the utilization of reclaimed asphalt pavement (RAP) aggregates for asphalt and concrete pavements, very few attempted its possible utilization for precast concrete applications like concrete paver blocks (CPBs). Moreover, few attempts made in the recent past to improve the strength properties of RAP inclusive concrete mixes by incorporating certain supplementary cementitious materials (SCMs) have reported an insignificant or marginal effect. The present study attempts to comprehensively investigate the utilization potential of some locally and abundantly available materials having suitable physicochemical properties to improve the performance of a zero-slump CPB mix containing 50% RAP aggregates. The studied filler materials, namely, wollastonite (naturally occurring calcium metasilicate mineral) and jarosite (hazardous zinc industry waste), were used to replace 5-15% and 10-20% by volume of Portland cement in the 50% RAP CPB mix. Apart from their individual effects, the efficacy of wollastonite-jarosite blends was also investigated. Considering the lack of indoor storage facilities and economic aspects of CPBs, the influence of water spray curing regime on the performance of the RAP CPB mixes was studied and compared to that of continuous water curing regime. Inclusion of the considered fillers was found to statistically and significantly enhance the flexural strength, tensile splitting strength, and abrasion resistance of the 50% RAP CPB mix; however, the compressive strength (in most cases), permeable voids, water absorption, and water permeability properties showed an insignificant improvement. Results of thermogravimetric analysis confirmed the occurrence of pozzolanic reactivity, and microstructure analysis revealed improvements in packing of concrete matrix and ITZ with filler inclusion qualitatively substantiating the improvements in strength and durability characteristics. The toxicity characteristics of heavy metals that may leach from the hazardous jarosite-based RAP CPB mixes were found to be within permissible limits. Based on the performance requirements specified by IS, IRC, and ASTM standards, all the RAP CPB mixes with filler inclusions fulfilled the acceptance criteria for heavy traffic applications, and water spray curing can enact as an alternate method for curing these mixes. However, to avail maximum performance benefits, it is recommended to use 5% wollastonite, 15% jarosite, and a combination of 10% wollastonite and 10% jarosite as a Portland cement substitute to produce sustainable eco-friendly RAP CPB mixes.

Dynamic mechanical response of hot central plant recycling asphalt pavement considering the rutting deformation of existing structure: pollution reduction and durability promotion.

In the pavement industry, there is a pressing need for the reuse of recycled asphalt pavement (RAP) materials. However, the rutting deformation in existing pavement structures is often overlooked in the design of recycled asphalt pavement, which hinders long-term performance prediction and durability assessment. This study examined the viscoelastic properties and fatigue performance of recycled asphalt mixtures. Different combinations of surface layers with varying RAP contents and binder layers with different rutting damage levels were designed. A 3D-Move Analysis model was used to analyze the dynamic mechanical response of these structures under moving loads. Results showed that the stiffness of recycled asphalt mixture increased with the RAP content, but the fatigue performance decreased by 39.4% when the RAP content reached 50%. Incorporating 50% RAP in the surface layer can reduce the compressive stress caused by vehicle loading, thus reducing the vertical compression strain and permanent deformation of the asphalt layers and the subgrade. However, the surface layer with higher RAP content is exposed to intense alternating tensile and compressive strains, leading to poor fatigue durability. The dynamic mechanical behavior of recycled asphalt pavement structures was found to be significantly impacted by the characteristics of the binder layer. The lower dynamic modulus of the binder layer (e.g., 18 mm rutting depth) can lead to more deformation and an increased risk of fatigue cracking. Moreover, the dynamic performance of mixtures with 0% and 50% RAP in the surface layer is even more affected by changes in the binder layer properties. It is recommended to consider the design of dynamic modulus combinations of existing binder layer materials and surface materials with higher RAP, in order to increase the utilization of RAP for high-grade highways and improve the stress distribution to enhance their durability.