High RAP Content Research Articles

Effect of Blending Degree between Virgin and Aged Binder on Pavement Performance of Recycled Asphalt Mixture with High RAP Content

In this study, the influence of the blending degree between virgin and aged binder on the pavement performance of hot-mix recycled asphalt mixture (HMRAM) with high RAP content is analyzed. The aggregate gradation of AC-16 was selected. The RAP contents were 30, 40, and 50%. HMRAMs with different degrees of blending (DOBs) were prepared by changing the mixing temperature (150, 165, and 180°C) without the occurrence of excessive aging for asphalt binders. An improved Hirsch dynamic modulus prediction model was then used to quantitatively characterize the DOB of HMRAM. Finally, the high-temperature, low-temperature, moisture stability, and fatigue resistance performance of HMRAM were tested and the effect of the DOB between the virgin and aged asphalt binder on the pavement performance was analyzed. The results showed that the DOB between the virgin and aged asphalt binder cannot reach 100% at the three mixing temperatures for HMRAM with 30, 40, and 50% RAP contents, which is inconsistent with the assumption of complete blending in China’s specification. The dynamic stability of the mixture gradually decreases with the increased DOB for HMRAM with a high RAP content, while the moisture stability, low-temperature, and fatigue resistance performance are continuously improved. This means that with the increase in DOB in the stage of open to traffic, meeting high-temperature performance criteria at the design stage may become unsatisfactory for HMRAM. The moisture stability, low-temperature performance, and fatigue resistance performances of HMRAM measured at the design stage were reasonable and conservative. The change in DOB significantly affects the content and properties of total free binder in HMRAM, affecting pavement performance. The content and physical properties of the RAP aggregate also have a significant impact on pavement performance.

Investigating short-term and long-term binder performance of high-RAP mixtures containing waste cooking oil

The environmental and economic benefits of recycling asphalt pavements have received much attention in recent years. Because of the increase in the cost of raw materials and energy carriers, the reuse of large portions of reclaimed asphalt pavement (RAP) is critical in reducing both the cost and environmental footprint of asphalt pavements. High-RAP mixtures are more prone to low temperature cracking and poor mixture workability because of the higher stiffness of RAP binder. Recycling agents are one of the additives which are used to improve these deficiencies. However, there is some ambiguity about the optimum content of recycling agent to assure proper performance of recycled asphalt pavement during its service life. The current study used 60% and 100% fractionated RAP with waste cooking oil as a recycling agent and crumb rubber to alleviate the aforementioned problems. Laboratory evaluation showed that increasing the amount of recycling agent in the high-RAP mixtures improved their workability and low temperature performance while decreasing moisture damage and rutting resistance. The long-term susceptibility to aging of recycled binder with the organically-based recycling agent was also investigated. A procedure to obtain the optimum percentage of recycling agent was devised to strike a balance between the performance characteristics of mixtures with a high-RAP content.

Effect of rejuvenator and mixing methods on behaviour of warm mix asphalt containing high RAP content

Rejuvenators are normally used in the hot in plant or hot in place recycling process of asphalt pavement. The use of rejuvenators in recycling RAP in warm mix asphalt (WMA) remains very limited. This study was carried out to investigate the use of a rejuvenator which was normally used for HMA, in producing WMA containing RAP. Laboratory tests were done on the binder rheological properties and the mechanical behaviours of the mixtures. Mechanical behaviours of WMA with RAP mixtures produced by the rejuvenator were compared with that of a control HMA and other WMA-RAP mixtures produced by using Evotherm WMA additive. Tests were carried out on resilient modulus, indirect tensile strength, semi-circular bending test, and four-point bending fatigue test. Results showed that it is possible to produce WMA by adding RAP and by using rejuvenators. WMA adding RAP mixtures produced with the rejuvenator performed better than WMA adding RAP produced with Evotherm additive in fatigue cracking resistance. The study further investigated the effect of different mixing methods of the rejuvenator with the binder on the mechanical properties of the WMA adding RAP mixtures. The study found that when the content of the RAP is lower than 50%, the mechanical behaviour of mixtures did not significantly change regardless of different mixing methods. However, when the content of the RAP is 50% or higher, adding the rejuvenator directly into the RAP significantly improved the moisture resistance of WMA RAP mixtures. For overall results, adding the rejuvenator into RAP was found more effective than adding the rejuvenator into the hot bitumen before mixing.

Evaluation of Waste Engine Oil‐Rejuvenated Asphalt Concrete Mixtures with High RAP Content

The use of large proportions of reclaimed asphalt pavement is necessary to meet the increasing demand for road construction materials in a sustainable way. One of the challenges of using a greater percentage of reclaimed asphalt pavement (>30%) is the greater stiffness of mixes incorporating it. While this stiffness problem is usually resolved by using different commercial rejuvenators, there are circumstances in which commercial rejuvenators are not available. Therefore, this study evaluates the potential of using waste engine oil as a substitute for commercial rejuvenators for the higher percentage of reclaimed asphalt pavement that could meet the increasing demand in a more sustainable way. To assess the possibility of using a higher percentage of reclaimed asphalt pavement in road construction, different percentages of reclaimed asphalt pavement (30%, 40%, and 50%) are used. Following the property of the aged binder, three different percentages (7%, 13%, and 20%) of waste engine oil are considered. Each percent of waste engine oil is incorporated with one of the three mixes. The mixes (with the minimum required Marshall criteria) are evaluated for different properties, namely, their indirect tensile strength, resilient modulus, and durability. Finally, those properties are compared to those of the mixes rejuvenated by commercial rejuvenators. It is observed that, for the aforementioned properties, 7% to 13% of waste engine oil is identical to the commercial rejuvenator for the mixes with 30% to 40% of reclaimed asphalt pavement.

Research on Performance of Recycled Mixture with High RAP Content from Central Plant Hot Recycling and Evaluation Method of Its Durability

Based on pavement maintenance project of the national road, a series of laboratory tests were conducted to investigate the road performance of recycled mixtures with different RAP content by wheel tracking test, immersing Marshall test, freeze-thaw splitting test and low temperature bending test. During these tests, virgin mixture without RAP is used as a control group. Furthermore, the durability of recycled mixture was verified by a new test method by which the impact-freeze-thaw damage degree can be obtained. On the basis of laboratory experiments, three types of trial sections have been successfully paved on the national road. The results show that the performance of recycled mixture with 30% RAP is better while recycled mixture with 50% RAP can also satisfy the existing standards by adding the recycling agent and reinforcing agent. The new test method is efficient to distinguish the durability difference between different mixtures. The performance of these recycled trial sections meet the existing standards, and recycled mixture with high RAP content can be used in national road project on a large-scale.

Reclaimed asphalt binders and mortars fatigue behaviour

Fatigue cracking is one of the most important failure mechanisms occurring in asphalt pavements, especially when mixtures incorporate considerable amount of rReclaimed asphalt pavement (RAP). In fact, aged binders contained in RAP generally make asphalt more brittle and specifically reduce fatigue resistance of the resulting asphalt mixtures. Binders and mortars play a key role in this phenomenon, considering fatigue cracking usually starts within these asphalt components. However, performance-related tests and specifications commonly regard binders and there are no sound methodologies allowing the use of mortars to predicting fatigue performance of asphalts containing RAP. For this reason, in this paper, fatigue resistance of extracted binders from high-RAP content mixtures and of RAP mortars (passing sieve with an opening size of 0.15 mm) were assessed and compared. Binders were extracted from asphalt mixtures manufactured with 30%, 60% RAP and rejuvenators. Mixtures recipes were then reproduced to manufacture mortars accordingly. Time sweep tests in stress-controlled mode were carried out on both materials (binders and mortars) and the resulting fatigue laws were compared. As a result, a strict correlation was obtained, leading to affirm fatigue-related properties of RAP mixture could be assessed by directly testing RAP mortars. This makes the recovery of RAP binders unnecessary. Moreover, a relationship between the two fatigue laws versus the percentage of fine particles in the mortar was found. This latter relationship allows determining the fatigue law of mortars corresponding to any percentage of fine particles and therefore corresponding to any percentage of RAP.

A novel approach to evaluate fracture surfaces of aged and rejuvenator-restored asphalt using cryo-SEM and image analysis techniques

Low temperature cracking potential is a primary concern for asphalt mixtures with high RAP contents. To minimize the thermal cracking, various rejuvenators have been utilized in the past. In this study, Fourier Transform Infrared Spectroscopy (FTIR) was used to determine the level of oxidation of asphalt. To evaluate the low-temperature cracking potential of aged asphalt with and without rejuvenators, the fracture surface images were captured using Cryo-Scanning Electron Microscopy (Cryo-SEM). The Cryo-SEM images were then analyzed using the image processing technique. The rejuvenated asphalt specimens exhibited less fractured surface than the aged asphalt. Finally, the Fracture Index was computed to rank each asphalt sample in terms of low-temperature cracking potential. Based on the test results, it can be concluded that the use of the Cryo-SEM technology combined with the image processing technique is a promising method to visually observe the fracture surface of asphalt and compute the Fracture Index to estimate the low-temperature cracking susceptibility.

Effects of High Reclaimed Asphalt-Pavement Content on the Binder Grade, Fatigue Performance, Fractionation Process, and Mix Design

AbstractThe primary objective of this research is to examine the effects of reclaimed asphalt pavement (RAP) amounts and fractionation methods on the mix design of high-RAP content surface mixes. T...

Multi-scale evaluation of the effect of rejuvenators on the performance of high RAP content mixtures

Atomic Force Microscopy (AFM) techniques were used to study the effects of rejuvenators on the nano-mechanical properties of the interfacial blending zone that forms between RAP and virgin asphalt binders in a high RAP content mixture. In addition, examined links between the nano-scale properties and the macro-scale performance were evaluated. This was done by evaluating the macro-scale properties and performance of RAP and the virgin asphalt binders’ blends as well as the mixtures with high RAP content. The results of the AFM indentations tests indicated that the rejuvenators did not have a significant effect on the modulus of the virgin binder. However, the indentation modulus of the interface blending zones was significantly decreased. Furthermore, the AFM force spectroscopy results showed that the rejuvenators increased the interfacial blending zone adhesive bonding energy. The comparison between the Dynamic Shear Rheometer (DSR) and AFM results indicated that the interfacial blending zone properties are different than those of the blends prepared by manually mixing RAP and virgin binders. This might suggest that the 100 percent blending is not attainable and an alternative method such as the one presented in this paper could be a better tool to evaluate the composite asphalt binder in mixtures with high RAP content. The AFM indentation modulus of interfacial blending zone correlated well with the Hamburg Wheel Tracking test of the high RAP content mixtures. Finally, the results the beam fatigue test suggested that the interfacial blending zone bonding energy might be one of the factors dictating fatigue performance of high RAP mixtures.

Performance characteristics of high reclaimed asphalt pavement containing bio-modifier

This paper investigates the performance characteristics and workability of high reclaimed asphalt pavement (RAP) mixtures in the presence of a bio-modified binder. Accordingly mixtures with high percentages of RAP were designed with and without bio-modification to examine whether bio-modification can facilitate the incorporation of RAP. The bio-modification was performed by modifying a virgin asphalt binder with a bio-binder produced from swine manure. The four mixtures that were designed and evaluated were a control mixture incorporating virgin materials, the control mixture incorporating 40% RAP, the control mixture incorporating the bio-modified binder, and the control mixture incorporating the bio-modified binder and 40% RAP. The effect of the bio-modified binder on the stiffness and workability of the control mixture with and without RAP was evaluated by measuring the dynamic modulus and the torque resistance of the mixtures, respectively. The performance of each mixture was evaluated for fatigue cracking (overlay tester) and moisture susceptibility/rutting potential (Hamburg wheel-tracking device). Finally, the degree of blending between the virgin and RAP binders was evaluated for each mixture. The data indicated that the addition of the bio-modified binder helped reduce the stiffness of the control mixture with 40% RAP to a level closer to the stiffness of the same mixture without RAP. In addition, the presence of the bio-binder led to improving the workability of the mixtures, especially this was very evident at high-RAP content of 40%. The data indicated that the bio-modified binder improved the fatigue properties and cracking characteristics and had no negative effect on the moisture susceptibility/rutting characteristics of the control mixture with 40% RAP. Overall, data indicated that there was a good degree of blending between the virgin/bio-modified and RAP binders.

Strategies for Incorporating Higher Recycled Asphalt Pavement Percentages

Because there is a greater emphasis on promoting sustainable materials within transportation infrastructure, state agencies in the U.S. Northeast are investigating different strategies that will enable the use of higher percentages of recycled asphalt pavement (RAP) while not sacrificing the performance of the asphalt pavement. In particular, most state agencies in the Northeast are concerned with the fatigue and thermal cracking performance, as well as the general workability and handling of the higher-RAP-content asphalt mixtures when greater percentages are used. In conjunction with the Transportation Pooled Fund study TPF 5(230), Evaluation of Plant-Produced High-Percentage RAP Mixtures in the Northeast, three potential strategies were evaluated for incorporating higher RAP contents: using a softer asphalt binder grade to offset the stiff RAP asphalt binder, limiting the amount of RAP binder credited to the total asphalt content of the asphalt mixture, and using a performance-based specification that the high-RAP content mixture must meet for acceptance. The findings of the strategies through plant-produced mixtures, as well as case studies evaluated in detail through laboratory test procedures and analysis, are summarized. The project trials and results shown will, it is hoped, provide guidance to other agencies looking to increase the percentage of RAP used in their asphalt mixtures.

Modeling the Effects on Energy and Carbon Dioxide from the Use of Recycled Asphalt Pavement in Hot Mix Asphalt

ABSTRACT The transportation sector greatly influence the sustainable development of a society, contributing to pollution from vehicular emissions, global warming, consumption of energy resources, disturbance of natural space from infrastructure construction, and noise pollution. With an increased awareness of sustainable development, more recycled materials are being used for infrastructure construction. However, there is a lack of quantitative evaluation of how energy use and greenhouse gas emission are impacted by the use of recycled materials. Such an evaluation is critical for a comprehensive analysis of the effects of using recycled materials in pavement design. This study develops a mathematical model to quantify the impact of using recycled asphalt pavement in hot mix asphalt on energy consumption and greenhouse gas emission. The energy use and greenhouse gas emissions are affected by the RAP content in HMA, the moisture in the RAP, and the HMA discharge temperature. It was found that it takes more energy to dry/heat HMA with a low percentage of RAP than HMA with only virgin aggregate, while the opposite is true at high RAP percentage. After accounting for the amount of energy used in transporting and processing HMA, and the calorific energy of HMA, the use of RAP in HMA results in reduced energy consumption at all levels of RAP percentage, moisture content, and HMA discharge temperature. For low level of RAP content in HMA, the use of RAP in HMA increases CO2 emissions, while at high RAP content levels CO2 emissions decreases

Modeling and evaluation of the cracking resistance of asphalt mixtures using the semi-circular bending test at intermediate temperatures

The semi-circular bend (SCB) test configuration has been favored by many researchers due to the ease of sample preparation, including cores removed from the field and the quick and simple testing procedure. It offers the potential of assessing the cracking resistance of asphalt mixes in the laboratory in the design phase as well as in QA (quality assurance) testing activities. The objective of this study was to conduct a comprehensive evaluation of the SCB test and to utilize this test to evaluate a number of asphalt mixtures against cracking failure. Results of the experimental program were used to validate a three-dimensional (3D) finite element (FE) model, which was used to interpret and to analyze the failure mechanisms in the SCB test. Results of the experimental program showed that the SCB test results successfully predicted the fracture performance of the evaluated mixes and was able to differentiate between them in terms of cracking resistance. Mixtures prepared with polymer-modified binders were the best performers in this test against fracture. Results of the SCB test were in agreement with the DCSE (Dissipated Creep Strain Energy) test and identified the mixtures with high RAP content and the one prepared with unmodified binder as possible poor cracking performers in the field. The SCB test process as well as the propagation of damage were successfully simulated using 3D FE and cohesive elements. The presented modeling approach was in good agreement with measured test results for all mixtures. Based on the results of the FE model, damage that propagates in the vicinity of the notch is mainly caused by a combination of vertical and horizontal stresses in the specimen. The effect of shear was negligible in progressing damage in the specimen.

Full-Scale Structural Evaluation of Fatigue Characteristics in High Reclaimed Asphalt Pavement and Warm-Mix Asphalt

Warm-mix asphalt (WMA) and the inclusion of higher percentages of reclaimed asphalt pavement (RAP) are two strategies for developing environmentally friendly pavement structures that can also reduce pavement cost. Although demonstration projects have evaluated the constructability and short-term performance of these technologies in the field, questions remain about the structural characterization and longer-term field performance. As part of the 2009 National Center for Asphalt Technology test track, four sections were constructed; they included both WMA and high-RAP contents (50% RAP). A control section did not include either technology. Every section featured embedded instrumentation that facilitated strain versus temperature characterization under truck loading. Statistical comparisons of measured strain response were conducted at three reference temperatures. At the lowest temperature (50°F), the measured strain in the control section was not statistically different from the strains of the experimental sections. At the intermediate temperature (68°F), strains in the RAP with WMA section were statistically lower than the control, but the other sections were not distinguished from the control. At the highest temperature (110°F), the strain in the control section was statistically higher than all other sections. The WMA sections were next highest, and the RAP sections were the lowest. The base mixtures of each section underwent beam fatigue testing from which fatigue transfer functions were developed. Strains entered into their section-specific transfer functions showed that the RAP–WMA section would perform the best. Continued testing and monitoring of the sections are necessary to validate this finding.