Aged Reclaimed Asphalt Pavement Binder Research Articles

Laboratory and Field Performance Evaluation of Cracking of Airfield Warm Mix Asphalt with Reclaimed Asphalt Pavement at the National Airport Pavement and Materials Research Center

The U.S. Federal Aviation Administration is exploring initiatives to decrease transportation greenhouse gas emissions by developing carbon reduction strategies, including using low-embodied carbon materials, such as reclaimed asphalt pavement (RAP), in airport pavement construction. However, verifying RAP’s viability for airfield pavements with laboratory and field performance measures is essential. This study compared the cracking susceptibility of a P-401 hot mix asphalt and warm mix asphalt (WMA)+RAP airfield mixes using laboratory performance tests and conducted a preliminary evaluation of pavement responses from accelerated pavement testing (APT) fatigue tests. The observations and outcomes presented in this paper found that adding 20% of recycled materials with WMA additives had a decreasing impact in mix performance but did not overly affect the asphalt mix properties, as cracking properties from the different test procedures were found with comparable outcomes. Additional observations from strain gauges and temperature probes in the National Airport Pavement and Materials Research Center test cycle 2 APT fatigue test sections showed that the maximum tensile strains in the WMA surface lane 5 south section were consistently higher than those in the WMA+RAP lane 6 south section, which may be because of the higher load level that it was exposed. Additionally, the hardened or aged RAP binder in the entire lane 6 south section may have increased its stiffness, resulting in lower strain levels than in the lane 5 south section. Notably, both sections showed an increase in tensile strains with an increase in asphalt concrete temperature, which confirmed the temperature dependency behavior of asphalt concrete.

Tailored enhancement of reclaimed asphalt pavement with waste engine oil/vacuum residue blend as rejuvenating agent

In recent years, there has been a noticeable increase in the production of Reclaimed Asphalt Pavement (RAP) resulting from the maintenance and rehabilitation activities conducted on asphalt pavements. However, the presence of aged binder in RAP gives rise to asphalt mixtures with unfavourable characteristics. To address this concern, the use of rejuvenating agents has been examined as a viable solution to restore the properties of aged asphalt. In this study, an investigation was undertaken to assess the efficacy of incorporating waste engine oil (WEO) and vacuum residue (VR) as hybridized rejuvenating agents for RAP. Various characteristics including penetration, softening point, ductility, viscosity, and stiffness were measured to ascertain the optimal dosage of the hybridized rejuvenating agent. Subsequently, the performance of the rejuvenated asphalt was evaluated through Marshall tests, indirect tensile strength (ITS), moisture damage, and Kim tests, comparing it with different samples. Moreover, the Creep compliance, semi-circular bending (SCB), and Cantabro loss measurements were employed in the evaluation. The findings of the study indicate that a 6.5% hybrid rejuvenator composed of WEO and VR effectively rejuvenates asphalt mixtures containing 30% RAP material by softening the aged binder. Furthermore, the rejuvenated mixture exhibited significant improvements when compared to both the virgin asphalt and RAP mixtures. In conclusion, the incorporation of WEO and VR as a hybridized rejuvenating agent showcases promising results in enhancing the performance of RAP mixtures. This, in turn, contributes to sustainable and efficient pavement practices.

Use of the Iron Chloride Type of Lewis Acid Catalyst in High Reclaimed Asphalt Pavement Content Asphalt Mixtures

The use of reclaimed asphalt pavement (RAP) as a partial replacement for virgin aggregates and asphalt binders has received considerable attention recently. This approach is one of many promising methods for improving sustainability. However, many state Departments of Transportation are cautious in adopting high RAP content into their designs because of cracking and durability issues resulting from the aged RAP binder. A Lewis acid catalyst has been used to modify the asphalt binder’s chemical composition and disrupt the associated molecules formed in the aged RAP binder. The objective of this study is to assess the effectiveness of the use of a Lewis acid catalyst in improving the cracking resistance of an asphalt mixture containing high RAP contents. A suite of laboratory mechanical tests was performed, namely, the dynamic modulus test for linear viscoelastic properties; the semi-circular bend, Illinois flexible index, ideal cracking tolerance, and simplified viscoelastic continuum damage tests for fracture and fatigue resistance; the loaded wheel tracking test for rutting resistance and moisture susceptibility; indirect tensile creep compliance and strength tests for low-temperature cracking resistance; and the Cantabro abrasion test for durability. Further, AASHTOWare Pavement ME software was used to predict the long-term performance of asphalt pavements containing mixtures with high RAP contents and a Lewis acid catalyst. Results showed that the use of the Lewis acid catalyst can disrupt associated molecules formed in the aged RAP binder. Thus, asphalt mixtures containing high RAP contents (recycled binder ratio > 0.20) and a Lewis acid catalyst exhibited similar performances to conventional mixtures. Further, Pavement ME predicted fatigue cracking was lower for a structure containing a FeCl3-modified mixture as compared to a similar one with no FeCl3, illustrating the effectiveness of FeCl3.

Dilauryl thiodipropionate as a regeneration agent for reclaimed asphalts

Constructing asphalt pavements using reclaimed asphalt pavement (RAP) instead of exclusively virgin materials can significantly reduce environmental impacts and costs. However, the adverse effect of the aged RAP binder on asphalt mixtures’ workability and pavements’ performance restricts the percentage of RAP added to asphalt mixtures. As a solution, regeneration agents can be used to restore (even if partially) the physical, rheological, and chemical properties lost during the aging of the pavement in the field. Therefore, this paper evaluates the feasibility of using Dilauryl thiodipropionate (DLTDP) as a regeneration agent for RAP binders. This study considered two RAP binders (artificial and field). The impact of the DLTDP on the continuous performance grade of each RAP binder was investigated using the Dynamic Shear Rheometer (DSR). The antioxidant and regenerative effects of DLTDP on RAP binders were assessed by Fourier Transform Infrared spectroscopy (FTIR) and SARA fractionation. The adhesion between each RAP binder and granite aggregate (at dry and wet conditions) was evaluated using the bitumen bond strength (BBS) test. The rheological results indicated the softening effect of DLTDP on RAP binders. This softening effect may be explained by the increase of the maltene fractions (resins) and the reduction of the asphaltene fraction. Additionally, regenerated binders showed better oxidative aging and moisture susceptibility resistance than non-regenerated binders. Overall, the results indicated that adding DLTDP to RAP binders partially restored RAP binders' rheological and chemical composition to the target neat asphalt binder without significantly compromising the adhesion properties and rutting resistance. Moreover, the mentioned results verified the great potential of using DLTDP as a regeneration agent for RAP binders, making it possible to produce good-performing asphalt mixtures with a high RAP percentage.

Chemical and thermodynamic properties of palm oil-based materials and their impact on recycled binder blends

• We characterised chemical and thermodynamic properties of palm oil-based materials. • We assessed the impact of adding these agents to binder blends of an HMA with high RAP. • Surface free energy was used to assess the adhesion quality and durability of the bonds between aggregates and recycled binder blends with these agents. • Key chemical compounds present in the palm oil materials contributed to the rejuvenation effectiveness. • Palm oil-based materials are promising candidates to be used as rejuvenators in HMA with high RAP. Rejuvenators are agents added during the production of hot mix asphalts with high contents of reclaimed asphalt pavement (RAP) to restore some properties of the aged RAP binder. These materials can be obtained from numerous sources; hence, their chemical composition and physical properties vary greatly, which can have an impact on the final mixtures’ properties. This work assesses key chemical properties of crude palm oil and two of its solid by-products to understand their rejuvenation effect on a blend of a virgin and an aged RAP asphalt binder. The evaluation included thermogravimetry analysis (TGA), Fourier transform infrared (FTIR) spectroscopy and chromatography analysis. Besides, surface free energy measurements (SFE) on the recycled binder blends (i.e., virgin asphalt binder, RAP asphalt binder and rejuvenator) and of two aggregate sources were used to evaluate the impact of the palm oils in the adhesive bonds’ quality and moisture sensitivity of the recycled binder blends-aggregates systems. Results indicate that the palm oil materials have good thermal stability and contain several large molecular size (LMS) compounds that contribute to the rejuvenation effect. Besides, recycled binder blends produced with the palm oil materials developed strong adhesive bonds in dry and wet conditions. Overall, results highlight the potential of palm oil and its solid by-products as rejuvenators for high RAP content asphalt mixtures.

Investigation of the aging behaviors of reclaimed asphalt

Reclaimed asphalt pavement (RAP) has been extensively used in asphalt pavement nowadays. Under the coupled impacts of traffic loading and environmental factors, aged binder in RAP would suffer the secondary aging, and seriously affect the performance of the reclaimed asphalt binder. This study explored the aging behaviors of the composite asphalt binder (50% RAP binder + 50% SBS binder). Comparison was made in aging performance between RAP binder, virgin SBS binder and their composite by conducting RTFOT test with different aging durations. Centrifugal extraction and rotary evaporator methods were firstly adopted to recover RAP binder. Rheology tests, including the DSR temperature sweep test, multiple stress creep recovery (MSCR) test and linear amplitude sweep (LAS) test, were conducted. Results showed that the high temperature stability of composite binder increased significantly after the secondary aging. With increasing the aging duration, the stiffness of the composite binder increased, which led to the decrease of creep deformation and deformation recovery. The effect of RAP binder on the creep characteristics of composite binder was greater than that of the SBS binder, and the variations of R, Jnr, R-diff and Jnr-diff of the composite binder with the aging duration remained basically the same as that of the RAP binder. The fatigue resistance of binders decreased gradually with the increasing the aging duration. For a given level of aging duration and strain, the fatigue life Nf of the composite binder always lay between the RAP binder and the SBS binder. The fatigue life attenuation law of composite binder is almost the same as that of RAP binder in the short-term aging stage (less than 85 min), while for long-term aging the fatigue life attenuation law is more similar to that of SBS binder.

Towards very high RAP content asphalt mixes: A comprehensive performance-based study of rejuvenated binders

Hot recycling of reclaimed asphalt pavement (RAP) from replacement of deteriorated asphalt pavements is a widespread technique, and able to ensure clear economic and environmental benefits. For this reason, paving industries, agencies and researchers are spending significant efforts in order to maximize such advantages by increasing the amount of RAP within new asphalt mixtures. Nevertheless, adequate performance of recycled mixtures must be guaranteed despite the re-use of high amounts of RAP which involves the presence of aged, oxidized and stiffened binder. In this perspective, the present study aimed at evaluating the rheological properties at mid-service and high-service temperatures of bituminous blends composed by 40% of virgin binder and 60% of aged rejuvenated bitumen (simulating the aged hard bitumen coming from the RAP). Such proportion was selected to represent a high recycling rate of RAP (about 60% of the total weight of aggregates, RAP included). A chemical commercial additive at the liquid state was selected as rejuvenator; it was dosed at the optimum content based on empirical and rheological preliminary characterization. The performance of the recycled blend was then compared to that of a virgin reference bitumen. Dynamic shear rheometer tests were carried out to determine the master curves and the failure characteristics (at mid and high service temperatures) of the selected binders. The effect of aging (related to the durability over the material lifetime) was also studied analyzing binders’ responses in unaged, short-term and long-term aged conditions. Overall, experimental findings demonstrated the efficacy of the rejuvenation of recycled binders containing very high amount of aged bitumen. • Rejuvenation of aged RAP binder was able to restore original rheological properties. • Dosage of rejuvenator was crucial to restore adequately the binder properties. • Rejuvenated blend showed comparable or enhanced performance than the virgin binder.

Detection of Reclaimed Asphalt Pavement Presence in Asphalt Mixtures Using a Method of Successive Asphalt Binder Extraction

The work deals with the detection of presence of RAP (reclaimed asphalt pavement) in asphalt mixtures. Information about the presence of RAP in an asphalt layer can be technically advantageous, for example, when planning further recycling of the layer. The method described in the paper can also be used to verify the success of a treatment of an aged binder in RAP, which is dosed in the production of new asphalt mixtures. The asphalt binder was obtained by a method of successive extraction from asphalt mixtures with different RAP content. Basic empirical tests of the asphalt binder (needle penetration and softening point) were chosen to detect the presence of RAP. The complex shear modulus G* was further determined on the extracted binders using a dynamic shear rheometer (DSR).

Effect of Aged Binder Distribution on the Fracture Tolerance of Asphalt Mixtures with Reclaimed Asphalt Pavement

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.

Investigating Degree of Blending Between Reclaimed Asphalt Pavement and Virgin Binder Using Atomic Force Microscopy and Focused Ion Beam

Adding reclaimed asphalt pavement (RAP) into asphalt mixes is a common practice and has many merits such as reducing costs and emissions. In recent decades, many state highway agencies have embarked on investigating asphalt mixes with high RAP content. As the RAP content increases, understanding how well the RAP binder blends with virgin binder becomes more crucial. Lack of knowledge on how much of the residual RAP binder actively blends with virgin binder during production is one of the reasons preventing full exploitation of RAP materials. Obviously, the amount of aged RAP binder blending into virgin binder affects the properties of asphalt mixes. A study was undertaken to investigate the degree of blending, that is, the amount of RAP binder blended with virgin binder, through atomic force microscopy (AFM) and focused ion beam (FIB). The AFM measurements were conducted on both binder samples and RAP aggregate samples; the former consisted of extracted and recovered RAP binder, virgin binder, and blended binder, while the latter covered blended RAP aggregate and virgin binder samples. AFM measurements on binders indicated that blended RAP and virgin binder, at the blending zone between RAP and virgin binder, has moduli between that of pure RAP binder and pure virgin binder. AFM was also explored to investigate the degree of blending using RAP aggregate and virgin binder, but preparation of acceptable samples for such work was not possible, in spite of extensive work in preparation of such samples through mechanical polishing and FIB.

Effect of reclaimed asphalt pavement on cracking performance of asphalt mixtures with regular and high polymer modified binders

Since reclaimed asphalt pavement (RAP) provides economic savings, incorporating RAP may reduce high cost of high-polymer (HP) binder typically used to address severe cracking. However, RAP is currently not allowed in HP mixtures in Florida, because aged RAP binder may reduce benefits of HP binder. This study focused on determining whether RAP can be used in HP mixtures, while maintaining the premium performance expected of HP binder. Eight RAP sources covering a broad range of RAP characteristics were assessed using the interstitial component fracture energy (FEIC) and the mixture fracture energy (FEmix). Mixtures with HP binder exhibited better cracking resistance than those with PG 76–22 binder. However, introduction of 20% RAP in HP mixtures reduced 20–60% in FEIC and 30–45% in FEmix, depending on RAP characteristics. Therefore, RAP characteristics need to be carefully reviewed, and more caution is needed when adding RAP into HP mixtures.

Double-Recycled Reclaimed Asphalt Pavement: A Laboratory Investigation at Low Temperatures Based on Different Mathematical Approaches.

Using recyclable materials in asphalt pavement is a fundamental design approach not only for limiting the environmental impact of the construction industry, but also for reducing the overall costs of the road infrastructures. Over the past years, road agencies have developed different policies to incorporate various types of recyclable material into conventional asphalt mixtures. reclaimed asphalt pavement (RAP) is one of the most highly recycled construction materials. However, the aged RAP binder and its stiffer and brittle characteristics compared to the fresh binder may negatively affect the performance of the recycled mixture, especially when operating in cold climates. In this study, the low-temperature response of asphalt mixture prepared with single-recycled RAP (SRRAP) and double-recycled RAP (DRRAP), prepared in the laboratory, is experimentally investigated based on creep testing performed with the bending beam rheometer (BBR). Then, the data were analyzed based on three simple mathematical models to extract information on material behavior. Finally, a new indicator named thermal stress factor (TFS) on low-temperature response is proposed. Relatively poorer performance was observed from SRRAP mixture compared to the asphalt mixture prepared with virgin material. However, the low-temperature response between SRRAP and DRRAP did not present significant differences. The values of TFS support the experimental results and suggest the possibility of considering re-recycling technology for further research with the objective of a possible application in the asphalt pavement industry.

Rejuvenating effect of soft bitumen, liquid surfactant, and bio-rejuvenator on artificial aged asphalt

Challenges are existing when applying high percentages of reclaimed asphalt pavement (RAP) into construction as the aged RAP binder became more brittle, and stiffer after second-round usage. The bio-rejuvenator with dramatic environmental effects can alleviate stiffness and increases viscous components of aged RAP binder and is becoming popular in the incorporation with RAP. Unfortunately, till now, there is no research available to fully characterize and compare the regenerating effect between bio- rejuvenator, soft bitumen, and warm mix asphalt additives on high artificial RAP binder. To overcome this issue, in this study, a bio-rejuvenator and the other two rejuvenators including soft bitumen and Evotherm-DAT, were used to quantify the difference on regenerating effects of asphalt binder with different contents of artificial RAP binder. Penetration, softening point, rotational viscometer, dynamic shear rheometer (DSR), and bending beam rheometer (BBR) test were performed to characterize the basic properties, workability, and rheological properties of prepared samples. Test results showed that the bio-rejuvenator had the most effective rejuvenating impact, while its improvement on low-temperature performance was limited when it was used on binder containing 80% of artificial RAP binders. In addition, Evotherm-DAT had a significant softening effect on binder containing 30% of artificial RAP binders. Finally, it was found that Evotherm-DAT and bio-rejuvenator can perform well when maximum artificial RAP binder contents were 50% and 80%, respectively. The results of this study indicate possible uses of three different rejuvenators to improve the rejuvenating performance on the high percentage of RAP binder.

Effect of rejuvenator types and mixing procedures on volumetric properties of asphalt mixtures with 50% RAP

The use of Reclaimed Asphalt Pavement (RAP) in asphalt mixtures has several benefits, such as reducing the consumption of virgin materials and protecting the environment. However, as high RAP content (e.g., 50%) is used, asphalt mixtures become brittle so that premature failure (cracking) may occur. To improve the cracking resistance of asphalt mixtures with high RAP contents, one of the approaches considered is the use of rejuvenators. Such rejuvenators, when used in high RAP asphalt mixtures, counteract the effects of the aged RAP binder and may have an impact on the volumetric properties of the mixtures. The objective of this study is to evaluate the effect of rejuvenator types and mixing procedures on the volumetric properties of asphalt mixtures prepared with high RAP content (i.e., 50%). To achieve this objective, three rejuvenators and three rejuvenator mixing procedures were utilized to prepare asphalt mixtures containing 50% RAP. Volumetric properties of the mixtures (air voids (AV), voids in mineral aggregate (VMA), and dust to binder ratio) were determined. Testing results indicate that some volumetric properties of mixtures (AV and VMA) could significantly change when different mixing procedures and rejuvenator types were used. Therefore, the mixing procedures and the rejuvenator types should be taken into considered when conducting mixture design.

A review on the mechanisms involved in reclaimed asphalt pavement

Reclaimed Asphalt Pavement (RAP) is a widely used recycled material in pavement construction. Whereas the integration of RAP into asphalt mixtures is a complex subject and need to understand every aspect that entailed in the mix design. The aim of this review paper is to provide comprehensive knowledge about the developments and challenges of the RAP in the asphalt mixtures, along with the mechanisms involved. The blending process and rejuvenator are two key factors that govern RAP content, and this can even surge up to 100% in the asphalt mixtures. The blending between the RAP and the virgin materials is very crucial in the context of performance and durability of RAP mixtures. While rejuvenator is an additive which may act as a catalyst and enhance the aged RAP binder properties. A detailed description of distinct types of the rejuvenators and their performances are discussed in this paper. Several aspects of the RAP mixtures including mix design, constituent materials, performance, RAP with polymer modified asphalt binder, as well as environmental benefits are highlighted. This study gives information to the researchers, engineers, and designers about the RAP technology.

Production, Construction, Properties, and Performance of a Test Road with High Reclaimed Asphalt Pavement Content

The two primary factors that drive the use of reclaimed asphalt pavement (RAP) are economic savings and environmental benefits. However, highway agencies are concerned about the use of a high percentage of RAP in asphalt pavements. This study addressed issues related to the production, construction, properties, and performance of asphalt pavements that contain high percentages of RAP. Mixtures that contained up to 40% RAP were successfully designed, produced, and constructed after proper procedures were followed and attention to detail was paid during design, production, and construction. A separate drum for drying and heating RAP, called a parallel heating system, was used to produce high RAP content asphalt mixtures in a batch plant. Rejuvenating agents were mixed directly in a surge bin to allow the rejuvenator enough time to diffuse into aged RAP binder. Comprehensive laboratory tests were performed to evaluate the air voids, the resilient modulus, the rut depth, and the Cantabro weight loss of asphalt mixtures with high RAP content. A test road was constructed in 2014 to monitor how high RAP asphalt pavements would perform under real traffic and environmental conditions. An in-depth investigation was conducted of pavement performance, including cracking, friction, and rutting. The engineering properties of plant-produced mixtures and field cores were well correlated with the pavement performance of the test road. Test results indicated that high RAP content asphalt mixtures could perform as satisfactorily as those produced with virgin materials to meet in-service requirements.

Effect of rejuvenator on performance characteristics of high RAP mixture

As more reclaimed asphalt pavement (RAP) is utilised in asphalt mixtures, there are increasing concerns about the potential negative effect of the aged RAP binder on the field performance, especially cracking resistance, of the high RAP mixtures. To address the concerns, there have been increasing interests in utilising rejuvenators to improve the cracking performance of high RAP mixtures. The objective of this study was to determine the benefits of using a new rejuvenator made from renewable sources in asphalt mixtures with high RAP contents. The study was conducted by determining and comparing the laboratory performance properties of three mixtures and the binders extracted from the mixes. The three mixtures evaluated in this study included two 50% RAP mixtures (RAP binder ratio = 0.55) with and without the rejuvenator and a comparable virgin mix. Results of this study suggested that the new rejuvenator was effective in improving both the intermediate and low-temperature cracking performance characteristics of the 50% RAP mix close to those of the virgin mix at the short-term laboratory ageing condition without affecting its rutting and stripping resistance. It is recommended that a field study of this rejuvenator be conducted to further evaluate its effect on the long-term field performance of high RAP mixes.

Influence of Waste Engine Oil on Asphalt Mixtures Containing Reclaimed Asphalt Pavement

This paper presents the results from a laboratory study in which the influence of waste engine oil on the performance of hot-mix asphalt (HMA) containing reclaimed asphalt pavement (RAP) was evaluated. The lab test consists of binder test and mixture test. For binder test, the extracted RAP binder was blended with virgin binder and waste oil to investigate the rheological properties as well as fatigue properties. The waste engine oil was collected from a local auto repair shop. Performance Grade 64-22 was selected as virgin binder. For mixture test, the HMA containing RAP was evaluated at three RAP contents [(1) 0%, (2) 25%, and (3) 40%] and three waste oil contents [(1) 0%, (2) 2%, and (3) 5%]. Binder master curves, linear amplitude sweep, Superpave indirect tension, beam fatigue, and asphalt pavement analyzer rutting tests were conducted to evaluate the engineering properties of asphalt and asphalt mixtures. The results from the research reported in this paper indicated that the incorporation of waste engine oil into HMA with RAP may offset the increase of stiffness caused by aged binder in RAP. The inclusion of waste engine oil decreased optimum asphalt content, and reduced rut resistance. Meanwhile, it may also have limited improvements on fatigue resistance of the mixtures.

Hot Mix Asphalt with High RAP Content

Due to increasing cost of asphalt binder, significant economic savings can be realized using high content of reclaimed asphalt pavement (RAP) in the production of new hot mix asphalt (HMA). Moreover, this is an environmentally friendly alternative as it reduces the need for virgin materials. It has to be noted that in Latvia RAP is rarely used in production of HMA and this valuable material is mostly degraded for use in lower value applications. Three mixtures were designed, which were the combination of two different RAP sources and local dolomite aggregates. The RAP binder had significantly aged having penetration of around 38mm, softening point of 56°C and Fraass temperature of -10°C. RAP was added at rates 30% and 50% for each RAP source. A softer binder grade (70/100 versus traditional 50/70) was added to compensate for the aged RAP binder. Hamburg wheel tracking test results demonstrated that all mixtures have high rutting resistance and fatigue test results using four-point bending beam were similar to those of virgin mixture. This demonstrated that mixtures with high RAP content can be successfully designed to meet the local volumetric and performance-specification requirements.

Low-temperature properties of plant-produced RAP mixtures in the Northeast

The impact of reclaimed asphalt pavement (RAP) materials on pavement performance is an important topic of study in the industry due to environmental and cost benefits. The primary concern for increasing allowable RAP percentages in hot mix asphalt relates to the presence of aged materials, which may embrittle the mixture and decrease cracking resistance. Low-temperature cracking is a major distress in cold temperature climates, such as the Northeastern United States. Currently, there are several procedures to analyse low-temperature performance of asphalt binders and mixtures. However, these methods use different starting (initial) temperatures and cooling rates that may not represent actual field temperatures and cooling rates. This paper presents the results of a study on low-temperature performance of plant-produced RAP mixtures. Eighteen mixtures from three states were tested with varying RAP contents (0–40%) and different virgin binder grades. The objectives of the study were to: (1) evaluate the impact of cooling rate and starting temperature on the critical cracking temperature of RAP materials; (2) evaluate the impact of RAP content on the low-temperature properties of mixtures; (3) evaluate the benefit of using softer virgin binder grades to mitigate the impact of the aged RAP binder in the mixture; and (4) to compare the low-temperature cracking properties determined from different mixture and binder tests. Based on the results, warmer starting temperatures and faster cooling rates result in warmer critical cracking temperatures for all mixtures. Through use of the uniaxial thermal stress strain test, it was found that the addition of RAP alters fracture behaviour from ductile failure towards a brittle failure. Based on results from the indirect tensile test, tensile strength increases with RAP content. However, due to a faster-building thermal stress, warmer critical cracking temperatures result. It was also determined that degree of blending may impact the effectiveness of using softer binder grades at higher RAP percentages to improve low temperature cracking resistance. The data also show that analysis procedure and test protocols can have a profound effect on critical cracking temperature. The conclusions presented reinforce the need for more accurate representation of RAP materials, and careful selection of analysis parameters.