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Asphalt mastic, the combination of fine-grained mineral particles and asphalt binder, plays a significant role on the performance of Hot Mix Asphalt mixtures. A clear understanding of the effects o...

With the increasing usage of cold recycling techniques on maintenance of flexible pavements, increases also the need to better characterise the properties of cold recycled mixtures, usually compose...

Mineral filler, fine-grained mineral particles naturally present in or manufactured and added to aggregates play a significant role on the performance of asphalt mastic and asphalt mixtures. A clea...

Hydrated lime has been used in hot mix asphalt (HMA) to reduce moisture sensitivity and stripping since 1910 in the United States. During the past 40 years, researchers from all over the world have...

Funding Information: The authors would like to acknowledge the contributions of the active members of the RILEM technical committee TC 264-RAP in terms of experimental results, data analysis and proofreading. The authors would also like to thank Nynas AB, Kraton Chemical BV and Technical University of Braunschweig for supporting the interlaboratory activity by providing bituminous materials, ARA and RA binder. Publisher Copyright: © 2022, The Author(s). This recommendation is based on the results of an inter-laboratory study organised by the RILEM technical committee TC 264-RAP "Asphalt Pavement Recycling"—Task Group 3 (TG3) focusing on Asphalt Binder for Recycled Asphalt Mixture. The TG3 aimed to evaluate the effect of a specific family of materials known as asphalt recycling agent (ARA) on the aged binder under different configurations. Even though ageing is an irreversible phenomenon, effective ARA must have the capability to improve the flexibility of the bituminous materials and their resistance against cracking susceptibility with no adverse effect on the rutting resistance of pavements containing reclaimed asphalt. A total of 17 participating laboratories analysed the properties of binder blends composed of aged binder from reclaimed asphalt in three different contents (60, 80, 100%), ARA and virgin binder. The physical properties of the blends were thoroughly evaluated through traditional and rheological binder testing. This recommendation proposes to restore the original material properties at low and intermediate temperatures (i.e. cracking resistance) while balancing the high-temperature characteristics (i.e. rutting susceptibility) with durable impact throughout the progression of ageing phenomena. Therefore, useing of the Dynamic Shear Rheometer is foreseen as a more suitable and sustainable means to evaluate binder blends containing an asphalt recycling agent. Compared with conventional testing, the proposed approach requires fewer materials while resulting in a faster experimental procedure with one single test.

A better understanding of the interaction between old and new bitumen is considered of key importance in the production of new hot asphalt mixtures with high percentages of reclaimed asphalt pavement. This improvement could potentially avoid shorter service life of the material and failure due to reduced performance in rutting and fatigue. This study is part of an on-going research in the framework of a PhD thesis. The aim of this paper is to present the experimental results focussed on the characterisation of the diffusion phenomenon between two different bitumens. A DSR has been used to experimentally measure the changes in shear complex modulus during time at 50 °C of a double-layer specimen. The main hypothesis is that a changing in the measurements of the shear complex modulus is stemmed from a changing in the structure of the sample: this implies that a blending phenomenon between the two bitumens is going on, mainly driven by diffusion between the two materials.

Cold recycling of reclaimed asphalt (RA) is a promising technique to build or to maintain roads, combining performance and environmental advantages. Although this technique has been extensively used worldwide, there is no unique and internationally-shared method to characterize cold recycled mixtures. The previous work of the RILEM TC 237-SIB TG6 successfully attempted to characterize different RA sources with both traditional parameters (gradation, bitumen content and geometrical properties) and non-conventional properties (fragmentation and strength testing). The current RILEM TC 264-RAP TG1 mainly focuses on the influence of different RA sources on physical and mechanical characteristics of cement-bitumen treated materials (CBTM) using foam or emulsified bitumen, taking into consideration compaction and curing methods. This paper presents results from the first step of the inter-laboratory project in which foamed bitumen and cement were used as binders. The influence of two RA sources, one from Alabama (USA) and one from San Marino, were investigated through the collaboration of several laboratories. Specimens were manufactured with the same diameter by means of both Marshall and gyratory compactors and then cured following two procedures: free surface drying (FSD) and partially-surface drying (PSD). A preliminary study allowed obtaining specimens with similar volumetric properties. Along with compactability and water loss, the indirect tensile stiffness modulus was measured and analyzed. The results have shown that the RA source and curing procedure influence the CBTM mechanical properties.

The use of rejuvenators has seen a consistent increase over the years in the asphalt pavement industry. This is due to the need for maximizing the demand for incorporating a higher amount of Reclaimed Asphalt (RA) in the pavement asphalt mixtures. In order to tackle this challenge, the Task Group 3, focusing on asphalt binders and additives, of the RILEM TC RAP conducted an interlaboratory activity to evaluate the effect of aging on blends of virgin and rejuvenated RA binders. A set of conventional tests including penetration value at 25 °C, softening point temperature and rheological measurements by means of Dynamic Shear Rheometer (DSR) were selected to involve a large number of participants. A binder, recovered from field RA, was treated with a bio-based rejuvenator and blended with a virgin binder to simulate recycling at three different percentages 60, 80, and 100%. These blends, as well as the pure virgin binder, were next short and long term aged and tested to evaluate the changes in the corresponding properties. Relatively consistent results were obtained for the entire set of blends. The aging of combined rejuvenated RA and virgin binders was comparable to that experienced for the pure virgin binder. DSR data provided a more precise evolution of the impact of aging on the materials.

This paper presents a laboratory investigation aimed at evaluating the effect of employing hyper-modified asphalt binders in surface asphalt courses. Two different Hot Mix Asphalt (HMA) surface lay...

A laboratory investigation was performed to better understand the performance of Cement-Treated Base (CTB) mixtures containing Recycled Asphalt Pavement (RAP) during a long-lasting service period. Two CTB mixtures, one containing only virgin aggregates and the other containing RAP and virgin aggregates, were tested by triaxial tests (static and cyclic) and resonant column tests to evaluate stiffness and dampening at very small deformations. Similar mechanical properties and response to cyclic loadings were obtained for the two mixtures. The results led to the conclusion that the use of RAP as a replacement for virgin aggregates for a CTB mixture does not cause any significant alteration in terms of mechanical performance.

Cold recycled bituminous materials can consist of up to 100% reclaimed asphalt pavement (RAP) treated with different binders such as bituminous emulsion and foamed bitumen, as for Hot recycling the...

This study investigated the effect of RAP gradation on the fracture tolerance of asphalt mixtures in terms of fracture energy density (FED). Experimental factors included two RAP sources, one virgin binder and four RAP contents of 0, 20, 30 and 40%, resulting in a total of seven mixtures. Binder fracture energy tests were conducted to determine the FED of blends of virgin and extracted RAP binders. Moreover, interstitial component direct tension (ICDT) tests were employed to measure the FED of the interstitial component, which is the fine portion of a mixture that governs cracking performance. Finally, Superpave IDT tests were performed to obtain the FED of RAP mixtures. Increasing RAP content led to reductions in FED at binder, IC and mixture levels. More importantly, the reduction in FED was almost identical for mixtures and IC, whereas a less pronounced drop was observed for binders. This finding substantiates that full blending between RAP and virgin asphalt as artificially created in binder specimens did not occur in the actual RAP mixtures. Coarse RAP yielded greater IC and mixture FED values than fine RAP despite the lower RAP binder stiffness of the latter, substantiating that RAP gradation controls the distribution of RAP binder in mixtures and consequently, high RAP binder content in IC portion reduces the fracture tolerance of a mixture. A new design guideline that considers RAP binder content and properties along with RAP gradation is proposed to determine the maximum allowable RAP content, so that cost savings and environmental benefits can be maximized by reducing the need for virgin pavement materials and landfill space.

ISBM 2020, RILEM International Symposium on Bituminous Materials , Lyon, FRANCE, 14-/12/2020 - 16/12/2020; The Task Group 2 of the RILEM Technical Committee 264-RAP on non-cold recycling identified the need to gather some insights about possible durability issues associated with the combination of Warm Mix Asphalt (WMA) and of Reclaimed Asphalt (RA) in order to prioritize the characteriza-tion or research needs for relevant damage types. For this purpose, an interna-tional inter-laboratory testing program was launched in 5 different laboratories. This was developed on the basis of the challenges which a road material de-signer commonly faces: reduce the temperature, add RA, but preserve the same properties. Each laboratory characterized, according to its internal protocol, two variations of the same type of mixture (similar grading curve, binder content, etc.): a Hot Mix Asphalt (HMA) without RA taken as reference and a WMA with 40% RA. The performances of all the WMA with 40% RA are then com-pared in order to see if common trends emerge from the different characteriza-tion methods and reveal property issues specific to WMA+RA combinations.

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.

Asphalt cold recycling technologies allow the use of up to 100 % reclaimed asphalt pavement (RAP) from an existing asphalt pavement to construct new base layers and new subbase layers. Bituminous stabilized materials (BSM), obtained from cold recycling technologies, are susceptible to traffic-induced accumulation of permanent deformation. In the current design methods, BSM pavement layers are typically assumed to have a linear elastic response under traffic loading application, and this does not account for plasticity initiation and accumulation in the material. This research study provides insight on how to integrate plasticity behavior in numerical simulations of rehabilitated pavement structures with BSM. A BSM mixture prepared with 1.5 % cement by weight of total mixture and 1.5 % foamed asphalt binder content by weight of dry aggregates is characterized in the laboratory. Subsequently, a three-dimensional elastic-perfectly plastic finite element model is developed for the simulation of triaxial shear strength tests. Lab measured force-displacement curves are matched with the numerical simulations at different confining pressures. The calibrated mechanical properties are then used as input parameters in multilayer pavement models for pavement evaluation. Different pavement structures with and without BSM layers are compared in terms of a maximum allowable number of loading repetitions before reaching a 20-mm rut depth on the surface of the pavement. The results indicate that structures with BSM and traditional granular base layers yield comparable results in terms of rutting potential. In addition, the study presents a framework for the design and analysis of cold recycled pavement layers and a method to integrate the plasticity behavior of partially-bonded and unbounded layers for pavement evaluation.

The use of reclaimed asphalt (RA) in road pavements is continuously gaining interest thanks to the technical, economic and environmental advantages guaranteed by such sustainable practice. Cold recycling techniques compared to traditional asphalt mixes allow a significant reduction of energy, fume emissions, use of natural resources, etc. In this perspective, the Task Group 1 on “Cold Recycling” of the RILEM Technical Committee on “Asphalt Pavement Recycling” (TC 264-RAP) launched an interlaboratory test program (ITP) aimed at ensuring a better understanding for cold recycled mixtures. The paper presents the results collected by a restricted group of the participating laboratories testing cement-bitumen treated materials that included a single RA source and prepared with foamed bitumen. Gyratory compacted specimens were used to evaluate the influence of curing (free, partial or restricted-surface drying for 14 days at 40 °C at a relative humidity of 55 ± 5%). Stiffness was evaluated as a function of the curing stage and the corresponding water loss; strength was tested after 14 days of curing testing specimens in both dry and wet conditions to also determine the water sensitivity. As expected, the different curing conditions clearly influenced the rate of water loss of tested samples with clear effects on mechanical properties and durability.

Black Curve and White curve are a well-known method to fully characterize a RAP source, however involves a major effort in terms of laboratory equipment and time-consuming process. RILEM has validated two protocols for a fast RAP characterization: Fragmentation test and Cohesion test. In this study, the authors show the results of a reliability evaluation of the Fragmentation test. Considering this test evaluates the stability of aggregates gradation of the RAP under compaction, the authors have induced an artificial variation in the RAP gradation source to create different RAPs that can be considered just apparently the same. A certain amount of RAP aggregates has been gradually replaced with steel slags to assess the sensitivity of this test. One source of RAP has been used and three different batches were selected: 100% RAP, 50% RAP + 50% steel slags and finally 100% steel slags. Steel slag aggregates have been chosen because of its low Los Angeles abrasion coefficient and its increasingly use on hot mix asphalt with RAP. A series of laboratory tests have been performed using the modified Proctor, as required by the investigated RILEM protocol, and the percentage of material passing through a control sieve has been assessed. The obtained results are encouraging, as they fit with the initial assumption that RAP sources with different percentages of RAP clusters are differentiated by the Fragmentation test. Thus, a simple job site laboratory can provide a key information on the quality of the material to be used on field applications.

In the last few decades, the need for reducing the exploitation of finite sources has led to an increasing use of reclaimed asphalt pavement (RAP) for the construction, maintenance, and rehabilitation of road pavements. During hot mix asphalt (HMA) plant production, RAP can be added at ambient temperature or preheated into special drums. When designing an RAP mixture, it is essential to dose the correct amount of virgin binder according to the percentage of the reactivated aged one. RAP preheating plays a key role in this process, although no reliable methods are available for achieving an accurate estimation. This article presents an innovative digital image-based methodology, named overlapped digital image (OIA) analysis, to better understand the role of reactivated binder on the cracking behavior of HMA-RAP mixtures. A recycled mixture was produced in the laboratory by adding RAP both at room temperature (25°C) and after preheating (150°C) and subsequently tested according to the Superpave IDT at 10°C and 25°C. The tests were combined with the OIA analysis to identify how the strain patterns and the initiation and propagation of fractures developed, according to the reactivation of the aged asphalt binder. The results show important outcomes in terms of cracking behaviors highlighting the important role of RAP preheating for inducing aged binder reactivation.

In this paper the effect of reclaimed asphalt pavement (RAP) on the low-temperature properties of asphalt mixture is experimentally investigated and modelled. Two test methods are used: bending beam rheometer (BBR) mixture creep test, which is based on static loading, and dynamic shear rheometer (DSR) mixture complex modulus test, which uses oscillatory loading. First, creep stiffness, m-value, thermal stress, critical cracking temperature and complex modulus are derived, and then, statistically and graphically compared. Then, the rheological Huet model is used to evaluate the experimental BBR measurements and to derive a simple relationship associating the characteristic time of mixtures to the RAP content. The statistical results indicate that most of the mixtures prepared with RAP have relatively poorer performance compared to virgin mixtures up to a RAP content of 25%. Based on rheological modelling, it appears that RAP and characteristic time are linked through an exponential relationship.

When producing asphalt concrete mixture with high amounts of reclaimed asphalt pavement (RAP), the mixing temperature plays a significant role in the resulting spatial distribution of the components as well as on the quality of the resulting mixture, in terms of workability during mixing and compaction as well as in service mechanical properties. Asphalt concrete containing 50% RAP was investigated at mixing temperatures of 140, 160 and 180°C, using a multiscale approach. At the microscale, using energy dispersive X-ray spectroscopy the RAP binder film thickness was visualized and measured. It was shown that at higher mixing temperatures this film thickness was reduced. The reduction in film thickness can be attributed to the loss of volatiles as well as the mixing of RAP binder with virgin binder at higher temperatures. X-ray computer tomography was used to characterize statistically the distribution of the RAP and virgin aggregates geometric features: volume, width and shape anisotropy. In addition using X-ray computer tomography, the packing and spatial distribution of the RAP and virgin aggregates was characterized using the nearest neighbour metric. It was shown that mixing temperature may have a positive effect on the spatial distribution of the aggregates but did not affect the packing. The study shows a tendency for the RAP aggregates to be more likely distributed in clusters at lower mixing temperatures. At higher temperatures, they were more homogeneously distributed. This indicates a higher degree of blending both at microscale (binder film) and macroscale (spatial distribution) between RAP and virgin aggregates as a result of increasing mixing temperatures and the ability to quantify this using various imaging techniques.

This recommendation describes how to characterize the reclaimed asphalt through the fragmentation test. The guidelines given hereafter are based on the results of a round robin test organized by the RILEM Technical Committee 237-SIB ‘‘Testing and characterization of sustainable innovative bituminous materials and systems’’ and provide information on the testing procedure, data analysis and indications for the preparation of a test report.

This recommendation proposes an experimental protocol to characterize Recycled Asphalt (RA) materials. The guidelines presented in this document are based on the results of a Round Robin Test (RRT) organized by the RILEM Technical Committee 237-SIB “Testing and characterization of sustainable innovative bituminous materials and systems” and provide information on the testing procedure, data analysis and indications for the preparation of a test report.

Interstitial component (IC), referring to the finer portion of asphalt mixture, is primarily responsible for tensile properties and thereby strongly affects mixture cracking performance. Whereas mixture tests are usually complex and labor-intensive, determination of fracture properties with a simpler test on the IC portion will add values in terms of ranking mixtures and predicting mixture fracture properties. An interstitial component direct tension (ICDT) test, which was derived from the dog bone direct tension test originally developed for asphalt mixtures, was applied to determine the fracture energy density (FED) of mixture IC portion. FED describes the damage tolerance before fracture occurs and it is also a component associated with crack propagation. Two methods of strain determination were evaluated including a digital image correlation (DIC) system and a predictive equation derived from finite element analysis with load-head displacement as input. ICDT tests were conducted on the IC portion of two sets of four mixtures, which had identical coarse aggregate structure. The DIC system yielded greater failure strain than those based on load-head displacement. However, the ratios between the two values for all mixtures were almost constant, supporting the use of the predictive equation as a surrogate. Moreover, IC FED ranked these mixtures in the same order as mixture FED and more importantly, an excellent correlation was observed between IC FED and mixture FED of these mixtures. In conclusion, the ICDT test can be used to determine the IC FED, which provides valuable insights regarding the effect of IC characteristics on mixture FED.

This paper presents the preliminary experimental activity conducted to develop the round robin test (RRT) plan on the use of rejuvenators for the Task Group (TG) 3 on Asphalt Binder for Recycled Asphalt Mixtures as part of the RILEM TC 264-RAP. For this purpose, a reference Reclaimed Asphalt (RA) binder was extracted from a single RA source. This material was then fully characterised with conventional experimental methods and with Fourier Transform Infrared Spectroscopy (FTIR) for evaluating the chemical structure. The RA binder was found to be very hard compared to target binder of PEN50/70 grade and the use of virgin binder cannot restore its properties. In this condition, a rejuvenator dosage of 9% per weight of RA binder is foreseen as optimum value to restore the binder properties close to target PEN50/70 grade for the final binder-rejuvenator blend over a RA content ranging from 60% and 100%.

This recommendation describes how to evaluate the presence of potentially active bitumen in recycled asphalt (RA) materials through the cohesion test. The experimental protocol is designed according to the research performed by the RILEM Technical Committee 237-SIB ‘‘Testing and characterization of sustainable innovative bituminous materials and systems’’ with the purpose, to develop a new, simple and fast method for the characterization of RA while limiting the need for conventional rheological tests. The guidelines in this recommendation focus on the testing procedure including specimen preparation, data analysis and provide information on the preparation of a tests report.

Pavement engineers have in front of them multiple challenges linked to addressing issues related to social development and society’s expanding needs. One of the most substantial of these issues is perhaps how to effectively rehabilitate and/ or maintain the existing road network while preserving and sustaining limited natural resources. The re-usage of existing pavement materials to reconstruct/ rehabilitate our future pavements is the solution that is now more and more selected by the different road administrations around the world. However, upon closer inspection, one can find many areas and details, not negligible issues, that are simply extensions of HMA technology (i.e. mix design process in cold recycling) or empirical arrangements; in particular RAP still does not have an internationally recognized classification. So SIB – TG6 decided to develop a classification protocol of RAP, depending on its intended application. The objective has been followed by considering the procedures generally utilized to classify the natural aggregates: tests able to identify the main components (i.e. the geometrical and mechanical prop- erties of aggregates and the characterization of recovered bitumen for RAP) and provide information on their behaviour under specific conditions, near to real life usage (e.g. the Los Angeles test for aggregates gives an idea of the potential behaviour of aggregates under the action of a roller compactor). The following sections illustrate and explain the actions of the TG in order to achieve the goals outlined above: the review of current standards, the protocol designed to classify RAP and the round robin tests carried out to validate the protocol.

The previous chapters describe numerical models and testing methods designed to simulate, to repeat and to understand the cracking phenomena in asphalt materials and asphalt pavement (or pavements with at least one asphalt layer). This chapter shows some of the most advanced systems to measure the parameters related to cracking. They are classified using a classification grid that considers the most relevant characteristics of the measurement system. The proposed classification method was designed to provide a quick understanding of what data the systems are able to provide and what they can analyze.

A laboratory investigation was conducted to evaluate the effect of active fillers on the cracking resistance of bitumen-stabilised mixtures. Nine types of stabilised mixtures composed by 100% recyc...