Virgin Binder Research Articles

A comparative life-cycle assessment of asphalt mixtures for railway sub-ballast containing alternative materials

Bituminous sub-ballast in railway track-bed can mitigate the variation of the moisture content in the subgrade and reduce vertical stiffness variations of the track leading to a more durable infrastructure. Nevertheless, durability is only one of the aspects that affects the sustainability of an infrastructure. Other relevant aspects are related to the environmental and economic issues. This research work joins the worldwide effort towards a paradigm shift in civil engineering devoted to assess the sustainability of infrastructures at the design stage. With this in mind, in this study different alternative bituminous sub-ballast mixtures containing recycled materials, namely crumb rubber (CR) and reclaimed asphalt pavements (RAP) were compared by means of the results of a Life-Cycle Assessment (LCA). In comparison with a traditional bituminous sub-ballast the Crumb Rubber Modified (CRM) mixtures showed higher impacts due to the treatment of the rubber as well as the higher amount of bitumen employed in the mixture. In turn, when RAP is used, the LCA results report an improvement of all the indicators considered. The reduction of the impacts is even higher when full blending between the aged and the virgin binder is assumed because it allows reducing the amount of virgin bitumen employed. The results are intended to be used by engineering experts and practitioners to make more assertive judgments on the advantages and disadvantages associated with the use of emerging and commonly called sustainable strategies and practices for railway track-bed.

Estimation of Blending of Rap Binder in a Recycled Asphalt Pavement Mix

Many of the recycled asphalt pavement (RAP) mix design methods assume 100% blending of the RAP binder with virgin binder to estimate the properties of the binder in the RAP mix. However, 100% blending is not practically achieved. Thus, it is essential to have procedures for determination of the degree of blending so that the properties of the blend can be estimated more accurately from the properties of RAP and virgin binders. To achieve this objective, a detailed study is conducted to evaluate the level of interaction between RAP and virgin binders. This study considers two proportions of RAP (20 and 35%) and two viscosity grades of virgin binders (VG10 and VG30). The difference in the qualities of the binders in the RAP and virgin aggregate portions is evaluated in terms of different binder properties such as G*/sinδ, penetration, and softening point. The results show that the grade of virgin binder and RAP content in the hot mix asphalt concrete governs the degree of blending achieved. Based on the results of the study, a simple approach is proposed for estimation of the properties of the combined (blended) binder in the recycled mix.

Multi-scale evaluation of the effect of ras on the fracture properties of asphalt mixtures

A comprehensive laboratory testing program was conducted to examine the blending between recycled asphalt shingles (RAS) and virgin asphalt binders and to evaluate the effect of RAS on resistance of asphalt mixes to fatigue and low-temperature cracking. To this end, atomic force microscopy (AFM) was utilized to study the blending between the RAS and the virgin asphalt binders. Manufacturing waste RAS and tear-off RAS were used in this paper. A new sample-preparation procedure was developed to simulate the blending between the RAS and the virgin asphalt binders that occurs during the asphalt mixture production. The stiffness and the adhesive properties were evaluated along the blending zone between the RAS and virgin binders. Several asphalt mixtures were also used to evaluate the effect of the incorporation of RAS on the mix performance, including a control mixture with virgin materials only, and two mixtures containing 5% RAS materials. The resistance of the asphalt mixtures to fatigue cracking was evaluated using the semi-circular bend (SCB) test. In addition the potential for low-temperature cracking was evaluated using the asphalt concrete cracking device (ACCD). The AFM test results showed that very limited to no blending between manufacturing waste or tear-off RAS materials and the virgin binder considered. The asphalt mixture test results also showed that the use of tear-off RAS in asphalt mixes significantly reduced their resistance to low-temperature and fatigue cracking, which can be attributed to the very limited blending observed in the AFM experiments between the RAS and the virgin asphalt binders.

Minimum Virgin Binder Content Needed in Recycled Superpave Mixtures to Resist Fatigue Cracking and Moisture Damage

Use of recycled materials such as recycled asphalt pavement (RAP) and recycled asphalt shingle (RAS) in hot-mix asphalt (HMA) is common now due to their economy and sustainability. However, the effects of RAP and RAS on mixture performance are not fully known. In this research, three recycled Superpave mixture with 9.5 and 19 mm nominal maximum aggregate size (NMAS) were studied as control mixtures. Binder grades in mixtures containing higher percentages of recycled materials (RAP and RAS) were established using a blending chart. Nine laboratory-designed mixtures with different virgin binder contents were evaluated for potential early fatigue cracking using the dynamic modulus and simplified viscoelastic continuum damage direct tension fatigue tests. Moisture susceptibility of the mixtures was evaluated using the Hamburg wheel tracking and modified Lottman tests. Decreased virgin binder content resulted in inferior moisture and rutting performance for 9.5-mm mixtures. Similar fatigue performance was predicted for the mixtures made with the same source of materials regardless of NMAS. In general, mixtures with virgin binder content of 65% of total effective asphalt content and higher showed better performance properties.

Aging effect on rheology and cracking behaviour of reclaimed binder with bio-based rejuvenators

Abstract Reclaimed asphalt pavement (RAP) is stiffer than the virgin material due to aging, thus it is expected to have worse cracking resistance. By adding bio-based rejuvenators, RAP binder mechanical performances at low temperatures improve: fracture toughness temperature of RAP decreases after the addition of rejuvenators to a level similar to the virgin binder. Furthermore, work to fracture of RAP binder increases after the addition of rejuvenators. Addition of rejuvenators to RAP binder can restore both mechanical properties and toughness at low temperature. However, despite the rejuvenators’ addition, physio-chemical oxidation did not reverse as mechanical changes were not caused by chemical changes at functional groups level. Results confirmed how considering the effect of aging is crucial when studying how rejuvenators affect the RAP binder chemically and mechanically.

Application of Low Field Nuclear Magnetic Resonance to evaluate asphalt binder viscosity in recycled mixes

The newly developed method to estimate asphalt viscosity and aging trends using Low Field Nuclear Magnetic Resonance (LF-NMR) was applied to characterize the effect of incorporating recycled materials and recycling agents in asphalt mix samples. The measurements were conducted on asphalt mix samples prepared with different binders: (1) a virgin binder, (2) a recycled binder from Reclaimed Asphalt Pavement (RAP), (3) a blend of virgin and RAP binder (recycled blend) and (4) a rejuvenated blend that consists of the recycled blend with the addition of a recycling agent (tall oil). The LF-NMR measurements were performed at room (25 °C) and magnet (36.4 °C) temperatures. The Relative Hydrogen Index (RHI) obtained from LF-NMR captured the expected binder viscosity trends for the asphalt mix samples prepared with each of the different binders. The viscosity of the binders and blends was estimated from Dynamic Shear Rheometer (DSR) measurements. The relationship between dynamic viscosity and RHI agreed with previous findings. The samples prepared with the rejuvenated blend had lower viscosity and higher RHI than the recycled blend, indicating that the tall oil was effective in lowering its viscosity. Small discrepancies in the trends of the rejuvenated blend as compared to the virgin binder were attributed to their similar detectable hydrogen content, obtained in the rejuvenated blend with the addition of tall oil, but different oxidation state, molecular distribution and steric hindrance. This indicates that the LF-NMR method is more influenced by the chemistry of the asphalt binders rather than their viscosity. The asphalt mix samples with virgin and rejuvenated binders were also subjected to an aging treatment at 70 °C for a month. A significant decrease of the RHI was detected for the samples prepared with rejuvenated binder whereas no significant change was detected for those prepared with virgin binders, which indicates that rejuvenated binders were more susceptible to additional aging that resulted in increased viscosity.

Conditioning and Testing Protocol Combinations to Detect Asphalt Mixture Damage

Asphalt mixes often have many ingredients that can interact with each other. When put into service, where there are multiple environmental effects, there are many interactions that need mixture testing. This paper’s objective was to evaluate laboratory conditioning protocols coupled with subsequent property measurements for their ability to detect damage of asphalt mixtures in the southeastern U.S. climate (or similar climates). The investigation’s focus is the property measurements themselves, and in particular how a given test can simultaneously assess multiple types of damage (i.e. oxidation, moisture damage, and freeze-thaw damage). While in service, mixtures can be damaged in multiple manners so laboratory conditioning protocols that expose specimens to multiple types of damage are needed as are test(s) that can detect these damages in a manner that can help assess performance during service. Four plant produced mixtures with all virgin ingredients were evaluated at intermediate temperatures with mixture and binder tests. The mixtures were well suited for such a comparison because they consisted of all virgin binder. Indirect tensile (IDT) strength did not relate to Cantabro Mass Loss (CML) or binder test results, which was concerning. Even more concerning was IDT’s inability to respond to laboratory conditioning protocols that considered multiple environmental effects (i.e., oxidation, moisture, and freeze-thaw). CML results related to binder properties and were able to reasonably detect multiple types of environmental effects. As such, Cantabro testing is recommended over tensile strength for intermediate temperature mixture property assessments related to non-load associated environmental effects.

Enhanced mortar approach to characterize the effect of reclaimed asphalt pavement on virgin binder true grade

The asphalt community seeks a solvent-free method to determine the properties of RAP binder and those of its blends with virgin binders. A promising approach is to test mortars composed of fine fractions of RAP and a virgin binder, and to calculate grade change rate (GCR) to predict blended binder true grade at any binder replacement rate (BRR). However, the existing mortar approach underestimates the effect of RAP on binder grade, particularly at high temperatures. This study identified the use of a shift factor in the existing method as the source of underestimations. An alternative data analysis method was developed, which eliminates the shift factor by using the relationship between binder and mortar properties. Dynamic shear rheometer tests were conducted on a total of 12 mortar combinations, including 4 virgin binders and 3 RAP sources at a BRR of 15%, and then, RAP GCR values were determined by following both the existing and the alternative methods. Satisfactory comparisons were only observed between grades predicted with the alternative method and measured values of manual RAP binder blends: the average difference was lower than 1 °C for BRR of 15 and 30%, and < 4 °C for BRR of 100%. This not only validated the alternative method but also substantiated that RAP GCR is constant, i.e., the grade of RAP blends linearly increased with BRR. Further evaluation of the enhanced mortar approach is recommended at intermediate and low temperatures as well as with blends including recycled asphalt shingles.

Novel Methodology to Investigate and Obtain a Complete Blend between RAP and Virgin Materials

Pavement engineers are continually attempting to resolve the problems associated with the disposal of highway construction materials and conserve the natural resources in line with producing a more economically and environmentally friendly asphalt mixture. This study presents a novel methodology to investigate and obtain a complete blending in the laboratory using a nanomechanical approach so that designers can be more confident in estimating the performance of asphalt mixtures incorporating reclaimed asphalt pavement (RAP) materials. The study also presents an effect of warm additives, Sasobit and Rediset LQ, on the level of blending between RAP and virgin materials. Images obtained from nanoindentation were validated using a scanning electron microscope (SEM), while the level of blending was linked to the overall fatigue cracking of asphalt mixtures, which was measured using dynamic shear rheometer (DSR). It was revealed that although Rediset LQ improved the fatigue life and nanomechanical properties of the virgin interfacial transition zone (ITZ) and mastic phases, it has no effect on the diffusion of virgin binder into aged binder (binder surrounding RAP aggregate) or rejuvenating of aged binder, whereas Sasobit decreased the viscosity of binder and has a great influence in accelerating complete blending between RAP and virgin materials. In summary, nanoindentation integrated with an optical microscopy is a powerful technique to investigate and obtain complete blending between RAP and virgin materials.

Viscoelastic properties of recycled asphalt binder containing waste engine oil

Abstract This study elaborates on the effect of addition of waste engine oil on the viscoelastic properties of asphalt blends containing aged binder and virgin binder. Several asphalt blends were prepared using varying percentages of waste engine oil, virgin binder, and aged binder. These blends were tested for its engineering, and viscoelastic properties. It was observed that the addition of waste engine oil decreased the viscosity (at given temperature), and softening point values when compared to control blend (containing virgin and aged binder only). Among all waste engine oil modified blends, addition of waste engine oil resulted in corresponding decrease in complex modulus values at all frequencies. Further, addition of waste engine oil led to increase in phase angle values at any given frequency. Comparison of curves in black space indicated significant changes with short-term aged blends when compared to corresponding unaged blends. Among all blends, at any given time, lower relaxation modulus was obtained with increase in waste engine oil content. However, this decrease was not significant beyond addition of 6% waste engine oil. Broadly it was observed that the addition of 2–4% of waste engine oil negates the effects caused by addition of aged binder. This indicates that waste engine oil can act as a rejuvenator while providing elasticity and flexibility to asphalt binder.

Comparison of asphalt mixture specimen fabrication methods and binder tests for cracking evaluation of field mixtures

One of the most influential variables in determining the performance-based properties of the asphalt mixtures is the specimen fabrication method. This study investigates the impact of specimen fabrication methods through a comprehensive study of six test sections constructed in 2011that include a range of RAP contents and two different virgin binders. Complex modulus and fatigue characterisation was conducted on asphalt binders and mixtures. Three specimen fabrication methods were evaluated: specimens compacted from plant sampled loose mix with and without reheating, and specimens fabricated from raw materials in the laboratory. Predicted performance from lab tests were compared to field performance. The mixtures with PG 58-28 binder showed expected trends with increasing RAP content (higher modulus, lower phase angle); however, mixes with PG 52-34 did not. Similar trends were observed for specimens fabricated with plant mix (not reheated), and the specimens fabricated with raw materials in the lab. Binder results and performance prediction using the plant mix agree with the observations in the field.

Toward Utilization of ground tire rubber and reclaimed pavement materials with asphalt Binder: Performance evaluation using essential work of fracture

Utilization of ground tire rubber (GTR) binder in combination with reclaimed asphalt pavements (RAP) binder can provide added benefits in terms of material, cost and environmental saving, and hence a promising step toward sustainable construction of pavements. The present study utilized essential work of fracture (EWF) principal to evaluate performance of a GTR binder blended with two different types of RAPs: RAP-A and RAP-S, having different rheological properties. The GTR binder was mixed with different percentages (0%, 15%, 25% and 40% by weight of virgin binder) of RAP-A and RAP-S. First, Superpave performance grade (PG) of different combinations of asphalt binders was determined in the laboratory. Thereafter, the EWF of binders was determined using a newly developed double edge notch tension (DENT) test. Further, the data obtained from the DENT test were used to estimate critical crack tip opening displacement (CTOD). The results showed that addition of RAP decreased fracture resistance of GTR binder. Addition of RAP-A resulted in a faster decrease in performance of GTR binder compared to RAP-S. It can be concluded that low percentage of RAP may be utilized with GTR binder. Further, analyses indicated that RAP sources and its quantity could have significant impact on performance of asphalt mixes.

Physical and rheological properties of nano zinc oxide modified asphalt binder

The main objectives of this work were to investigate the physical and rheological properties of nano zinc oxide (NaZO) flake structure as a modifier in asphalt binder. NaZO was produced with hydrothermal method by using two precursors, which are zinc nitrate and sodium hydroxide. NaZO was mixed with virgin binder 60/70 penetration grade at 3%, 5% and 7% of asphalt binder weight, respectively. The physical properties were evaluated by conventional testing, such as penetration, softening point and viscosity. Meanwhile, the rheological property, such as rutting resistance, was measured by using a dynamic shear rheometer (DSR) for unaged and rolling thin film oven (RTFO) aged. It was observed that the penetration value was decreased and the softening point increased with increasing NaZO concentrations. In addition, the rutting resistance factor was increased for the modified binder. A comparison between the modified binder, 7% NaZO, showed a greater resistance to rutting before and after aging. Results of this study showed that the NaZO addition had increased the asphalt binder stiffness ; thus, could contribute to better resistance to permanent deformation.

Investigation of reclaimed asphalt pavement blending efficiency based on micro-mechanical properties of layered asphalt binders

The challenge in mix design and application of reclaimed hot mix asphalt (HMA) lies in the unknown blending efficiency between reclaimed asphalt pavement (RAP) binder and virgin binder. By using a combination of staged extraction method and Atomic Force Microscopy (AFM) imaging technique, this paper focused on the investigation of interaction and extent of blending between RAP-virgin binders under different mixing temperature and residence time, based on the micro-mechanical properties of layered binders in real reclaimed HMA. In addition, the impact of chemical solvent used in staged extraction, i.e. Trichloroethylene (TCE), on the AFM images of extracted asphalt binder was also explored. It was found that the topographic features of asphalt binder in terms of “bees” structure were obviously altered by TCE, which were not suitable for analysis on RAP blending. A possible blending scenario, indicating non-homogenous blending between RAP-virgin binders in the layered binder system, was put forward for the mixing stage of reclaimed HMA, in which increased DMT modulus and decreased adhesion force and energy dissipation were observed from the outermost towards to the innermost layers. Both mixing temperature and residence time have significant effects on the blending efficiency between RAP-virgin binders. With the decrease of mixing temperature, diffusion of the virgin binder into RAP binder is impaired, thus leading to less blending efficiency between the two binders. Besides the mixing process, the blending between RAP-virgin binders continues with the passing residence time, until a complete and homogeneous blending being reached after sufficiently long time.

Blending efficiency evaluation of plant asphalt mixtures using fluorescence microscopy

With the use of high percentage recycled asphalt pavement (RAP), there is an increasing concern over how much of the aged binder in RAP that can be blended into virgin binder. In this study, a laboratory procedure was proposed based on fluorescence microscopy for quantifying the mobilization rate of aged binder in plant-produced RAP mixtures. This procedure was derived from the mean gray value of an asphalt-coated aggregate particle. A linear blending chart was developed and used to relate aged binder content to the mean gray value of binder blend. The mobilization rate of aged binder was calculated on the basis of surface area proportion of aggregates with different size. Three types of asphalt mixtures, including one warm mix with foaming technology, two hot mixes with or without rejuvenator, were used to validate the proposed method. Results indicated that the mobilization rate varied by aggregate type (virgin or RAP). Compared with hot mix, warm mix with foaming technology showed a slightly higher mobilization rate.

Performance evaluation of plant-produced warm mix asphalts containing RAP and RAS

In the present study, rutting performance, cracking resistance, and durability of five plant-produced asphalt mixes containing 12% reclaimed asphalt pavement (RAP) and 3% recycled asphalt shingles (RAS) and produced with different warm mix asphalt (WMA) technologies were evaluated through characterisation of extracted asphalt binder and performance tests conducted on asphalt mix specimens. For all of the extracted and recovered asphalt binders, continuous grades and difference between critical low temperatures, ΔTcr parameter, were determined from performance grading and a Glover–Rowe (G–R) damage zone was evaluated at 45°C and 10 rad/s. It was revealed that the application of a rejuvenating agent (RA) significantly reduced high PG grade of the overall asphalt binder. The binder test results also indicated that the chemical-additive-based WMA technology had an advantage over the foaming-based technology in terms of asphalt binder durability. Furthermore, the application of RA improved the asphalt binder durability. Comparison of G–R parameters of the recovered asphalt binders showed that using RA and lowering virgin binder high PG true grade improve the overall binder ductility and damage resistance. Asphalt mix performance tests included dynamic modulus (DM), flow number, and semi-circular bend. The DM test data indicated that the application of RA and lowering the virgin binder high PG grade lowered the mix stiffness at low frequencies. Comparison of the methods to compensate the effect of highly aged RAP and RAS binders indicated that the mix prepared with RA and one level high PG grade drop performed better than the mix prepared by dropping the PG grade by two levels in terms of cracking resistance and rutting performance. The findings give credence to utilisation of RAs and softer virgin binders in balanced RAP/RAS mix design approaches.

Application of intermediate temperature semi-circular bending test results to design mixtures with improved load-associated cracking resistance

This paper describes the development and practical application of regression equations to estimate the relative load-associated cracking resistance of asphalt mixtures from properties that are included in specifications and controlled through current quality control and acceptance procedures. This work was part of a research study performed through the Wisconsin Highway Research Program to evaluate changes to the composition of asphalt concrete mixtures that should be considered to improve the durability of flexible pavements. Based on the findings of a synthesis of current research, a laboratory experiment was conducted to quantify the effect of (1) effective binder volume, (2) virgin binder low temperature performance grade, (3) recycled binder content, and (4) polymer modification on the resistance of typical Wisconsin mixtures to ageing and load-associated cracking. For the types of mixtures normally used in Wisconsin, the laboratory experiment found mixture composition had little effect on ageing; however, load-associated cracking resistance was significantly affected. The laboratory experiment produced a regression equation that was used to recommend revised volumetric criteria that provide equivalent load-associated cracking resistance and allow producers the flexibility to design mixtures using a range of effective binder contents, recycled binder contents, and virgin binders.

Development of a new methodology to effectively predict the fracture properties of RAP mixtures

The existing design method for reclaimed asphalt pavement (RAP) mixtures assumes virgin and RAP binders fully blend. However, full blending may not occur and the impact of partial blending on mixture cracking performance is still unclear. A previous study revealed that RAP gradation, which is not currently considered from the standpoint of binder blending, controls the distribution of RAP binder within a mixture and consequently affects cracking performance. The objective of this study was to develop a methodology that overcomes the uncertainty of blending and effectively predicts fracture properties of RAP mixtures. This methodology is based on the evaluation of the interstitial component (IC) of a mixture (i.e. the fine portion that governs cracking performance) by means of a direct tension test named interstitial component direct tension (ICDT) test. Two RAP sources and four RAP contents were considered. ICDT specimens were produced by blending the fine portion of RAP and virgin aggregate with virgin binder in the same way and corresponding proportions as in RAP mixtures. Binder and mixture fracture properties from the previous study were used for comparison. Mixture and IC exhibited almost similar reduction in fracture energy density with increasing RAP content, whereas fully blended binder exhibited a less pronounced reduction. This indicated that IC better simulated the actual blending that occurred in mixtures. Mixtures with coarsely graded RAP (less RAP content in the IC) exhibited better fracture properties; thus, the key to satisfactory cracking performance appeared to be minimising the amount of RAP in IC. Consequently, the stiffening effect of RAP on the fine portion that controls cracking performance should be directly evaluated, instead of placing focus on the fully blended binder or the whole mixture. The ICDT test was proven to be a valuable tool to predict fracture properties of RAP mixtures.

Evaluation of recycling agent dosage selection and incorporation methods for asphalt mixtures with high RAP and RAS contents

Economic and environmental demands motivate transportation agencies to increase the amount of reclaimed asphalt pavement (RAP) and recycled asphalt shingles (RAS) used in asphalt pavements. These pavements often require a recycling agent to reduce the likelihood of premature cracking. Estimating an optimum recycling agent dosage is critical to maximize its benefit. In this study, three recycling agent dosage selection methods based on the restoration of the performance grade (PG) of the recycled blend (virgin binder, recycled binder, and recycling agent) were explored. Based on the performance of the recycled blends, the method to restore high-temperature PG is recommended to determine the optimum recycling agent dosage.

Molecular dynamics study of rejuvenator effect on RAP binder: Diffusion behavior and molecular structure

This study developed molecular dynamics (MD) models to study the rejuvenator diffusion behavior and its impact on molecular structures and thermodynamic properties of asphalt binder in Reclaimed Asphalt Pavement (RAP). A two layered model was developed to study the inter-diffusion process between rejuvenator and RAP binder. Results show that the inter-diffusion process can be described by Fickian equation. Molecular Dynamics (MD) simulations yield reasonable diffusion coefficient which is comparable to experimental result. A mixture model was prepared to investigate the effect of rejuvenator on molecular interactions of saturate, aromatic, resin, and asphaltene (SARA) fractions in RAP binder. Thermodynamic properties including density, surface energy, and cohesive energy density of RAP binder were studied. It was found that oxidative aging changed both thermodynamic properties of RAP binder, and adding rejuvenator could restore thermodynamic properties to those of virgin binder to a certain extent. The visualization of molecule-molecule radial distribution functions (RDFs) suggests that rejuvenator increases the self-association of asphaltene in RAP binder. The study findings directly contribute to better understand the rejuvenator diffusion behavior which is difficult to observe from laboratory experiments. The developed MD models serve as benchmark for further study of rejuvenation using computational experiments.