The Impact of Asphalt Blended with Re-refined Vacuum Tower

The Impact of Asphalt Blended with Re-refined Vacuum Tower Bottoms (RVTB) and Its Effect on HMA Mixture Performance

Jason C. Wielinski Asphalt Research Engineer

Anthony J. Kriech

Director of Research

Gerald A. Huber Associate Director of Research

Andreas Horton

Asphalt Research Engineer

Linda V. Osborn Senior Project Chemist

Heritage Research Group

Indianapolis, Indiana

Acknowledgements

The Authors would like to acknowledge the contributions of William Gorman, Erin Clark, Brittani Burton, Michael Brinton and Zachary Robinson of HRG, as well as William Pine of Milestone Contractors and Jeff Kern of Open Roads Paving.

© Copyright Canadian Technical Asphalt Association 2014

402 ASPHALTS WITH RVTB AND ITS EFFECT ON HMA PERFORMANCE

ABSTRACT

In the past few years, there has been increased interest in the properties of asphalt binders containing Re-refined Vacuum Tower Bottoms (RVTB), the non-distillable fraction from the re-refining of used engine oils, on Hot Mix Asphalt (HMA) performance. Recently published research has provided conflicting results. This study will provide additional information regarding the viability, compatibility and integrity of RVTB in asphalt binders and mixtures.

One source of RVTB was blended with PG 64-22 to achieve binder grade of PG 58-28. A second PG 58-28 was formulated without RVTB for comparison. The asphalt binders were analysed for Superpave™ PG binder testing, X-Ray Fluorescence (XRF), Polycyclic Aromatic Compound (PAC) content, Gel Permeation Chromatography (GPC) and Thermo-Gravimetric Analysis (TGA). The binder testing provides a comparison of the effects of blending RVTB on binder grading, chemical composition, environmental impact, and compatibility of RVTB and asphalt.

The second portion of the study compares mixture performance of HMA prepared with neat PG 58-28 and PG 58-28 containing RVTB. Analysis includes volumetric analysis, resistance to moisture damage, resistance to rutting, mixture stiffness and leachate testing on the mixtures according to Environmental Protection Agency (EPA) methods.

RÉSUMÉ

Au cours des dernières années, il y a eu un intérêt accru pour les propriétés des bitumes contenant des résidus de distillation sous vide du procédé de ré-raffinage des huiles à moteur usées [RVTB] et leur effet sur la performance des enrobés. Des études publiées récemment ont donné des résultats contradictoires. Cette étude fournira des informations supplémentaires en ce qui concerne la viabilité, la compatibilité et l'intégrité des RVTB dans les bitumes routiers et leurs enrobés.

Une source de RVTB a été mélangée avec PG64-22 pour obtenir un bitume PG58-28. Pour fin de comparaison, un deuxième PG58-28 a été formulée sans RVTB. Les bitumes ont été analysés selon les essais Superpave ™, par fluorescence Rayon ’’X’’ (XRF), pour leur contenu en composés aromatiques polycycliques, par chromatographie par perméation de gel (GPC) et par analyse thermogravimétriques (TGA). Cette méthode d’analyse sur les bitumes présente une comparaison des effets de l’ajout du RVTB sur le grade du bitume, la composition chimique, l’impact sur l'environnement, et la compatibilité entre le RVTB et le bitume.

La deuxième partie de l'étude compare la performance des enrobés à chaud préparés avec un PG58-28 régulier et un PG58-28 contenant du RVTB. L'analyse comprend l'analyse volumétrique, la résistance à la dégradation par l'eau, la résistance à l'orniérage, la rigidité et la lixiviation des enrobés selon les méthodes de l'EPA.


WIELINSKI, KRIECH, HUBER, HORTON & OSBORN 403

1.0 INTRODUCTION

Re-refined Vacuum Tower Bottoms (RVTB) are the non-distillable fraction from the re-refining of used engine oils. RVTB have been blended with paving grade binders to improve the low temperature properties for over 20 years. In the past few years, there has been increased interest in the properties of asphalt binders containing RVTB and the effect on Hot Mix Asphalt (HMA) performance. Recent research has been done related to the chemical integrity, binder performance, and in turn HMA mixture performance with such asphalt binders. Published research has provided conflicting results. Some research shows that RVTB have an adverse effect on the long-term aging properties of the asphalt and in turn the cracking resistance of in-service HMA pavements. Other research shows that, if added at proper dosages, RVTB blended asphalt has equivalent or better HMA mixture performance than HMA with neat asphalts of similar stiffness. This study will provide additional information regarding the viability, compatibility, and integrity of RVTB in HMA asphalt and mixtures.

In this study, one source of RVTB was blended with a neat PG 64-22 resulting in a Superpave™ binder grade of PG 58-28. Binder analysis performed on the three binders (PG 64-22, PG 58-28 and PG 58-28 with RVTB) used in this study included: Superpave PG binder testing, X-Ray Fluorescence (XRF), Polycyclic Aromatic Compound (PAC) content, Gel Permeation Chromatography (GPC) and Thermo-Gravimetric Analysis (TGA). This thorough set of binder testing will provide a before and after comparison of the neat PG 64-22 binder and the effects of blending RVTB on binder grading, chemical composition, environmental impact, and compatibility with neat asphalt. The PG 58-28 containing RVTB was then compared to a neat PG 58-28 for chemical compatibility and performance properties.

The second portion of the study compared mixture performance of HMA prepared with the neat PG 58-28 and the PG 58-28 containing RVTB. HMA mixture analysis included volumetric analysis to determine the effect of RVTB on the Voids in the Mineral Aggregate (VMA), air voids or required asphalt content. Resistance to moisture damage was quantified through comparison of Tensile Strength Ratio (TSR) data. Engineering properties including resistance to rutting and mixture stiffness were also analyzed. Data from Hamburg wheel testing, dynamic modulus testing, and flow number testing is presented to show comparison of mixtures with and without the RVTB in the asphalt binder. Finally, the mixtures were evaluated for leachate characteristics using Environmental Protection Agency (EPA) methods.

2.0 BACKGROUND

RVTB are the heavy distillation bottoms (non-distillable fraction) from the re-refining of used engine oils. Used oils are collected and screened for re-refining suitability. In the first processing step, the oil is dehydrated to remove water and any light volatiles that are recovered. The second step involves vacuum distillation to separate the lighter portion, or lube cut, of the recycled stream from the heavy oils, which are referred to as RVTB. The final step of re-refining is to fractionate remaining lube cut into different grades.

Blending RVTB with an asphalt binder to improve the low temperature properties is a practice that has been used in many parts of the Midwestern United States as well as parts of Canada including Ontario. The Federal Highway Administration (FHWA) Turner Fairbank laboratory has recently tested more than 1000 asphalt samples from various parts of the U.S. and found approximately 20 percent of the samples contain RVTB [1]. Some State Departments of Transportation (DOTs) have expressed concern about HMA performance based on recent published research that suggests RVTB have an adverse effect on


404 ASPHALTS WITH RVTB AND THEIR EFFECT ON HMA PERFORMANCE

pavement performance. Publications have been primary from two authors: Simon Hesp [2, 3 and 6] and John D’Angelo [4, 5]. Their findings are summarized in the following paragraphs.

In 2010, Hesp and Shurvell [2] published a study investigating a method to detect waste engine oil residue using XRF and the effect of RVTB on cracking of pavements in service. XRF results indicated that zinc and other heavy metals could be detected in binders blended with waste engine oil residue. Using this approach they analyzed asphalt binders from in-service pavements and determined whether RVTB were present or not. The authors had evaluated the effect of RVTB on physical hardening and loss of strain tolerance for laboratory-aged asphalt binders and concluded that RVTB would cause increased cracking. For in-service pavements that tested positive to the presence of zinc the authors concluded that observed premature and excessive cracking failures in Ontario pavements were related to the presence of RVTB. Their conclusions were based on visual distress surveys of 15 poorly performing (cracked) pavements that showed levels of zinc in the recovered asphalt from XRF. They also found that of the eleven good performing projects included in the study, none had contained zinc.

In 2011, Hesp and et al [3] published a study on the effects of waste engine oil on asphalt cement quality. The primary objective of the study was to investigate how engine oil residue affects the oxidative hardening of a single source of asphalt cement. A secondary objective was to determine if and how the current Rolling Thin Film Oven (RTFO) and Pressure Aging Vessel (PAV) protocols can be improved to better capture effects of asphalt durability, ultimately developing improved asphalt cement aging and specification test methods.

In the outline of the research, the authors state that Engine Oil Residues (EOR) have high ash contents from high concentrations of metals in the residue and state the EOR are high in saturated paraffin oil and degraded polymeric dispersants typically found in engine oil. The authors suggest that EOR increases oxidization in asphalts due to the presence of metal catalysts and oxidized engine components. They state that higher oxidation rates lead to more rapid gelation increasing restraining stress during winter which causes premature fatigue and thermal cracking [3].

In the 2012 CTAA Proceedings, D’Angelo et al [4] published a study that provided an in-depth evaluation to determine the performance characteristics of binders blended with different levels of Re-refined Heavy Vacuum Distillation Oil (RHVDO), which in this document is referred as RVTB. The RVTB were analyzed for chemical analysis using Iatroscan and component metals determination. Multiple asphalt sources were blended with varying percentages of RVTB. The blends of asphalt and RVTB were tested for Superpave binder grade determination, Multiple Stress Creep and Recovery (MSCR), extended PAV and separation testing.

The chemical analysis showed that the RVTB is approximately half polar aromatics and half saturates. The authors stated that saturates from the RVTB help disperse the asphaltenes reducing associations of the asphaltenes that cause embrittlement. In the metals analysis, the authors found higher than normal levels of calcium, phosphorus, zinc, sodium and iron based on Induced Coupled Plasma (ICP) testing. Also, the RVTB contained no greater than 0.32 percent wax, which as the authors stated, cause physical hardening of asphalt binders [4].

D’Angelo et al [4] found that addition of RVTB reduces the high, intermediate and low temperatures properties of the asphalt binder and is dependent on RVTB and base asphalt source. One major observation made by the authors was that RVTB addition rates of 20 percent did not change the overall aging rate of the binders based on PAV-treated binders. Increased PAV aging from 20 to 35 hours did not



increase the growth rate of asphaltenes and aging. The authors also found that no appreciable separation of RVTB and asphalt resulting in a stable material.

In 2013, D’Angelo et al [5] followed up the 2012 study with an in-depth analysis of HMA mixes blended with RVTB at varying levels. Mix designs meeting IDOT specifications for 90 gyrations and 70 gyrations were done using 100 percent virgin aggregates and evaluated for rutting resistance, resistance to moisture damage, fatigue resistance and low temperature properties. Major findings of this research included that mixes produced with RVTB blended binders performed as well or better than the control mixes of similar binder stiffness. Stripping potential of mixes with up to 6 percent RVTB was not indicated through TSR testing. Fatigue and low temperature properties of mixes with RVTB were equal to, or better than, the performance of the control mixtures. This leads to the conclusion that binders blended with RVTB should provide good field performance.

In 2014, Hesp and Johnson [6] presented a study investigating the effect of Waste Engine Oil (WEO) residues on the quality and durability of Strategic Highway Research Program (SHRP) Material Reference Library (MRL) binders. In that study, the authors explored the hardening tendencies from WEO modification for a sample of asphalt from the SHRP MRL. All binders were mixed with 15 percent WEO. Similar to the study published in 2011, the authors tested the MRL binders under typical AASHTO M320 grading as well as extended PAV and extended BBR protocols discussed in prior works. Their study compared the loss of phase angle from original to PAV-aged binders for neat binders and binders blended with WEO. Binders were subjected to both PAV ageing and advanced PAV ageing. They found that binders containing WEO show a greater loss in phase angle. No binder grades or Dynamic Shear Rheometer (DSR) values were reported after RTFO, PAV and extended PAV aging. Grade loss was reported on the set of binders after extended PAV aging with variable results (Figure 9 of [6]). Ultimately Johnson and Hesp concluded again that WEO modification causes formation of gel type binders when base asphalts with high asphaltenes are used. These binders are then concluded to result in early failures due to excessive physical and chemical hardening.

Ultimately over the past half-decade, the collection of studies presented conflict widely with one another. D’Angelo’s work in 2011 contradicts the work of Hesp in 2011 showing that paraffin waxes are not necessarily in RVTB based in his analysis. He also suggests that if Hesp et al had based their carbonyl content on increased carbonyl content rather total carbonyl content, the results would show that RVTB blended binders have the same aging rate and neat binders [4]. Hesp contradicts D’Angelo’s work in his 2014 study suggesting that some claims D’Angelo made regarding the components of the RVTB (half saturates and half polar aromatics) is untrue and suggest they are better classified as half saturates and half polar saturates rather than aromatics [6]. Hesp in his collection of work does not include HMA mixture testing as part of his analysis; his studies are predominantly based on binder testing alone as well as field observations of roads with and without distress. The population sample of these roads and, more importantly, details of their construction, mix properties, mix volumetrics and construction conditions are never reported. It is critical that this practice of using RVTB is thoroughly investigated from all angles including chemical, binder and mixture performance in the laboratory as well as in controlled field trials.

3.0 RESEARCH OBJECTIVES

The objective of this research was twofold. The first objective of the research was to perform a chemical analysis of a neat asphalt and an asphalt with similar stiffness and binder grade blended with RVTB. The base asphalt blended with the RVTB was also studied. The analysis encompassed the chemical



composition of the studied binders to determine RVTB indicators, polycyclic aromatic compound content, molecular weight and thermogravemetric analysis.

The second objective of the research plan was to develop an IDOT approved mix design with a neat PG 58-28 and a PG 58-28 with RVTB and to determine if there are any significant differences in HMA performance. The mix was developed to meet all volumetric requirements including air voids and VMA. HMA mixture performance testing of particular importance to IDOT is TSR and rutting resistance as measured by the Hamburg Wheel Tracking (HWT) test. In addition to these tests, dynamic modulus and flow number were also performed and analyzed to compare mixes.

4.0 EXPERIMENTAL PLAN

4.1 Overview

The first portion of the experimental plan was to compare asphalt binders manufactured with and without RVTB. Both binders were sampled from an asphalt manufacturing facility in the Midwest U.S. A neat PG 58-28 binder without any RVTB was identified as the control. It comprised of a blend of 20 percent PG 64-22 and 80 percent of a PG 52-28 neat asphalt. The PG 58-28 containing RVTB used the same PG 64-22 asphalt binder blended with 9 percent RVTB. The PG 64-22 was also analyzed. All three asphalt binders were tested to determine its chemical composition, percentage of Poly-Aromatic Compounds (PAC) and thermal decomposition.

The second portion of the experimental plan focuses on the HMA engineering properties using the two PG 58-28 binders with and without RVTB. The first step was to design a mixture containing each of the PG 58-28 binders meeting IDOT specifications. The design was selected to best represent a mix typically used for IDOT work, therefore a mix design with RAP was chosen. The amount of RAP included and in turn binder replacement ratio was selected to require a change in grade from a PG 64-22 to a PG 58-28. The maximum binder replacement permitted in IDOT mixes before requiring a change in asphalt grade is 20 percent.

Once the job mix formulas of the respective PG 58-28 mixes were designed, performance testing could be completed. Performance testing of importance to IDOT includes TSR and HWT. In addition to these tests, dynamic modulus and flow number were completed to quantify any difference between mixes in terms of stiffness and rutting potential. Figure 1 is a flowchart of the experimental plan.

4.2 Testing Procedures

4.2.1 X-Ray Fluorescence Testing (XRF)

XRF testing was conducted in order to obtain elemental and chemical analysis of the studied binders. Asphalt binder samples were run on a Thermo Advant’X WDXRF equipped with a 4.2 kW Rh tube under helium atmosphere with 4 micron prolene support film. Data is processed through Thermo Uniquant™ using the integrated fundamental parameters calculations. The advantage of this instrument is that it is a Wavelength Dispersive instrument so it can determine a broader range of metals with improved sensitivity.



Note: GPC is Gel Permeation Chromatography, HMA is Hot Mix Asphalt, PAC is Polycyclic Aromatic Compounds, PG is Performance Grade, RAP is Reclaimed Asphalt Pavement, RVTB is Re-refined Vacuum Tower Bottoms, TGA is Thermo-Gravimetric Analysis, TSR is Tensile Strength Ratio, and XRF is X-Ray Flourescence.

Figure 1. Experimental Plan of Re-refined Vacuum Tower Bottoms (RVTB) in Asphalt Cement and Hot Mix Asphalt (HMA) Study

4.2.2 Polycyclic Aromatic Compound (PAC) Testing

The purpose of testing the PAC content of the neat and RVTB treated binders was to determine if the introduction of RVTB in the asphalt binder increases the levels of PACs in the blended binder. PACs are related to environmental and health concerns.

Experimental Plan

Binder Chemical Analysis

PG 58‐28 Neat

XRF

PACs

TGA

GPC

PG Binder Grade

PG 58-28 RVTB

XRF

PACs

TGA

GPC

PG Binder Grade

PG 64-22 Neat

XRF

PACs

TGA

GPC

PG Binder Grade

HMA Mix Analysis

Design IDOT N70 w/ RAP PG

58-28 Neat

TSR

Hamburg Wheel

Dynamic Modulus

Flow Number

Leachate Testing

Design IDOT N70 w/ RAP PG

58-28 RVTB

TSR

Hamburg Wheel

Dynamic Modulus

Flow Number

Leachate Testing



4.2.3 Extraction of Polycyclic Aromatic Compounds from Asphalt

A liquid-liquid micro-extraction, based on modifications of British Standards Method BS 2000-346 was employed to extract PACs from three asphalt samples. Approximately 0.50 g of asphalt was weighed into a glass vial, and then transferred using 10 mL MeCl2 into a 100 mL volumetric flask. After transfer, the flask was filled to 100 mL with hexane and mixed with ultra-sonication for twenty minutes. After centrifuging to precipitate asphaltenes, the maltenes remained. An aliquot of hexane was triple extracted with Di-Methyl Sulfoxide (DMSO) to extract the PACs (aliphatics are retained in the hexane fraction). DMSO extracts were combined, and then 4 percent NaCl water added. Iso-octane was added to this mixture, and then triplicate extracted the PACs back to iso-octane. Iso-octane was then cleaned with 70°C 4 percent NaCl water to remove trace DMSO (twice), and then passed through Na2SO4 column to dry. This dried extract was then concentrated to meet detection limit needs and brought to a final effective volume of 10 mL.

4.2.4 Analysis of Polycyclic Aromatic Compounds

Forty PACs, shown in Table 1 were determined using gas chromatography/time-of-flight mass spectrometry (GC/TOFMS) following the guidelines of EPA SW-846 8270C [7] and a published procedure by Kriech et al. [8].

Table 1. List of the 40 Polycyclic Aromatic Compounds (PACs) Determined in Air Samples using Gas Chromatography/Time-of-Flight Mass Spectrometry

Benzene Rings

Polycyclic Aromatic Compound

Benzene Rings

Polycyclic Aromatic Compound

1 1+ Benzothiophene 21 4 1-Nitropyrene 2 2 Naphthalene 22 4+ Cyclopenta[cd]pyrene 3 2+ Acenaphthene 23 4+ Benzo[b]fluoranthene 4 2+ Acenaphthylene 24 4+ Benzo[j]fluoranthene 5 2+ Benz[a]acridine 25 4+ Benzo[k]fluoranthene 6 2+ Benz[c]acridine 26 4+ 7H-Dibenzo[c,g]carbazole 7 2+ Carbazole 27 4+ 3-Methylcholanthrene 8 2+ Dibenzothiophene 28 5 Benzo[a]pyrene 9 2+ Fluorene 29 5 Benzo[e]pyrene 10 3 Anthracene 30 5 Dibenz[a,h]anthracene 11 3 Phenanthrene 31 5 Dibenz[a,h]acridine 12 3+ Benzo[b]naphtho[2,1-d]thiophene 32 5 Dibenz[a,j]acridine 13 3+ Fluoranthene 33 5 Dibenz[c,h]acridine 14 3+ Benzo[b]naphtho[2,3-d]thiophene 34 5+ Dibenzo[a,e]fluoranthene 15 4 Benz[a]anthracene 35 5+ Indeno[1,2,3-cd]pyrene 16 4 5-Methylchrysene 36 6 Benzo[ghi]perylene 17 4 Chrysene 37 6 Dibenzo[a,e]pyrene 18 4 Pyrene 38 6 Benzo[rst]pentaphene 19 4 7,12-Dimethylbenz[a]anthracene 39 6 Dibenzo[a,h]pyrene 20 4 Triphenylene 40 6 Dibenzo[a,l]pyrene



4.2.5 Gel Permeation Chromatography (GPC)

GPC is a type of analysis in which molecules in solution are separated by their size or molecular weight. Including this test in the analysis would provide information whether a significant change in apparent molecular weight is observed between the neat and RVTB blended PG 58-28 binders, as well as the base PG 64-22. The three asphalts were tested in original, RTFO and PAV-aged conditions to evaluate the effect of aging on molecular weight. GPC conditions used were two 300X7.5 mm Resi-Pore 3µ columns purchased from Agilent. Tetrahydrofuran was used as the carrier solvent at 30°C, with an injection loop of 100 µl. Both a refractometer and differential viscometer were used as detectors and were calibrated with a 91,800 Dalton polystyrene standard. The molecular weights were calibrated using twelve narrow Mw polystyrene standards from 162 to 91,800 Daltons. 4.2.6 Thermogravimetric Analysis (TGA)

TGA is an analysis method in which changes in mass of the studied asphalt binders are measured as a function of increasing temperature. TGA analysis was performed using a TA Instruments Q500 model.

4.2.7 Asphalt Binder Testing

The asphalt binders were tested for complete AASHTO M320 binder grade characterization.

4.2.8 Tensile Strength Ratio (TSR)

TSR is a test that has been used for many years to determine moisture susceptibility. The test used in this study was the Illinois modified procedure. The Illinois Modified TSR procedure is similar to AASHTO T283. The main differences include that the freeze thaw cycle is not required and the minimum passing TSR ratio for acceptance is 0.85.

4.2.9 Hamburg Wheel Track (HWT) Testing

HWT testing was performed according to the Illinois Modified Test Procedure for HWT, which is slightly modified from AASHTO T 324. The HWT test is performed on submerged samples at 50±1°C. The minimum number of wheel passes at the rut depth criteria of 12.5 mm is 7,500 for a PG 64-22 HMA mixture. The criteria for the IDOT test method also states that if one or both of the ruts depths exceed 12.5 mm after the required number of passes, the mix fails. Testing was completed with a PMW Wheeltracker.

4.2.10 Dynamic Modulus

The dynamic modulus test measures the stiffness of an asphalt mixture over a range of testing frequencies and temperatures. Dynamic modulus testing of the two HMA mixtures was completed according to AASHTO T342 using an IPC Global Simple Performance Tester (SPT) device. In this test, a haversine axial compressive stress is applied to a specimen of HMA at a given temperature and frequency and the stress response of the specimen is measured. The response is used to calculate the dynamic modulus and phase angle of the specimen. The dynamic modulus data is an input used in DarwinME for characterization of HMA for use in pavement thickness design. Test temperatures used in this study were 4, 30 and 40°C.



4.2.11 Flow Number

Flow number testing is another test used to quantify the rutting potential of an HMA mix. In this test, the HMA specimens are subjected to cyclic loading with a 0.1 second axial load followed by a 0.9 second rest period. The test runs for 10,000 cycles or until the specimen fails. The flow number is defined as the number of cycles achieved before the mixture exhibits tertiary flow. The testing in this study was performed at 50°C.

4.2.12 Leachate Testing

The purpose of the leaching testing was to determine if RVTB in the binder impacted the leachate potential from HMA pavements. The Toxicity Characteristic Leaching Procedure (TCLP) was performed according to SW846-1311 [10]. There were three components of the testing: metals analysis for the regulated 8 elements, semi-volatile organic analysis and analysis of 40 PACs with detection limits significantly lower than that of traditional testing.

Acid digestion using SW846-3010A [11] was performed followed by ICP analysis according to SW846-1311 [10]. A separate method is required for mercury, which was determined using SW846-7470A [12]. A liquid-liquid extraction was performed on the leachate water to determine the concentrations of semivolatile organics following method SW848-3510C [13] followed by GC/MS analysis using SW846-8270C [7]. We also analyzed the leachate extract using GC-TOFMS for 40 PACs, which provided detection limits between 0.1 and 5 ppb versus 50 ppb using the traditional methods.

5.0 DISCUSSION OF RESULTS

5.1 Chemical Analysis of Asphalts

The chemical analysis results include i) XRF results to determine elemental present in the asphalt samples, ii) PAC content to determine if the introduction of RVTB changes PAC content compared to the neat asphalts, iii) TGA to determine if there is a difference in the change of physical properties of the asphalts as a result of increasing of temperature, and iv) GPC to determine if there is a significant difference in the molecular weights of the studied asphalts.

5.1.1 X-Ray Fluorescence (XRF) Results

The results of the XRF testing are shown in Table 2. The data was converted from percentage of sample mass to parts per million (ppm). Elements lighter than Sodium are not detected by XRF.

The results show that some elements are found in higher concentrations in the PG 58-28 RVTB sample than in the neat PG 64-22 or the PG 58-28. Calcium (CA), Sodium (Na), Phosphorus (Px), and Zinc (Zn) were found at much higher levels in the RTVB binder than in the neat asphalts. Recall that Zinc (Zn) was identified by Hesp [2] as an indicator of RVTB being present in asphalt binders. The data presented herein confirms his observation that Zinc is significantly higher in the RVTB sample than in neat asphalts.

Other elements that had higher presence in the RVTB samples include Magnesium (Mg), Iron (Fe), Chlorine (Cl), Potassium (K) and Molybdenum (Mo). Small traces of Copper (Cu), Platinum (Pt), and Titanium (Ti) were found in the RVTB sample and not found in the neat asphalt samples, however, this may be test variability as it is approaching the lowest capability of the testing device.



Table 2. X-Ray Fluorescence (XRF) Results

Sample Element

PG 58-28 Neat PG 58-28 RVTB PG 64 -22 Neat ppm ppm ppm

Calcium, Ca 24 729 32 Sodium, Na 390 680 450

Phosphorus, P 18 324 4.8 Zinc, Zn 41 377 39

Vanadium, V 203 226 257 Magnesium, Mg 133 204 163

Silicon, Si 95 123 124 Iron, Fe 38 131 29

Nickel, Ni 83 93 105 Chlorine, Cl 20 112 16 Potassium, K 0 64 0

Aluminum, Al 28 36 38 Molybdenum, Mo 11 31 13

Copper, Cu 0 14 0 Platinum, Pt 0 11 0 Titanium, Ti 0 7.8 0

Note: PG is Performance Grade and RVTB is Re-refined Vacuum Tower Bottoms. The metals found in the RVTB samples are remnants from either engine wear (i.e. Iron) or from compounds used in the original engine oil such as anti-wear additives, friction reducers and antioxidants (e.g., Zinc and Phosphorus in the form Zinc Dialkyldithiophsophate and Molybdenum in the form of Molybdenum Disulfide).

The results of the XRF analysis confirm the findings of D’Angelo [4]. In his analysis of RVTB, D’Angelo found higher levels of Calcium, Phosphorus, Zinc, and Iron using an Induced Coupled Plasma (ICP) analysis.

5.1.2 Polycyclic Aromatic Compound (PACs) Results

The purpose of testing the PAC content of the neat and RVTB treated binders was to determine if the introduction of RVTB in the asphalt binder increases the levels of PACs in the blended binder resulting in increased environmental and health concerns. A list of 40 PACs were investigated (Table 1). Of these, 19 compounds were not detected in any of the samples (Table 3).

For the remaining 21 PACs, all detectable results are reported in Table 4. A subset of the PACs, a large majority of those with 4-6 rings, is known to be carcinogenic so they were targeted in this analysis. As shown in Table 4, the total of 4-6 ring PACs is 41.6 ppm for PG 58-28 neat asphalt, 48.7 ppm for PG 58-28 asphalt with VTBs and 40.5 ppm for PG 64-22 neat asphalt. Kriech et al [8] have published data for 29 of these same PACs. Results for a typical asphalt cement, labeled as Paving 4, are shown in the last column of the table. Generally, an asphalt binder is considered to have high PACs if the 4-6 ring PACs are above 1,000 mg/kg. As shown in Table 4, the results of both PG 58-28 asphalt binders, the PG 64-22, as well as the reference asphalt are well below the threshold of concern. Additional studies have shown that these PACs under normal paving conditions remain trapped in the asphalt and are non-leachable. [9].



Table 3. Polycyclic Aromatic Compounds Not Detected in Analyzed Asphalts

1 Benzothiophene 10 7H-Dibenzo[c,g]carbazole

2 Acenaphthene 11 3-Methylcholanthrene

3 Acenaphthylene 12 Dibenz[a,h]acridine

4 Benz[a]acridine 13 Dibenz[a,j]acridine

5 Benz[c]acridine 14 Dibenz[c,h]acridine

6 Carbazole 15 Dibenz[a,h]anthracene

7 Benzo[b]naphtho[2,1-d]thiophene 16 Dibenzo[a,e]fluoranthene

8 1-Nitropyrene 17 Dibenzo[a,e]pyrene

9 Cyclopenta[cd]pyrene 18 Dibenzo[a,h]pyrene

19 Dibenzo[a,l]pyrene

Table 4. Polycyclic Aromatic Compounds Detected and Concentration in Analyzed Asphalts

No of Benzene

Rings Sample Concentration (mg/kg)

PG 58-28 Neat

PG 58-28 RVTB

PG 64-22 Neat

Kriech et al [7]* Paving 4

2 2 Naphthalene 0.58 0.03 0.06 8 2+ Dibenzothiophene 0.27 0.34 0.23 9 2+ Fluorene 0.26 0.32 0.19 1.80

10 3 Anthracene 0.19 0.13 1.5011 3 Phenanthrene 0.82 0.87 0.38 30.013 3+ Benzo[b]naphtho[2,3-d]thiophene 2.06 2.36 1.73 14 3+ Fluoranthene 0.41 0.57 0.26 15 4 Benz[a]anthracene 0.47 0.53 0.23 2.0016 4 Chrysene 1.31 1.42 1.12 12.017 4 7,12-Dimethylbenz[a]anthracene 10.60 11.53 11.73 18 4 5-Methylchrysene 1.24 0.85 0.73 9.2020 4 Pyrene 2.17 1.89 1.00 9.1021 4 Triphenylene 1.73 1.47 1.02 22 4+ Benzo[b]fluoranthene 3.15 3.32 2.85 0.7423 4+ Benzo[j]fluoranthene 0.21 0.15 24 4+ Benzo[k]fluoranthene 0.19 0.12 28 5 Benzo[a]pyrene 3.39 4.24 3.01 29 5 Benzo[e]pyrene 6.84 9.13 7.36 30 6 Benzo[ghi]perylene 8.96 11.37 9.19 31 6 Benzo[rst]pentaphene 0.54 0.61 0.48 37 5+ Indeno[1,2,3-cd]pyrene 1.27 1.91 1.54

Summary Data

∑ 40 PACs (mg/kg) 46.0 53.4 43.5 66.3∑ 4-6 ring PACs (mg/kg) 41.6 48.7 40.5 33.0% ∑ 40 PACs 0.0046 0.0053 0.0043 0.0066% ∑ 4-6 ring PACs 0.0042 0.0049 0.0041 0.0033

Note: Detection limit for each PAC was 1.0 ppm [7], versus current study; DL = 0.1 ppm. RVTB is Re-refined Vacuum Tower Bottoms.



In summary, these analyses show a slight increase in PAC content for the PG 58-28 VTB as compared to the PG 58-28 or PG 64-22 neat asphalts. The relative standard deviation between the 3 results was 10.8 percent for the total PACs and 10.2 percent for the ∑ 4-6 ring PACs. These differences are within the error of the method, so the slight increase is not deemed significant.

5.1.3 GPC Testing Results

GPC testing was completed on original, RTFO and PAV aged asphalts to determine if there was a significant difference in changes of the molecular weight distributions due to the aging process. Table 5 show the GPC results for the three binders at different aged conditions.

The Mw value is a good measure of the overall molecular weight of the distribution. As samples age and oxidize, they form larger and more polar molecules. This can lead to increased asphaltene formation and stiffening of the binder. As asphaltenes come together, the binder hardens and becomes more susceptible to cracking. The Mw values increase for each binders between the original and PAV aged residues.

The RTFO asphalts undergo some aging, as expressed by the increased Mw values between original and RTFO-aged results, but not as significant as the PAV-aged values, as expected. The neat PG 58-28 and PG 64-22 have very similar original and RTFO-aged Mw values. After PAV aging, the neat and RVTB PG 58-28 binders have very similar Mw values. The addition of RVTB to the neat PG 64-22 slightly lowered the original Mw value and significantly lowered the PAV-aged Mw value.

Table 5. Weighted Average Molecular Weight (Mw) of Asphalt Binders Studied

Binder Mw

58-28 Original 3900

-RTFO Aged 4700

-PAV Aged 4600

58-28 RVTB Org. 3100

-RTFO Aged 3100

-PAV Aged 4800

64-22 Original 3900

-RTFO Aged 5000

-PAV Aged 7300

Note: PAV is Pressure Aging Vessel; RTFO is Rolling Thin Film Oven; and RVTB is Re-refined Vacuum Tower Bottoms.

Overall, the difference in Mw for the original conditions of the three binders is not significantly different. As expected, after aging through RFTO and the PAV, the average molecular weight increases for all three binders. The PAV conditions for the PG 58-28 binders are very similar whereas the PG 64-22 is higher because of its higher binder grade [14].



5.1.4 TGA Testing Results

TGA testing was used to evaluate if there was any significant difference in thermal decomposition between the three studied asphalt binders. Figure 2 shows the weight loss (by percent of mass) as a function of increasing temperature. During the first portion of the curve, the sample is heated in a nitrogen atmosphere, so combustion does not occur. Once the mass loss plateaus, air is introduced into the sample chamber and combustion occurs causing additional mass loss.

The results indicate that all three asphalt samples have similar thermal decomposition properties. The rate at which the samples volatilize in the nitrogen atmosphere is similar for all three asphalt binders. The temperature at which they plateau, and the percentage remaining at the plateau, is not considered to be significantly different. And finally, the mass remaining, less than two percent in all three cases, is within the ability of the equipment to resolve differences.

Figure 2. Thermo-Gravimetric Analysis (TGA) Results of Studied Asphalt Binders

5.2 Binder Testing Results

The asphalt binders used in this study were sampled from an asphalt manufacturing facility. The neat PG 58-28 asphalt binder was produced with a blend of 20 percent PG 64-22 and 80 percent of a neat PG 52-28. The PG 58-28 VTB sample consisted of 91 percent PG 64-22 and 9 percent RVTB. The results of the PG binder grade analysis are shown in Table 6.



Table 6. Superpave Performance Grade (PG) Testing Results

Asphalt Sample PG 58-28 Neat PG 58-28 RVTB PG 64-22 Neat

Flash Point Temp, ºC 322 308 327 Rotational Viscosity @ 135 ºC, PaS 0.255 n.a. 0.434 Original Binder DSR, G*/sin(delta), KPa 1.07 @58°C 1.11 @58°C 1.39 @64°C

Original Binder DSR Fail Temp, ºC 58.6 59.2 66.7

RTFO Mass Loss, % -0.094 -0.154 0.040

RTFO Binder DSR, G*/sin(delta), KPa 2.35 @58°C 3.07 @58°C 3.20 @64°C RTFO Binder DSR Fail Temp, ºC 58.5 60.6 67.0 PAV Binder DSR, G*sin(delta), KPa 3671 @19°C 3214 @19°C 3911 @25°C BBR Creep Stiffness, -18ºC, MPa 227 137 187

BBR m-value, -18ºC 0.323 @-18°C 0.313 @-18°C 0.327 @-12°C

Estimated PG PG 58-30 PG 59-28 PG 66-24

Actual PG PG 58-28 PG 58-28 PG 64-22 Note: BBR is Bending Beam Rheometer, DSR is Dynamic Shear Rheometer, PAV is Pressure Aging Vessel, RTFO

is Rolling Thin Film Oven, and RVTB is Re-refined Vacuum Tower Bottoms.

The results of the binder grade testing show that the PG 64-22 asphalt studied and used to make the PG 58-28 RVTB binder had an estimated, or continuous, binder grade of PG 66-24 with an actual grade of PG 64-22. The PG 58-28 neat asphalt binder passed as PG 58 on the high end with an original binder DSR failure temperature of 58.6°C. The PG 58-28 RVTB sample had an original DSR failure temperature of 59.2°C, setting the actual PG of the RVTB sample at PG 58-28.

Both of the -28 grade asphalts meet the low temperature requirements with estimated grades of -30 and -29, respectively. The RVTB sample had lower creep stiffness than the neat 58-28 sample.

Based on the RTFO and PAV treated binder DSR results, there is not a clear trend showing there is a difference in aging properties of the neat and RVTB blended binders. The ratio between the RTFO and Original DSR for the RVTB binder is slightly higher (2.63) compared to the neat binder ratio (2.20). However, when the DSR results of the PAV binders are compared, the neat binder has a slightly higher DSR (3,671 kPa) compared to the RVTB binder (3,071 kPa). Based on these tests results, it would be hard to conclude that the neat and RVTB blended 58-28 binders have different aging properties.

5.3 HMA Mixture Testing Results

The HMA mixture testing results include the volumetric designs of the neat and RVTB PG 58-28 N70 mixes, TSR and HWT, as well as dynamic modulus and flow number using the AMPT.

5.3.1 HMA Volumetric Design Results

One of the objectives of this research effort was to design an HMA mixture with neat and RVTB blended PG 58-28 in an approved IDOT mix design. To better simulate a field application type mix, it was decided to include RAP in the studied mix. It also is imperative in the sense that IDOT requires a grade bump down from a PG 64-22 to a PG 58-28 when the binder replacement ratio exceeds 20 percent. The new requirements established by IDOT require a minimum 15.0 percent VMA and air voids at 4.0 percent.



Table 7 shows the gradations of the aggregates and RAP sources used in the studied mixture. All of these aggregates as well as the Fractionated RAP (FRAP) source are approved by IDOT.

Table 7. IDOT Aggregate Classifications and Gradations Used for HMA Mix Design

Aggregate Classification

CM 16 FM 20 FM01Mineral

Filler +3/8" FRAP

-3/8" FRAP

Per

cen

t P

assi

ng

Sei

ve S

ize

(mm

) (%

)

19.0 100.0 100.0 100.0 100.0 100.0 100.0 12.5 100.0 100.0 100.0 100.0 86.3 99.9 9.5 98.0 100.0 100.0 100.0 59.5 98.3

4.75 29.0 99.5 99.8 100.0 30.4 72.0 2.36 4.9 73.9 91.9 100.0 21.2 48.1 1.18 3.6 44.9 70.0 100.0 15.9 34.1 0.6 3.1 27.8 45.0 100.0 12.4 25.3 0.3 2.8 15.5 14.6 100.0 9.2 17.9

0.15 2.6 7.2 2.8 95.0 7.0 13.6 0.075 2.4 3.7 1.5 85.0 5.7 10.9

Note: FRAP is Fractionated Reclaimed Asphalt Pavement.

Table 8 shows the mix volumetric properties for the two PG 58-28 mixes along with the percentages of aggregates sizes used in the trials. An interesting observation was made based on the first trial comparing both mixes. In Trial 1, the percentages of each aggregate added to the mixes were the same, resulting in identical gradations for the mixes. Based on the principal of the Bailey method, since compaction effort, as well as the gradation, shape, size and texture of the mixes were held equal, it was expected that the VMA of the two mixes would be the same.

Table 8. Mix Volumetric Properties and Aggregate Proportions of Studied Mixes

Trial Mix Total AC (%)

Avg. Voids (%)

VMA (%)

CM 16

FM 20

FM 02

Min Fill

+ 3/8" FRAP

- 3/8" FRAP

1 PG 58-28 Neat 6.1 4.3 15.4 46.8 18.2 7.5 0.5 1.6 25.4

PG 58-28 RVTB 6.1 3.3 14.8 46.8 18.2 7.5 0.5 1.6 25.4

2 PG 58-28 Neat 6.1 3.8 15.2 43.8 25.7 5.0 0.5 1.6 23.4

PG 58-28 RVTB 6.1 4.0 15.0 43.8 23.7 5.0 0.5 1.6 25.4 Note: AC is Asphalt Cement, FRAP is Fractionated Reclaimed Asphalt Pavement, RVTB is Re-refined Vacuum

Tower Bottoms, and VMA is Voids in the Mineral Aggregate.

The results from Trial 1 show that the VMA of the neat PG 58-28 blend was 15.4 whereas the PG 58-28 RVTB blend VMA was 14.8. This is a significant difference in VMA. Interestingly, the volumetric properties of the N70 mixes D’Angelo studied in 2013 with RVTB showed that 6 of 7 RVTB mixes had lower VMA than the control mix [5].

The change in VMA between the neat and RVTB blended asphalts may be a function of the lubricity of the asphalt binder. The PG 58-28 RVTB may provide more lubricity during compaction resulting in the



particles compacting closer together resulting in lower VMA. Although this is a plausible explanation, it is important to remember that this study includes only one mix design. Additional studies should be done before concluding that RVTB asphalt binders have an effect on VMA.

For Trial 2, both mixes met the required minimum VMA of 15.0 percent by IDOT specifications.

5.3.2 HMA Moisture Damage Results

The IDOT N70 mixtures were tested for resistance to moisture damage according to IDOT Test Procedure, which is a modified AASHTO T283 protocol. The IDOT procedure does not require the freeze thaw cycle to be performed on the conditioned samples. IDOT also requires a minimum TSR of 0.85 for laboratory prepared samples. The results of the TSR testing are shown in Table 9.

Table 9. Tensile Strength Ratio of IDOT N70 Mixes

Parameter IDOT N70 PG 58-28 Neat IDOT N70 PG 58-28 RVTB

Dry Samples Wet Samples Dry Samples Wet Samples Sample 1 2 3 4 5 6 1 2 3 4 5 6

Air Voids 7.3 6.5 6.6 6.7 6.5 7.4 7.2 7.2 7.5 7.3 7.3 7.5

Avg. Air Voids 6.8 6.9 7.3 7.4

Saturation, % N/A N/A N/A 71.1 78.4 71.1 N/A N/A N/A 71.3 70.6 75.2

ITS, psi 134.0 138.5 122.9 98.3 107.2 107.2 117.2 117.2 97.3 101.7 99.5 97.3

Avg. ITS, psi 131.8 104.2 110.6 99.5

TSR 0.79 0.90

Note: ITS is Indirect Tensile Strength and TSR is Tensile Strength Ratio.

Per specifications, all samples tested had the required 7.0±0.5 percent air voids. The saturation levels of both the PG 58-28 Neat and PG 58-28 RVTB conditioned samples were between 70 and 80 percent. The results show that the N70 mix with the PG 58-28 neat asphalt did not meet the required minimum TSR of 0.85, whereas the mix with PG 58-28 RVTB passed at 0.90. The average dry indirect tensile strength of the PG 58-28 neat mix was significantly higher (131.8 psi) than the average dry strength of the PG 58-28 RVTB (110.6 psi). The PG 58-28 neat mix would require an anti-strip to meet IDOT requirements. This suggests that using the RVTB in the mixture does not have an adverse effect on moisture damage susceptibility.

5.3.3 HMA Rutting Resistance Results

Rutting resistance of the two mixes was measured by two tests: the HWT test and flow number. The results from the HWT test are discussed first. HWT samples were prepared at a target of 7.0 air voids and were subjected to 7500 cycles in a 50°C water bath. The requirement per IDOT specifications for PG 64-22 mixtures is an average rut depth less than 12.5 mm. The mixture is to be evaluated as a PG 64-22 mix because it requires a grade bump down to a PG 58-28 due to the binder replacement from RAP being greater than 20 percent.

Figure 3 shows the average rutting curves for the PG 58-28 neat and PG 58-28 RVTB mixes. The results show that on average, the mixes behave very similar in the HWT. Both mixes met the requirement of average rut depth below 12.5 mm. The rate at which rutting develops in the mixes is also very similar



with maybe the PG 58-28 neat showing slightly higher rut depths up at 2,500 passes. After 3,500 passes, the two curves essentially lie on top of each other.

Figure 3. Average Hamburg Wheel Tracking (HWT) Test Rutting Curves

Table 10 shows the individual results for HMA pills tested. Again, IDOT requires that all samples fall below 12.5 mm rutting after 7,500 cycles. The data shows that for both mixes, all samples have rut depths well below the 12.5 mm threshold with the PG 58-28 RVTB pills having a slightly lower average rut depth of 7.7 mm compared to the average rut depth of 8.6 mm for the neat PG 58-28 mix.

Table 10. Individual and Average Hamburg Wheel Tracking (HWT) Results for Samples Tested

Parameter IDOT N70 PG 58-28 Neat IDOT N70 PG 58-28 RVTB

Sample L1 L2 R1 R2 L1 L2 R1 R2

Air Voids 7.1 6.8 7.5 7.0 7.4 6.9 6.8 7.4

Avg. Air Voids 7.2 7.1

Highest Rut @ 7500, mm 8.6 7.4 8.5 6.8

Avg. Rut @ 7500, mm 8.6 7.7 Note: RVTB is Re-refined Vacuum Tower Bottoms. Flow number was also tested on the mixes to evaluate the rutting resistance of the mixes and to provide comparison to the HWT testing.

0

2

4

6

8

10

12

14

0 2500 5000 7500

Measured Rut Dep

th (mm)

Number of Passes

58 ‐28 Neat & 58‐28 VTB HWT Comparison

58 ‐28 Neat Average

58 ‐ 28 RVTB Average

Failure Criteria



Figure 4 is a bar chart of the individual samples with the average flow number for each mix tested. A higher flow number signifies a stiffer mix. The results were similar to those of the HWT testing. On average, the PG 58-28 RVTB mixes had a flow number of 207 whereas the PG 58-28 neat mix had a flow number of 168. The difference in magnitude of the results is not very significant meaning the mixes have similar resistance to rutting potential.

Figure 4. Flow Number Results

5.3.4 HMA Stiffness Testing Results

Stiffness testing of the PG 58-28 with and without RVTB was completed using the Asphalt Mixture Performance Tester (AMPT) to determine the dynamic modulus of the material. Table 11 shows the dynamic modulus results at three different testing temperatures at multiple frequencies. The samples were fabricated to reach the target 7.0±1.0 percent air voids with the average voids between the two mixes being only 0.3 percent different. The stiffness of the mixes decreases with increase in temperature and decrease in frequency, as expected. At all temperatures and frequencies, the PG 58-28 neat mixes were slightly higher than the PG 58-28 RVTB mixes.

Figure 5 is a bar chart of the mixes at the three testing temperatures at 10 Hz testing frequency. The height of the bars represents the average dynamic modulus. The average number is also shown within each bar. The error bars represent the high and low dynamic modulus results for the samples. For all temperatures, the high and low modulus values all fall within the range of stiffness signifying that there is no significant difference in stiffness between the neat and RVTB PG 58-28 mixes.

0

50

100

150

200

250

PG 58‐28

RVTB

1

PG 58‐28

RVTB

2

Avg. P

G 58‐

28 RVTB

PG 58‐28

Neat 1

PG 58‐28

Neat 2

Average P

G

58‐28 Neat

Flow Number



Table 11. Dynamic Modulus Results

Test Temp. (°C)

Sample PG 58-28 Neat #1

PG 58-28 Neat #2

PG 58-28 Neat

Average

PG 58-28 RVTB # 1

PG 58-28 RVTB # 2

PG 58-28 RVTB

Average Air Voids 6.7 7.5 7.1 7.3 6.3 6.8

4°C

Dyn

amic

Mod

ulus

at F

requ

ency

(M

pa)

25 Hz 14855 11298 13077 10765 14170 12468

20 Hz 14568 10976 12772 10553 13673 12113

10 Hz 13449 9934 11692 9635 12341 10988

5 Hz 12300 8933 10617 8565 11022 9794

2 Hz 10806 7621 9214 7294 9402 8348

1 Hz 9733 6695 8214 6371 8258 7315

0.5 Hz 8733 5809 7271 5512 7204 6358

0.2 Hz 7421 4715 6068 4511 5899 5205

0.1 Hz 6495 4020 5258 3875 5075 4475

30°C

Dyn

amic

Mod

ulus

at F

requ

ency

(M

pa)

25 Hz 3907 2608 3258 2601 3020 2811

20 Hz 3756 2466 3111 2500 2929 2715

10 Hz 3082 1973 2528 2020 2359 2190

5 Hz 2495 1549 2022 1617 1874 1746

2 Hz 1833 1085 1459 1168 1330 1249

1 Hz 1434 831.6 1133 916.7 1027 972

0.5 Hz 1114 629.4 872 701.2 781.4 741

0.2 Hz 781.6 428.2 605 492.6 540.8 517

0.1 Hz 589.3 318.1 454 370.4 407.5 389

40°C

Dyn

amic

Mod

ulus

at F

requ

ency

(M

pa)

25 Hz 2092 1227 1660 1370 1619 1495

20 Hz 1983 1146 1565 1266 1485 1376

10 Hz 1546 866.7 1206 966.5 1137 1052

5 Hz 1178 642.4 910 724.3 836.2 780

2 Hz 793.7 414.5 604 477.2 552.7 515

1 Hz 594.4 307.2 451 357.3 415.1 386

0.5 Hz 441.2 224.7 333 265.5 313.4 289

0.2 Hz 304.2 152.6 228 183.9 221.7 203

0.1 Hz 229.6 114.5 172 141.4 175 158

Note: RVTB is Re-refined Vacuum Tower Bottoms.



Figure 5. Average Dynamic Modulus Results at 10 Hz at Multiple Test Temperatures

5.3.5 Leachate Testing Results

Leachate testing of the HMA PG 58-28 with and without RVTB involved three different analyses after the TCLP. Metals analysis for the regulated 8 elements (Arsenic, Barium, Cadmium, Chromium, Lead, Mercury, Selenium, and Silver) showed that only barium was detected in either the control sample or the VTB sample at similar concentrations as shown in Table 12. The regulatory level for barium is 100 mg/L whereas the sample concentrations were 0.13 mg/L and 0.11 mg/L. The barium levels typically come from limestone in the aggregate.

Table 12. Results for Leachable Elements in Asphalt Mix Samples

Element CAS No. PG 58-28

Neat PG 58-28

RVTB Detection

Limit Regulatory

Level (mg/L) Arsenic 7440-38-2 BDL BDL 0.05 5 Barium 7440-39-3 0.13 0.11 0.05 100 Cadmium 7440-43-9 BDL BDL 0.025 1 Chromium 7440-47-3 BDL BDL 0.05 5 Lead 7439-92-1 BDL BDL 0.05 5 Mercury 7439-97-6 BDL BDL 0.002 0.2 Selenium 7782-49-2 BDL BDL 0.05 1 Silver 7440-22-4 BDL BDL 0.05 5

Note: BDL is below detection limit, PG is Performance Grade, and RVTB is Re-Refined Vacuum Tower Bottoms.

Semi-volatile organic analysis included a total of 29 organic compounds as shown in Table 13. All results were below the detection limit of 50 – 250 µg/L for both the control sample and the VTB sample.

11691.5 10988

2527.5 2189.5 1206.351051.750

1000

2000

3000

4000

5000

6000

7000

8000

9000

10000

11000

12000

13000

14000

Dynam

ic E‐M

odulus (M

Pa)

Dynamic Modulus @ 10Hz

PG 58‐28 Neat 4C

PG 58‐28 RVTB 4C

PG 58‐28 Neat 30C

PG 58‐28 RVTB 30C

PG 58‐28 Neat 40C

PG 58‐28 RVTB 40C



Table 13. Results for Leachable Semi-volatiles in Asphalt Mix Samples

Compound PG 58-28

NEAT PG 58-28

RVTB Detection

Limit µg/L 1,4-DICHLOROBENZENE (P-DICHLOROBENZENE) BDL BDL 50

2,4-DINITROTOLUENE BDL BDL 50

HEXACHLOROBENZENE BDL BDL 50

HEXACHLOROBUTADIENE BDL BDL 50

HEXACHLOROETHANE BDL BDL 50

NITROBENZENE BDL BDL 50

PYRIDINE BDL BDL 250

2-METHYLPHENOL (O-CRESOL) BDL BDL 50

3-METHYLPHENOL (M-CRESOL) BDL BDL 50

4-METHYLPHENOL (P-CRESOL) BDL BDL 50

PENTACHLOROPHENOL BDL BDL 250

2,4,5-TRICHLOROPHENOL BDL BDL 50

2,4,6-TRICHLOROPHENOL BDL BDL 50

ACENAPHTHENE BDL BDL 50

ACENAPHTHYLENE BDL BDL 50

ANTHRACENE BDL BDL 50

BENZO(A)ANTHRACENE BDL BDL 50

BENZO(A)PYRENE BDL BDL 50

BENZO(B)FLUORANTHENE BDL BDL 50

BENZO(G,H,I)PERYLENE BDL BDL 50

BENZO(K)FLUORANTHENE BDL BDL 50

CHRYSENE BDL BDL 50

DIBENZ(A,H)ANTHRACENE BDL BDL 50

FLUORANTHENE BDL BDL 50

FLUORENE BDL BDL 50

INDENO(1,2,3-CD)PYRENE BDL BDL 50

NAPHTHALENE BDL BDL 50

PHENANTHRENE BDL BDL 50

PYRENE BDL BDL 50

Surrogate Recoveries % %

2-FLUOROPHENOL 46 53

PHENOL-D5 34 44

NITROBENZENE-D5 76 79

2-FLUOROBIPHENYL 84 81

2,4,6-TRIBROMOPHENOL 101 96

TERPHENYL-D14 101 93


Analysis of 40 individual PACs with detection limits significantly lower than that of traditional testing using GC-TOFMS showed detectable levels for 8 PACs in both the control and the VTB samples (see



Table 14); all results were below 3 µg/L (ppb). The sum of the 8 detectable PACs was 12.3 ppb versus 13.2 ppb for the control and VTB samples respectively. Pyrene was the only 4-ring compound detected and is not considered carcinogenic.

Table 14. Results for Leachable PACs in Asphalt Mix Samples using GC-TOFMS

Sample Concentration (µg/L) PG 58-28 Neat PG 58-28 RVTB Detection Limit, µg/L Naphthalene 1.98 2.70 0.33 Acenaphthylene BDL BDL 0.45 Acenaphthene BDL BDL 0.49 Fluorene BDL BDL 0.79 Phenanthrene 1.08 1.16 0.76 Anthracene 1.41 1.32 0.86 Fluoranthene 1.13 1.01 1.54 Pyrene 1.30 1.30 1.13 Benzo[b]naphtho[2,3-d]thiophene 1.70 1.77 1.57 Benzo[b]naphtho[1,2-d]thiophene BDL BDL 1.57 Benz[a]anthracene BDL BDL 0.58 Cyclopenta[cd]pyrene BDL BDL 3.18 Triphenylene BDL BDL 3.34 Chrysene BDL BDL 0.30 5-Methylchrysene BDL BDL 0.26 1-Nitropyrene BDL BDL 1.75 Benzo[b]fluoranthene BDL BDL 0.22 7,12-Dimethylbenz[a]anthracene BDL BDL 0.26 Benzo[k]fluoranthene BDL BDL 0.21 Benzo[j]fluoranthene BDL BDL 0.22 Benzo[e]pyrene BDL BDL 0.11 Benzo[a]pyrene BDL BDL 0.25 3-Methylcholanthrene BDL BDL 0.11 Dibenz[a,j]acridine BDL BDL 0.74 Dibenz[a,h]acridine BDL BDL 1.36 Indeno[1,2,3-cd]pyrene BDL BDL 1.92 Dibenz[a,h]anthracene BDL BDL 4.76 Benzo[ghi]perylene BDL BDL 0.19 7H-Dibenzo[c,g]carbazole BDL BDL 0.20 Dibenzo[a,e]fluoranthene BDL BDL 0.35 Dibenzo[a,e]pyrene BDL BDL 0.26 Benzo[rst]pentaphene BDL BDL 1.22 Dibenzo[a,h]pyrene BDL BDL 0.30 Dibenzo[a,l]pyrene BDL BDL 0.31 Benzo[b]thiophene BDL BDL 0.18 Dibenzothiophene 1.95 2.10 0.19 Carbazole 0.63 0.66 0.21 Benzo[c]acridine BDL BDL 0.42 Benzo[a]acridine BDL BDL 1.09 Dibenz[c,h]acridine BDL BDL 1.34 7H-Dibenzo[c,g]carbazole BDL BDL 0.56




6.0 SUMMARY AND CONCLUSIONS

A study was done to compare the properties of a PG 58-28 asphalt binder formulated with and without Re-refined Vacuum Tower Bottoms (RVTB). Asphalt binder properties were evaluated using both standard specification tests and other investigative tests. Asphalt mixtures were made with the two formulations of PG 58-28 and mixture properties were evaluated. Significant observations and findings are listed below.

Chemical analysis by XRF showed higher presence of certain metals than in the neat asphalt binders. Zinc, which has been identified as an indicator for RVTB, had higher levels in the RVTB blend than in the neat asphalts. Other metals with greater presence in RVTB binder than in neat asphalts included Magnesium, Iron, and Calcium.

Testing results for PAC showed no significant difference in carcinogenic known PACs between the RVTB blended binder and the neat asphalts. Levels tested in the analyzed asphalts were comparable to levels found in other studies. Based on these results, adding RVTB to the asphalt binder does not pose environmental or health issues.

There was no significant difference in molecular weight of the original asphalts analyzed by GPC. After undergoing aging through RTFO and PAV, the molecular weights increased as expected. The average molecular weights of the neat and RVTB PG 58-28 binders after PAV aging were very similar.

There was also no appreciable difference in thermal decomposition of the PG 58-28 Neat, PG 58-28 RVTB and the PG 64-22 neat as measured by TGA.

Blending 9 percent RVTB with a neat PG 64-22 produced an asphalt binder that meets the PG 58-28 specification. The PG 58-28 RVTB and PG 58-28 had comparable DSR results after RTFO and PAV aging protocols.

N70 9.5-mm Nominal Maximum Aggregate Size (NMAS) HMA mixtures were designed with both the PG 58-28 neat and PG 58-28 RVTB asphalt to meet IDOT HMA volumetric requirements.

Results for TSR for the mixes analyzed show better TSR values for the PG 58-28 RVTB than for the PG 58-28 neat asphalt mix.

Rutting resistance measured by HWT testing and by flow number was about equal for both neat and RVTB binder mixes. Both mixes passed the rutting requirement of 12.5 mm after 7500 passes in the HWT test.

Stiffness of the HMA mixes were found to be equal based on dynamic modulus testing at low and intermediate temperatures across all testing frequencies.

Leachate results show trace levels of barium for both the asphalt mix and asphalt mix with RVTB at similar concentrations. No other regulated metals were detected in either sample.

Leachate and subsequent organic analysis showed that all compounds tested were below the limit of detection. Additional analysis using GC-TOF/MS to obtain lower detection limits revealed trace levels of eight PACs; the sum was 12.3 ppb vs 13.2 ppb for the asphalt mix control and the asphalt mix with RVTB, respectively.



Overall, the results of this study indicate that introducing RVTB into an asphalt binder at a moderate level of 9 percent does not compromise mixture stiffness or resistance to moisture damage through laboratory testing. The RVTB additive did not significantly affect PAC levels and were similar to other asphalt reported in the literature.

REFERENCES

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[12] “Mercury in Liquid Waste (Manual Cold-Vapor Technique)”, Test Method SW846-7470A, U.S.

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Test Methods for Evaluating Solid Waste, U.S. Environmental Protection Agency (EPA) Washington, D.C. (1996).

[14] Gorman, B. Personal Communication (May 2014).


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