Fundamental Properties of Asphalts andModified Asphalts, III
Quarterly Technical Progress ReportJuly 1-September 30, 2008
September 2008
Prepared forFederal Highway AdministrationContract No. DTFH61-07-D-00005
ByWestern Research Institute
www.westernresearch.org
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TABLE OF CONTENTS
TASK 1. COORDINATION ........................................................................................................1
TASK 2. CONTINUED RESEARCH .........................................................................................3
Subtask 2-1. Moisture Damage.................................................................................................3
Subtask 2-2. Aging..................................................................................................................13
Subtask 2-2.1. Impact of Water on Aging ........................................................................13
Subtask 2-2.2. Support of the Mechanistic-Empirical Pavement Design Guide ..............19
Subtask 2-3. Nanotechnology: AFM Analysis of Asphalt Thin-Film MicrostructurePhenomenology..................................................................................................................47
Subtask 2-4. Low-Temperature Properties .............................................................................55
Subtask 2-5. Modified Asphalts..............................................................................................65
Subtask 2-6. Validation Site Monitoring ................................................................................79
TASK 3. OTHER RESEARCH ACTIVITIES (IDIQ)............................................................81
TASK 4. INFORMATION DEPLOYMENT ...........................................................................83
Subtask 4-1. Publications, Presentations, Newsletters, Flyers and Brochures .......................83
Subtask 4-2. Website Maintenance.........................................................................................85
Subtask 4-3. Research Database—Contractor Team Activities .............................................87
Subtask 4-4. Research in Progress Database ..........................................................................89
Subtask 4-5. Support of the Mechanistic-Empirical Pavement Design Guide .......................93
Subtask 4-6. Semi-Annual Meetings ......................................................................................95
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TASK 1. COORDINATION
The goals of this task are to maintain contact with current State-of-the-Art and State-of-the-Science in fundamental research on asphalts and modified asphalts, to keep abreast of currentand on-going science and technology in asphalt research, and to learn the needs of the asphalttechnical community.
During this quarter, WRI hosted the 2008 Petersen Asphalt Research Conference (July 14-16)and the Pavement Performance Prediction (P3) Symposium (July 16-18). The topics for the P3Symposium were current practices and problems with the use of recycled asphalt pavements andwarm-mix asphalts. Problems and needs identified during the Symposium are discussed in Task4.
During this quarter, WRI researchers Mike Harnsberger, Fran Miknis, and Fred Turner attendedthe Binder and Mix Expert Task Group meetings in Reno, Nevada, September 16-18, 2008. FranMiknis presented a summary of WRI’s magnetic resonance studies of polyphosphoric acid inasphalts. Fred Turner presented an overview of WRI’s new on-column precipitation and re-dissolution technology for characterizing asphaltic materials.
WRI rheologist, Changping Sui, as part of her familiarization and training with asphalticmaterials, developed new dynamic shear rheology methods for measuring low-temperatureproperties. This work is discussed in the Low-Temperature Properties subtask (2-4).
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TASK 2. CONTINUED RESEARCH
SUBTASK 2-1. MOISTURE DAMAGE
Subtask Manager: Eric W. KalbererOther Investigators: Ryan Boysen, Will Grimes, Troy Pauli, Shin-Che Huang, Fran Miknis
2-1.1 Fines and Organics
Statement of Problem
Asphalts and aggregates demonstrate different performance characteristics, especially in thepresence of moisture. From a chemical standpoint, the question is: How are moisture damage ofasphalt concrete and the chemistry of the pavement materials related?
Approach
The work described below represents an attempt to gain insight into moisture damage using theHamburg Wheel Test which subjects asphalt concrete specimens to stress under a steel wheel ina water bath. The damage to the specimen results in the loss of material from the sample into thewater bath. This material is both inorganic (aggregate) and organic (asphalt) and, when properlysampled, it might be possible to determine the chemical make-up of each. This chemicalcharacterization could be used to establish correlations, or lack there of, between pavementfailures due to the presence of moisture and chemical make-up of the asphalt and aggregate.
Goal
The goal of this research is to improve the understanding of the relationship betweenasphalt/aggregate chemistry and roadway performance in the presence of moisture. This requiresa better fundamental understanding of the chemistry of asphalt and aggregate material propertiesand the relationship to pavement performance. Better understanding of fundamental propertieswill promote an improved definition of asphalt-aggregate interfacial phenomena and will lead totruly defining the performance of the pavement. The ultimate goal for this work is to add to thematerial science development for asphalt pavements.
Work Conducted this Quarter
Work this quarter has included subjecting Gyratory Compacted cores to Hamburg Wheel Tracker(HWT) conditioning to generate materials due to core failure for the “Fines and Organics”project. This study is designed to characterize the inorganic and organic material generatedduring HWT conditioning. The primary aim of this project is to determine whether the materialliberated from a failing core sample can be correlated with previous and ongoing moisturedamage studies of asphalt-aggregate interfacial phenomena. Currently, this work has involvedusing the HWT to perform rutting tests on numerous road cores obtained from various sites aswell as on specimens compacted using a Superpave Gyratory Compactor.
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This quarter marked the start of using the Gyratory Compactor to form test cores rather thanexcess core samples from the numerous validation sites WRI currently surveys. Asphalts AAD-1 and AAM-1 were chosen for this study because they are very different asphalts and present twovery different scenarios for the sake of comparing the materials generated in the water bathduring HWT testing. AAD-1 is a highly acidic, high asphaltene material while AAM-1 is a lowasphaltene, non-acidic asphalt. The mix design and aggregate were supplied by the NebraskaDOT as they were both provided for a previous study into premature failure. The aggregate waschosen because it is a known stripper and there is a plentiful supply on hand. It is a mix of PlatteRiver gravel and limestone from the Martin Marietta formation in Weeping Water. Eachcompacted core contained 5.7% asphalt compacted to 5.0% ± 0.5% air voids. After mixing, eachsample was aged for 2 hours at 160°C to simulate the effects of the hot mix plant. Samples werethen compacted with an internal contact angle of 1.16° according to AASHTO T312-04. Thecompacted specimens were then cut, mounted, and securely fastened in a Hamburg WheelTracker. The water tank was filled with tap water and upon heating to 40°C, the wheel, with 155pounds weight, was lowered to contact the compacted specimen. The test was run and rut depthwas recorded until sufficient sediment was present in the water for isolation and analysis. All sixsamples performed very well, table 2-1.1, as 10 mm or less rutting had occurred after 20,000passes.
Table 2-1.1. Summary of the samples run in the Hamburg rut test with the stripping inflectionpoint and rut depth at the center when the sample was taken.
Trial Passes to Stripping Passes to Rut Depth at CenterSample Number Inflection Point Sample Taken when Sample was Taken (mm)
AAM1-Nebraska 1 40000 48000 4.9AAM1-Nebraska 2 40000 44000 8.2AAM1-Nebraska 3 28500 32250 10.5
AAG1-Nebraska 1 22500 27850 8.8AAG1-Nebraska 2 27500 32750 9.3AAG1-Nebraska 3 25000 29200 8.9
A simple format for collecting inorganic and organic materials for further analysis was chosenafter much discussion. Once testing was completed, the sediment was allowed to settle at roomtemperature and the tank was drained. At this point enough material was present on the floor ofthe bath to collect. It was decided that there is no acceptable format for collecting inorganic ororganic materials in real-time increments as they are generated during HWT testing. This is acomplication of using such a large water bath (~ 40 gallons) while generating a very smallamount of material and the constant perturbation of the material in the water due to wheelmovement. It would be possible to stop the test and allow the sediment to settle to the bottombefore continuing. However, the tests did not generate enough sediment for isolation untildamage to the sample was particularly evident, at which point the test was stopped for collectionanyway.
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After the material was collected, the asphalt was extracted from the aggregate using an 85:15toluene:ethanol mixture. Solvent was then removed from the extracted, organic material using arotary evaporator. The remaining asphalt was subjected to FTIR analysis. As is seen in figures2-1.1 and 2-1.2, there is little difference in the FTIR spectra of HWT tested asphalt and the“virgin” binder for either AAM-1 or AAD-1. The only differences identified in either spectrumwere the increase in carbonyl and sulfoxide due to the increased aging observed in the HWTtested samples. At this point it is important to note that the rutting damage from such a rigoroustest appears to be due primarily to the effect of the wheel on the core surface rather than to aninteraction at the asphalt-aggregate interface. This is evident from the asphalt that sometimessticks to the wheel, the variety of aggregate sizes that are displaced from the core (mostlycoated), and now the representative sample of asphalt that has been identified by FTIR.
600110016002100260031003600Wavenumber (cm
-1)
Ab
so
rba
nce
AAG-1 Recovered from Hamburg
AAG-1 Control
Figure 2-1.1. Representative FTIR spectra of AAG asphalts in CS2.Spectra are superimposed to show only minor differences.
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600110016002100260031003600Wavenumber (cm
-1)
Ab
so
rba
nc
e
AAM-1 Recovered from Hamburg
AAM-1 Control
Figure 2-1.2. Representative FTIR spectra of AAM asphalts in CS2.Spectra are superimposed to show only minor differences.
The insoluble inorganic material, after asphalt extraction, was analyzed at the University ofWyoming Department of Geology by X-ray diffraction (XRD) to determine the minerals presentand electron probe microanalysis (EPMA) to determine elemental composition. Both coarse andfine aggregate materials (> 30 micron) were subjected to analysis. Here again problems existwith the collection of material as well as with the analytical techniques by which the material canbe characterized. There are shortcomings for both EPMA and XRD. In general, EPMA analysisis typically run first to get a ratio, or number of counts for each of the elements that are ofinterest to mineral characterization. XRD is then used to determine what minerals are presentbased on the EPMA footprint that is established. The drawback to using XRD is it is typicallyoverkill; in other words, a veteran technician is aware of what minerals are most common basedon EPMA results, therefore, XRD is not typically needed. This is an example of anotherproblem inherent to these analyses: EPMA is subject to the bias of the technician conducting theanalysis. Figure 2-1.3 includes representative photographs from this study for the two types ofmedia used for securing the sample aggregates to conduct EPMA. Obviously, for the sake of thisstudy, there are major differences in what the EPMA probe is exposed to depending on themethod of securing the sample that is chosen. Secondly, for each analysis there are numerousmeasurements taken (~20), each at a different location on the sample. Looking at figure 2-1.3 itis apparent that different measurements could regularly be observed depending on where theinstrument is focused on either the disc or a tape. However, it appears that there is a more evenparticle distribution using the tape method and a more uniform set of measurements would beexpected. Another drawback for either the tape or disc method is that only a small percentage ofthe material collected is actually analyzed, leaving in question whether a true representativesample was chosen.
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Figure 2-1.3. Photos of EPMA techniques; Disc method on the right side,ad tape method on the left.
Results from EPMA analysis for this study have been disappointing. Table 2-1.2 includes thedata generated from the EPMA analysis of the three Hamburg tested mixes containing AAM-1.Each sample displays 1000 counts for silicon because that is used as a baseline for determiningthe number of counts of other elements. EPMA is similar to atomic force microscopy in that atype of probe is used to determine what elements are present in the area of focus. The twodifferent methods from each sample demonstrate a high degree of variation in concentration fornine elements analyzed. The relative standard deviations for elemental counts throughout thesampling presented in table 2-1.2, regardless of method used (disc or tape), range from as low aszero to as high as 75 percent. A relative standard deviation of less than 5% is needed to drawany sort of reasonable conclusion for the sake of this study. In other words, these numbers aremuch too inconsistent to be depended on for quantitative analysis. The high degree of variationin EPMA counts rules out further XRD analysis as well. The clear conclusion is that this methodis not viable for the characterization of inorganic material generated during HWT testing for thereasons discussed in the paragraph above.
The current work on characterizing aggregate and asphaltic materials has lead to somewhat of acrossroads. Current methods indicate no difference in isolated material or are incapable ofsupplying quantitative analytical data. First, FTIR analysis indicates that the organic materialgenerated is representative of the bulk asphalt. There is no particular functional group that canbe correlated to moisture damage using HWT testing. Second, the extremely high relativestandard deviations of the EPMA, aggregate test results rendered the use of powder XRDunnecessary. The main drawbacks to this method are a result of the inability to obtain anyrepresentative sample that is uniform throughout. In addition, a great deal of ambiguity in resultsis observed based on what technician is employed. The difficulties in obtaining quantitativecharacterization may, in fact, be a result of the rigors of the HWT test procedure. It’s possiblethat the physical nature of the test makes it impossible to obtain aggregate or asphalt materialsthat are generated by stripping alone using the techniques employed thus far.
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Table 2-1.2. Results of EPMA using both the tape and disc method for samples collected fromasphalt AAM-1 and Nebraska aggregate mixes.
Na Mg Al Si Cl K Ca TI Fe
Ne Control Standard Deviation 12 3 46 4 26 65 1 4Disc Average Count 39 4 196 1000 14 66 96 1 3
Ne Control Standard Deviation 4 1 27 1 13 19 0 1Tape Average Count 44 13 276 1000 11 82 203 1 8
AAM-1 Trial 1 Standard Deviation 8 2 27 5 11 19 0 1Disc Average Count 39 3 196 1000 13 71 40 1 3
AAM-1 Trial 1 Standard Deviation 3 1 17 2 6 4 0 0Tape Average Count 46 6 153 1000 6 85 70 1 9
AAG-1 Trial 2 Standard Deviation 7 2 29 2 14 36 0 1Disc Average Count 40 10 214 1000 15 75 145 1 3
AAG-1 Trial 2 Standard Deviation 4 3 7 1 4 17 1 1Tape Average Count 43 13 267 1000 10 86 185 1 7
A few other alternatives exist for sampling and have been discussed but not attempted due,primarily, to the extreme steps that would need to be taken with no guaranteed payout. Thequestion of what actually exists in the water bath still persists. To determine whether there is afraction of asphalt present as a suspension in the water the organics would have to be extractedfrom a 40 gallon water bath. Furthermore, determining what fine material (< 30 micron) mightbe present in the water bath after the sediment settles out would require use of distilled waterduring testing as well as a large scale process to remove the water from the extremely finematerial.
Work to be Conducted Next Quarter
Explore other possible methods of sample collection and analysis for the fines andorganics process.
Explore alternative testing techniques to develop a better process than the HWT foranalysis of materials failure due to moisture damage.
Further optimize the automated SARA separation under prescribed conditions. Expandthe separation into multi-phase methods to generate samples of interest for furtherinterfacial studies.
Establish year three research sketches.
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Problems and Solution to Problems
No major hurdles were encountered this past quarter. A technician may be required to make anyappreciable gains in this area in the coming year.
Support of FHWA Strategic Goals
The work conducted in this subtask is in support of the FHWA strategic goal that pertains to theoptimization of pavement performance. There is a broad-based need for a better understandingof the mechanisms of moisture damage and advanced methods for the detection and mitigation ofmoisture damage. Progress in these areas, especially understanding the root causes, will lead toimproved material selection for new pavements as well as enhanced maintenance capability forexisting roads.
Task 2-1.2 Chromatographic Separations
Statement of Problem
Asphalts and aggregates demonstrate different performance characteristics, especially in thepresence of moisture. From a chemical standpoint, the question is: How are moisture damage ofasphalt concrete and the chemistry of the pavement materials related?
Approach
An alternative approach to examining moisture damage can be taken using theoreticalcalculations that represent interactions between asphalt and aggregate to help define whatchemical characteristics of each material will result in favorable interactions. In other words,this method theoretically predicts what types of molecules in asphalt will interact favorably withcertain aggregate molecules. These predictions eventually require a proof-of-concept experimentin the laboratory. Therefore, based on theory, certain types of molecules can be added into orremoved from an asphalt to test for changes in adhesion characteristics that could support ordisagree with the predictive calculations. This requires complex separations of asphalt intovarious fractions that are based on the overall, chemical make-up of the material.
Goal
The goal of this research is to improve the understanding of the relationship betweenasphalt/aggregate chemistry and roadway performance in the presence of moisture. This requiresa better fundamental understanding of the chemistry of asphalt and aggregate material propertiesand the relationship to pavement performance. Better understanding of fundamental propertieswill promote an improved definition of asphalt-aggregate interfacial phenomena and will lead totruly defining the performance of the pavement. The ultimate goal for the body of this work is toadd to eventually developing the material science for asphalt pavements.
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Work Conducted this Quarter
Another project that is being developed under subtask 2-1 is to revisit the use of chromatographyto separate asphalt into fractions that could prove useful for the study of moisture damage.Chemical functional groups have been identified through past work at WRI as being strong orweak binders to aggregate in the presence of water. Current research on interfacial properties ofasphalt and aggregate are starting to provide detailed information on what might truly be bindingto the rock. The use of high performance liquid chromatography (HPLC) will be a useful tool inisolating pinpointed fractions of the asphalt that could be used as a proof-of-concept for thesurface studies. This work relates to some of the initial size exclusion chromatography and ionexchange chromatography methods that were previously developed at WRI. Other recentdevelopments at WRI have involved automating the SARA (saturates, aromatics, resins,asphaltenes) separation. New methods incorporating past and current developments can be usedto isolate subfractions of particular interest to moisture damage studies for doping experimentsamong other things. For example, if theoretical or interfacial studies attribute good bindingcharacteristics to an acidic fraction of the aromatics fraction in asphalt, it would then be possibleto isolate assorted acidic fractions of aromatics from asphalt and to eventually perform dopingexperiments.
In the past quarter a new, Waters 600 HPLC system was assembled and initialized. Several daysof training under the watchful eyes of a Waters representative were completed by Ryan Boysen,Eric Kalberer, Will Grimes, and Troy Pauli that detailed the inner-workings of the systemhardware as well as the layout of the Empower software. To date, several iterations of theautomated SARA separation indicating good separation of the maltene fraction on manuallypacked stationary phase. This work will continue in earnest until a workable method is in placefor use on all asphalts. A method of this sort will be further coupled with other methods toestablish multi-phase chromatographic separations that enable the isolation of minutesubfractions of the SARA fractions.
Work to be Conducted Next Quarter
Further optimize the automated SARA separation under prescribed conditions. Expandthe separation into multi-phase methods to generate samples of interest for furtherinterfacial studies.
Establish year three research sketches
Problems and Solution to Problems
No major problems were encountered this past quarter.
Support of FHWA Strategic Goals
The work conducted in this subtask is in support of the FHWA strategic goal that pertains to theoptimization of pavement performance. There is a broad-based need for a better understandingof the mechanisms of moisture damage and advanced methods for the detection and mitigation ofmoisture damage. Results from this research will aid in understanding the fundamentals of
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material behavior at the asphalt/aggregate interface. Advances in this area will lead to improvedmaterial selection for new pavements as well as enhanced maintenance capability for existingroads.
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SUBTASK 2-2. AGING
Subtask Manager: Fred TurnerOther Personnel: Shin-Che Huang, Mike Farrar, Will Grimes, Steve Salmans, Will Schuster
SUBTASK 2-2.1. IMPACT OF WATER ON AGING
Statement of Problem
Many attempts have been made to simulate road aging with laboratory tests. These efforts havegenerally not been very successful. One reason is that other causes of road failure, such as heavytraffic or construction deficiency, can obscure the effect of the asphalt binder. Other reasons arethat the pressure aging vessel (PAV) test temperature that has been used may be too high torelate laboratory aging to road aging and that the roles played by atmospheric humidity and dewpoint on the road have long been ignored. Recent research [Thomas 2002; Huang et al. 2008]has shown that the presence of moisture increases the rate at which aging progresses in pavingasphalts. Since aging ultimately leads to embrittlement and pavement failure, determining andmodeling the influence of moisture is important to the prediction of pavement performance.
Approach
The sensitivity of asphalts to environmental factors is being determined using laboratory PAVaging tests at pavement service temperature on unmodified asphalts at different film thicknesseswith and without moisture in the oven. Testing includes spectroscopic (FTIR) and rheologic(DSR) analysis of the aged materials. Master curve and shift factors are used to quantifychanges between oxidation and diffusion.
Goal
The goal of this project is to develop relationships that predict the long-term aging of asphalts inthe presence of moisture.
Support of FHWA Strategic Goals
In the laboratory, the ability to reliably reproduce in-service pavement aging is vital to thehighway community. The development of a correlation between laboratory aging data and fieldpavement performance could help to predict the advent of distresses in the field, therefore,improving the cost effectiveness of the preventative maintenance and/or rehabilitation measuresthat used. This subtask supports the FHWA Strategic Goal of Optimizing PavementPerformance.
Work Conducted This Quarter
To evaluate the impact of moisture on the aging characteristics of asphalt binders, in terms ofphysical-chemical relationships, previously collected rheological and chemical data of eightRTFO- and RTFO/PAV-aged SHRP asphalts were analyzed. The RTFO-aged asphalts were
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PAV aged for different lengths of time in the absence and presence of water. To further developa mathematical understanding of the relationship between rheological properties and chemicalproperties, the complex modulus was plotted against carbonyl content for aging times of 140,240, and 480 hours for eight asphalts. The detailed results were presented in previous quarterlyreports (December 31, 2007 and March 31, 2008) but revisited here for comparison. Figures2-2.1.1 and 2-2.1.2 show the relationship between complex modulus and carbonyl content foreight asphalts that were PAV-aged at 80°C for different lengths of time in the absence andpresence of water, respectively. It was reported that both the complex modulus and carbonylcontent increase with increasing aging time and that different asphalts have different sensitivitiesto aging. In addition, the increase in complex modulus with increasing carbonyl content isasphalt dependent.
A statistical equation, logistic with three parameters, was applied to describe the relationshipbetween the asphalt complex shear modulus and carbonyl formation upon aging. This equationis shown as follows:
]exp1[*
)(
*
Carbonyl
gGG (2-2.1.1)
Where G* = complex modulus, PaG*
g = glassy modulus, 109 Pa was assumed in this caseβ = shape of the curveCarbonyl = carbonyl content in infrared absorption units
γ = correlation constant
This same equation can be applied for wet oxidized samples. The complex modulus andcarbonyl content for wet oxidized samples is similar to those of dry oxidized samples. Bothcomplex modulus and carbonyl content increase with increased aging time, and asphaltsensitivities to oxidative aging vary. Table 2-2.1.1 displays the values of each parameteremployed in equation 2-2.1.1 for different asphalts. To determine the relationship of “β” tomaterial compatibility, it was plotted against the Gaestel index for eight asphalts subjected to dryoxidation as shown in figure 2-2.1.3. An exponential equation with three parameters was appliedto describe this relationship:
)*(exp* GIba (2-2.1.2)
Whereβ = the shape of the curve,a and b = coefficient,GI = Gaestel index,
It is evident from this figure that “β” is related to asphalt compatibility in a non-linear,monotonic relationship. The same type of plot for wet oxidation, figure 2-2.1.4, indicates thataging in the presence of water improves the relationship between the shape of the curve (β value)
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and material compatibility. In this case, the R-squared value improved from 0.81 for dryoxidation to 0.95 for wet oxidation. Detailed information regarding how group compositionsrelate to their performance characteristics have also been presented at the 45th annual PetersenAsphalt Research Conference in Laramie, July 14-16, 2008.
Note that asphalts can be separated into simpler fractions based on chemical composition.Separating asphalt into less complex fractions has aided in determining how different moleculartypes affect the physical and chemical properties of the whole asphalt [Traxler 1961]. TheGaestel Index is an example.
Because the physical properties of an asphalt are controlled by the interactions of the moleculesfrom which it is composed, an understanding of these interactions should provide the basis forunderstanding the physical behavior. To develop a workable understanding of an asphalt, onemust sufficiently characterize the primary chemical features of the asphalt fractions, how theyinteract with one another, and how this relates to the durability of a pavement
An abstract entitled “Relationship between Group Composition of Asphalts and TheirPerformance Characteristics” submitted to the “Geohunan International Conference onChallenges and Recent Advances in Pavement Technologies and Transportation Geotechnics(www.geohunan.org)” has been accepted for presentation and publication. A manuscript isbeing prepared at the present time.
Table 2-2.1.1. Parameter values for different asphalts after dry and wet oxidation.
β γ Asphalt
Dry Wet Dry Wet
AAA-1
AAB-1
AAC-1
AAD-1
AAF-1
AAG-1
AAK-1
AAM-1
ABD
27.29
21.37
21.06
36.43
16.06
7.07
12.57
10.17
10.42
29.62
26.72
19.48
51.34
15.85
6.128
20.41
9.164
8.226
0.5051
0.6121
0.7510
0.3678
0.7340
1.8040
0.8453
1.1770
1.2060
0.4862
0.5371
0.8235
0.3173
0.7715
2.0470
0.5960
1.3070
1.4740
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Carbonyl Content, a.u.
0.0 0.1 0.2 0.3 0.4 0.5
Com
ple
xM
odulu
s,G
*,P
a
1e+5
2e+5
3e+5
4e+5
5e+5
AAA-1AAB-1AAC-1
AAD-1AAF-1AAG-1AAK-1AAM-1ABD
PAV at 80°C1000
AAG-1
ABD
AAA-1
AAD-1
Control
480 hrs
Dry Oxidation
Figure 2-2.1.1. Relationship between complex modulus and carbonyl content for differentasphalts before and after PAV aging in the absence of water.
Carbonyl Content, a.u.
0.0 0.1 0.2 0.3 0.4 0.5
Com
ple
xM
odulu
s,G
*,P
a
1e+5
2e+5
3e+5
4e+5
5e+5
AAA-1AAB-1AAC-1
AAD-1AAF-1AAG-1AAK-1AAM-1ABD
PAV at 80°C1000AAG-1
ABD
AAA-1
AAD-1
Control
480 hrs
Wet Oxidation
Figure 2-2.1.2. Relationship between complex modulus and carbonyl content for differentasphalts before and after PAV aging in the presence of water.
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Gaestel Index
0.0 0.1 0.2 0.3 0.4 0.5 0.6
-V
alu
e
0
10
20
30
40
50
AAA-1AAB-1AAC-1AAD-1
AAF-1AAG-1AAK-1AAM-1ABD
AAA
AAB
AAC
AAD
AAF
AAG
AAKAAM
ABD
Frequency= 10 rad/s, R2=0.81
b=3.351*exp(5.269GI)
, R2=0.81
Dry Oxidation
Figure 2-2.1.3. Relationship between b-value and Gaestel index for eight differentasphalts in dry oxidation.
Gaestel Index
0.0 0.1 0.2 0.3 0.4 0.5 0.6
-V
alu
e
0
10
20
30
40
50
60
AAA-1AAB-1
AAC-1AAD-1AAF-1AAG-1AAK-1
AAM-1
ABDAAAAAB
AAC
AAD
AAF
AAG
AAK
AAM ABD
Frequency= 10 rad/s, R2=0.95
Y=1.431*exp(8.056X), R2=0.95Wet Oxidation
Figure 2-2.1.4. Relationship between b-value and Gaestel index for eight differentasphalts in wet oxidation.
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Work to be Conducted Next Quarter
● Prepare the manuscript entitled “Relationship between Group Composition of Asphalts and Their Performance Characteristics” for the conference.
● Correlate oxidation master curve parameters (i.e., shift factor and rheological index) to chemical parameters (i.e., FTIR and compatibility parameters, Corbett fractions) as wellas low temperature properties (i.e., data from DSC) on the aged asphalts when they areavailable.
● Construct oxidation master curves for asphalts recovered from field core samples and correlate master curve parameters (i.e., shift factor and rheological index) to chemicalparameters (i.e., carbonyl content and compatibility parameters).
● Samples with different levels of asphalt film thicknesses (from thin film of 50 microns to standard film thickness of 1/8 inches) will be subjected to PAV aging at pavement servicetemperature in the presence and absence of water to investigate the relationship betweenoxidation and diffusion. Extensive rheological analysis will be conducted when theexperiments are complete.
Problems and Solution to Problem
No problems were incurred during the past quarter.
References
Huang, Shin-Che, Thomas F. Turner, and Kenneth P. Thomas, 2008, The Influence of Moistureon the Aging Characteristics of Asphalt Binders. Proc., 4th Eurasphalt & Eurobitume Congress2008, Copenhagen. Paper number: 406-002.
Thomas, Kenneth, 2002, Impact of Water During the Laboratory Aging of Asphalt. RoadMaterials and Pavement Design, 3(3), 299-315.
Traxler, R.N., 1961, Asphalt, Reinhold Publishing Co., New York, NY, Chapter 5.
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SUBTASK 2-2.2. SUPPORT OF THE MECHANISTIC-EMPIRICAL PAVEMENTDESIGN GUIDE
Subtask Manager: Mike FarrarOther Personnel: Ron Glaser, Shin-Che Huang, Will Grimes
Statement of Problem
The global aging system is a series of models that attempt to predict the change in binderviscosity in hot-mix asphalt (HMA) pavement with time and depth. These models are an integralpart of the NCHRP 1-37A Mechanistic-Empirical Pavement Design Guide. The models weredeveloped from an extensive database consisting of capillarity viscosity, and penetration andsoftening point measurements converted to viscosity, over a broad range of temperatures [Mirzaand Witczak 1995]. Christensen and Bonaquist [2006] modified the global aging system modelsto make use of rational rheological measurements and binder master curve parameters whilemaintaining consistency with the original models. They noted in a part of their study, whichemployed the global aging system, that the results should be considered approximate, since“there are many questions concerning the accuracy of the global aging system.”
WRI, also in 2006, evaluated how well the GAS models predicted the actual aging that occurredat the FHWA/WRI Arizona validation site [Farrar et al. 2006]. One of the main findings of thestudy was that the oxidative aging occurring at the Arizona site was substantially greater thanpredicted by the GAS models, particularly in the top 13 mm of the pavement. Al-Azri et al.[2006] in an extensive investigation of selected Texas highway pavements concerningunmodified binder aging reported the level of hardening reached in pavement binderssignificantly exceeded estimated values calculated by the global aging system both at thepavement surface and 125 mm below the surface.
More specifically, the global aging system was developed based on laboratory tests ofconventional “S” binders. These linear or straight-line Class “S” asphalts were non-modified,and the authors of the global aging system (Mirza and Witczak) advised that the global agingmodels should not be used for modified asphalts, Class “W” (waxy) or Class “B” (blown)asphalts. The S, B, and W designations were originally developed by Heukelom [1973] whoobserved the linear and nonlinear relationships of asphalts using the Bitumen Test Data Chartdeveloped in the 1960’s.
In addition: (1) the global aging system does not address photo-oxidation effects on the surface,(2) the air void adjustment factor is based on limited data and considered “optional,” (3) theglobal aging system does not take into account sealer/rejuvenator, chip seals, or open gradedfriction course effects on pavement aging, and (4) the global aging system is not based on“fundamental” binder properties.
Approaches
The accuracy and possible modifications to the global aging system are being studied at WRI byanalyses of data and materials from the FHWA/WRI validation sites and laboratory aging(RTFO and PAV). Analytical tests applied include infrared spectroscopy and dynamic shear and
20
bending beam rheometry of unaged and aged materials. Master curves of unaged and agedasphalts and age based shift factors are being studied to quantify age related changes.
Goals
The purpose of this subtask is twofold: (1) to improve the general understanding of thephysiochemical changes that occur with time and depth in asphalt pavement due to aging, and (2)to recommend specific modifications to the global aging system to improve its accuracy andexpand its application to modified asphalts.
Support of FHWA Strategic Goals
The work conducted in this subtask supports FHWA’s ultimate pavement research anddevelopment goal of providing performance-based models and tools to facilitate effectivemanagement of the national highway infrastructure. Expanding our understanding of howpavements age in terms of time and depth is critical to developing accurate models to predictrutting and cracking in rehabilitation and new construction projects, and to allow better timing ofpreventive maintenance strategies that are cost effective in mitigating pavement aging.
Background
Over the last several decades, there have been many studies on oxidative aging in asphaltpavements; however, few have dealt with how oxidative aging varies with depth. Of the studiesavailable on the subject, perhaps the most well known is by Coons and Wright [1968]. In thisstudy and other related studies [Mirza and Witczak 1995; Houston et al. 2005; Farrar et al. 2006;Al-Azri et al. 2006], the method used to evaluate aging involved slicing cores parallel to thepavement surface. In these studies the thickness of the slices varied from as little as 1.6 mm(1/16 inch) in the upper 6.3 mm (1/4 inch) of the core in the Coons and Wright study, to 25 mm(1 inch) in the upper area of the core in the Houston et al. study. How the cores were sliced mayhave determined the conclusions reached. For example, the Coons and Wright study showed aroughly 50% higher viscosity for asphalt recovered from the top 6.3-mm slice versus asphaltrecovered from the next lower 6.3-mm slice. In addition, a very fine film at the surface of thecore had a higher viscosity than the average viscosity in the top 6.3 mm. On the other hand, theHouston et al. study found that the viscosity did not vary significantly with depth. Sincedifferent pavement designs, binders, and ages were used in these studies, the results for both maybe valid. However, it is also possible that the 25-mm thickness of the slices used in the Houstonet al. study masked a viscosity profile that would have been apparent if thinner slices had beenexamined.
The conflicting conclusions are not surprising and point out the difficult nature of not onlymeasuring aging in HMA, but developing a global aging system to predict aging. An extensiveliterature review indicates the global aging system as developed by Mirza and Witczak is theonly system or set of models attempting to predict binder aging in HMA pavement on a “global”basis. Research to date suggests that while the system is an excellent starting point, it is at best“semi-global” and given that it is an integral part of the MEPDG, research to improve itspredictive capability is clearly warranted.
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Work Conducted This Quarter
2-2.2.1 Advanced Data Analysis
In the arena of asphalt research, it is certainly true that all of the data generated, particularly withmodern spectral instruments, have not been fully investigated or correlated. A number ofrelationships between important parameters may exist that could be revealed using theappropriate data mining techniques. Even in cases where the underlying physical and chemicalprocesses are not well understood, suitable mapping of easily obtained spectral data to moredifficult to obtain properties would be of great utilitarian value. A prime example of this ideawould be the ability to correlate infrared spectral data to the more difficult to obtain rheologicaldata. Such an endeavor may also lead to here-to-fore unknown relationships that could improveour fundamental understanding of asphalt.
Multiple Wave Number Correlations
Correlations previously developed at WRI using a data set consisting of four PAV aged SHRPasphalt binders did not work well with the addition of four Arizona validation site PAV agedasphalt binders. This indicated a need to investigate multiple wave number correlations.However, to use some commonly available algorithms, such as multivariable linear regression,the elimination of co-linear data is required. Co-linear data, when examining infrared spectra,are those wave numbers having absorbances that provide the same information. These are wavenumbers that are somehow related to one another by either describing points on the same spectralpeak, points on other peaks due the same chemical functional group, or process responses thatchange proportionally to other wave numbers. In the simplest of terms, the co-linear data in anasphalt aging data set are those wave numbers that change proportionally to each other as theasphalts age. Co-linearity can be tested by simply regressing one wave number against eachother in the entire data set to determine if they change proportionally to each other. By “crosscorrelating” the entire spectrum, these wave numbers that essentially provide the sameinformation can be grouped together and averaged, producing a new “compressed” version of thespectra. This level of compression can be adjusted depending upon how strict a threshold forcorrelation is selected. The selection criteria used is the regression coefficient determined duringthe cross correlation calculation. A cross correlation threshold of R-squared of 0.99 typicallyproduces 300 groups of wave numbers out of a spectra data set containing 3400 wave numbers,while an R-squared of 0.90 more aggressively groups the spectra into about 70 groups. Thegroupings at an R-squared of 0.99 are typically just adjacent wave numbers, but reducing the R-squared to 0.90 produces some banded groups. In addition to resolving some numerical methodissues, cross correlation of spectral data sets can reveal relationships between different areas ofthe spectra in response to PAV aging.
Ratio Indices
A number of researchers have successfully used ratios of absorbances at different wave numbersto improve correlations. These ratios, or indices, tend to minimize variance caused by a numberof factors, and thereby improve correlation results with asphalt property data. An exhaustivesearch of the spectra obtained during aging studies on SHRP and validation site asphalts for the
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best correlations to property data using ratios was performed. Every possible set of ratios wastested. The data set included spectra from PAV-aged asphalts at several tempertures and timesand consisted of, 65 spectra compressed using the R-squared equal to .99 criterion using crosscorrelation. The resulting linear correlations are of the form shown:
Log G*60C,10 rad/s = A (ABSi/ABSj) +Bδ60C,10 rad/s = A (ABSi/ABSj) +BLog G”60C,10 rad/s = A (ABSi/ABSj) +BLog G’60C,10 rad/s = A (ABSi/ABSj) +B
where ABSi is the average absorbance of the members of group i
All of these exhibit R-squares ranging from 0.91 to 0.92 using similar wave number ratios.
Table 2-2.2.1. Correlation equation constants and indices.
Group i
Begin wn*
Group i
End wn*
Group j
Begin wn*
Group j
End wn*
A - slope B - intercept
Log G*60C,10 rad/s 2983 2985 1254 1267 -3.998 11.263
δ60C,10 rad/s 1254 1267 2995 2997 -122.83 181.2
Log G”60C,10 rad/s 2980 2982 1254 1267 -3.058 10.581
Log G’60C,10 rad/s 2983 2985 1254 1267 -5.308 12.988
* wn = wave number
Group 119 contains wave numbers 1254-1267 and is common to all regressions, and occupiesthe spectral region shown below in figure 2-2.2.1.
Groups 221 and 222 are adjacent and contain 3 wave numbers each, 2980-2982 and 2983-2985.At less restrictive cross correlation thresholds they likely coalesce to the same group. Group 226is a bit distant containing 2995-2997, but still is in the same general area. (See figures 2-2.2.2,2-2.2.3, and 2-2.2.4.)
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Figure 2-2.2.1. Wave numbers 1254-1267.
Figure 2-2.2.2. Wave numbers 2980-2982.
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Figure 2-2.2.3. Wave numbers 2983-2985.
Figure 2-2.2.4. Wave numbers 2995-2997.
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A closer look in figure 2-2.2.5 at the region between wave numbers 2980 and wave numbers3000 indicates the difference (or similarity) in these groups:
Figure 2-2.2.5. Wave numbers in the region from 2980 to 3000.
Multivariable Linear Regression
A numerical analysis and matrix math library for implementation in the “.NET” (pronounceddot-net) development environment was purchased this quarter to expedite complex regressionanalysis. This Quinn-Curtis package provides several algorithms for multiple regression – thestandard least squares approach, which regresses only the independent variables you specify, andthree other methods, forward selection, backward elimination and stepwise selection, whichautomatically choose the final regression coefficients, starting with your best guess, andeliminating variables with marginal F-test statistics.
The algorithms have different properties, and each one can be the best for a particular regressionproblem and specific data set. As a rule, in the case of not very highly correlated independentvariables, the model obtained using general standard least squares regression will produce thesmallest error if checked on the same data set on which it was built. The other methods produceresults slightly less accurate, but generate simpler and more reliable, models.
The package also allows the programmer with the option of manually selecting the independentvariables for consideration by the algorithm, not considered by the algorithm, or unconditionally
26
contained in the regression analysis. This feature is essential, as cross-correlation at high rsquare values still often produces more independent variables than observations (The data set weare working with produces 283 independent groups, but we only have 66 spectra. Direct solutionis impossible.). Over-specified regression cannot be performed using simple multivariateregression techniques. Selection strategies, such as F-test rejections, must be employed toconsider the entire collection of possible information in a spectral data set. The ability to setwave numbers for consideration also allows the investigator to use experience and conceptualmodels as a guide for the selection of significant wave numbers.
When performing a regression with an over-specified data set, one must guard against artificialgood fits that have no fundamental basis. If, for example, we consider a fit that uses 66 wave-numbers to perfectly fit 66 spectra, what we have is the exact solution of this system ofsimultaneous equations. As the number of observations exceeds the number of fit parameters, sodoes our confidence that significant parameters are included. This is the realm of modelselection, and a number of statistical measures exist that provide some guidance. However, thesestatistics only provide a measure of probabilities, and certainty can only be approached as thenumber of observations grows very large. Consequently, R-squared measures are not the finalword in multivariable regression analysis, and a careful look at the F-test and the ratio ofobservations to parameters provides some measure of whether to include a parameter in thecorrelation or not.
The Stepwise Selection method will automatically reduce the parameter list from 283 to 17 wavenumber groups in the PAV data set currently being examined when fitting Log G*. The resultantR-squared is 0.996. Manually reducing the list based upon the F-test slowly reduces thecorrelation coefficient until only 8 wave numbers are used, after which further reductions in theparameter list count have a much stronger effect in diminishing the quality of the regression. Anexamination of figure 2-2.2.6 indicates that eight or even five wave numbers produce the level ofprecision justified by the level of precision present in the original data. A regression that is moreprecise than the data that generated it is artificial and probably unstable in extrapolation. It isinteresting to note that using the F-test to systematically reduce the parameter list ultimately toone does not produce the best correlating single wave number group.
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Parameters vs R squared
0
0.2
0.4
0.6
0.8
1
1.2
0 2 4 6 8 10 12 14 16 18
Number of Parameters
Rsq
uare
d
Figure 2-2.2.6. The influence of parameter list length on the regression coefficient.
2-2.2.2 Arizona FHWA/WRI Validation Site
One of the objectives of this study is to validate the accuracy of laboratory fundamental materialproperty tests using field performance data. To accomplish this, four asphalts used in Arizonafield validation site were subjected to laboratory RTFO/PAV aging at pavement servicetemperature of 60°C for different durations: 96 hours, 192 hours, 336 hours, and 504 hours.Analyses of these materials are being compared with field performance. Some of the rheologicalanalyses were reported in previous quarterly reports (March 31, 2008 and June 31, 2008). It wasreported that rheological analyses obtained from the laboratory agree well with 5 year old fieldpavement performance. The plots of G* versus phase angle were found to be particularly usefulto graphically fingerprint conventional asphalt binder rheology related to field pavementcracking performance.
To further elucidate how phase angle relates to the flow properties of asphalt binder, the phaseangle was plotted against temperature, as shown in figure 2-2.2.7, for one asphalt that was PAVaged for different times. As shown, the phase angle increases as a sigmoid shape as temperatureincreases.
28
Temperature, °C
-60 -40 -20 0 20 40 60 80 100
Phase
Anlg
ea
t10
rad/s
,de
gre
e
0
10
20
30
40
50
60
70
80
90
0 hr
96 hrs
192 hrs
336 hrs
504 hrs
4-Year/Top Slice
4-Year/2nd Slice
4-Year/3rd Slice
4-Year/Bottom Slice
AZ1-1 Lab PAV Aging at 60°C
Figure 2-2.2.7. Phase angle as a function of temperature for asphalt AZ1-1before and after lab and field aging.
A statistical logistic model with three parameters was used to construct all curve fits for the plotof phase angle versus temperature on all unaged and aged asphalts to establish a suitablemathematical relationship of the phase angle and temperature at the selected frequency. Theequation used is
]exp1[ )(*(
T (2-2.2.1)
where
δ = phase angle at a given frequency, degreesα = maximum phase angle for ideal fluid material, 90 degrees was used in this case.β = correlation constant,γ = inflection point. T = testing temperature, °C
Figure 2-2.2.8 shows the phase angle as a function of temperature for asphalt AZ1-1 beforeaging. It can be seen from the figure that the phase angle slowly increases initially in a sigmoidform as temperature increases up to approximately -20°C and then the phase angle rapidlyincreases linearly as temperature increases until around 70°C, and is less pronounced above70°C. Of particular interest is the γ value in the model. Parameter γ is the inflection point and is
29
defined as the transition temperature where the material flows from an elastic-dominantcondition to a viscous-dominant condition. Figure 2-2.2.9 shows the transition temperature as afunction of laboratory PAV aging times for four asphalts. The transition temperature for all fourasphalts increases initially as aging times increase, up to approximately 96 hrs, and then levelsoff as aging time increases further.
To interpret the parameters used in the model, the linear region shown in figure 2-2.2.8 isconsidered. An alternative method, derived from this phase angle-temperature relationship, isproposed to evaluate these binders. Note that the traditional PG grading system was based on amodulus value and a phase angle value at a certain temperature. The alternative method uses theintersection between the linear region and the sigmoid curve at both maximum phase angle andminimum phase angle values as high temperature grading and low temperature grading,respectively. Using this proposed approach, as shown in figure 2-2.2.8, asphalt AZ1-1 can begraded as approximately 69-22. The same approach was applied to estimate the other threeasphalts. The estimated gradings are 67-41, 57-22, and 58-22, for AZ1-2, AZ1-3, and AZ1-4,respectively.
The majority of the results were presented in a journal article that will be published in theproceedings of the 52nd annual conference of Canadian Technical Asphalt Association inNovember 2008 in Saskatoon, Saskatchewan.
Temperature, °C
-60 -40 -20 0 20 40 60 80 100
Ph
ase
An
gle
at1
0ra
d/s
.,d
eg
ree
0
10
20
30
40
50
60
70
80
90
Neat
Predicted linear region
AZ1-1 Lab Aging at 60°C
Te=-22.25 Tv=69.30Tve=23.43
e=9.57
v=80.50
Figure 2-2.2.8. Phase Angle versus Temperature Plot for Asphalt AZ1-1.
30
Time in PAV at 60°C, hrs
0 100 200 300 400 500 600
Tra
nsitio
nT
em
pera
ture
at10
rad
/s.,
C
0
10
20
30
40
50
60
AZ1-1
AZ1-2
AZ1-3
AZ1-4
PAV Aging at 60°C
Figure 2-2.2.9. Transition temperatures versus PAV aging times for four asphalts.
2.2-2.3 Difference infrared spectroscopy
Introduction
Typically, the infrared spectra of asphalt or aggregate from the pavement surface or at somedepth, or from reclaimed asphalt pavement (RAP) are acquired by first extracting the asphaltwith solvent. The process is time consuming and requires considerable solvent. Even anasphalt/aggregate micro-extraction (approximately 50 mg) can be tedious, and of course there isalways the concern that (1) the solvent may change the physical properties of the asphalt, and (2)the solvent may not adequately remove all the asphalt from the aggregate. In this study, thepossibility of using difference infrared spectroscopy to resolve the asphalt and aggregate spectrafrom mixture spectra is considered.
Beyond the potential benefit of eliminating solvent extraction, there is perhaps even moreimportantly the potential to evaluate the chemical interaction between asphalt and aggregate atthe aggregate surface. It is really just speculation at this point, but it may be possible, givenrefinement in our current infrared analysis technique to improve our understanding and predictthe stripping potential of asphalt/aggregate combinations from infrared spectra (see themultivariate analysis approach discussed in this report and the previous March ’08 Quarterly).Also, the asphalt/aggregate interaction on the molecular level may shed light on aggregatecatalytic effects and oxidative aging. In another section of this report, infrared differencespectroscopy is used to evaluate the chemical interaction of polyphosphoric acid in asphalt.
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Experimental
Asphalt Aging
Aging protocols included the rolling-thin-film oven (RTFO, AASHTO T-240) method and thepressurized aging vessel (PAV, AASHTO R28) method.
FTIR/ATR
A Perkin Elmer single-bounce diamond attenuated total reflectance (ATR) accessory coupled toa Spectrum One FTIR spectrometer was used to acquire the infrared spectra. All data werecollected using 16 scans, a resolution of 4 cm-1, and a spectral range of 650–4000 cm-1.Background spectra were obtained through the ATR element when it was not in contact with thesample. The spectra were collected by placing a small amount of asphalt or asphalt/aggregatemastic on the diamond and, in the case of the asphalt/aggregate mastic, pressing it down with ametal anvil to ensure good contact.
Materials
SHRP Asphalts
Strategic Highway Research Program (SHRP) asphalt AAD-1 was used in this study. Theasphalt was RTFO/PAV aged at 80˚C for 480 hours.
Aggregates
Strategic Highway Research Program (SHRP) aggregate RD was used in this study. RD is alimestone. Major RD elemental oxides are CaO (39%), and SiO2 (17%). Major mineralcomponents are calcite (61 %), quartz (7.4%), and organics (5%) [Robl et al. 1991].
Laboratory prepared mastic
Mastics were prepared by mixing aged AAD-1 asphalt (RTFO/PAV 80˚C, 480 hours) with RDaggregate (see table 2-2.2.2 for mastic gradation). Four relative concentrations of each masticwere prepared by mass: 20% aggregate/80% asphalt, 50% aggregate/50% asphalt, 80%aggregate/20% asphalt, and 90% aggregate/10% asphalt. The mastic was ground to a finepowder using a ceramic mortar and pestle before testing with the ATR. Smearing of the asphaltduring grinding was reduced by introducing liquid nitrogen into the mortar with the powderduring grinding.
Table 2-2.2.2. Gradation for fine, dense graded mastic.
Sieve Size, mm Percent Passing
1.19 100
0.600 75
0.300 50
0.150 30
0.075 20
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Results and discussion
The total absorbance tA of an asphalt/aggregate mixture can be expressed as
)()()( ract AAA (2-2.2.2)
where )(acA and )(rA are the contributions of the asphalt and aggregate to the total
absorbance at frequency , respectively. Given two spectra of a two component mixture, wherethe only difference is the concentration of the two components, the spectra of the twocomponents can be resolved without isolating them [Hirschfeld 1976; Koenig et al. 1977].
To resolve the asphalt spectrum )(acA from two asphalt/aggregate mixture spectra, the difference
is adjusted by a scaling factor. The factor can be determined subjectively thru continuousvariation with appropriate software or by calculation in a spreadsheet or program. In this study,the scaling factor was determined subjectively using a Perkin-Elmer software algorithm anddiminishing the difference band at 1800 cm-1, which is an overtone band solely attributable tolimestone carbonate absorption [Legodi et al. 2001; Vassallo et al. 1992].
Caution is required in interpreting difference spectra. Koenig noted some years ago that, “sincethe subtraction technique allows computer-scale expansion of the difference spectra, the resultanthigh sensitivity to real spectroscopic differences also applies to the detection of sampling andphotometric artifacts as well” [Koenig 1981]. There are two principle types of spectral artifactsin difference spectra: (1) wavenumber shifts in the spectrum of the mixture due to chemicalinteraction and (2) absorbance peaks with high amplitude may be so large that they do not followBeer’s law [Smith 1996].
Using the ATR technique results in very low absorbances compared to more commontransmission techniques and may resolve the problem of non-linearity at high absorptionamplitude. To aid in the reduction of spectral artifacts related to scattering and particle size theasphalt/aggregate mastics were ground to a fine powder. Grinding the mastic helps mitigatescattering, however, the massive increase in uncoated fractured faces dramatically increases theabsorption of the rock compared to the absorption of the asphalt. Absorption of the carbonyl andaromatic moieties in asphalt at approximately 1700 and 1600 cm-1, respectively, appear to beabsent or barely visible above the noise in the spectra shown in figure 2-2.2.10.
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Figure 2-2.2.10. FTIR/ATR spectra of RD limestone aggregate/aged AAD-1 asphalt masticafter grinding using a ceramic mortar and pestle with liquid nitrogen.An ATR correction or other spectral manipulation was not applied.
The aggregate absorption band internal peak heights (heights measured from approximately thebase of the band to the peak of the band) in the fingerprint region of the spectra appear to veryroughly correspond to the concentration of the aggregate in the original mastics. However, theC-H stretching bands of the asphalt, from about 2800 to 3100 cm-1 do not appear to correspondto the concentration of the asphalt in the original mastics.
These differences and the general appearance of the spectra suggest that additional investigationof the ATR technique is warranted to improve precision and accuracy. It is not unreasonable toassume there may have been a significant gap between the crystal surface and sample and thatthe gap was not consistent from sample to sample. The force applied to each sample with theanvil was not consistent and varied from 38 to 90 N. Also, the ATR correction calculation toadjust for varying depth of penetration, which is dependent on wave number, was not performed.The calculation is made assuming perfect contact and since the same correction would apply toall the spectra it was deemed unnecessary for quantitative analysis. This assumption seemsreasonable, but further analysis may reveal the correction would aid the quantitative analysis.Performing the ATR correction should aid in comparing ATR and transmission spectra.
34
Other factors such as the position and the condition of the ATR crystal can affect depth ofpenetration. Scratches on the ATR crystal affect crystal/sample contact and can influencepenetration depth [Smith 1996]. Also, contaminants or remnants not removed during cleaningcan significantly affect the results. In these exploratory tests a background was not performedbetween samples. Occasionally during a day’s testing, a new background was collected andratioed to the previous background. Typically, ratios of the background spectra suggested littlechange in ambient CO2 or H2O, or equipment parameters, but future testing will be conducted byperforming a background between every sample.
Regardless of the reasons for the relatively crude spectra in figure 2-2.2.10, the level ofabsorbance of the asphalt in the sample is simply too low to perform spectral subtraction in anacceptable quantitative manner. However, it was determined that heating and mixing thesamples under hot air for a very short interval (roughly 30 seconds) decreased the asphaltviscosity sufficiently to allow coating of a significant number of the uncoated faces developedduring the grinding process. Figure 2-2.2.11 shows the spectra after heating the ground samplesshown in figure 2-2.2.10.
Figure 2-2.2.11. FTIR/ATR spectra of RD limestone aggregate/aged AAD-1 asphalt mastic aftergrinding using a ceramic mortar and pestle with liquid nitrogen and then reheating.
An ATR correction or other spectral manipulation was not applied.
35
The quality of the spectra in figure 2-2.2.11 appears significantly improved compared to figure2-2.2.10, particularly in terms of the level of absorption of the asphalt. Spectral subtraction ofthe mixed spectra was performed to resolve the spectra of the asphalt component in the mixturesfor several combinations as displayed in figure 2-2.2.12. In addition, the figure also shows thespectrum of the pure asphalt used to produce the mastics. Visually the difference spectra appearquite similar although there are several aggregate absorption bands, such as the band at about870 cm-1 that do not appear to be completely removed.
Figure 2-2.2.12. FTIR/ATR difference spectra compared to “pure AAD-1 aged asphalt.No ATR correction or other spectral manipulation has been applied.
Interestingly, spectral subtraction between the mastics 80%RD/20%AAD and 90%RD/10%AADdid not provide a good spectrum of asphalt. At first it was assumed that there was simply toomuch aggregate in these mastics to subtract out the asphalt. However, upon further considerationit may be that chemical interaction between the aggregate and asphalt is causing wave-numbershifts leading to distortions in the subtracted spectrum. Mastics with high concentration ofaggregate and large surface area from the grinding process may have very thin films once theasphalt is reheated and spreads out over the uncoated fractured faces. Perhaps the film thicknessis in the micron or submicron range. Since the depth of penetration of the evanescent wave into
36
the sample is roughly one micron, a significant portion of the absorbance observed may be fromthe asphalt/aggregate interface. Whereas, the infrared spectra of mastics with significant asphaltconcentration are made up primarily of absorption from the bulk asphalt and aggregate.
Typically, the carbonyl peak at about 1700 cm-1 is used to estimate oxidation of the asphalt andestablish relationships to physical properties such as stiffness (for example the complex shearmodulus G*). For this study, a quick and relatively simple way to compare the differencespectra to the pure asphalt spectrum is shown in table 2-2.2.3 using a carbonyl index (CI)
13761700 / AACI (2-2.2.3)
where the carbonyl stretching band area (A1700) was normalized using the CH3 umbrella bendingband area (A1376). The CI’s are similar and suggest the spectral subtraction technique isrelatively quantitative.
Table 2-2.2.3. Carbonyl indices from difference spectra compared to thecarbonyl index of the pure asphalt.
FTIR/ATR spectra Carbonyl index
Difference spectra20%RD/80%AAD - 80%RD/20%AAD
0.38
Difference spectra50%RD/50%AAD - 80%RD/20%AAD
.40
Difference spectra50%RD/50% AAD - 90%RD/10%AAD
0.43
Difference spectra20%RD/80% AAD - 50%RD/50%AAD
0.38
Difference spectra20%RD/80%AAD - 90%RD/10%AAD
0.40
Aged AAD-1 asphalt 0.44
2-2.2.4 Explained Absorbance at 1730 cm-1
As part of this task we have been developing a micro-extraction technique which is used inconjunction with FTIR analysis to provide a relatively simple method to profile oxidation as afunction of depth beneath the pavement surface. In the first quarter of this year experiments ofthis type were conducted using a core from the Arizona validation site. These experimentsyielded an unexpected oxidation profile. For this core, it appeared that the pavement was moreoxidized in deeper layers than it was near the surface. Significant variations in oxidation werealso observed between the various samples taken from the same depth below the core surface.Duplicate IR analyses using a different technique showed the same unusual profile.
37
To develop an oxidation versus depth profile for a pavement sample, oxidation is quantified interms of a carbonyl index. The carbonyl index that we have been using is simply the ratiobetween the IR absorbances associated with carbonyl stretching motions (~1760-1670 cm-1) andCH3 umbrella deformation (~1376 cm-1). Use of this index provides a method for normalizingresults for easy comparison. To generate the index the IR absorbance was integrated overwavenumbers ranging from1760 to1670 cm-1 and the result was divided by the integratedabsorbance between 1356 cm-1 and1396 cm-1.
The Arizona highway core samples that showed an unusually high level of oxidation relative todepth beneath the surface all showed an additional IR absorbance centered around 1730 cm-1 inthe carbonyl region. This absorbance was observed only in the cores from the field and did notshow up in laboratory aged samples of the same asphalt. The absorbance at 1730 cm-1 stronglyinfluenced the carbonyl index for the samples in which it occurred. If the area associated withthe IR absorbance at1730 cm-1 was arbitrarily eliminated from the carbonyl index calculation, theoxidation/depth profile looked more as expected with oxidation decreasing with increasing depthin the pavement.
The available evidence seemed to indicate that we had somehow introduced a contaminant intopart of the sample set. However, because all of the samples had been prepared identically, wewere unable to explain how the contaminant could be present only in part of the sample set.Other possible explanations for the anomalous oxidation profile were considered, but noneseemed completely satisfactory. Identification of the source of the IR absorbance at 1730 cm-1
was left for future work.
Our effort to profile oxidation with respect to depth in the pavement was continued this quarterwith micro-extraction and FTIR analysis of two cores that were prepared and aged in thelaboratory. The cores were part of a set that was made to study laboratory aging techniques. Theset of cores was prepared in a gyratory compactor and then aged in an oven for various lengths oftime. The two cores that were used in experiments this quarter represented the shortest andlongest aging times from the set. The set of cores was prepared by an outside laboratory usingone of the SHRP core asphalts and a well characterized and carefully sized aggregate mix. Forthe two cores used in experiments this quarter, two separate sets of samples were collected andanalyzed on two different days.
Following procedures developed in previous work, the two cores were split axially using awedge and hydraulic press. Small pieces were then removed from the exposed core faces andthe asphalt was extracted and analyzed using FTIR. As in previous quarters, samples werecollected in rows parallel to the core top surface at various distances from that surface. A secondset of samples, collected with respect to distance from the circumference of the core, was alsoextracted and analyzed. The technique used to collect, extract, and analyze all of the varioussamples was identical to the technique used in previous quarters to measure the oxidation profilein cores collected from the Arizona field validation site.
The second set of samples was taken to provide an estimate of the lateral gradation of theoxidation profile (oxidation versus distance from the circumference of the core) for the ovenaged sample set. We assumed that oxidation would be greater in samples taken from near the
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circumference of the core cylinder than in samples from closer to the center of the core. Bycoincidence and the nature of the two sampling patterns used in the experiments, severalessentially duplicate samples were extracted and analyzed from these cores. The same procedurewas used to prepare and analyze both sets of samples.
Figures 2-2.2.13 and 14 show FTIR liquid-cell spectra (CS2 solvent, KBr cell) for samples takenfrom essentially identical locations on the core face on two different days. The second sampleshows an extremely large absorbance centered at ~1730 cm-1 as well as several other bands thatare clearly not present in the first sample. The relative size of the various new IR absorbancebands leaves no doubt that these features are not related to the asphalt sample, but instead have toresult from some other source.
Figure 2-2.2.13. FTIR liquid cell spectra for two extracted asphalt samples.
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Figure 2-2.2.14. FTIR liquid cell spectra for two extracted asphalt samples 2000-600 cm-1.
Considering the relative intensity of the new IR absorbance bands and the fact that all of theglassware and vials had been cleaned and muffled before the samples were extracted, theextraction solvent, or perhaps the nitrogen stream used to evaporate the solvent, was consideredto be the most likely source of the contaminant. All of the samples used in the experiments hadbeen extracted using an 85/15 v./v. mixture of toluene and ethanol. To determine where thecontaminant was coming from, an empty vial and vials containing the extraction solvent and theextraction solvent components (toluene and ethanol) were evaporated to dryness under flowingnitrogen using the N-EVAP apparatus that had been used to remove the solvent from the testsamples. After the solvent was evaporated, each vial was rinsed with CS2 which was thentransferred to a liquid cell and analyzed using FTIR.
Figure 2-2.2.15 shows the IR spectrum from the evaporated extraction solvent. A similarspectrum was obtained for the vial that had contained ethanol. The empty vial and the vial thathad contained toluene showed no indication of the contaminant. This test showed that theethanol that was used to prepare the extraction solvent was the apparent source of thecontamination. An FTIR library search for spectra matching that of the evaporated solventrevealed that the contaminant is probably dibutyl phthalate (figure 2-2.2.16).
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Dibutyl phthalate is a relatively common industrial chemical that is used as a plasticizer and as asolvent. Chemically it is an ester of benzenedicarboxylic acid, and as such, it exhibits a strong IRabsorbance centered near 1730 cm-1. Dibutyl phthalate is only slightly soluble in water, but it isvery soluble in many common organic solvents including alcohols. The contaminant, astentatively identified in these experiments, is almost certainly responsible for the unusualoxidation profile associated with the Arizona highway core that was analyzed in the first quarterof this year.
Even though the probable contaminant and its source with respect to the asphalt extractions usedin this task have been identified, several unanswered questions remain. Most important of theseis why the contaminant shows up in some of the asphalt samples and not others. All of thesamples were extracted with the same contaminated solvent mixture. Dissolution of the asphalt,separation of the aggregate solids, and evaporation of the solvent were all carried out using thesame procedure for each sample. All of the samples from a given set were extracted on the sameday.
Figure 2-2.2.15. FTIR liquid cell spectra of residue from evaporated extraction solvent.
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One possible variant from sample to sample could be the relative velocity of the nitrogen sweepin the individual vials on the N-EVAP apparatus. Each vial has a separate control valve for itsnitrogen stream. Variation in the settings of these valves could affect the rate of evaporation ofthe contaminant, possibly leaving some behind in the vials with the lowest relative sweepvelocities. This theory will be tested experimentally in future work.
Figure 2-2.2.16. IR spectrum of dibutyl phthalate from Perkin Elmer reference library.
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Work to be Conducted Next Quarter
2-2.2.1 Advanced Data Analysis
Future work next quarter is aimed at three general areas. These three areas should improve ourability to build a robust correlation technique and move our efforts closer to practical applicationin the asphalt paving industry.
Statistical Significance
Additional data sets will be investigated to improve our level of confidence in the significance ofindependent parameters selected. In addition, a number of model selection criteria statistics willbe evaluated for usefulness in parameter selection and these will be compared to parameters onewould expect from our current understanding of asphalt binder oxidation. Targeted data setsinclude validation site asphalts, and PPA and Polymer modified asphalts.
Fundamental Explanation
Ideally, the best parameter selection set should conform to our knowledge of oxidationchemistry, and, perhaps, add to it. Research chemists at WRI, along with the experience of Dr.Claine Petersen, will be employed to focus upon the fundamental significance of the parametersused to correlate infrared spectra with physical properties.
Time series (kinetic) correlations will also be attempted, using tradition chemical kineticapproaches and also time to rheology approaches using statistically inferred spectral responses.
Practical Application
Ultimately, practical application of this knowledge will allow pavement designers to rationallybuild and design better roads at significant savings to the taxpayer. WRI will continue toevaluate new and simpler pavement sampling techniques that will allow cost effectivemonitoring of pavement aging. Reliable IR to rheology correlations will also provide a rapid,cost effective technique to estimate the condition of recycled asphalt pavements, which is crucialto implementing rational blending designs and increased RAP utilization. In the research arena,IR to rheology correlations, because of the small sample size requirements, will open the door todetailed depth profiling in support of our Global aging Model improvement efforts.
Ultimately in order to fully apply the advantages of spectral difference spectroscopy and moreadvanced infrared chemometric analysis techniques such as the multivariate approach discussedin this report and the well know partial-least squares (PLS) and principal component analysis(PCA) techniques, it will be necessary to establish laboratory procedures to acquire highlyrepeatable, quantitative infrared spectra. WRI currently has the capability of performingstandard and micro, ATR, photoacoustic, transmission (thin film and liquid cell) in the mid-infrared range and up to approximately an 8000 wave number in the near infrared range. Futurework will attempt to provide the highest quality infrared spectra achievable proscribed only bythe ultimate limitations of the equipment.
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2-2.2.2 Arizona FHWA/WRI Validation Site
● Construct oxidation master curves for asphalts that were laboratory aged in PAV at different durations and correlate master curve parameters (i.e., shift factor and rheologicalindex) to chemical parameters (i.e., carbonyl content and compatibility parameters) andfurther to the field pavement performance.
● The same samples that were laboratory aged in PAV at 60°C will be subjected to the same PAV aging test at higher aging temperatures to develop aging kinetic master curvesto further assist the revised mechanistic empirical pavement design guide.
● Rheological analyses on neat asphalts used in Minnesota validation site will be conducted next quarter. Laboratory RTFO-aged and RTFO/PAV-aged samples will be analyzed aswell.
2-2.2.3 Difference Infrared Spectroscopy
The potential applications of advanced infrared spectroscopic analysis appear to be growing aswe become more familiar with the techniques. A potential application of differencespectroscopy is the spectral separation of the mixed phase system of an asphalt altered bydifferent annealing processes.
We will investigate developing an in-house fabricated thermal cell or acquire a commerciallyavailable cell to study temperature related changes in intermolecular bonding and oxidative agingkinetics in-situ by FTIR. The oxidative kinetic information is critical to developingmodifications to the global aging model to better account for environmental effects of aging.
2-2.2.4 Explained Absorbance at 1730 cm-1
LimitedOne possible variant from sample to sample could be the relative velocity of the nitrogensweep in the individual vials on the N-EVAP apparatus. Each vial has a separate control valvefor its nitrogen stream. Variation in the settings of these valves could affect the rate ofevaporation of the contaminant, possibly leaving some behind in the vials with the lowestrelative sweep velocities. This theory will be tested experimentally in future work.
Problems and Solution to Problem
There were no problems under this task for this quarter, except a contaminant was discovered inthe solvent used to perform asphalt/aggregate extractions. The contaminant has been identifiedas dibutyl phthalate. See section 2-2.2.4 of this report for a discussion on how it was discovered.
References
AASHTO, Standard Practice for Accelerated Aging of Asphalt Binder Using a PressurizedAging Vessel (PAV). AASHTO Designation: R28-02, America Association of State Highwayand Transportation Officials, Washington, D.C.
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Al-Azri, N. A., S. H. Jung, K. M. Lunsford, A. Ferry, J. A. Bullin, R. R. Davison, and C. J.Glover, 2006, “Binder Oxidative Aging in Texas Pavements: Hardening Rates, HardeningSusceptibilities, and the Impact of Pavement Depth,” Paper accepted for presentation at the 2006TRB January conference, Washington, D.C.
Coons, R. F., and P. H. Wright, 1968, An Investigation of the Hardening of Asphalts Recoveredfrom Pavements of Various Ages. Journal of Association of Asphalt Paving Technologists, 37:510-528.
Christensen, D. W., and R. F. Bonaquist, 2006, Volumetric Requirements for Superpave MixDesign, NCHRP 567, National Cooperative Highway Research Program.
Farrar, M. J., P. M. Harnsberger, K. P. Thomas, and W. Wiser, 2006, Evaluation of Oxidation inAsphalt Pavement Test Sections after Four Years of Service. Proc., International Conference onPerpetual Pavement, September 2006, Columbus, Ohio.
Heukelom, W., 1973, An Improved Method of Characterizing Asphaltic Bitumens with the Aidof their Mechanical Properties. Journal of Association of Asphalt Paving Technologists, 42: 67-98.
Hirschfeld, T., 1976, Computer Resolution of Infrared Spectra of Unknown Mixtures. AnalyticalChemistry, 48 (4): 721-723.
Houston, W. N., M. W. Mirza, C. E. Zapata, and S. Raghavendra, 2005, Environmental Effects inPavement Mix and Structural Design Systems, NCHRP 9-23, Preliminary Draft Final Report Part1, National Cooperative Highway Research Program, September 2005.
Koenig, J. L., L. D’Esposito, and M. K. Antoon, 1977, The Ratio Method for Analyzing InfraredSpectra of Mixtures. Applied Spectroscopy, 31 (4): 292-295.
Koenig, J. L., 1981, Fourier Transform Infrared Spectroscopy of Chemical Systems. Acc. Chem.Res., 14: 171-178.
Legodi, M. A., D. de Waal, and J. H. Potgieter, 2001, Quantitative Determination of CaCO3 inCement Blends by FT-IR. Applied Spectroscopy, 55 (3): 361-365.
Mirza, M. W., and M. W. Witczak, 1995, Development of a Global Aging System for Short andLong Term Aging of Asphalt Cements. Journal of Association of Asphalt Paving Technologists,64: 393-431.
National Cooperative Highway Research Program, 2004, Development of the 2002 Guide for theDesign of New and Rehabilitated Pavement Structures. NCHRP 1-37A, Final Report, NationalResearch Council.
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Robl, T. L., D. Milburn, G. Thomas, J. Groppo, K. O’Hara, and A. Haak, 1991, The SHRPMaterials Reference Library Aggregates: Chemical, Mineralogical, and Sorption Analyses,SHRP-A/UIR-91-509, Strategic Highway Research Program, National Research Council,Washington, DC.
Smith, B. C., 1996, Fundamentals of Fourier Transform Infrared Spectroscopy. CRC Press,Boca Raton, FL.
Vassallo, A. M., P. A. Cole-Clarke, L. S. K. Pang, and A. J. Palmisano, 1992, Infrared EmissionSpectroscopy of Coal Minerals and their Thermal Transformations. Applied Spectroscopy, 46(1): 73-78.
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SUBTASK 2-3. NANOTECHNOLOGY: AFM ANALYSIS OF ASPHALT THIN-FILMMICROSTRUCTURE PHENOMENOLOGY
Task Manager: Troy PauliOther Personnel: Will Grimes, Julie Miller, James Beiswenger
Statement of Problem
Asphalt pavements are known to fail over time by a combination of different mechanisms. Themodes of failure of asphalt pavements that are commonly sited are embrittlement due primarilyto steric and oxidative aging, fatigue cracking due primarily to loading cycles and moisture(traffic), rutting due primarily to densification and plastic flow, thermal cracking due primarily tolow temperature embrittlement, and formation of potholes due primarily to breakdown of thesub-base structure. It is further contended in the pavement community that all of theaforementioned modes of failure are somehow influenced by environmental conditions likeseasonal temperature swings and the presence of water. Why do pavements constructed to thesame specifications and subjected to similar environmental conditions and traffic loading fail atdifferent rates by different failure modes when different materials (e.g., asphalts and aggregatesderived from different sources) are used to construct the pavement?
Approach
In this subtask we have asked the question why pavements constructed with asphalt derived fromdifferent crude sources, if all other variables were to be kept the same, perform differently interms of moisture compounded fatigue resistance. For example, pavement cracking is oftenobserved to form distinct patterns during the lifespan of the pavement. In many other fields ofmaterial science, metallurgy for example, pattern forming cracking has been successfullycorrelated to the formation of microstructural grain boundaries which originate in these materialsduring casting [Cappelli et al. 2008; Bian and Taheri 2008]. This same pattern crackingphenomena can also be applied to paving materials [Robertson et al. 2005, 2006]. The approachwill be to develop quick and inexpensive experimental techniques derived from other fields ofmaterials nano-science. Results from these tests can then be combined with chemo-mechanicalmodels of asphalt-aggregate composite materials to predict pavement performance.
Goal
The goal of this work is to gain a more fundamental understanding of the composition of asphaltconcrete paving materials and how it relates to pavement performance (specifically fatiguecracking/self healing compounded by the presence of moisture).
Support of FHWA Strategic Goals
This work plan supports the following FHWA focus areas: Pavement Design and Analysis:This work will provide a more fundamental understanding of the physico-chemical nature ofasphalt-binder and chemo-mechanical properties of mastics as they relate to pavementperformance. Optimum Pavement Performance: A more fundamental understanding of thephysico-chemical nature of asphalt-binder will lead to better characterization and development of
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modified asphalts based on better materials selection criteria. Environmental Stewardship: Amore fundamental understanding of the physico-chemical nature of asphalt-binder will lead tobetter characterization of warm mix asphalts and recycled asphalt pavement technologies andshould ultimately result in refinement of the present technologies as well as lend insight intodeveloping other types of “green” technology.
Introduction/Hypotheses
Kandhal and Chakaraborty [1996] and Kandhal et al. [1998] have reported that the durability ofHMA mixes is directly related to the asphalt film thickness. Based on calculations of thegradation void-space volumetrics of aggregate in common pavement mix designs, they proposethat the average film thickness of asphalt in a pavement has a dramatic effect upon both theresilient modulus and the viscosity of a mix. As the average film thickness is decreased fromaround 15 microns to 3 microns, both the resilient modulus and the viscosity are observed toincrease almost exponentially. Kandhal and Chakaraborty [1996] and Kandhal et al. [1998] alsosuggest that the optimum film thickness of asphalt in a mix is between 6-8 microns, with thinnerfilms producing brittle mixes and thicker films being susceptible to increased rutting. Thiscorresponds to an air-void content of approximately 4%. Kandhal et al. [1998] further note thatreduced air-void content should also prevent thin-film oxidation, based on the finding that whenair-void was greater than 8%, the mix would age more rapidly than with 4% air-voids. Theseobservations suggest that “molecular ordering” of asphalt thin-films in mastic occurs, and thatthis molecular ordering becomes more pronounced by decreasing the asphalt film thickness.
The potential for crack initiation in most “composite” materials is shown to be related to thedevelopment of grain boundaries in addition to aging and other factors. These boundaries arecaused by molecular ordering phenomena corresponding to the development of individualmaterial phases within these types of systems [Cappelli et al. 2008; Bian and Taheri 2008].Grain boundaries have been observed in: (1) crystals, the cutting of diamonds for example, withfracturing occurring along lattice plane flaws of the crystal, (2) the crack-flaws that form in icecubes as a function of cooling rate and impurities in the water, and (3) the development ofdislocations in binary metal alloy solidification processes. Microstructuring of chemicallydistinct phases in asphalt “binder”, particularly at asphalt-aggregate interfaces, could contributeto the formation of such grain boundaries that serve as crack initiation points.
Crack initiation and propagation in metals and crystalline materials generally falls within thecategory of brittle fracture. However, polymers are more amorphous by nature which increasesfracture ductility and renders the system more difficult to model. The large number of differentpetro-organic-type molecules in asphalt may interact with themselves and with the mineralsurfaces to form distinct chemical phases that determine the viscoelastic properties of the binderin the pavement. These properties can then be used to determine the tendency of a pavement tofracture and self-heal.
In this subtask, uniform asphalt films are studied at near-molecular (< 5-nm), nano (1-100-nm),meso (10’s-100’s-nm) and microscopic (100’s-1000’s-nm) scales. Scanning probe microscopytechniques (i.e., atomic force microscopy) are employed to correlate the kinetic andthermodynamic processes of phase transformation phenomena of different chemical moieties
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present in asphalt with the materials’ performance in roadways. Asphalts differ by crude sourceand have historically been defined by chemists by their unique chemical classes of molecules.This is a simplified approach given that petroleum asphalt is comprised of tens of thousands ofdifferent types of molecules that otherwise would need to be characterized if a totallyfundamental approach to the problem were to be considered.
It has also been observed in previous experiments [Robertson et al. 2005, 2006] that differentasphalts tend to form self-ordered microstructural “features” to different degrees. This wasdemonstrated at the asphalt-air free surface interface in solvent spin-cast, thin-film coatings withthicknesses ranging from 3 microns to as thin as 150 nm. Generally speaking, structures withclearer phase boundaries are observed as the thickness of these “ultra-thin” films is decreasedbelow 2 microns [Robertson et al. 2005]. Thicker films tend to exhibit larger structures,particularly the bumble bee shaped structures that appear to “grow” to a limiting size in 10’s ofmicrons thick films with less distinguishable interface boundaries. Inevitably, the formation ofthese microstructures in very thin films of asphalt leads directly to the development of interfacialgrain boundaries between chemically different phases of materials. These interfacial grainboundaries then constitute discontinuities in the film that could lead to fracture initiation inactual pavement structures.
The current experimental approaches should not be considered a direct representation orsimulation of pavement structures. In the present research, thin films of asphalts are preparedthat have similar average thicknesses to those estimated for pavements ( 5-15 microns or 8 to 10-microns on average [Kandhal and Chakaraborty 1996; Kandhal et al. 1998]). In most cases theyare prepared as ultra-thin-films, representing “theoretical” slices of asphalt very close to and incontact with an aggregate interface. These systems are then investigated to determine thekinetics of microstructure formation as a function of film-thickness, temperature fluctuation, andmethod of film preparation (e.g., solvent spin-coating techniques). This approach has also beenadopted due to the difficulty of experimentally observing asphalt-aggregate interfacialinteractions. As a result, thin-film experimentation on ideal systems combined with computationsimulations will be needed to adequately study these types of systems to make recommendationsas to how to prolong the lifecycle of pavements.
Much of the motivation behind the work that has been proposed in this subtask stems from thedesire to know why and how the microstructures, as observed by atomic force microscopy[Loeber et al. 1996; Pauli and Grimes 2003], could contribute to pavement performance. Thethermo-kinetic processes of phase transformations (i.e., molecular order-disorder kinetics) arebelieved to directly influence the rheological properties of these materials at the mastic thin-filminterfaces in actual pavement structures. These processes include; wax melting/crystallization,flocculation of asphaltenes, chromatographic interactions of polar and aromatic molecules withmineral aggregates/filler surfaces, and others. All are influenced by fluctuations in temperatureand shear rate. An improved understanding of the correlations between these phasetransformations and rheological properties will help explain the nature of fatigue damage andsubsequent self-healing phenomena brought on during rest periods. In other words, how does theasphalt chemical composition lead to the order-disorder transitions that produce micro-structuring at interfacial boundaries and thin-film regions? Also, how does this ultimately lead
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to crack initiation brought on by fatigue, followed by pavement failure, as a function ofenvironmental conditions and loading cycles?
We believe that the process of combining asphalt with aggregate at high temperatures, placingthis composite material in a roadway, and then allowing it to cool and cure may be modeled as asolidification process. Solidification processes are generally considered to be non-equilibriumthermodynamic processes where fluxes in composition and heat are driven by both mechanicaland thermodynamic forces like chemical potential, surface tension and pressure differentials.These are the mechanisms for order-disorder transitions that result in the formation ofmicrostructural grain boundaries. These order-disorder transitions could also be responsible forcohesive failures when, for example, subjected to temperature fluctuations, shear andcompressive loading, and exposure to moisture. Thus, a thorough investigation of the “chemical-action” of asphalt binder as it exists in pavements is warranted in order to define the interfacialboundary conditions and kinetic driving mechanisms that describe the formation and destructionof microstructural phases in asphalt when adopted by continuum mechanical modelingapproaches used to simulate fatigue damage.
Background
In this subtask a somewhat simplified view has been taken to describe the composition of asphaltthin-films in a “pavement structure.” At the mastic level, this simplified view is similar tobuilding sandcastles with asphalt in place of water as the binding agent to adhere and maintainstructural form. While constructing such a system, many different forces can be considered thatcontribute to the strength of the system. These forces may include the capillarity and adhesionbetween asphalt and aggregate fine particles, the viscoelastic response of the asphalt thin-filmsbetween aggregate particles to compression and shear forces, and breakdown of both thecohesive strength of the asphalt and the adhesive bonds between asphalt and aggregate in thepresence of moisture. For the sake of the present discussion, figure 2-3.1 depicts a volumeelement slice of an 8-m thick asphalt thin-film adhering three aggregate fine particles togetherin a mastic sub-structure of a pavement structure.
If the presence of the aggregate particles has an influence on the ordering of the asphaltmolecules at the interface, at what distance away from this interface would long-range molecularordering dissipate? At what effective distance away from this interface would the asphalt layerhave properties similar to a bulk phase state? In the present scenario, asphalt “molecules”present at the interface would experience the strongest interactions with the aggregate surface.Four microns out into the film, approximately halfway between two of these particles, the asphaltshould exhibit properties more closely resembling that of asphalt in the “bulk” state.
Based on AFM surface imaging it has been observed that thicker thin-films of asphalt (>4.0 m)do not differ much in appearance from films that are 10’s of microns or even 1.0-mm inthickness. As these film thicknesses are decreased to <2.0 microns, micro structuringphenomena are observed to change. This suggests that, as shown in figure 2-3.1, the first 25% ofthe asphalt film, could have a different molecular arrangement from the bulk asphalt. This leadsto the question: how does the arrangement of molecules close to the aggregate, fine-particle
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interface influence the flow properties of the molecules farther away from the interface and theadhesive properties of the molecules in direct contact with the interface?
Figure 2-3.1. Pictorial of a volume element slice of an 8m thick film adhering threeaggregate fine particles together in a mastic sub-structure of a pavement structure D > d = 8 m.
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Work Conducted This Quarter
A Topical Report will be delivered October 3rd, 2008, summarizing findings from the past two tothree years of research. This report will be delivered in two parts and describes the present stateof practice for the investigation of the compositional nature of asphalts and aggregates.Discussion will include several experimental techniques including AFT, rheologicalmeasurements, FTIR and atomic force microscopy and presents modeling approaches forintegrating asphalt/aggregate physiochemical properties into continuum-damage models ofpavement performance. Finally, this report will suggest how work elements from the ARC workplan; ARC Work Element Subtask M1b-2-Work of Adhesion at Nano-Scale using AFM, ARCWork Element Subtask M2a-2-Work of Cohesion Measured at Nano-Scale using AFM, WorkElement Subtask F1d-7-Coordinate with AFM Analysis, and Work Element F3a-AsphaltMicrostructural Modeling [Western Research Institute 2008], will be coordinated with this task.
The robotic arm assembly and nano-syringe have been built for the automated spin castingapparatus and is presently being tested. Manufactures of high-speed video cameras are presentlybeing contacted to submit cost estimates. A demonstration by one of the manufacturers isplanned for the near future.
Experimental development of a revised ASTM D4124, test method for the separation of asphaltinto four fractions, referred to as saturates, aromatics, resins and asphaltenes, has beencompleted. A revised text will be submitted to ASTM D4 committee in late October.
Work Plan Next Quarter
Continuation: Research conducted to date in this subtask has been primarily concernedwith defining and measuring compositional properties of material thin-films whichexhibit and/or cause crazing phenomena. This is thought to be a result of materialdiscontinuity (heterogeneity) caused by variations in wax and asphaltene content in thefilm. It is hypothesized that this heterogeneity may be considered an indicator ofcracking and embrittlement in asphaltic materials. Thus, a natural avenue for futureresearch would then be to conduct measurements at micron and nano-scale that focusmore on physical/rheological properties of thin films related to the stiffness andembrittlement propensity, in addition to continuing compositional/chemicalcharacterization of these materials, in order to draw correlations between compositionaland rheological properties.
Continuation (near completion): In the next quarter, a revised SARA separation methodwill be employed to separate asphalt into saturate, aromatic, polar aromatic, andasphaltene fractions. In this procedure, iso-octane asphaltene/maltene separations will beconducted, and the maltenes from this separation will be further separated employing themodified SARA separation procedure. Based on the information gained from thesestudies, a revised method for ASTM 4124 will be submitted to the ASTM D4 committeefor approval.
Continuation (near completion): A solidification stage is being assembled as part of theatomic force microscope by employing both a heating stage and a cooling stage
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fabricated along with micrometer positioning devices. This apparatus will be used toimpart a thermal gradient across an asphalt thin-film resulting in a moving solidificationfront (liquid-solid) interface that may be monitored in time with AFM. Furthermore, anautomated wetting apparatus will also be assembled to better control the spin castingprocedure and to observe and quantify lubrication dynamics. Finally, metrology andnanoindentation accessories have been added to the existing AFM equipment to enhancecapabilities to include micro/nano-rheological testing of material thin-films.
Problems and Solutions to Problems
An upgrade to the AFM equipment, which includes a solidification stage, a dynamic wettingapparatus and metrology and nanoindentation capabilities will lead to the capability of measuringmicro and nano-rheological properties and flow properties of asphalt thin-film materials, inaddition to material composition. It is anticipated that these upgrades will provide very rapidmethods of analysis of asphalt binders that predict, individually, compositional and rheologicalproperties, as well as study how these properties are intimately related to the binding action ofpavement grade asphalts. Problems with the metrology scanner of the AFM have delayedresearch efforts, but malfunctioning components of the AFM have been replaced under warrantyby the manufacturer. The AFM system is presently being tested.
References
ASTM D4124-01, 2002, Standard Test Method for Separation of Asphalt into Four Fractions.Annual Book of ASTM Standards, Road and Paving Materials; Vehicle-Pavement Systems,Section 4, vol. 04.03. ASTM International, West Conshohocken, PA, 821-829.
Bian, L., and F. Taheri, 2008, Fatigue fracture criteria and microstructures of magnesium alloyplates. Materials Science and Engineering A, 48774–85.
Cappelli, M. D., R. L. Carlson, and G. A. Kardomateas, 2008, The transition between small andlong fatigue crack behavior and its relation to microstructure. International Journal of Fatigue,30: 1473–1478.
Kandhal, P. S., and S. Chakaraborty, 1996, Effect of Asphalt Film Thickness on Short and LongTerm Aging of Asphalt Paving Mixtures. NCAT Report No. 96-01.
Kandhal, P. S., K. Y. Foo, and R. B. Mallick, 1998, A Critical Review of VMA Requirements inSuperpave. NCAT Report No. 98-1.
Loeber, L., O. Sutton, J. Morel, J.-M. Valleton, and G. Muller, 1996, New direct observations ofasphalts and asphalt binders by scanning electron microscopy and atomic force microscopy.Journal of Microscopy, 182(1): 32-39.
Pauli, A. T., and W. Grimes, 2003, Surface Morphological Stability Modeling of SHRPAsphalts. American Chemical Society Division of Fuel Chemistry Preprints, 48(1): 19-23.
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Robertson, R. E., K. P. Thomas, P. M. Harnsberger, F. P. Miknis, T. F. Turner, J. F. Branthaver,S-C. Huang, A. T. Pauli, D. A. Netzel, T. M. Bomstad, M. J. Farrar, J. F. McKay, and M.McCann. “Fundamental Properties of Asphalts and Modified Asphalts II, Final Report, VolumeI: Interpretive Report,” Federal Highway Administration, Contract No. DTFH61-99C-00022,Chapters 1-4 submitted for publication, November 2005.
Robertson, R. E., K. P. Thomas, P. M. Harnsberger, F. P. Miknis, T. F. Turner, J. F. Branthaver,S-C. Huang, A. T. Pauli, D. A. Netzel, T. M. Bomstad, M. J. Farrar, D. Sanchez, J. F. McKay,and M. McCann. “Fundamental Properties of Asphalts and Modified Asphalts II, Final Report,Volume I: Interpretive Report,” Federal Highway Administration, Contract No. DTFH61-99C-00022, Chapters 5-7 submitted for publication, March 2006.
Western Research Institute, 2008, Asphalt Research Consortium Annual Work Plan for Year 2,April 1, 2008-March 31, 2009. Prepared for Federal Highway Administration, FHWA ContractNo. DTFH61-07-H-00009, January 2008.
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SUBTASK 2-4. LOW-TEMPERATURE PROPERTIES
Subtask Manager: Fred TurnerOther Personnel: Changping Sui, Pam Coles
Statement of Problem
The contributions of asphalt source (chemical composition) and environmental conditions topavement low-temperature pavement performance are not completely understood. Although thecurrent purchase specifications seem to prevent premature pavement failure, there is littleconfidence in any prediction of long-term pavement behavior.
Approach
Using differential scanning calorimetry and rheometry, the influences of asphalt componentsinfluences on low-temperature properties will be determined. This effort will validate the use oflow-temperature dynamic shear and stress relaxation rheometry tests for determining asphaltmechanical properties. A similar approach will be used to determine the influence of oxidativeaging on low-temperature properties.
Goal
The goal of this work is to provide information about the low-temperature properties of asphaltthat will help develop an advanced fundamental understanding of how chemical types, reactions,and structures determine the physical properties of asphalts and the long-term performance ofasphalt pavements.
Support of FHWA Strategic Goals
The work conducted in this subtask to better understand low-temperature asphalt behaviorsupports the FHWA strategic goal that addresses optimizing pavement performance through thedevelopment of longer lasting asphalt pavements, thus decreasing the demand for reconstructionof pavements.
Work Conducted This Quarter
According to the Contract DTFH61-07-D-00005 documents, Year-2 work on this topic must beshifted to Subtask 3-7. This Task 3 research has not been authorized. However, as part of anasphalt rheology training and familiarization exercise conducted in Task 1, Dr. Changping Suihas made significant progress towards extending the use of dynamic shear rheometry to very lowtemperatures. This work is summarized in this subtask (2-4) to provide consistent referencing tolow-temperature properties research.
Background and Objective
There are currently several well developed testing methods for measuring low-temperature(below 0 °C) properties of asphalts, such as the bending beam rheometer (BBR) for measuring
56
creep stiffness, the direct tension test (DTT) for measuring low temperature failure strength andfailure strain, and the dynamic shear test with torsion bar geometry on the dynamic shearrheometer (DSR) for measuring dynamic stiffness as well as phase angle under sinusoidaldynamic load. The combination of BBR and DTT is used as a method for determining the low-temperature specification of hot mix asphalt (HMA) binders. The disadvantages of the bendingbeam test are that it requires large amount of materials (35 g for one specimen) and hightemperature (above 135 °C) for preparing specimens. DTT and torsion bar on DSR have thesame disadvantages as BBR. In addition, specimen preparation for all three methods is timeconsuming. Furthermore, the current methods for determining low temperature properties forHMA are not applicable to either CMA or some WMA. Isolating large amounts of asphalt fromemulsions used in CMA technology would be time consuming, and high temperature coulddestroy the additive-asphalt structure in CMA or some WMA. Therefore, test methods thatrequire less time, material, and elevated temperatures would provide a great deal of benefit. Testmethods for cold mix asphalt (CMA) and warm mix asphalt (WMA) already require less materialand a low temperature to prepare the specimens. Similar methodology is highly desired fordetermining the low-temperature properties of in-service pavement cores because it wouldenable more rapid research using smaller asphalt samples.
Our objective is to develop new methods for obtaining the low temperature properties of warmmix asphalts, cold mix asphalts, and pavement cores using small samples. One method thatmeets the requirement of small sample size is DSR with cone and plate or parallel plategeometries. Only 25 mg of asphaltic material is needed to conduct a test with a parallel platemeasuring system of 4 mm in diameter. However, due to the machine compliance issue withDSR, this potential technology has not been applied. Even the torsion bar test on DSR hasmachine compliance issues, although the effect of machine compliance is much less comparedwith that of cone and plate and parallel plate measuring systems. The effects of machinecompliance on torsion bar data has been demonstrated [Christensen 1992] where the glassymoduli of eight SHRP core asphalts were determined, using the torsion bar test, to be lower thanthe real glassy modulus of 109 Pa. The issue of machine compliance is common to allrheometers and has attracted increasing attention in recent years. However, no resolution to theproblem had been found until McKenna and coworkers developed new methods to correctmachine compliance for both dynamic and stress relaxation data [Schröter et al. 2006; Hutchesonet al. 2007]. Recognizing the limitations due to machine compliance, software and firmwareupdates have been made by some companies in efforts to improve their systems. For example,TA Instruments has updated their system with an option to input machine compliance beforeexecuting experiments. The updated software and firmware subtract the displacement caused bythe compliance of machine from the total displacement during the test, which results in thecorrect displacement applied to the sample and the correct viscoelastic response. However, themachine compliance values for different geometries provided by TA Instruments are notconsistent with those reported in the literature. For the sake of this study, machine compliancewas calculated using the method developed by Schröter et al. [2006].
The development of machine compliance correction methods enables the use of DSR, with smallcone and plate or parallel plate geometries, for more rapid research with smaller samples. Due toa small, fixed truncation gap (~ 100 nm), experiments have shown it was nearly impossible toobtain acceptable data at temperatures close to the glass transition region using the cone andplate measuring system. On the other hand, both stress relaxation and dynamic frequency sweep
57
experiments on 4 mm diameter parallel plates can be performed at temperatures as low as -40 °C,and the glassy modulus measured from both types of experiments reaches 109 Pa. This indicatesthat DSR with a small size parallel plate can be used to obtain low temperature properties withsmall asphalt samples (25 mg). In addition, some previously collected dynamic data in the WRIdatabase were corrected using the method developed by Schröter et al. [2006] and the convertedBBR data was merged to the corresponding corrected dynamic data. The BBR data match thecorrected dynamic data very well, indicating that BBR data can be duplicated using DSR. Thisdiscovery points to the eventual development of new, DSR test methods using small samples fordetermining low temperature specifications of CMA and WMA.
Results and discussions
Machine compliance corrections have been applied using two methods. One is a correction forpreviously collected dynamic data using the method developed by Schröter et al. [2006]. Theother is a correction done automatically by inputting the right compliance of the measuringsystem to the updated software. Asphalt samples examined in this study are listed in table 2-4.1.
Table 2-4.1. SHRP and validation site asphalts examined.
MaterialsType of test
Tank RTFO RTFO-PAV
NV1-4 NV1-4
KS1-2 KS1-2 KS1-2Stress relaxation
ABD MN1-5
ABD NV1-4
KS1-2
MN1-5Dynamic Shear
AZ1-2
1. Machine compliance corrections for dynamic frequency sweep data (previously collectedwith 8 and 25 mm parallel plates) using method developed by Schröter et al. [2006].
Figure 2-4.1 shows the master curves of complex modulus vs. frequency at a referencetemperature of 0 oC for RTFO-PAV aged NV1-4 asphalt (from WRI’s Nevada validation site)before and after corrections. This plot shows how the correction works. The black curve isuncorrected data and the red curve is corrected data. As can be seen, at high temperature or lowfrequency where the material is soft and machine compliance is negligible, the correction doesnot make much difference. However, at low temperature or high frequency where the materialbecomes stiff and the machine compliance plays an important role, the correction moves the dataup to where it is supposed to be, that is the true value, and the curve eventually approaches 109
Pa. This indicates that Schröter method for machine compliance corrections works well andenables the comparison of data collected on the DSR with other data measured from otherexperimental techniques. The comparison between corrected dynamic data and converted BBRdata will be shown in the next section.
58
Figure 2-4.1. Master curves of complex modulus for corrected and uncorrected data for PAVaged NV1-4 asphalt as a function of reduced frequency at reference temperature of 0oC.
2. Comparison between corrected dynamic data (previously collected with 8 and 25 mmparallel plates) and BBR data
Figures 2-4.2 and 2-4.3 show the master curves of storage and loss moduli merged data fromboth corrected dynamic and converted BBR data for NV1-4 RTFO and RTFO-PAV agedasphalts. The pink dots are the converted BBR data and brown curves represent the correcteddynamic data. The BBR data match up with corrected dynamic data fairly well for bothmaterials. Similar results were observed for other asphalts that are not shown here. Therefore,we conclude that BBR data can be estimated from DSR tests. This also implies that a lowtemperature test method on DSR can be developed to provide low temperature specifications forasphalt binders by making correlations between BBR data and dynamic data from DSR. Tomake the correlations between BBR data and dynamic data, two parameters are important on thedynamic master curve. One is the crossover frequency, c, and another is the rheological index,R. We believe that c and R should correlate with m and S(t) from BBR data. So far, BBR datasets have been obtained for different asphalts from the database at WRI. However, enough lowtemperature DSR data has yet to be collected to make the correlations.
10-8
10-6
10-4
10-2
100
102
104
105
106
107
108
109
Tref
= 0oC
G*
()
Pa
rad/s
UncorrectedCorrrected
59
Figure 2-4.2. Master curves of storage and loss moduli merged data from BBR and correcteddynamic data as a function of frequency for NV1-4 RTFO aged asphalt.
Figure 2-4.3. Master curves of storage and loss moduli merged data from BBR and correcteddynamic data as a function of frequency for NV1-4 RTFO-PAV aged asphalt.
60
3. Low temperature properties collected on DSR with parallel plate of 4 mm in diameter
3.1 Low temperature dynamic frequency sweep
Figure 2-4.4 shows master curves of complex moduli for RTFO-PAV aged MN1-5 and KS1-2asphalts measured at low temperatures. Nine isothermal experiments were performed at -40, -35,-30, -25, -20, -15, -10, 0, 10, 20, and 30°C on an ARES rheometer with parallel plates of 4 mmdiameter. The machine compliance correction was applied automatically during the experimentsby pre-inputting into the software with the compliance value of the whole measuring systemcalculated using the method by developed Schröter et al [2006]. A comparison was madebetween the data corrected using the Schröter method and the data corrected automatically by theupdated software. It was found that the data obtained from both correction methods are fairlyconsistent; with a deviation of less than 5%. This makes it easy to pull out the correct datadirectly from the rheometer, if the right machine compliance software is used. The mastercurves were obtained by shifting all isotherm data to reference temperature of -35 °C. As can beseen in the figure, both materials exhibit similar and corrected glassy moduli that extrapolate toabove 109 Pa. This indicates that the calculated machine compliance value, 2.265 x 10-2
rad/N.m, for our measuring system is right. On the other hand, the glassy modulus is far below109 Pa if we input the value, 5.24 x 10-3 rad/N.m, provided by TA Instruments. The new versionof software for the ARES from TA Instruments provides only one value, 5.24 x 10-3 rad/N.m, fordifferent fixtures made of different materials including all 316 stainless steel plates, cone, anddisposable fixtures. This is not correct.
Figure 2-4.4. Master curves of complex moduli vs. reduced frequency for RTFO-PAV agedMN1-5 and KS1-2 asphalts.
10-13
10-10
10-7
10-4
10-1
102
104
105
106
107
108
109 T
ref= -35 °C
G*(
),P
a
.aT, rad/s
MN1-5KS1-2
61
The disposable plate is made of aluminum that is much softer than stainless steel. That meansthe disposable plate compliance correction should be larger than that for a stainless steel plate ofthe same size under the same torque and other loads. In addition, the compliance of the fixture issize related, it is proportional to 1/R4 (R is the diameter of the fixture). One should be careful toinput the compliance value before the experiment because it is related to the fixture size and thematerial that made of the fixtures.
The significances of the data shown in figure 2-4.4 are: (1) we have the right compliance valuefor our measuring system to get the correct data, and (2) good data can be collected attemperature as low as -40 °C. This shows that DSR with small size parallel plates can be used asa test method to measure low temperature properties with small samples.
3.2 Low temperature stress relaxation
Shear stress relaxation is a type of test method for measuring the stress relaxation behavior of amaterial after a sudden step strain. In other words, an instantaneous step strain is applied to thematerial being measured, the strain is held constant, and the stress relaxation profile with time isrecorded. As shown in figure 2-4.5, the shear stress relaxation profile is exhibited in the form ofa shear modulus for MN1-5 aged material, which is the generally accepted form. Shear stress,(t), and shear modulus, G(t), are correlated in the form of G(t) = (t)/ where is the stepstrain. Similar to the case in figure 2-4.4, the master curve of shear relaxation moduli in figure2-4.5 is constructed from nine isotherms at a reference temperature of -35 °C. Again, the glassymodulus, on the order of 109 Pa, was observed and it is very close the value measured indynamic tests as shown in figure 2-4.4. This further confirms that we have the correct machinecompliance value for our measuring system, and that low temperature properties with smallsamples can be investigated on a DSR with small parallel plates.
Theoretically, all linear viscoelastic functions are inter-convertible [Ferry 1980]. That meansany linear viscoelastic function can be converted into any other viscoelastic function. Forexample, the shear stress relaxation modulus can be calculated from dynamic frequency sweepdata using the empirical conversion method developed by Ninomiya and Ferry [1959]. Thedetails about the inter-conversion among the linear viscoelastic functions are beyond the goal ofthis summary. The point here is that it is not necessary to perform both dynamic shear and stressrelaxation shear experiments if the real measured data are consistent with the converted data.Since the dynamic shear experiment is generally accepted in asphalt research, we can keep thistype of experiment in our future work on DSR. Some work has been done to check theconsistency between the real measured and converted data. It turns out that for some asphaltslike ABD, the consistency is very good. But, it does not hold true for other asphalts likevalidation site asphalt MN1-5. Further work needs to be conducted on more asphalts.
62
Figure 2-4.5. Master curve of stress relaxation modulus vs. reduced time forRTFO-PAV aged MN1-5 asphalt
Summary
Machine compliance corrections have been applied using two methods. One is a correction forpreviously collected dynamic data using the Schröter method. The other is a correction doneautomatically by inputting the right compliance of the measuring system to the updated software.The two sets of data corrected by the two methods above are very consistent. Resolving themachine compliance issue enables us to develop a new test method for measuring the low-temperature properties of asphalt with small amounts of samples on DSR with small parallelplates. The successful dynamic shear and shear stress relaxation experiments on DSR with 4mmdiameter parallel plate at low temperatures indicate that DSR with small parallel plates can beused as a test method for measuring low temperature properties of asphalt with small amounts ofsamples (25 mg).
References
Christensen, D. W, 1992, Mathematical Modeling of the Linear Viscoelastic Behavior of AsphaltCement. PhD Thesis in Civil Engineering, Pennsylvania State University.
Ferry, J. D., 1980, Viscoelastic Properties of Polymers, John Wiley, New York.
Hutcheson S. A., K. Schröter, X. Shi, A. Mandanici, and G. B. McKenna, 2007, TheMeasurement of Mechanical Properties of Glycerol, m-toluidine, and Sucrose Benzoate under
10-2
101
104
107
1010
1013
104
105
106
107
108
109
Tref
= -35 °C
G(t
)),P
a
t/aT, s
MN1-5
63
Consideration of Corrected Rheometer Compliance: An in-depth Study and Review. J. Chem.Phys. 129(7): 074502.
Ninomiya, K. and J. D. Ferry, 1959, J. Colloid Sci.,14, 36.
Schröter K., S. A. Hutcheson, X. Shi, A. Mandanici, and G. B. McKenna, 2006, Dynamic ShearModulus of Glycerol: Corrections Due to Instrument Compliance. J. Chem. Phys., 125: 214507.
64
65
SUBTASK 2-5. MODIFIED ASPHALTS (continuing on Year-1 funds)
Subtask Manager: Shin-Che HuangOther Personnel: Fran Miknis, Will Schuster, Mike Farrar, and Ryan Boysen, Steve Salmans
Statement of Problem
Asphalt modifiers are often added to meet binder purchase specifications. Common modifiersinclude polymers to improve rutting resistance, lime and antistrip additives to mitigate moisturedamage, polyphosphoric acid for rutting resistance, and reclaimed asphalt pavement (RAP) forreducing costs. New modifiers are also being introduced to enable warm-mix asphalt (WMA)technologies where mix and compaction temperatures can be substantially reduced. One of thesemodifiers is water (typically used to foam the asphalt), which improves the workability ofbinders at mixing and laydown temperatures and appears to have little effect afterwards,although there is some evidence that entrapped moisture may increase stripping [Hurley andProwell 2005]. The long-term effectiveness of some modifiers under highway conditions is notknown. In addition, the mechanism of action of a modifier is often understood only in anempirical sense, and the effective treatment levels and economical treatment levels may differ.Modifier interactions may reduce effectiveness and waste resources.
Approaches
The sensitivity of PPA-modified asphalts to environmental factors is being determined usinglaboratory PAV aging tests on modified and unmodified asphalts in the presence and absence ofmoisture. Tests that are applied include spectroscopic (FTIR) and rheologic (DSR) analyses ofthe aged materials. Rheological parameters obtained from master curves such as shift factorsand rheological indexes are used to quantify changes. Fourier transform infrared spectroscopy(FTIR), along with attenuated total reflectance (ATR), is currently employed to investigate thehydrogen bonding interactions between PPA and asphalt binders. Nuclear magnetic resonancetechniques are also being applied to study the reactions between phosphorous-containingadditives including antistrips and PPA in asphalts.
Goals
The goal of this research is to develop a detailed description of the actions of modifiers inasphalts while varying environmental conditions. Where feasible, efforts are directed towarddeveloping relationships for predicting long-term behavior from initial laboratory tests.
Support of FHWA Strategic Goals
The work conducted in this subtask supports the FHWA strategic goal that addressesenvironmental stewardship and safety. State agencies need a better understanding of how andwhen to use additives to improve the performance of asphalt pavements. Obviously, betterperforming and longer lasting asphalt pavements, which incorporate the use of RAP, lead to theutilization of less asphalt, thus decreasing the demand for reconstruction of pavements andincidentally safer roads.
66
Background
The addition of polyphosphoric acid (PPA) to asphalt binders is known to affect a number of thechemical and physical properties of asphalts. However, the mechanisms by which this happensare not well understood. Several possible mechanisms have been advanced, and it has beennoted that the mechanisms of action may be asphalt source related [Baumgardner et al. 2005]. In2005, WRI initiated an investigation (subtask 14-4 of FHWA Contract DTFH61-99C-00022) toelucidate the mechanisms of action of polyphosphoric acid (PPA) in asphalt. SHRP asphaltsABD, AAD-1, and AAM-1 were modified with 1.5 mass percent of polyphosphoric acid (105percent). These modified asphalts were then used to verify observations reported by others.These observations included: (1) an increase in the high-temperature PG grade, (2) a slowincrease in the complex modulus upon storage in a heated tank, (3) a decrease in chemical aging,as defined by the amount of carbonyl-containing compounds produced, and (4) an increase in thegel character of the modified asphalt, i.e. the modified asphalt becomes less compatible. Thework conducted at WRI not only confirmed these observations but also provided additionalinsight into the mechanism of action of PPA. In general, it was concluded that the impact ofPPA modification on the rheological properties is related to the sol-gel character of the asphalt.While a concentration of 1.5 wt % is considered too high for paving applications, this wasconsidered a reasonable concentration to utilize when looking for chemical changes in asphaltbrought about by PPA. Others [Falkiewicz and Grzybowski 2004] have used up to 2 wt % PPAto look for changes in asphalt behavior with PPA modification. Nonetheless, our study indicatesthat PPA-modified asphalt binders should: (1) increase early resistance of the pavement torutting by increasing initial stiffness and, in the absence of complicating factors, (2) extend theuseful life of the pavement by improving the low-temperature flow properties. These improvedproperties should result in both reduced fatigue cracking and reduced low temperature cracking[Huang et al. 2008].
Based on both current and previous studies, it appears that there is a relationship betweenphysical properties (rheological) and a chemical property (carbonyl content) for unmodifiedasphalt binders with respect to long-term oxidative aging. However, addition of PPA to asphaltsdisturbs the relationship between physical and chemical properties of asphalt binders withrespect to their long-term aging.
Based on NMR spectroscopy and modified black plots, addition of PPA into asphalt binders doesnot appear to significantly change the internal structure of asphalt binders by chemical reaction,such as the formation of covalent bonds with asphalt components. Another importantobservation of the WRI work was the evidence of hydrolysis of polyphosphoric acid to ortho-phosphoric acid by residual water in asphalt [Miknis and Thomas 2008]. This was indicated in31P NMR spectra of PPA modified asphalts where the disappearance of phosphorous resonancesin the middle and terminal groups of phosphate chains was observed over time, with only anortho-phosphoric acid resonance remaining.
Work Conducted This Quarter
During this quarter, work continued on the rheological analysis of the unmodified and acid-modified asphalts that were PAV aged at 60°C in the presence of water.
67
Figures 2-5.1, 2-5.2, and 2-5.3 show the effect of PPA on the rheological index for threeasphalts, AAD-1, ABD, and AAM-1, with respect to 326 hours PAV aging in the absence andpresence of water, respectively. As seen from these three figures, addition of PPA increases therheological index of asphalt binders initially. In other words, PPA-modified asphalt binders havemore rubbery behavior (greater elastic modulus) than those of neat asphalts. Asphalt AAD-1,with high asphaltene content, increases the most and ABD, with low asphaltene content,increases the least. In addition, it can be seen from the difference of rheological index forunaged and aged samples that addition of PPA to AAM-1 causes the largest amount of rubberybehavior (elastic modulus) change due to the PAV aging. Furthermore, the addition of PPA toAAM-1 decreases the rheological index when the sample was subjected to PAV aging in thepresence of water.
The rheological index is defined as the difference between the glassy modulus and the dynamicmodulus at the crossover frequency (ω0). Crossover frequency is defined as the frequency whereG’ is equal to G’’ or tan delta is one. The rheological index has been speculated to be directlyproportional to the width of the relaxation spectrum of an asphalt binder [Christensen andAnderson 1992]. Basically, the rheological index indicates the amount of delayed elasticbehavior that an asphalt binder will show. Usually, the higher the rheological index, the flatterthe master curve will become and the behavior of the asphalt will become more rubbery (greaterelastic modulus).
PAV Aging Time, hrs
Rhe
olo
gic
alIn
de
x
0
1
2
3
4
5
AAD-1, Dry
AAD-1, Moist
AAD-1/PPA, Dry
AAD-1/PPA, Moist
PAV @ 60°C
0 326
Figure 2-5.1. Rheological index for asphalt AAD-1 and its PPA mixture before and after agingin the presence and absence of water.
68
PAV Aging Time, hrs
Rh
eo
log
ica
lIn
de
x
0
1
2
3
4
5
ABD, Dry
ABD, Moist
ABD/PPA, Dry
ABD/PPA, Moist
PAV @ 60°C
0 326
Figure 2-5.2. Rheological index for asphalt ABD and its PPA mixture before and after aging inthe presence and absence of water.
PAV Aging Time, hrs
Rhe
olo
gic
alIn
dex
0
1
2
3
4
5
AAM-1, Dry
AAM-1, Moist
AAM-1/PPA, Dry
AAM-1/PPA, Moist
PAV @ 60°C
0 326
Figure 2-5.3. Rheological index for asphalt AAM-1 and its PPA mixture before and after agingin the presence and absence of water.
69
FTIR Analysis
In this quarter, Fourier Transform Infrared Spectroscopy (FTIR) was used to study the effect ofpolyphosphoric acid (PPA) on asphalt binder. A Perkin Elmer FTIR Spectrum One instrumentwas used for all measurements. Attenuated total reflectance (ATR) allows examination of solidor liquid samples, requires little or no sample preparation, shows the hydrogen bondinginteractions as they occur in the field, and, consequently, was used for all measurements.
Reagent grade ortho phosphoric acid (ortho PA) or 105%PPA purchased from Sigma Aldrichwas used for the PPA experiments. β-tri-calcium phosphate (>96%) was obtained from Fluka,monobasic calcium phosphate from Sigma, and hydrated lime from a construction site. Dibasiccalcium phosphate (98-105%), reagent grade hydroxyapatite, and hydrogen phosphate dihydrate(98%) were purchased from Sigma Aldrich.
Figure 2-5.4 shows the FTIR/ATR spectra of AAM-1 neat asphalt and AAM-1 mixed with 1.5weight percent of PPA(105%). Using the process of spectral subtraction described in Subtask 2-2.2 of this report, figure 2-5.5 was generated which shows the residual IR spectra of phosphoricacid in both AAD-1 and AAM-1 with o-PA and 105% PPA included for reference. Thesedifference spectra are a measure of PPA plus the interaction of PPA and asphalt. The residualPA spectra in asphalt appear to be the same shape as ortho PA with shifts in the spectral features.These shifts are speculated to be either a function of hydrogen bonding.
600110016002100260031003600
Wavenumber (cm-1
)
Ab
so
rba
nc
e
AAM-1 modified with 1.5%PPA
AAM-1 Neat
Figure 2-5.4. FTIR/ATR spectra of neat AAM-1 (pink) and 1.5% PPAmodified AAM-1 asphalt (blue).
70
600800100012001400
Wavenumber (cm-1)
Ab
so
rba
nc
eDiffernce Spectrum AAM-1
Difference Spectrum AAD-1
Orth PA
105%PPA
Figure 2-5.5. Spectral subtraction shows the phosphates or PA present in 1.5%PPA(105%)modified AAM-1(black) and AAD-1(red).
The absorption peaks for o-PA (figure 2-5.5, grey) at 947 cm-1 and 1108 cm-1 are assigned to P-O and P=O stretches, respectively [Chapman and Thirlwell 1964]. These peaks shift to 1000 cm-
1 and 1100-1130 cm-1 when PPA is mixed with asphalt. Both the P=O stretch (hydrogen bondacceptor moiety) and P-O triply degenerate stretching (hydrogen bond donor, or phosphatebonding moiety) appear at distinctly different positions in AAM-1 with o-PA compared to AAD-1 with o-PA. Further, the upshift in the P-O stretch indicates that o-PA is involved in eitherstronger hydrogen bond donation or a phosphate bond when mixed with asphalt. These data aresummarized in table 2-5.1. Because there may be an interaction in asphalt obscuring the purePPA spectra, these data are considered preliminary. In the next quarter, asphalt will be mixedwith 0.5, 1.0 and 1.5% PPA, respectively, and IR spectra measured. Assuming that PPA’sinfluence on asphalt is consistent across this concentration range, the pure spectrum of PPA inasphalt will be obtained by spectral subtraction. A change in PPA asphalt interactions withconcentration would also be valuable information.
Future efforts will focus on measuring IR spectra of PPA with excesses of asphalt modelcompound types such as polyaromatic, 2-quinolone, phenolic, pyrolic, pyridinic, and sulfide.Spectral subtraction may then be used to calculate the relative quantitative strength of the PPA-model compound hydrogen bond or phosphate bond. The P-O (hydrogen bond donor, orphosphate bonding moiety) and P=O (hydrogen bond acceptor) IR shifts in the PA-modelcompound that most closely match the shifts in the PA-asphalt mixture may give insight into thephosphate or hydrogen bonding interactions responsible for PPA’s stiffening effect on asphalt.
71
Table 2-5.1. FTIR peak locations (cm-1) of the P-O and P=O stretches of PAin asphalt and water.
PA(cm
-1)
PA inwater(cm
-1)
1.5% PAin AAD-1
(cm-1
)
1.5% PAin AAM-1
(cm-1
)
Assign-ment
PA H-bondshift in AAD-1
(cm-1
)
PA H-bondshift in AAM-1
(cm-1
)
Cause of PeakShift
947 968 1000 994 P-O* 53 47 H-bond donation
1108 1123 1102 1133 P=O* -6 25 H-bond acceptance
*Ref [Chapman and Thirlwell 1964]
Discussion of Salts Produced by PPA and Lime Reaction
In a previous quarter, it was shown that one or multiple phosphate salts are formed when theasphalt was mixed with PPA and hydrated lime [WRI Quarterly Rept. March 31-June 30, 2007,pg. 59]. With the goal of identifying these salts, FTIR/ATR spectra of monobasic calciumphosphate, dibasic calcium phosphate, calcium hydrogen phosphate dihydrate, hydroxyapatite, β-tri-calcium phosphate, and hydrated lime were collected and are shown in figure 2-5.6. The neatAAM-1 spectrum was subtracted from AAM-1+1.5%(105%) PPA+10% hydrated lime to yieldthe spectrum of the phosphate and lime remaining in the asphalt. This spectrum (figure 2-5.6g)was compared with the known phosphate salts and is similar to the dibasic calcium phosphate. Asummary of the peak positions of the phosphate salts and phosphate in AAM-1 asphalt shown intable 2-5.2 support this assertion.
72
600110016002100260031003600
Wavenumber (cm-1
)
Ab
so
rba
nc
e
a
g
f
e
d
c
b
Figure 2-5.6. FTIR/ATR spectra of the phosphate salts that may be formed when PPA and lime aremixed in asphalt: (a) β-tri-calcium phosphate, (b) calcium hydrogen phosphate dehydrate, (c)
hydroxyapatite, (d) calcium phosphate monobasic, (e) hydrated lime, (f) calcium phosphate dibasic,and (g) salt in AAM-1 modified with PPA and treated with lime (from spectral subtraction).
Table 2-5.2. A list of FTIR/ATR peak positions of the phosphate in AAM-1+PPA+lime (bold, fromspectral subtraction) compared with the peak positions of several phosphate salts.
IR Peak Positions
Phosphate Salt cm-1
cm-1
cm-1
cm-1
cm-1
hydroxyapatite 1024calcium phosphate monobasic 1642 1210 1079 950 854
β-tri-calcium phosphate 117 1016 969 934calcium hydrogen phosphate dihydrate 1134 1061 986 873 788
calcium phosphate dibasic 1132 1066 991 885hydrated lime 3642 872
phosphate in asphalt 1130 1069 991 892
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31P NMR of MN Road Samples
During this quarter, 31P NMR analyses were performed on loose mix samples from Cells 33, 34,and 79 of the MN Road Pavement Test Track. The purpose for these measurements was todetermine whether lime had any effect on the properties of the polyphosphoric acid that wasadded to the binder. In a previous quarterly report, 31P NMR measurements indicated that whenlime is added to a PPA modified asphalt, the lime reacts with the PPA to form insoluble calciumphosphates. Furthermore, the order of addition to the asphalt (lime + PPA or PPA + lime) didnot make any difference, i.e., calcium phosphates were still formed [WRI Quarterly Rept. March31-June 30, 2007, pg. 59]. These measurements were obtained on samples made in a laboratorysetting. In the experiments performed this quarter, similar NMR measurements were applied tobona fide roadway samples from the MN Road Pavement Test rack facility. The MN Road testsamples are described in table 2-5.3. NMR measurements were not made on cell 35 because noPPA was added to that mix.
Table 2-5.3. Mn road test matrix.
Cell Number 33 34 35 77-79
PPA (115%) wt % 0.75 0.3 --- 0.3
Polymer wt% 0.0 1.0 2.0 1.0
Polymer Type -- SBS SBS Elvaloy
Innovalt W antistrip, wt% 0.5 0.5 -- 0.5
Hydrated Lime, % Mix 1.0 1.0 1.0 1.0
Samples of the loose mix aggregate were prepared in the following way. Loose mix samples(~20-40 g) were dissolved in a flask using 85/15 toluene/ethanol mix and allowed to soak for 30min. Solvent was decanted into a round bottom flask (RBF) with care taken to allow as muchfine particulate matter as possible. This process was repeated with less soak time until thesolvent extracted no color from the rocks. Then the entire content of the flask was poured outand the large particles and the rocks were collected on glass wool. The solution in the RBF wasthen placed on a rotary evaporator and solvent was removed. Pure toluene was used to dissolvethe asphalt/fines mixture and transfer it to a small vial. The solvent was once again removed byrotary evaporation and this time complete solvent removal was ensured by heating in a vacuumoven over night.
Solid State NMR rotors were loaded with extracted asphalt binders containing fines by smearingthe warm asphalt binders into a dish, then cooling the asphalts with liquid nitrogen. The coldbrittle asphalts could then be placed in the rotors without them sticking to the rotor walls. A heatlamp was then used to soften the asphalts to allow flow down into the bottom of the rotors.
Solid- and liquid- state 31P nuclear magnetic resonance (NMR) measurements were made on aChemagnetics CMX NMR spectrometer. NMR spectra were acquired at a nominal frequency of40 MHz. Chemical shifts were referenced to orthophosphoric acid at 0 ppm. Typically, 31PNMR spectra were acquired over a three hour period using a pulse repetition rate of 1 s. Solid-
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state measurements were made using single pulses with high power decoupling and magic anglespinning. Spinning rates were 4.5 kHz and 1.5 kHz. For liquid state measurements,deuterochloroform (CDCl3) was used as the solvent.
The results of the 31P NMR analyses for the MN Road cells are shown in figures 2-5.7, 2-5.8,and 2-5.9. In all figures, the top spectrum is a liquid state spectrum of the MN Road binderbefore it was mixed with the aggregate which contained lime. The samples contain PPA (115%),polymer and Innovalt W, a phosphate ester antistrip agent. The NMR spectra show that most ofthe PPA had hydrolyzed to orthophosphoric acid before it was mixed with the lime/aggregatecombination. The middle traces show the liquid state spectra after the loose mix samples fromthe cells were extracted in the toluene/ethanol mixture, and then dissolved in CDCl3 for theliquid state NMR measurements. The traces clearly show that there was no phosphorous presentin the liquid state.
The bottom traces are NMR spectra obtained on the extracted samples in the “solid state”, i.e.,the samples were not dissolved in CDCl3. These spectra were acquired using the solid-stateNMR technique of single pulse excitation with high-power decoupling and magic-angle spinning(SP/MAS). The spectra suggest that in the extracted samples the phosphorous is in a solid form,presumably some form of calcium phosphate(s) formed by reaction of the PPA with the lime.This type of reaction has been observed previously in laboratory prepared samples when PPAand lime were added into asphalt (WRI Quarterly Rept. March 31-June 30, 2007, pg 59).
31P NMR spectra of the solid extracted samples were also obtained at low spinning rates. Figure2-5.10 shows a comparison of solid-state spectra obtained at two different spinning rates. Theappearance of so-called spinning sidebands in the low spinning rate spectrum (1500 Hz) isanother confirmation that the phosphorous in the extracted samples is in a solid form. Sidebandswould not be formed in the liquid state under these conditions. The sidebands in the solid-statespectra in figure 2-5.11 indicate that in all three cells, the phosphorous was in a solid form afterhaving been mixed with the lime.
Based on the NMR results obtained thus far, it appears that the combination of PPA inconjunction with lime resulted in the formation of calcium phosphates in the MN Road TestTrack cells. However, this conclusion is based on NMR measurements of only three samples.Additional NMR analyses should be performed to conclusively verify these results.
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-100-80-60-40-20020406080100
Binder+0.75% PPA(105%)+0.5% Innovalt WLiquid-state spectrum
Extracted loose mixLiquid-state spectrum
Extracted loose mixSolid-state spectrum
MN Road Cell 33
Figure 2-5.7. 31P NMR spectra of MN Road cell 33.
MN Road Cell 34
-100-80-60-40-20020406080100
Binder+0.75%PA(115%)
+0.5% Innovalt WLiquid-state spectrum
Extracted loose mixLiquid-state spectrum
Extracted loose mix
Solid-state spectrum
Figure 2-5.8. 31P NMR spectra of MN Road cell 34.
31P Chemical Shift, ppm
31P Chemical Shift, ppm
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-100-80-60-40-20020406080100
Binder+0.3%PPA(115%)+0.5%Innovalt W+1.1% ElvaloyLiquid-state spectrum
Extracted loose mixLiquid-state spectrum
Extracted loose mixSolid-state spectrum
MN Road Cell 79
Figure 2-5.9. 31P NMR spectra of MN Road cell 79.
-200-150-100-50050100150200
1.5 kHz
4.5 kHz
Figure 2-5-10. Solid-state 31P NMR of MN Road cell 79 illustrating spinning sidebands at1.5 and 4.5 kHz sample spinning rate.
31P Chemical Shift, ppm
31P Chemical Shift, ppm
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-200 -150 -100 -50 0 50 100 150 200
Cell 33
Cell 34
Cell 79
MN Road Cells at slow spinning
Figure 2-5.11. Low speed spinning (1.5 kHz) solid-state 31P NMRspectra of MN Road Cells illustrating sidebands.
Work to be Conducted Next Quarter
● Continue the study to elucidate the mechanism of action of PPA in asphalt. The use of antistrip agents in conjunction with PPA modification of asphalts will be furtherinvestigated. Previous work was not sufficient to determine if any reactions occur thatmight negate the use of PPA in combination with the antistrips.
● Continue 31P NMR measurements on additional MN Road samples to establish to whatextent calcium phosphates are formed when lime is added to a PPA modified asphalt.
● Continue the study of multiple modifiers in asphalt. Changes in the rheological and spectroscopic (FTIR and 31P and 13C NMR), properties on PAV aged samples will bemonitored.
● Continue IR spectra measurements of PPA with excess of respective asphalt model compounds such as polyaromatic, 2-quinolone, phenolic, pyrolic, pyridinic, and sulfidetype molecules.
● Prepare a manuscript describing the NMR results on the use of adding PPA and lime in pavement mixtures, and submit it to a journal for consideration for publication.
Problems and Solution to Problem
No problems were encountered during this quarter.
31P Chemical Shift, ppm
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References
Baumgardner, G. L., J-F. Masson, J. R. Hardee, A. M. Menapace, and A. G. Williams, 2005,Polyphosphoric Acid Modified Asphalt: Proposed Mechanisms, Proceedings of the Associationof Asphalt Paving Technologists, 74: 283-305.
Chapman, A. C., and L. E. Thirlwell, 1964, Spectra of phosphorus compounds: The infra-redspectra of orthophosphates. Spectrochimica Acta, 20: 937-947.
Christensen, D. W., and D. A. Anderson, 1992, Interpretation of Dynamic Mechanical Test Datafor Paving Grade Asphalt. Journal of the Association of Asphalt Paving Technologists, 61: 67-116.
Falkiewicz, M., and K. Grzybowski, 2004, “Polyphosphoric Acid in Asphalt Modification.”Presented at the Pavement Performance Prediction Symposium, Cheyenne, Wyoming, June 23-25, 2004.
Huang, S-C., T. F. Turner, F. P. Miknis, and K. P. Thomas, 2008, Long-Term AgingCharacteristics of Polyphosphoric Acid Modified Asphalts. Journal of Transportation ResearchRecord (in press).
Miknis, F. P., and K. P. Thomas, 2008, NMR analysis of polyphosphoric acid-modifiedbitumens. Road Materials and Pavement Design, 9: 59-72.
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SUBTASK 2-6. VALIDATION SITE MONITORING
Subtask Manager: Mike Harnsberger and Mike FarrarOther Personnel: Mark Pooler, Steve Salmans, Janet Wolf, and Ron Glaser
Work Conducted This Quarter
Validation site monitoring of the Minnesota CR 112 sections was performed in late August 2008.These sections have two years of service and most of the sections are performing well with nodistress noted, however, the sections using the MN1-4 asphalt are beginning to show sometransverse cracking. Some transverse cracking was noted in a survey conducted by Ed Johnsonof MnDOT in March 2008. The cracking identified by Ed Johnson was confirmed and additionaltransverse cracking was noted in our survey in August 2008. The majority of the transversecracks occur in the transition areas between the MN1-3 asphalt source and the MN 1-4 asphaltsource. There are three lifts of hot-mix at this site and the transition areas are where the lifts ofthe different sources overlap or where the mix was changing during construction from one sourceto another. Future monitoring visits will continue to note distress in the transition areas, as it canbe accommodated, even though this is not the general practice. Propensity to crack in thetransition areas where different asphalt sources occur in the different lifts may be an unexpectedfinding that needs to be followed and investigated as this site ages in service.
During the current monitoring visit, two core samples were obtained from just outside each ofthe ten monitoring sections for a total of 20 cores. There are two monitoring sections per asphaltsource/mix. The core samples obtained from the Minnesota sections are to assess the aging thathas occurred during the first two years of service. Analysis of the cores is in progress.
Work to be Conducted Next Quarter
Monitoring of the Arizona and Nevada validation sites is planned for November 2008.
Problems and Solution to Problems
No problems have been encountered.
Support of FHWA Strategic Goals
The comparative pavement validation sites support the FHWA Focus Area of OptimizingPavement Performance by correlating pavement performance to the specific materials used inconstruction.
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TASK 3. OTHER RESEARCH ACTIVITIES (IDIQ)
During this quarter, a task order contract for mechanical testing of validation site cores wasapproved. It is the only Task 3 work element approved.
Subtask 3-1 (TOPR No. 1) Minnesota & Arizona Mix TestingSubtask Manager: Mike HarnsbergerSubcontractor: Advanced Asphalt Technologies
The following description was extracted from the subcontractor statement of work.
Description of Work
Background
During the Fundamental Properties of Asphalts and Modified Asphalts - II Contract, WesternResearch Institute (WRI) constructed comparative pavement validation sites in coordination withstate DOT’s where asphalts from different sources (crude oil source or crude oil blend) of thesame Performance Grade (PG) were compared at the same location. The major variable in thecomparative pavement validation sites is the asphalt source (of the same grade), while all othervariables, such as aggregate source and mix design, are kept as constant as possible.
A series of mechanical property tests were performed on loose hot-mix and as-constructed coresamples from the comparative pavement validation sites in Nevada and Kansas. This testing wasdesigned to evaluate the structural stiffness, permanent deformation, fatigue and thermalcracking characteristics of the mixtures from the different sections of each validation site. Theoverall objective of the comparative pavement validation study is to relate pavementperformance to chemical composition of the asphalt binder.
Mechanical property testing for the Minnesota site was not accomplished under the FundamentalProperties of Asphalts and Modified Asphalts – II Contract because this validation site wasconstructed near the end of contract period; therefore, there was not enough time and funding tocomplete this testing. Additionally, mechanical property testing for the Arizona site was notaccomplished because the original Arizona mix was not available after the Arizona site wasconstructed; however, ADOT recently informed WRI that the necessary samples are nowavailable.
Objective
The objective of this Task Order is to perform mechanical property testing of the mixes and coresamples from the Minnesota and Arizona sites in a manner that is consistent with previoustesting of the mixes and cores from the Nevada and Kansas sites. A report detailing thedifferences in the mixes based on the mechanical property testing will be provided. The ultimateuse of material and data from this and all other field validation sites will be to validate newpavement performance prediction test methods.
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TASK 4. INFORMATION DEPLOYMENT
SUBTASK 4-1. PUBLICATIONS, PRESENTATIONS, NEWSLETTERS, FLYERS ANDBROCHURES
Publications
Goual, L., J. Schabron, B. Towler and T. Turner, On-column Separation of Wax and Asphaltenesin Petroleum Fluids. Energy & Fuels, accepted for publication.
Huang, S-C., K. P. Thomas and T. F. Turner, The influence of moisture on the agingcharacteristics of bitumen. Proc., 4th Eurasphalt & Eurobitume Congress 2008, Copenhagen.Paper number: 406-002.
Huang, S-C., T. F. Turner, F. P. Miknis, and K. P. Thomas, Long-Term Aging Characteristics ofPolyphosphoric Acid Modified Asphalts. Transportation Research Record 2008, in press.
McCann, M., J. F. Rovani, and K. P. Thomas, “Instrumental Method Suitable for the Detectionof Polymers in Asphalt Binders,” in preparation.
Netzel, D. A., and T. F. Turner, 2008, NMR Characterization of Size ExclusionChromatographic Fractions from Asphalt. Petroleum Science and Technology, 26(12): 1369-1380.
Thomas, K. P., and T. F. Turner, 2008, Polyphosphoric-acid Modification of Asphalt Binders.Impact on Rheological and Thermal Properties. Road Materials and Pavement Design, 9(2):181-205.
Presentations
Ron Glaser, “Preliminary Infrared and Rheological Correlations in Asphalt Binders” presented atthe 45th Annual Petersen Asphalt Research Conference, University of Wyoming, Laramie,Wyoming, July 14-16, 2008.
Shin-Che Huang, P. M. Harnsberger, M. J. Farrar, T. F. Turner, R. W. Grimes, S. Salmans, andR. E. Robertson, “Fundamental Asphalt Characteristics in Relation to Pavement Performance”presented at the 45th Annual Petersen Asphalt Research Conference, University of Wyoming,Laramie, Wyoming, July 14-16, 2008.
Fran Miknis, “Phosphorous Magnetic Resonance Studies of Acid-modified Asphalts” presentedat the Binder Expert Task Group Meeting, Reno, Nevada, September 16-17, 2008.
Troy Pauli, J. Miller, J. Beiswenger, W. Grimes and J. Wolf, “Wetting/Compatibility--NCHRPProject 9-43; Mix Design Practices for Warm Mix Asphalt” presented at the 8th Annual
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Pavement Performance Prediction Symposium, Warm Mix and Recycled Asphalt Pavements,University of Wyoming, Laramie, Wyoming, July 16-18, 2008.
John F. Schabron, J. F. Rovani, and M. Sanderson, “On-Column Precipitation and Re-dissolutionTechnique for Separation of Asphaltenes and Waxes in Asphalt Binders” presented at the 45th
Annual Petersen Asphalt Research Conference, University of Wyoming, Laramie, Wyoming,July 14-16, 2008.
John F. Schabron, “On-Column Precipitation And Re-Dissolution: Automated SolubilitySeparations” presented by Fred Turner at the Binder Expert Task Group Meeting, Reno, Nevada,September 16-17, 2008.
Changping Sui, “Determination of Low-Temperature Properties of Asphalt using Dynamic ShearRheometry” presented at the 45th Annual Petersen Asphalt Research Conference, University ofWyoming, Laramie, Wyoming, July 14-16, 2008.
Conferences and Meetings Attended
45th Annual Petersen Asphalt Research Conference, University of Wyoming, Laramie,Wyoming, July 14-16, 2008. Most members of the Transportation Technology Business Unitattended the meeting.
8th Annual Pavement Performance Prediction Symposium, Warm Mix and Recycled AsphaltPavements, University of Wyoming, Laramie, Wyoming, July 16-18, 2008. Most members ofthe Transportation Technology Business Unit attended the meeting.
Binder and Mix Expert Task Group Meetings, Reno, Nevada, September 16-18, 2008. MikeHarnsberger, Fran Miknis, and Fred Turner attended.
Newsletter
Volume 3, Number 2 of the Transportation Technology e-Transfer newsletter was releasedSeptember 8, 2008. To highlight WRI’s 25th anniversary, the issue includes stories on theorigins of the PAV, WRI’s continuing work to improve the global aging system for the MEPDG,profiles of four Transportation Technology scientists who celebrate 25 years of contributions toWRI, and links to the July 2008 Pavement Performance Prediction Symposium presentations onthe topic of warm mix asphalt and recycled asphalt pavement. The newsletter is sent by e-mailto approximately 600 members of the transportation materials community. Newsletters arearchived at http://168.215.197.234/transportation.aspx?id=254. The next TransportationTechnology e-Transfer newsletter (Vol. 3, No. 3) is planned for December 2008.
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SUBTASK 4-2. WEBSITE MAINTENANCE
The Western Research Institute web site and the www.petersenasphaltconference.org site wereupdated for the WRI- and FHWA-sponsored 2008 Petersen Asphalt Research Conference andPavement Performance Prediction (P3) Symposium held in Laramie, Wyoming, in July 2008.The subject of the P3 Symposium was “Warm Mix and Recycled Asphalt Pavements.”Presentations from the symposium are posted at http://www.petersenasphaltconference.org.
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SUBTASK 4-3. RESEARCH DATABASE—CONTRACTOR TEAM ACTIVITIES
This database is to include recent, ongoing and planned research and outreach activities. Morespecifically, research problem statements, timelines, research results, contacts and relationshipsto other studies are to be posted. It is to be designed in a format similar to the (portland)concrete pavements database found at http://www.cproadmap.com//research/search.aspx. WRIhas interpreted this to mean that WRI is to develop its own such database and the COTR hasagreed to this. It is the opinion of the COTR that this database is not to have restricted access aswith the concrete pavements database. This effort is being accomplished as follows: As each setof work plans has been accepted by FHWA (with revisions if necessary), and as quarterly reportsare submitted, each has been posted at www.asphaltmodelsetg.org . Outreach activities can beseen at www.westernresearch.org . Click Transportation Technology and choose from among 18outreach activities listed in the left column. Although these two sites do not exactly duplicate theportland concrete database format, the two web sites do provide all of the information requiredfor this subtask.
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SUBTASK 4-4. RESEARCH IN PROGRESS DATABASE (Two parts)
The effort in this subtask is to incorporate various types of data from this project into twodatabases. The contract requires listings in the Transportation Research Board (TRB) Researchin Progress (RIP) database and the FHWA R&D Project Tracking System.
The TRB RIP Database
On the next two pages is a copy of the TRB RIP entry for this project. Note that the URL forthis project is given on the page of this entry. The general URL for the TRB RIP ishttp://rip.trb.org/browse/additions.asp?days=7
The FHWA R&D Project Tracking System
Since the beginning of this project, every quarter (and sometimes more frequently) WRI hasinquired as to whether the FHWA R&D Project Tracking System was developed and ready foruse. Each time through August 27, 2008, FHWA (TFHRC) responded that the system is not yetready for use.
Although (obviously) WRI has not seen the format for the FHWA R&D Project TrackingSystem, from the title of this part of Subtask 4-4, it appears to call for the same information thatis already reported in Subtask 4-3. If this is the case it raises the question of whether the sameinformation should be reported twice.
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SUBTASK 4-5. SUPPORT OF THE MECHANISTIC-EMPIRICAL PAVEMENTDESIGN GUIDE
In this subtask WRI is to supply relevant models, materials and materials data to the NCHRP9-30A Project Administrator, Mr. Harold Von Quintus, to further develop or contribute to theMechanistic-Empirical Pavement Design Guide. This process will begin as new data and modelsare available from research on the FHWA-approved work plans for this contract. Mr. VonQuintus has requested and has been supplied with a copy of Chapters 1 and 6 of the DTFH61-99C-00022 Final Report (which is in press). Mr. Von Quintus also requested that 600 pounds ofloose mix be shipped to him from each section of all future WRI validation sites.
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SUBTASK 4-6. SEMI-ANNUAL MEETINGS
Work Conducted this Quarter
The subjects for the 2008 P3 Symposium were “Warm Mix and Recycled Asphalt Pavements.”This meeting was held July 16-18, 2008 in the Washakie Center on the University of WyomingCampus. The Symposium linked 81 researchers, highway officials, producers and others with aneed to understand how asphalts may perform in a given application over time.
Warm Mix processes and technologies were discussed in detail. There was much discussionabout RAP and the need to understand factors affecting the long term performance of RAPpavements.
During the symposium, there were two discussion sessions held for each topic which helpedWRI identify the research gaps listed below.
Gaps Identified During 2008 P3 Symposium on RAP and Warm Mix Asphalt
RAP:
Degree of mixing of virgin and RAP binder with time must be investigated further.
Compatibility of virgin and RAP binder requires more in-depth investigation.
Effects of polymers, anti-stripping agents, lime, acid and other additives not fullyunderstood.
Solvent-less approach to RAP extraction and characterization is needed.
MEPDG has no input for RAP properties.
Aging properties of pavements containing RAP needs to be studied.
Consistency and characterization of RAP piles is very important for reproducibility.
Definitions of RAP processing and material handling is needed for users.
A greater focus on durability and low temperature cracking is needed.
RAP Operational Issues:
Economics
Pavement Management Systems for tracking RAP usage
WMA:
Long-Term aging, plant aging and initial field aging must be focused on.
Development of tests that can be run without extraction of binder to evaluate mix andpredict performance
Understanding of mechanisms for each WMA process
Workability test development
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Also during this quarter, all of the reservations were made for next year’s symposium.
Work to be Conducted Next Quarter
During the next quarter we will work with FHWA to choose a topic for the 2009 P3 Symposium.
Work for the 2009 Annual Project Review in Washington, DC, will not begin until September orOctober of this year. It is believed that it will remain at the Marriott Wardman Park directlyfollowing TRB 2009.
Support of FHWA Strategic Goals
The work conducted in this subtask supports the FHWA strategic goal to optimize pavementperformance.
