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Engineering Chemistry Thesis Presentation (PowerPoint 2007)
- 1. Development of a Dynamic Torsion Test for Measuring Low Temperature Response in Asphalt Binders CHEM 417 Research Project ShananWalsh April 7th, 2008
- 2. Outline
- 5. Weak chemical bonds – broken via heat or shear stress.
- 6. Bonds re-from upon cooling – not original structure
- 8. Molecules are polar (elastic network)non-polar (form around network)
- 9. Asphaltenes Polycondensed aromatic benzene, oxygen, nitrogen, sulfur, small quantities of heavy metals Vanadium and nickel (porphyrin structures) Side-chains up to C30 Maltenes = smaller MW versions; “resins” Aromatic hydrocarbons w/o O, N, S
- 10. Asphaltenes
- 11. Asphaltenes
- 17. Ways Asphalts can fail
- 18. Ways Asphalts can fail
- 19. Ways Asphalts can fail
- 20. HWY 11
- 21. HWY 41
- 22. Hwy 416
- 23. Original Empirical Grading Methods
- 24. Problem with Binder selection… @ 25oC, Samples A = C @ 135oC, A ≠ C @ 60oC, B=C, otherwise vastly different Samples A and B: same temperature dependency, differing consistencies at all temperatures All three binders classified as same grade (within viscosity range at 60oC).
- 25. Superpave Strategic Highway Research Program (SHRP) sponsored $50 million in 1987 for research Superpave specification – for modified and unmodified asphalts Performance Grade (PG) specification Criteria = constant Temperature range differs Example: PG 64-34
- 27. Superpave Specification Evaluated by American Association of State Highway and Transpotation Officials (AASHTO) and American Society for Testing and Materials (ASTM) AASHTO M320 – standard specification AASHTO MP-1a – more rigorous LTTPbind software (Federal Highway Administration) Geographic area Pavement temperature Air temperature Software contains data from 6092 weather stations
- 29. Tested Contracts
- 30. Analysis of Current Contracts
- 31. Analysis of Current Contracts
- 32. Analysis of Current Contracts
- 33. The Idea
- 34. Experimental
- 35. Experimental
- 36. Experimental
- 37. Experimental
- 38. Experimental
- 39. Experimental
- 40. Experimental
- 41. Experimental
- 42. Analysis High T, viscous behaviour (no capacity for recovery) Low T, elastic solids (rebound from deformation) Asphalt 2 more elastic than Asphalt 1 Smaller phase angle, δ
- 43. RESULTS
- 45. G* Comparison
- 46. Relation to Cracking severity
- 47. Testing of modified binders
- 48. Testing of Modified Binders
- 49. Sources of Error
- 50. Conclusion
- 51. Future Work
- 52. Acknowledgements
- 53. References Isacsson, U, and H Zeng. "Low-Temperature Cracking of Polymer-Modified Asphalt." Materials and Structures 31 (1998): 58-63. Loh, Ssu-Wei, and Jan Olek. Contributions of PG Graded Asphalt to Low Temperature Cracking Resistance of Pavement. Dept. of Civil Engineering, Purdue University. West Lafayette, Indiana, 1999. Lee, Stephen, Anita Vanbarneveld, and Michael A. Corbett. Low Temperature Cracking Performance of Superpave and Cold in-Place Recycled Pavements in Ottawa-Carleton. Environment and Transportation Department, Regional Municipality of Ottawa-Carleton. Ottawa. 1-21. Mihai, Marasteanu, Adam Zofka, MugurTuros, and Xinjun Li. Investigation of Low Temperature Cracking in Asphalt Pavements. Minnesota Department of Transportation. Minnesota, 2007. Hesp, Simon. "Improved Asphalt Binder Grading." Queen's University. Ontario Ministry of Transportation. 4 Mar. 2008. Mihai, Marasteanu O., Xue Li, Timothy R. Clyne, and Vaughan R. Voller. Low Temperature Cracking of Asphalt Concrete Pavements. Dept. of Civil Engineering, University of Minnesota. St. Paul: Minnesota Department of Transportation, 2004. Hesp, Simon, and MihaiMarasteanu. An Improved Low-Temperature Asphalt Binder Specification Method. Imperial Oil, Ministry of Transportation of Ontario, National Cooperative Highway Research Program, Natural Sciences and Engineering Research Council of Canada, Queen's University, University of Minnesota. 2004. PG Vs. AC - Why Change? CITGO Asphalt. CITGO Asphalt Refining Company, 1999. 1-4. Read, John, and David Whiteoak. The Shell Bitumen Handbook. 5th ed. London: Thomas Telford, 2003. 31, 39, 125, 196. Superpave: Performance Graded Asphalt Binder Specification and Testing. 1st ed. Vol. 1. U.S.A.: Asphalt Institute, 2003. Hesp, Simon. "Ontario Case Studies of Extraordinary Variability in Pavement Performance." Queen's University. Kingston, Ontario. 2007. Hoiberg, Arnold J. "Asphalt-Solvent Blends: Retardation of Viscosity Rise with Time." Industrial and Engineering Chemistry 43 (1951): 1419-1423 Jung, D H., and T S. Vinson. Low-Temperature Cracking: Test Selection. Dept. of Civil Engineering, Oregon State University. Washington: Strategic Highway Research Program, 1994. Champion, L, J F. Gerard, J P. Planche, D Martin, and D Anderson. "Low Temperature Fracture Properties of Polymer-Modified Asphalts Relationships with the Morphology." Journal of Materials Science 36 (2001): 451-460. McCrum, N G., C P. Buckley, and C B. Bucknall. Principals of Polymer Engineering. 2nd ed. New York: Oxford UP Inc., 1997. 117-179. "Vikopol: EpoxidizedPolybutene." Arkema Inc. 2000. Arkema. <http://www.arkema-inc.com/tds/740.pdf>. "Vikolox Products: 1, 2, Epoxy Alkanes." ArkemaEpoxides. 2000. Arkema Inc. <http://www.arkema-inc.com/tds/739.pdf>. Baumgardner, Gaylon, Jean-Valery Martin, Buzz Powell, and Pamela Turner. Binder Modified with a Combination of Polyphosphoric Acid and Styrene-Butadiene-Styrene Block Co-Polymer: the NCAT Test Track Experience Over the First Two Research Cycles. National Center for Asphalt Technology. 1-20.
- 54. Thank You
- 55. Questions?
Editor's Notes
- -Asphalt is a viscoelastic material at room temperature, meaning it behaves as a viscous fluid at high temperatures, whereas it is a brittle solid at low temperatures.-Asphalt, otherwise referred to as bitumen within North America, is a tar-like mixture of hydrocarbons (given that carbon and hydrogen make up 90-95 wt% of its composition) derived from petroleum naturally or via distillation, and is used for road surfacing and roofing. -The properties of asphalt have proven useful in engineering as it is strong, readily adhesive, highly waterproof, and durable. Furthermore, it provides limited flexibility to mixtures of mineral aggregates with which it is usually combined.
- -Asphalt has a complex molecular structure, with the size and chemical bonds involved differing according to the asphalt blend or source.-Overall, three different types of asphalt molecules exist: aliphatics, cyclic, and aromatics.-These molecules interact with each other in various ways to present differing physical and chemical behavior across different asphalts. -The weak chemical bonds that hold these molecules together can be broken via the application of heat or shear stress. Upon cooling, the bonds will re-form, though not necessarily to the same structure.-The viscoelastic nature of asphalt can be attributed to this feature.-The molecules within an asphalt can be polar, which provide its elastic network, or non-polar, which form around the polar network and contribute to the viscous properties of asphalt. -The complex behavior between the molecules ultimately affects its performance in the field. For example, asphalt with large quantities of high molecular-weight, non-polar molecules tend to exhibit poor low-temperature behavior (brittle).
- -Asphaltenes can be separated from the bulk of asphalt materials via the chromatographic method of Corbett, and the precipitation method of Rostler.-The Rostler method utilizes sulfuric acid of varying strength to analytically separate groups within the material, whereas the Corbett method uses differential absorption and desorption. -Both methods separate out asphaltenes using either n-heptane or n-pentane.-Asphaltenes are composed primarily of polycondensed aromatic benzene units with oxygen, nitrogen, and sulfur, combined with minor amounts of a series of heavy metals, particularly vanadium and nickel, which occur in porphyrin structures.-Although the asphaltene structure itself may vary somewhat, depending on its source, an example of the structure of an asphaltene molecule is presented -- Molecular asphaltene structure as seen in a crude oil from Mexico.-The nickel to vanadium contents of asphaltenes reflect the pH and Eh conditions of the oil source, and is used in the petroleum industry for the identification of potential oil sources.-Depending on the asphaltene source, the C:H ratio is approximately 1:12.-The unique network of asphaltenes that is found within an asphalt binder is evident in Figure 3a-b.Asphalt is a collodial system which has a disperse phase and a continuous phase. The components of highest molecular weight, i.e., micelles constitute the disperse phase and are known as asphaltenes. The continuous or intermicellular phase represents the compounds of lower molecular weight and are called maltenes.Maltenes constitute the fraction of asphalt which is soluble in n-alkane solvent such as pentane and heptane. Their chemical characteristics are as follows:Contain smaller molecular weight versions of asphaltenes called "resins"Contain aromatic hydrocarbons with or without O, N and S (also called "first acidaffins")Contain straight chained or cyclic unsaturated hydrocarbons called oleifins (also called "second acidaffins")Contain cyclic saturated hydrocarbons known as naphthenes (also called "saturates")Contain straight or branch chain saturated hydrocarbons (also "saturates"Their molecules are also known as "naphthene-aromatics"Asphaltenes are complex hydrocarbons having the following components:Condensed aromatic hydrocarbons with sidechains up to C30Hetero-aromatic compounds with sulfur present in benzothiophene rings and nitrogen in pyrrole and pyridine ringsBi- or polyfunctional molecules with nitrogen as amines, amides, and oxygen in groups such as: ketones, armides, phenols, and carboxylic acidsMetals nickel and vanadium complexed with pyrrole nitrogen atoms in porphyrin ring structures
- -Asphalt cement examined using a Scanning Electron Microscope. -The technique is useful to analyze such structures, as irridation of the sample with the electron beam-Evaporates the oils within the asphalt cement, making the resins/asphaltenes visible
- -Asphalt cement examined using a Scanning Electron Microscope. -The technique is useful to analyze such structures, as irridation of the sample with the electron beam-Evaporates the oils within the asphalt cement, making the resins/asphaltenes visible
- -The binder acts as a water-proofing agent and serves to hold the aggregate framework together. The primary purpose of the aggregates is to contribute to the overall strength of the asphalt.-At high temperatures, the binder is a viscous fluid and flows easily, whereas at low temperatures, it behaves like an elastic solid.-This suggests that an asphalt binder is capable of returning to its original shape, to a certain extent, upon the removal of an applied load. However, if the binder is too stiff, its ability to deform elastically diminishes.-Binder sensitivity to load duration is also an important factor and should be considered when testing for specific roads. -As time passes, binders age by reacting with oxygen via oxidative hardening, a process that is known to occur more rapidly when under sustained high temperature conditions.-Age hardening produces harder asphalt, which are more prone to cracking.-As a result, if an asphalt binder has aged, the chance of this binder cracking at low temperatures is increased significantly. -Therefore, in order to avoid cracking in pavements, softer asphalt binders need to be used.-While all binders age, the rate at which they do so varies across different binder compositions.
- -The binder acts as a water-proofing agent and serves to hold the aggregate framework together. The primary purpose of the aggregates is to contribute to the overall strength of the asphalt.-At high temperatures, the binder is a viscous fluid and flows easily, whereas at low temperatures, it behaves like an elastic solid.-This suggests that an asphalt binder is capable of returning to its original shape, to a certain extent, upon the removal of an applied load. However, if the binder is too stiff, its ability to deform elastically diminishes.-Binder sensitivity to load duration is also an important factor and should be considered when testing for specific roads. -As time passes, binders age by reacting with oxygen via oxidative hardening, a process that is known to occur more rapidly when under sustained high temperature conditions.-Age hardening produces harder asphalt, which are more prone to cracking.-As a result, if an asphalt binder has aged, the chance of this binder cracking at low temperatures is increased significantly. -Therefore, in order to avoid cracking in pavements, softer asphalt binders need to be used.-While all binders age, the rate at which they do so varies across different binder compositions.
- -The binder acts as a water-proofing agent and serves to hold the aggregate framework together. The primary purpose of the aggregates is to contribute to the overall strength of the asphalt.-At high temperatures, the binder is a viscous fluid and flows easily, whereas at low temperatures, it behaves like an elastic solid.-This suggests that an asphalt binder is capable of returning to its original shape, to a certain extent, upon the removal of an applied load. However, if the binder is too stiff, its ability to deform elastically diminishes.-Binder sensitivity to load duration is also an important factor and should be considered when testing for specific roads. -As time passes, binders age by reacting with oxygen via oxidative hardening, a process that is known to occur more rapidly when under sustained high temperature conditions.-Age hardening produces harder asphalt, which are more prone to cracking.-As a result, if an asphalt binder has aged, the chance of this binder cracking at low temperatures is increased significantly. -Therefore, in order to avoid cracking in pavements, softer asphalt binders need to be used.-While all binders age, the rate at which they do so varies across different binder compositions.
- -The binder acts as a water-proofing agent and serves to hold the aggregate framework together. The primary purpose of the aggregates is to contribute to the overall strength of the asphalt.-At high temperatures, the binder is a viscous fluid and flows easily, whereas at low temperatures, it behaves like an elastic solid.-This suggests that an asphalt binder is capable of returning to its original shape, to a certain extent, upon the removal of an applied load. However, if the binder is too stiff, its ability to deform elastically diminishes.-Binder sensitivity to load duration is also an important factor and should be considered when testing for specific roads. -As time passes, binders age by reacting with oxygen via oxidative hardening, a process that is known to occur more rapidly when under sustained high temperature conditions.-Age hardening produces harder asphalt, which are more prone to cracking.-As a result, if an asphalt binder has aged, the chance of this binder cracking at low temperatures is increased significantly. -Therefore, in order to avoid cracking in pavements, softer asphalt binders need to be used.-While all binders age, the rate at which they do so varies across different binder compositions.
- -The binder acts as a water-proofing agent and serves to hold the aggregate framework together. The primary purpose of the aggregates is to contribute to the overall strength of the asphalt.-At high temperatures, the binder is a viscous fluid and flows easily, whereas at low temperatures, it behaves like an elastic solid.-This suggests that an asphalt binder is capable of returning to its original shape, to a certain extent, upon the removal of an applied load. However, if the binder is too stiff, its ability to deform elastically diminishes.-Binder sensitivity to load duration is also an important factor and should be considered when testing for specific roads. -As time passes, binders age by reacting with oxygen via oxidative hardening, a process that is known to occur more rapidly when under sustained high temperature conditions.-Age hardening produces harder asphalt, which are more prone to cracking.-As a result, if an asphalt binder has aged, the chance of this binder cracking at low temperatures is increased significantly. -Therefore, in order to avoid cracking in pavements, softer asphalt binders need to be used.-While all binders age, the rate at which they do so varies across different binder compositions.
- -Empirical specifications do not relate directly to asphalt binder performance in pavements-Asphalts A and C have the same consistencies at low temperatures, but are completely different at high temperatures.-Asphalt B has the same consistency as asphalt C at the specification temperature, 60oC, but otherwise it is very different from asphalt C.-Asphalts A and B display the same temperature dependency, however they demonstrate vastly different consistencies at all temperatures.-All three are classified as the same grade, only because they fall within the specified viscosity range at 60oC. As a result, one may erroneously expect the same characteristics during construction and the same performance during hot and cold weather conditions.
- -1987, the Strategic Highway Research Program (SHRP) sponsored $50 million of research on asphalt binders to relate the specifications to actual pavement performance.-The result was the Superpave binder specification, which is intended for both modified and unmodified asphalts. -The new Performance Grade (PG) asphalt binder specifications is unique in that the specified criteria remain constant, but the temperature range within which the criteria is achieved (i.e. climate conditions asphalt must perform in) changes for the various grades.
- -An example of a performance-graded asphalt is a PG 64-34 asphalt binder. The first number, 64, indicates that the asphalt performs adequately at a high temperature up to 64oC. The second part of the classification, -34, indicates that the asphalt binder is able to perform acceptably at temperatures as low as -34oC. -The high and low temperatures extend as far as necessary in six-degree increments.The higher the grade, the stiffer the binder and the more resistant it is to rutting.The lower the number, the more resistant to thermal cracking.The greater the difference, the higher the cost.
- -Superpave binder specification and test methods used to characterize asphalt are evaluated by the American Association of State Highway and Transportation Officials (AASHTO) and the American Society for Testing and Materials (ASTM).-AASHTO M320, the Standard Specification for a Performance-Graded Asphalt Binder, standardizes the specification requirements. -AASHTO’s provisional standard, MP-1a, incorporates an alternate procedure for determining the critical low cracking temperature of an asphalt binder, and is considered more rigorous and inclusive of most modified asphalts.-To select an asphalt binder grade for the construction of a pavement LTTPbindSuperpave software, developed by the Federal Highway Administration. -The software contains three methods by which the user can select an asphalt binder grade: Geographic area, pavement temperature, and air temperature. -The first step is the determination of the air temperature range in the service area. -These temperatures are then converted to pavement temperatures, upon which asphalt binder selection is based. -The software contains temperature data from 6092 weather stations across the United States and Canada.-Only those weather stations were included in the database for which at least 20 years worth of observations were available.
- -Early 1990s, the Strategic Highway Research Program (SHRP) developed a method of specifying asphalt binders to meet the climatic conditions in which pavement would have to perform. -Based on a series of binder tests at specific temperatures. -Objective of SHRP was to develop test methods that better correlate with pavement performance. -The product of the program is the system of tests and specifications known as the Superpave (Superior Performing Asphalt Pavements) system. -Present Superpave specifications are based on linear viscoelastic analysis of creep and strength data at low temperatures on asphalt binders and mixtures. These specifications helped to improve the selection of asphalt materials for better low temperature performance.-However, such a specification method is unable to predict the evolution of cracks over time. Furthermore, traffic loading, variable aging of the asphalt, and thermal behavior of the asphalt is not taken into consideration. In addition to this, the binder grading methods developed with straight asphalts may not be sufficient for the performance prediction of modified and specialty asphalt binders.-Due to a lack of time and resources, only the bending beam rheometer (BBR) and the direct tension test (DTT) were developed under the Superpave program, and no direct comparison was ever made with more sophisticated fracture mechanics-based failure tests. While these tests have proven to be relatively accurate in the determination of poor binders, these tests can take up to three days – a testing period that is considered too long by the Ministry.It is a general understanding that all pavements, unless rehabilitated or rebuilt regularly, will eventually fail. Low temperature cracking can be controlled by the proper selection of asphalt binders. The important point in the selection of a binder is to ensure that the stiffness of the asphalt material is lower than the critical stiffness this material will experience when exposed to the lowest temperature expected to occur in the pavement. -The Superpave binder tests are also conducted at temperatures that are encountered by in-service pavements. A dynamic shear rheometer is typically used at high pavement temperatures (64oC) to ensure that an asphalt will not become too soft and be susceptible to rutting8. In such a test, a small sample of asphalt is placed between two round plates. The lower plate is fixed, and the upper one turns back and forth. In the presented research, a similar method was utilized to test low temperature performance. However, instead of testing a small asphalt disc sample between two plates, a small bar was formed and placed within the rheometer vertically between two grips. The twisting action taking place as liquid nitrogen is used to maintain a low temperature, places a stress on the asphalt being tested. The reaction of a material to stress is strain, and the ratio of stress to strain yields a stiffness value. The DSR is capable of measuring the phase angle, δ, and thereby helps identify the viscous and elastic components of the asphalt being tested.
- -Geographical representation of all sites tested-Total of 20 sites tested and analyzedToo young = pinkIncorrect grade = blue
- Based on data previously obtained through a series of bending beam rheometer tests (as performed by Kevin Houlihan and SathishSubramani), all contracts were analyzed to gain greater perspective on their performance in the field versus how they were graded.-Two contracts are highlighted: Roger Stevens and Trout Creek. This is to indicate that these contracts consist of the wrong asphalt cement for their respective location. Therefore, these data points are presented for the sake of interest, but should not be analyzed in great detail with respect to the other contracts shown.-Cracking severity demonstrated in the field (LEFT Figure).-Nine contacts have exhibited very little (if any) cracking. -Of particular interest are those constructed as much as fifteen years ago. -Eleven contracts tested have shown severe cracking in the field, with cracks noted every few metres. -Compare the degree of cracking with the binder specification each had been assigned. -Figure on RIGHT shows that the present specification method does not properly distinguish the ideal-performance binders from those that have exhibited poor performance.-Specifically, contracts pertaining to Bat Lake, Monkland, and Northbrook, all passed the industry standards despite their poor performance in the field.-Overall, the asphalt cements are graded within a fairly narrow range, with no clearly defined separation between the good and poor performing asphalts.-Several of the contracts appear to lay on the boundary between what is acceptable and what is not (Bannockburn, Little Current, and Denbigh). -Furthermore, given that the Ministry of Transport accepts a 3oC margin of error when grading the asphalts, that the tested roads are only aged 3-15 years, it’s likely that all tested binders would have ultimately passed the grade requirements for the respective contracts, exposing the unreliability within the test.
- -Tests based on the LTTPBind© software specifications have also been run on the tested contracts at -10oC and -20oC, from which the worst grade loss after three days of conditioning was plotted.-While this serves as a reasonable basis for future specifications, increasing the grade loss by an additional 1-2oC accounts for any possible error and increases the reliability of the results. -It should be noted that the sample tested from HWY 41 Dacre Northerly has not yet reached extremely cold temperatures, and as such will likely crack once it reaches a low enough temperature in the area. -It is important to note as well that the peculiar results presented by the Vennachar Jct. contract. -Figure 8a shows that this particular contract has exhibited very little cracking overall. However, Figure on the LEFT shows that this contract failed the LS-308 test (an extended BBR correlation program) by a significant amount. This also holds true for the Smooth Rock Falls contract. Although this particular contract has presented very little cracking, it lays on the border between a pass or a fail. -While experimental error could be considered, the test clearly shows greater reliability in accepting good performing asphalts as a whole. -Only one poor contract of note, Northbrook, was seen to pass the test. Overall, despite this oddity, the LS-308 method has shown to prove a high correlation with transverse cracking within contracts. -Figure on the RIGHT demonstrates the strong correlation between the grade loss for each sample after three days of conditioning at -10oC and their associated cracking severity as noted from the field. -The accuracy in these results is considered to be roughly 95%, with the only outliers seen in the Vennachar Jct. (HWY 41) contract, a polymer modified asphalt, as well as in Elk Lake (HWY 65). -Most contracts that were observed to pass the LS-308 test successfully demonstrated a low overall performance grade loss. This supports the results as shown in Figure 9a, demonstrating the use of superior binders within the asphalts that exhibited a low level of cracking.
- -Figure on LEFT presents the relationship between cracking severity in the tested contracts and their respective worst grade loss, measured at both -10oC (red) and -20oC (blue). -As expected, most contracts presented the highest level of grade loss at the lower temperature of -20oC. -Superiorperforming asphalts demonstrated losses < 3oC at -10oC over a span of three days. -Contracts that consisted of inferior binders presented a grade loss of up to 7.2oC, as seen with HWY 17 Petawawa and HWY 41 Denbigh. -At -20oC, it’s evident that a few of the better performing binders will undergo considerable losses at such low temperatures. -This suggests that the binders were over-designed for the area in which they are used, and will likely crack in the event that the temperature drops significantly at the site. -The LTTPBind© LS-299 strain tolerance specification test (RIGHT Figure) is an indication of fatigue within a binder. -Should the transverse cracking as shown in the LS-308 specifications (Figure 8a) be improved upon, the values as obtained via the LS-299 method will be more acceptable. -RIGHT Figure shows that the most problematic binders are those shown on the left of the graph. -These data points specifically correspond to contracts that cracked within the first few years post-construction, and have continued unabated. -Goal of research to establish a method that is able to replicate these results in a much shorter time period. -Preliminary testing more feasible to the Ministry of Transportation-Encourage the development of binders more suitable to a specific area and climate.
- -Vectors G*1 and G*2 represent the complex moduli of Asphalts 1 and 2-When load applied, part of deformation is elastic, and part is viscous = viscoelastic material.-Asphalt 2 is more elastic than Asphalt 1 (because of the smaller δ).-Asphalt 2 will recover from a greater deformation inflicted by an applied load.-HOWEVER, at lower temperatures Asphalt 2 will become more brittle and therefore more prone to fracture.-High temperatures, asphalts behave like viscous fluids with no capacity for recovery.-Represented by the vertical axis (viscous component only); there would be no elastic component of G*, since δ = 90o. -Low temperatures, asphalts behave like elastic solids which rebound from deformation completely. -Represented by the horizontal axis (elastic component only). In this case, there is no viscous component of G*, since δ = 0o . -An asphalt should exhibit a fair degree of viscous behaviour as well – better response to heavy loads in cold temperatures.
- -Research began with the general calibration of the rheometer and development of the test itself. -To determine the ideal parameters at which the rheometer must be set, a series of trials were run on several sections from HWY 417 (specifically, sections 7 and 3). -Tests were run at -20oC, -10oC, and 0oC. This was intended to help gain a clearer picture with respect to how the asphalt binder behaviour responds to the change in low temperatures. -Sample 7 of Highway 417, known to be a poor asphalt-With lower temperatures the elasticity increases-Seen when comparing the slopes of the tests run at -10oC and 0oC (5.164 x 106 Pa and 1.046 x 106 Pa, respectively).-The sample at 0oC is much more viscous in nature, though not as much as was originally expected.-For this particular section, future tests at 0oC should be executed to ensure that the most accurate results feasible are achieved. -Sample 3 of Highway 417 was also tested at -10oC, and was seen to be much more elastic to the temperature change. -The G* slope pertaining to section 3, seen in Figure 7 as the green data set, has a magnitude five-times smaller than that seen for section 7 at -10oC. This is considerably large, and shows a much faster hardening rate for Sample 7. After a series of trials using the samples noted, the final test parameters were decided upon; largely based on the results that were found to be the most reproducible. Specifically, all following tests were performed at -10oC. This was also considered a reasonable temperature at which to test contracts, as it is a temperature often reached over the course of a Canadian winter.
- -At -10oC, all twenty contracts were tested, and data pertaining to the change in G’, G’’, G* and tan delta over time were collected via RSI Orchestrator© software. -The data for each contract was plotted separately, and the slopes pertaining to the tan delta and G* curves in each trial were collected and compared with each other. -The measurement of the tan delta slope, otherwise known as the loss tangent, for each of the contracts allowed for the determination the elastic or viscous nature of the binder. -Tan delta is the ratio of the loss modulus (which characterizes the viscous nature of a material) and the storage modulus (which characterizes the elastic nature of the material).-Therefore it can be concluded that a decrease in the loss tangent of a binder is indicative of an increase in the elasticity of the material. -Notably seen for the samples from HWY 138 Monkland Northerly, HWY 17 Petawawa, and HWY 11 Trout Creek Bypass. -Referring to the cracking severity seen in Figure 8a, the increase in elasticity within the asphalts has a strong correlation to the increase in cracking potential within the asphalt cement. -Odd that the tan delta as noted for Trout Creek Bypass is so low, particularly given that the tan delta as determined for HWY 138 Monkland is slightly higher (suggesting a slightly more viscous property). -Additional trials would need to be performed to confirm this result, or the extraction of an additional sample from this road section be considered. -A general observation of all lower tan delta values, however, does support that this test is able to correctly indicate which binders may lead to fracture cracking. -Comparing the poor contracts with those that exhibit high tan delta values, such as HWY 62 Bloomfield Northerly, HWY 138 Cornwall Northerly, and HWY 33 Conway Easterly, supports the concept that a more viscous binder is ideal at such low temperatures. -These particular contracts gave ideal results under the M320, LS-308, and LS-299 tests. The fact that similar results were obtained through use of the dynamic rheometer in a fraction of the time (two hours versus three days) shows promising progress.
- -Good representation of the viscous or elastic nature of an asphalt binder from the G*.-Samples that yielded a large slope value, as seen with HWY 33 Conway Easterly, demonstrated the highly viscous nature of the asphalt at low temperatures. This has proven to be an ideal characteristic, as this same contract has shown very little cracking in the Field (Figure 8a). -This is further seen when comparing the G* slope obtained for HWY 138 Monkland Northerly. -The slope presents a more elastic structure within the binder, which ultimately increases the probability of cracking in the field. This, once again, is evident when referring to Figure 8a. -When comparing the results presented, the same general trend between contracts should be evident. -There are only a few discrepancies, such as the low level of viscosity of HWY 138 Cornwall in comparison with a section such as that from HWY 416 Roger Stevens. -It is interesting to note that HWY 11 Trout Creek Bypass suggests a strong elastic characteristic – an oddity that was also observed in the previous graph.-Given that both forms of analysis yielded similar results, it is possible that the binder used in that particular location was overdesigned, and may fail more easily when subjected to cooler temperatures.
- -Loss tangent values obtained from each trial were plotted against the cracking severity recorded for each contract-Results present a clear boundary between the superior performing binders and those which exhibited considerable cracking within the asphalt cement.-The only outlier in this case is that pertaining to the Vennachar Junction test sample. -This can be attributed to the fact that this is a polymer-modified binder. As such, the properties of the polymer may not be able to prevent the crystallization of asphaltenes within a binder at the temperature drops, yielding more elastic properties. -Smooth Rock Falls contract was shown to perform the best as it presented the highest loss tangent value. However, the fact that a small level of cracking has been seen in this area, similar tests should be executed at lower temperatures and compared in order to rule out the possibility that the binder is over-designed for its field location. -Cluster of contracts, seen around the loss tangent value of 0.65, have presented optimal results consistently in both the BBR test and the dynamic shear rheometer (DSR) test. -Results obtained via the presented DSR method are roughly 95% accurate, future research utilizing this test would serve as an acceptable means of binder property characterization within a short period of time.
- -Since the implementation of the Superpave PG binder specification in the 1990s, the use of additives to improve the overall properties of asphalt binders has increased.-Given the success of previous tests, a series of additives were tested on a control sample.-This was executed in an effort to determine a more ideal binder composition for low-temperature climates, reducing the probability of cracks occurring. -A total of five different additives were tested on a binder sample from HWY 655, section 6. -All trials contained a small level of polyphosphoric acid, as well as one additional additive. -The four additional additives (three of which are commercially available through Arkema) tested were: -VikopolTM (VP64) – Polyisobutaline with 64 carbon units and one epoxy group (structure: Appendix A, Figure A9). It has an estimated molecular weight of 973 g/mol, and a viscosity of 300 Poise at 25oC. In epoxies, this chemical provides a balance between strength and flexibility, enhances impact resistance, improves water resistance, and improves low temperature flexibility.VikoloxTM (VL1618) – A blend of carbon-16 and carbon-18 dimers with a single epoxy group (Structure: Appendix A, Figure A10). This product is capable of adding hydrophobic domains.17VikoloxTM 30+ (VL30+) – Consists of C30 carbon chains with a single epoxy group at the end. The structure is similar to that seen for the noted VL1618 additive in Appendix A, Figure A10.130M20-460 – A comb-graft polymer consisting of a polybutadiene backbone and polyethylene with a molecular weight of 460 g/mol. This additive was produced in the lab under high temperature conditions within a vacuum. It was hoped that the polyethylene would become inserted into the asphaltene crystal lattice, and prevent the further growth of crystals in low temperature conditions (thereby maintaining an ideal level of viscosity within the asphalt binder)Comb polymer There is a main polymer chain from which uniform branches of another polymer regularly protrude. The described binders were mixed with a binder sample from HWY 655, section 6. The epoxy groups within each additive were assumed to react with the asphaltenes in the sample in such a manner that “gelling” (crystallization) would be prevented, thereby increasing the tan delta While polyphosphoric acid (PPA) has been used for decades to yield improved binders, there is little concrete data available pertaining to the performance of asphalt containing the enhanced binder. Of particular interest is data that has been collected over a period of time, and has taken into account varying traffic conditions and weather changes. One study, based on the NCAT Test Track (a closed off track course built specifically to evaluate binder behavior under a variety of conditions, materials, and constructions), assessed the impact of PPA on a test track over a period of six years. In addition to PPA, Styrene-Butadiene-Styrene (SBS) was an additional additive used in the asphalt cement18. What is unique about this study is that the research involved allowed for the collection of credible data in 2-3 years, what would normally be collected in 15-20 years in the field18. While this accelerated testing may have yielded more severe results than a typical highway, use of a PPA/SBS additive was proven to improve the overall performance of the asphalt cement. Furthermore, it was found that the use of PPA allowed for the reduction of polymer within the mixture, maintaining a steady economically feasible state while still obtaining the desired asphalt performance.
- -For each sample, two runs were executed in order to test reproducibility -The G’, G’’, G* and tan delta values were measured over time, and the slopes pertaining to the tan delta and G* graphs were noted. -The slope values derived from each trial were plotted against each other for comparison purposes, and are presented -Repeated trials for a particular sample are noted with a “b”. -Unfortunately, no strong, differing results were achieved with the additives and/or the concentrations of the various additives used. -With respect to ideal changes in the loss tangent, an increase would suggest greater viscosity with a reduction in temperature. -The only samples that demonstrate this physical change in Figure on the LEFT are 655-6 (2) and 655-6 (4). -Replicated results (2b and 4b), a small degree of error has skewed the results slightly. -Given the general trend, however, amongst all samples tested, it is reasonable to assume that the loss tangents amongst all modified binders are relatively similar. -Therefore, future tests should focus more on the addition of a greater concentration of a particular additive in order to determine how greatly it affects the elasticity or viscosity of the tested sample.-Comparison of the G* slopes derived from each sample yielded similar findings. -Once again, a higher G* value would increase the decrease the probability of cracking within a moderately low temperature environment. -Samples 655-6(4) and 655-6(5), as seen in Figure on RIGHT, show a very slight increase in this respect. However the degree of change is not large enough to yield significantly different results when exposed to the environmental temperature.-Overall, while there were no findings of great significance in terms of the tested modified asphalts. -However, the reproducibility of the results, as well as the success in predicting what binders may yield future cracking in presently used contracts demonstrate the potential in using the dynamic shear rheometer for low temperature testing.
- -Sample preparation unseen deformations may have been present and thus allowed the asphalt to become more susceptible to cold temperatures.-Removal of the sample from the mold required the careful use of a razor. -This was necessary to remove the teflon from the surface of the sample. -Small notches created along the edges of the sample, thereby creating possible points of stress. -Rheometer the clamps used to secure the sample could have inflicted additional strain upon the sample if adjusted too tightly. -Discrepencies seen when analyzing the data obtained from the RSI Orchestrator software. -Machine was set to have a typical soak time of ten minutes, and a measuring period of ten seconds (with one measurement taking place at both the beginning and end of this time period), the recorded times were significantly different – at times differing from what was requested by several minutes. While this ultimately would not skew the results too greatly, in order to achieve the most accurate results possible, the machine and software used must be properly calibrated with each other in future tests.
- -Use of the dynamic shear rheometer has proven to give relatively accurate results, particularly when comparing the results to contracts that are presently active in the field.-The LS-308 and LS-299 test results, as previously determined, have been shown to be 90+% accurate in the prediction of low temperature cracking. Therefore, given that the DSR results as performed at -10oC mimic the BBR results with a high degree of accuracy, it can be concluded that the use of such a method would yield highly reliable results within a more acceptable period of time. -The test has also helped to prove that there lays a strong correlation between the viscosity of a material, and the probability that the material will crack when subjected to cold temperatures. -The results provide a solid basis for future research to develop from, particularly in the testing of modified binders. This will ultimately lead to the discovery of more appropriate binders for specific locations, and save the Ministry the high expenses presently being distributed for the constant upkeep of roads.
- -To gain a deeper understanding of this topic area, comparisons between good and poor performing asphalt cements should continue to be made.-From this, more reliable binders can be created in the lab and compared with these samples. -A comparison of old and new asphalt binders also helps to gain a greater understanding of how different pavements will be classified under Superpave classifications, and expose any more flaws within the grading system that need to be addressed. -Another means to determine how the PG classification of an asphalt is to further develop the extraction and recovery procedures used to obtain as pure of a binder sample as feasible. Any solvents used in such procedures should also be closely analyzed to determine if there is any resulting impact on PG classification. -Several more test sites should be monitored throughout the year, as this will create a better picture of the behavior of asphalt under varying environmental conditions. -Such conditions can be monitored through use of instrumentation installed at site, and data obtained may help to fine tune the current Superpave classification guidelines. -The test method as used in the presented research should be tested further. -Reasonable predictor for how an asphalt binder will react at low temperatures. -Accurate results can be easily obtained within a matter of hours, versus several days (as is the case with several other tests currently in use). -Isolation and removal of any flawswill allow agencies to better predict the performance of an asphalt binder in a given location, particularly the potential for thermal fracture at low temperatures, and concurrently its expected lifetime will be more accurate. -Analyze the effects of different cooling rates on a given sample.-While this was somewhat tested in the early stages of the project, the results were not as accurate as those obtained wherein the test was run under one continuous temperature. This may be the result of general computer programming associated with the test, or parameters set too high/low. -Modification of the program may allow for a variety of cooling rates to be used (i.e. 1oC, 2oC, 5oC, or 10oC an hour). A sample could be cooled down to, for example, 5oC, where it is held for a period of time (or until thermal equilibrium is reached). From here the temperature can be reduced further until thermal equilibrium is once again obtained. In running such a test, real-life environmental effects on the sample would be observed, and a more accurate data representation obtained.
- -Dr. Simon Hesp for the continuous support throughout the course of the project, and boundless knowledge on the topic at hand. -RasoulSoleimani for his assistance with the execution of the tests, and guidance in using the tools within the lab. -William Newstead for acting as an examiner throughout the course of this research project. -Kevin Houlihan and SathishSubramani for use of their data collected via BBR method for comparison purposes. -Michael Faba, a Masters student within the department of Chemical Engineering for providing the groundwork on how to use the rheometer and software associated with it. -Bruce Rudolph of Maple Instruments Ltd., for the instruction in how to create a customized computer program that ultimately lead to the development of the testing method outlined in this report.