Fundamental Properties of Asphalts and Modified Asphalts, III

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Goals The purpose of this subtask is twofold: (1) to improve the general understanding of the physicochemical 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 and expand its application to modified asphalts. Support of FHWA Strategic Goals The work conducted in this subtask supports FHWA’s ultimate pavement research and development goal of providing performance-based models and tools to facilitate effective management of the national highway infrastructure. Expanding our understanding of how pavements age in terms of time and depth is critical to developing accurate models to predict rutting and cracking in rehabilitation and new construction projects, and to allow better timing of preventive 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 asphalt pavements; however, very few have dealt with how oxidative aging varies with depth. Of the few studies available on the subject, perhaps the most well known is by Coons and Wright [1968]. In this study 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 make the evaluation involved slicing the cores parallel to the pavement 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 may have determined the conclusions reached. For example, the Coons and Wright study showed an increase of roughly 50% in the viscosity of asphalt recovered from the top 6.3-mm slice versus asphalt recovered from the next lower 6.3-mm slice. In addition, a very fine film at the surface of the core had a higher viscosity than the average viscosity in the top 6.3 mm. On the other hand, the Houston et al. study found that the viscosity did not vary significantly with depth. Since different pavement designs, binders, and ages were used in these studies, the results for both may be valid. However, it is also possible that the 25 mm thickness of the slices used in the Houston et al. study masked a viscosity profile that would have been apparent if thinner slices had been examined. The opposing conclusions are not surprising and point out the difficult nature of not only measuring aging in HMA, but developing a global aging system to predict aging. An extensive literature review indicates the global aging system as developed by Mirza and Witczak is the only 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 its predictive capability is clearly warranted. 12
Work Conducted This Quarter Introduction Both liquid-cell and photoacoustic (PA) infrared spectroscopy experiments are described for aged and unaged asphalt samples. In addition, aggregates and mixed aggregate-asphalt samples (mastics) are examined using PA spectroscopy. PA spectroscopy is unique in several ways to other more traditional infrared sampling techniques such as attenuated total reflectance (ATR). For example, the PA technique requires little sample preparation and has low sensitivity to surface condition [McClelland et al. 2002]. This is a very important concept that makes it possible to examine photo-oxidation of the pavement surface without use of solvents. Also, an evaluation of pavement distress at the FHWA/ WRI Arizona validation site and related rheological parameters is presented. Data presented here were collected under the Fundamental Properties of Asphalts and Modified Asphalts, III, FHWA project (DTFH61-07-D-00005) and to a small extent under the Asphalt Surface Aging Prediction (ASAP) project (DTOS59-07-H-0006) for the Research and Innovative Technology Administration (RITA). The projects are complimentary in terms of achieving a better understanding of how asphalt pavement ages, but the ASAP project is specifically directed towards providing a tool and methodologies for determining the appropriate time for the preemptive application of rejuvenating surface treatments. Experimental Asphalt Aging Aging protocols, for this project, included the rolling-thin-film oven (RTFO, AASHTO T-240) method and the pressurized aging vessel (PAV, AASHTO R28) method. Rheology The complex shear modulus and phase angle of the original and laboratory aged asphalts were measured using a Rheometrics Model RDA II Dynamic Analyzer (a research-grade dynamic shear rheometer, DSR). DSR measurements for the SHRP asphalts were performed at 25˚C and 60˚C and a frequency range of 0.1 to 100 radians/sec at each temperature. DSR measurements for the Arizona validation site asphalts were performed at 10 degree intervals over a temperature range of 0 to 80°C and a frequency range of 0.1 to 100 radians/second. FTIR Instrument The infrared spectrometer used for this survey was a Perkin-Elmer Spectrum One ® equipped with a deuterated triglycine sulfate (DTGS) detector. The spectrometer was controlled by a desktop PC running Spectrum v5.0.1 software. Available optical path difference (OPD) velocities were 0.1, 0.2, 0.5, 1.0 and 2.0 cm/sec. 13
Page 1: Fundamental Properties of Asphalts
Page 5: TASK 1. COORDINATION The goals of t
Page 8 and 9: Support of FHWA Strategic Goals The
Page 11 and 12: SUBTASK 2-2. AGING SUBTASK 2-2.1. I
Page 13 and 14: To further evaluate how water influ
Page 15: SUBTASK 2-2.2. SUPPORT OF THE MECHA
Page 19 and 20: greater than 100 micrometers are co
Page 21 and 22: limestone. Major RA elemental oxide
Page 23 and 24: Log G* at 10 rad/s 8 7 6 5 25°C y
Page 25 and 26: Table 2-2.2.3b. Experiment status m
Page 27 and 28: Table 2-2.2.4b. Experiment status m
Page 29 and 30: (a) (b) PA Intensity (arbitray unit
Page 31 and 32: PA - Carbonyl total peak ht. (1700
Page 33 and 34: SHRP RA (granite) PA spectra of RA
Page 35 and 36: Mastics Several asphalt mastics wer
Page 37 and 38: 4000.0 3600 3200 2800 2400 2000 180
Page 39 and 40: • LTA1 (long term aging Level 1):
Page 41 and 42: The increase in carbonyl at the cen
Page 43 and 44: figure 2-2.2.19 to show the correla
Page 45 and 46: The majority of the results were pr
Page 47 and 48: Hirschfeld, T., 1976, Computer Reso
Page 49 and 50: SUBTASK 2-3. NANOTECHNOLOGY: AFM AN
Page 51 and 52: comprised of tens of thousands of d
Page 53 and 54: to the aggregate fine particle inte
Page 55 and 56: a. Sample, b. cold stage, c. hot st
Page 57 and 58: Problems and Solutions to Problems
Page 59: SUBTASK 2-4. LOW-TEMPERATURE PROPER
Page 62 and 63: Background The addition of polyphos
Page 64 and 65: All different aging times were shif
Page 66 and 67:
Log a A 2.5 2.0 1.5 1.0 0.5 AAM-1,
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KAO Gripper. The minor resonance wa
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Dadey et al. [1988] proposed Scheme
Page 72 and 73:
Problems and Solution to Problem No
Page 75:
SUBTASK 2-6: VALIDATION SITE MONITO
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TASK 4. INFORMATION DEPLOYMENT SUBT
Page 83:
SUBTASK 4-3. RESEARCH DATABASE—CO
Page 89:
SUBTASK 4-5. SUPPORT OF THE MECHANI
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