Long-Term Aging of Asphalt Mixtures for Performance Testing and Prediction (2017) / Chapter Skim
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24 Findings Sensitivity Study Temperature–frequency sweep tests were first performed to determine the modulus values of the materials and subsequently the aging ratio (AR)
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Findings and Applications 25 Error in AR Range of Required AP Accuracy Binder Mastic FAM 1% 1.1% – 1.9% 1.1% – 1.9% 1.5% – 3.6% 10% 11.0% – 18.9% 11.1% – 19.5% 14.8% – 35.6% 20% 22.0% – 37.7% 22.2% – 39.1% 29.6% – 71.2% Error in AR Range of Required AP Accuracy FAM 1.5% – 3.6% 14.8% – 35.6% 1% 10% 20% Binder 0.5% – 0.9% 6.3% – 9.1% 12.3% – 18.3% Mastic 1.1% – 1.9% 11.1% – 19.5% 22.2% – 39% 29.6% – 71.2% Table 5. Summary of sensitivity study findings.
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26 Long-Term Aging of Asphalt Mixtures for Performance Testing and Prediction and asphalt concrete, the sensitivity level of a full asphalt concrete mixture would be expected to be lower than for FAM, but by only a relatively small amount. The findings presented in this section are based on the AP-based sensitivity assessment; however, the same conclusions are reached when the assessment is based on G*
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Findings and Applications 27 Results Selection of Chemical AIP. The chemical AIPs were evaluated based on their correlation to the aging duration.
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28 Long-Term Aging of Asphalt Mixtures for Performance Testing and Prediction Log G* at 64°C and 10 rad/s was selected as the rheological AIP to evaluate oxidation levels within the project.
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Findings and Applications 29 testing at 0.005 rad/s was not possible. In contrast, the G*
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30 Long-Term Aging of Asphalt Mixtures for Performance Testing and Prediction were applied to both loose mix and compacted specimens and the potential integrity problems associated with the two specimen types were evaluated. Study of Aging of Compacted Specimens Trials for aging the compacted specimens were conducted using both the oven and PAV.
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Findings and Applications 31 the loose mix specimens are compacted following aging. In addition, the aging gradient was not a problem, because the loose mix is aged as a single layer of coated aggregate particles and, thus, oxygen and heat could circulate easily throughout the mix.
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32 Long-Term Aging of Asphalt Mixtures for Performance Testing and Prediction level of oxidation of the binder extracted from the surface of the field core. This condition is considered to represent an extreme level of oxidation, as oxidation levels are drastically reduced with the depth of the pavement.
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Findings and Applications 33 evident between the dynamic modulus values of the short-term aged and PAV-aged compacted specimens, indicating that either (a) no significant aging occurred or (b)
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34 Long-Term Aging of Asphalt Mixtures for Performance Testing and Prediction relationship between material integrity and damage and are path-independent (i.e., independent of loading and thermal history)
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Findings and Applications 35 Figure 17 depicts the DR energy-based failure criterion plots. Average DR values for different aging conditions are presented in Table 8.
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36 Long-Term Aging of Asphalt Mixtures for Performance Testing and Prediction allows for the assessment of aging gradients. In this study, this assessment was accomplished by first coring and cutting the specimens into slices from which the binder was recovered.
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Findings and Applications 37 0.0635 0.0918 0.0746 0.0885 0.0905 0.0871 0.0868 0.0823 0.0801 0.0850 0.0926 0.0972 4.45 4.93 4.59 4.75 4.84 4.80 4.84 4.63 4.71 4.82 5.00 4.94 3.0 3.5 4.0 4.5 5.0 5.5 6.0 0.00 0.02 0.04 0.06 0.08 0.10 0.12 0.14 Ca rb on yl + S ul fo xi de P ea k (A U) Carbonyl+Sulfoxide Peak log G*
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38 Long-Term Aging of Asphalt Mixtures for Performance Testing and Prediction significantly higher than those of the short-term aged loose mixtures based on the previously defined thresholds. However, the AIP values of all the long-term aged compacted specimens are lower than those for the RTFO+PAV-aged binder.
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Findings and Applications 39 high rate of failure at the end locations where oxidation was most significant in the cyclic direct tension fatigue tests. However, the high rate of end failure could be overcome by aging specimens 178 mm in height and then trimming the ends to produce a 130-mm tall specimen for testing.
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40 Long-Term Aging of Asphalt Mixtures for Performance Testing and Prediction Evaluation of the Selected Aging Procedure To verify the findings of the loose mix aging trials with the NC mix, the FHWA ALF SBS- modified mixture was subjected to loose mix oven aging trials at 70°C, 85°C, and 95°C. Small samples were removed periodically from the oven and subjected to extraction and recovery to determine the binder AIPs.
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Findings and Applications 41 top surface of a field core, the material in the top 19 mm of the specimen has aged more than the material at the 19 mm depth. Also, the material in the bottom 19 mm of the specimen has aged less than the material at the 19 mm depth.
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42 Long-Term Aging of Asphalt Mixtures for Performance Testing and Prediction Comparisons between the dynamic modulus and cyclic fatigue damage characteristic curves of the short-term aged material and the long-term aged material were used to evaluate the specimen integrity of the compacted long-term aged material based on expected trends of increased aging. Figure 23 presents the dynamic modulus master curves.
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Findings and Applications 43 results of three tests that were conducted using various cross-head displacement amplitudes. The long-term aged specimens have higher damage characteristic curves than the short-term aged specimen, which follows expected trends.
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44 Long-Term Aging of Asphalt Mixtures for Performance Testing and Prediction increased from 95°C to 135°C. The FHWA ALF-SBS–modified mixture was selected in order to include a common asphalt-modified asphalt binder in the study and because field core data were available for it.
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Findings and Applications 45 because the same G* value for mixtures aged at two different temperatures will result in two different C + S absorbance peaks.
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46 Long-Term Aging of Asphalt Mixtures for Performance Testing and Prediction and SHRP AAG materials, respectively. To match the aging levels between the loose mixtures aged at 95°C and 135°C, first the relationship between the log G*
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Findings and Applications 47 were conducted at multiple temperatures. In addition to material testing, the effect of the aging temperature on fatigue performance was evaluated at the pavement level.
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48 Long-Term Aging of Asphalt Mixtures for Performance Testing and Prediction (b) presents the C versus S curves.
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Findings and Applications 49 The pairs with significant differences (p < 0.05) are shaded in Table 10.
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50 Long-Term Aging of Asphalt Mixtures for Performance Testing and Prediction second triangle is located at the bottom of the bottom asphalt layer and its vertex is positioned at the surface layer. Figure 33 presents the final shape of these overlapping triangles, which defines the reference area for percent damage.
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Findings and Applications 51 modulus value with long-term aging. The results also indicate a significant difference in the dynamic modulus master curves that correspond to the mixtures aged at 95°C for 8.9 days and at 135°C for 16.8 hours, despite the mixtures' equivalent binder rheology.
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52 Long-Term Aging of Asphalt Mixtures for Performance Testing and Prediction sulfur content and is highly structured, indicating high potential for changes between the oxidation products of laboratory aging at 135°C versus 95°C. Figure 35 (b)
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Findings and Applications 53 values and fatigue performance for the SHRP AAD mixture. In spite of the matched binder rheology at the 95°C and 135°C aging temperatures, the significant difference is observed in the dynamic modulus and fatigue performance test data between the 95°C and 135°C aging treatment.
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54 Long-Term Aging of Asphalt Mixtures for Performance Testing and Prediction only also are provided for reference. The results indicate a significant increase in the dynamic modulus value with long-term aging.
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Findings and Applications 55 test results for these two temperatures is evident. This observation suggests that the 135°C aging temperature induces more brittle behavior than the 95°C aging temperature.
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56 Long-Term Aging of Asphalt Mixtures for Performance Testing and Prediction durations of laboratory aging to reach the oxidation levels in the field than lower temperatures, whereas aging temperatures higher than 100°C can result in changes in binder chemistry that do not occur in the field. Aging of WMA Mixtures Loose mixture aging in the oven at 95°C is the proposed long-term aging method for HMA mixtures.
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Findings and Applications 57 data obtained from the NCAT-HMA and NCAT-Foam (WMA) sections.
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58 Long-Term Aging of Asphalt Mixtures for Performance Testing and Prediction compacted WMA and compacted HMA log G* versus the laboratory aging duration curves are similar.
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Findings and Applications 59 All of the models presented herein were obtained when investigating the AIPs of asphalt binders aged in thin films at elevated temperatures and/or under pressure. The oxidation of an asphalt will be kinetics-controlled if the binder film thickness is thin enough to allow oxygen to diffuse through the film faster than the rate of the reaction itself.
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60 Long-Term Aging of Asphalt Mixtures for Performance Testing and Prediction the non-isothermal aging process and subjected to AIP testing. The measured AIPs were then compared against those predicted by the kinetics model.
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Findings and Applications 61 These results indicate that kinetics models can be derived from loose mixture aging results without the need to consider diffusion. Kinetics Modeling of Loose Mixtures under Isothermal Aging.
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62 Long-Term Aging of Asphalt Mixtures for Performance Testing and Prediction used to calibrate the kf and kc parameters. The results demonstrate good agreement between the measured and predicted values of log G*
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Findings and Applications 63 the non-isothermal aging history applied to the loose mixture specimens. The temperatures were varied between 40°C and 70°C over the course of 43 days.
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64 Long-Term Aging of Asphalt Mixtures for Performance Testing and Prediction match field aging as a function of pavement temperature history and depth. It is important to note that loose mixture oven aging is kinetics-controlled whereas field aging is diffusion- controlled.
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Findings and Applications 65 Furthermore, if the short-term aging of the field and laboratory mixtures is assumed to be equal (i.e., G*
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66 Long-Term Aging of Asphalt Mixtures for Performance Testing and Prediction laboratory aging durations at 95°C that are required to match the oxidation level at several times during the non-isothermal aging experiment. The results indicate that the aging duration at 95°C that is required to match the level of oxidation induced by the non-isothermal experiment is the same for the FHWA ALF-Control and WesTrack Fine mixtures, thereby validating the use of Equation 19 for equating laboratory aging to field aging.
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Findings and Applications 67 diffusion-controlled. Figure 48 demonstrates that the duration of laboratory aging that is required to match field aging is the same for the FHWA ALF-Control and SBS-modified mixtures.
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68 Long-Term Aging of Asphalt Mixtures for Performance Testing and Prediction (the oxygen pressure term)
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Findings and Applications 69 at periodic intervals and from corresponding field cores at various depths. The laboratory aging duration that is required to match the level of aging of the field cores was determined subsequently based on matching the G*
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70 Long-Term Aging of Asphalt Mixtures for Performance Testing and Prediction M ea su re d Du ra tio n at 95 °C (D ay s)
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Findings and Applications 71 It should be noted that climatic indices have been used in other applications to quantify the effect of temperature history on aging. The GAS model uses the MAAT to predict G*
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Findings and Applications 73 (c) Figure 52.
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Findings and Applications 75 (c) Figure 53.
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Findings and Applications 77 (c) Figure 54.
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78 Long-Term Aging of Asphalt Mixtures for Performance Testing and Prediction Aging Model to Predict Field Aging Throughout Pavement Depth Prediction of Field Aging Using Mix-Specific Kinetics Parameters The kinetics model developed herein could potentially be used as the basis for improving the prediction of changes in asphalt binder properties with oxidative aging within pavement performance prediction frameworks, including Pavement ME Design. To evaluate the ability of the kinetics model to predict the evolution of oxidative aging in pavements, Equation 25 was applied to predict the log G*
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Findings and Applications 79 of log G* obtained for binder extracted and recovered from field cores.
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80 Long-Term Aging of Asphalt Mixtures for Performance Testing and Prediction 0 20 40 60 80 100 120 140 160 180 200 0.0 0.5 1.0 1.5 2.0 2.5 3.0 D ep th (m m)
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Findings and Applications 81 0 10 20 30 40 50 60 0.5 1.0 1.5 2.0 2.5 3.0 3.5 D ep th (m m)
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82 Long-Term Aging of Asphalt Mixtures for Performance Testing and Prediction Three WesTrack sections constructed with fine gradation were included in the calibration step shown in Figure 59. These sections were constructed with optimum binder content (5.4%)
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Findings and Applications 83 The calibrated kinetics model was used to predict log G* values after 19 years of field aging in the WesTrack sections and these values were compared against field core measurements.
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84 Long-Term Aging of Asphalt Mixtures for Performance Testing and Prediction determining the kinetics model parameter values using loose mixture aging is cumbersome. The loose mixture must be prepared and conditioned in an oven at 95°C.
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Findings and Applications 85 Figure 61 shows the log G* at 64°C and 10 rad/s results for both the USAT and loose mix aging trials for the five mixtures evaluated that contain hydrated lime.
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86 Long-Term Aging of Asphalt Mixtures for Performance Testing and Prediction log G*
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Findings and Applications 87 0 0.5 1 1.5 2 2.5 3 3.5 4 0 10 20 30 40 lo g G *
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88 Long-Term Aging of Asphalt Mixtures for Performance Testing and Prediction mixtures with and without hydrated lime. The model also considers the amount of filler that is present in the mixture using the mass percentage of aggregate that passes the No.
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Findings and Applications 89 034, hydrated lime 0.5, other fillers (29)
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90 Long-Term Aging of Asphalt Mixtures for Performance Testing and Prediction The proposed model was applied to the binder log G* results obtained from the USAT binder aging tests to predict the corresponding loose mixture aging evolution.
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Findings and Applications 91 design to determine stresses, strains, and deformations using layered elastic analysis. The response model output is used to predict the corresponding pavement distress development over the design period.
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92 Long-Term Aging of Asphalt Mixtures for Performance Testing and Prediction 0 0.5 1 1.5 2 2.5 3 3.5 4 0 10 20 30 40 lo g G *
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Findings and Applications 93 Asphalt binder samples were extracted and recovered from the aged loose mixtures and subjected to DSR testing to determine the binder G* input for the dynamic modulus predictive models.
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94 Long-Term Aging of Asphalt Mixtures for Performance Testing and Prediction Conclusions The accurate characterization of asphalt mixture properties in terms of the service life of a pavement is becoming more important as more powerful pavement design and performance prediction methods are implemented. This project sought to develop a procedure to simulate the long-term aging of asphalt mixtures as a function of climate and depth for performance testing and prediction.
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Findings and Applications 95 long-term aging procedure and associated kinetics model. The following conclusions pertain to the selection of the chemical and rheological AIPs.
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96 Long-Term Aging of Asphalt Mixtures for Performance Testing and Prediction • The results indicate that loose mix aging at 95°C is the optimal procedure for the long-term aging of asphalt concrete for performance testing. The literature indicates that the disruption of polar molecular associations and sulfoxide decomposition become critical at temperatures that exceed 100°C (Petersen 2009)
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Findings and Applications 97 Aging Model to Predict Field Aging This study evaluated the ability of the kinetics model developed herein to predict the evolution of oxidative aging in pavements. The prediction of the changes in asphalt binder properties with oxidative aging is important for the simulation of changes in asphalt mixture properties that are induced by aging within pavement performance prediction frameworks, including Pavement ME Design.
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