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Long-Term Field Performance of Warm Mix Asphalt Technologies (2017)

Chapter: Chapter 4 - Wheel-Path Longitudinal Cracking

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Suggested Citation:"Chapter 4 - Wheel-Path Longitudinal Cracking." National Academies of Sciences, Engineering, and Medicine. 2017. Long-Term Field Performance of Warm Mix Asphalt Technologies. Washington, DC: The National Academies Press. doi: 10.17226/24708.
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Suggested Citation:"Chapter 4 - Wheel-Path Longitudinal Cracking." National Academies of Sciences, Engineering, and Medicine. 2017. Long-Term Field Performance of Warm Mix Asphalt Technologies. Washington, DC: The National Academies Press. doi: 10.17226/24708.
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Suggested Citation:"Chapter 4 - Wheel-Path Longitudinal Cracking." National Academies of Sciences, Engineering, and Medicine. 2017. Long-Term Field Performance of Warm Mix Asphalt Technologies. Washington, DC: The National Academies Press. doi: 10.17226/24708.
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Suggested Citation:"Chapter 4 - Wheel-Path Longitudinal Cracking." National Academies of Sciences, Engineering, and Medicine. 2017. Long-Term Field Performance of Warm Mix Asphalt Technologies. Washington, DC: The National Academies Press. doi: 10.17226/24708.
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Suggested Citation:"Chapter 4 - Wheel-Path Longitudinal Cracking." National Academies of Sciences, Engineering, and Medicine. 2017. Long-Term Field Performance of Warm Mix Asphalt Technologies. Washington, DC: The National Academies Press. doi: 10.17226/24708.
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Suggested Citation:"Chapter 4 - Wheel-Path Longitudinal Cracking." National Academies of Sciences, Engineering, and Medicine. 2017. Long-Term Field Performance of Warm Mix Asphalt Technologies. Washington, DC: The National Academies Press. doi: 10.17226/24708.
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Suggested Citation:"Chapter 4 - Wheel-Path Longitudinal Cracking." National Academies of Sciences, Engineering, and Medicine. 2017. Long-Term Field Performance of Warm Mix Asphalt Technologies. Washington, DC: The National Academies Press. doi: 10.17226/24708.
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Suggested Citation:"Chapter 4 - Wheel-Path Longitudinal Cracking." National Academies of Sciences, Engineering, and Medicine. 2017. Long-Term Field Performance of Warm Mix Asphalt Technologies. Washington, DC: The National Academies Press. doi: 10.17226/24708.
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Suggested Citation:"Chapter 4 - Wheel-Path Longitudinal Cracking." National Academies of Sciences, Engineering, and Medicine. 2017. Long-Term Field Performance of Warm Mix Asphalt Technologies. Washington, DC: The National Academies Press. doi: 10.17226/24708.
×
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Suggested Citation:"Chapter 4 - Wheel-Path Longitudinal Cracking." National Academies of Sciences, Engineering, and Medicine. 2017. Long-Term Field Performance of Warm Mix Asphalt Technologies. Washington, DC: The National Academies Press. doi: 10.17226/24708.
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31 Introduction This chapter focuses on wheel-path longitudinal cracking that is fatigue-related. Figures 4.1 (a) and (b) show typical longitudinal cracks in the wheel-path. These cracks are nor- mally 2 to 4 ft away from the shoulder or centerline. Based on field cores extracted from the tip of wheel-path longitu- dinal cracks, such longitudinal cracks in the wheel-path typi- cally are top-down fatigue cracks. It is noted that bottom-up fatigue cracking was not identified at any field sites evaluated in this study. Wheel-Path Longitudinal Cracking in the Field Comparisons Based on First-Round Distress Survey Results This section presents a summary of the HMA versus WMA pavement comparisons in terms of wheel-path longitudinal cracking based on the first-round distress survey results. Fig- ure 4.2 (a) shows that eight projects exhibited longitudinal cracking. The first-round wheel-path longitudinal cracking comparison includes 41 HMA-WMA pairs. For those proj- ects that did not exhibit wheel-path longitudinal cracking, the HMA-WMA pairs within the project are treated as “compa- rable.” Figure 4.2 (b) indicates that, as a whole, the HMA pave- ments show longitudinal crack lengths that are comparable with those of the WMA pavements. Only two pairs showed that the WMA pavement had more wheel-path longitudinal cracking than the HMA pavement: the MO Hall St. project (HMA < Aspha-min), and the OH SR 541 project (HMA < Aspha-min). This trend remained in the second-round dis- tress survey. Figure 4.3 plots wheel-path longitudinal crack length versus pavement age for the first-round distress survey. In general, 4-year-old pavement begins to exhibit wheel-path longitudinal cracking. Figure 4.4 presents comparisons for wheel-path longitu- dinal cracking between the HMA pavements and the spe- cific WMA technology pavement based on the first-round distress survey results. The WMA pavements show compa- rable wheel-path longitudinal cracking with that of the HMA pavements. Again, the breakdown of the projects by WMA technology led to a small population for each category. Also, factors other than the HMA and WMA properties, such as pre-overlay conditions and pavement structure variation in the existing asphalt pavements, may confound the results. Based on the first-round distress survey, a comparison of wheel-path longitudinal cracking among different WMA technologies was performed and the results are presented in Figure 4.5. In most cases, the three WMA technologies result in similar field performance in terms of wheel-path longitu- dinal cracking. It is noted that all the projects had a pavement age of 7 years or younger when the first-round distress sur- vey was conducted. Comparisons Based on the Second-Round Distress Survey Results Figure 4.6 presents a summary of the HMA versus WMA pavement comparisons in terms of wheel-path longitudinal cracking based on the second-round distress survey results. Figure 4.6 (a) shows that 14 in-service projects exhibited wheel-path longitudinal cracking. The second-round wheel- path longitudinal cracking comparison includes 44 HMA- WMA pairs. For those projects that did not exhibit wheel-path longitudinal cracking, the HMA-WMA pairs are treated as “comparable.” Figure 4.6 (b) shows that HMA and WMA pavements have comparable wheel-path longitudinal crack- ing. These results are consistent with the findings from the first-round distress survey. C H A P T E R 4 Wheel-Path Longitudinal Cracking

32 Figure 4.7 plots the wheel-path longitudinal crack length versus pavement age for the second-round distress survey. As shown, although some longitudinal cracks start to develop when the pavements are 3 years old, more longitudinal cracking is seen in pavements that are 6 years old or older. Figure 4.8 presents comparisons for wheel-path longitu- dinal cracking between the HMA pavements and the WMA pavements in terms of specific WMA technology based on the second-round distress survey results. The WMA pavements show comparable longitudinal crack lengths with those of the HMA pavements. The findings based on the second- round distress survey are similar to the results obtained from the first-round distress survey. Again, after breaking down the results into the different WMA technologies, the number of projects for comparison is too small for statistical analysis. The comparison among the WMA pavements is further examined using the second-round distress survey results. The findings are similar to the results the research team obtained for transverse cracking. Out of seven WMA-WMA pairs, three organic modified WMA pavements (CO I-70, TN SR 46, and OH SR 541) have significantly higher longitudinal cracking than their companion WMA chemical and foaming pavements [see Figures 4.9 (a) and (c)]. Figure 4.9 (b) shows the WMA chemical and foaming pavements have similar resistance to longitudinal cracking. The relatively high pavement age (7 to 9 years) of all three pavements plus the ultra-thin overlay thickness in the TN SR 46 project suggests that organic WMA pavement could be more sensitive to the aging effect than the other WMA technologies. In the long term, the longitudinal cracking resistance of chemical and foaming WMA pavements could be better than that of organic WMA pavements. (a) (b) Figure 4.1. Typical longitudinal cracking in the wheel-path of an asphalt pavement overlay. Note: H > W, H = W, and H < W denote that the HMA pavement has longer, comparable, or shorter longitudinal crack lengths than the WMA pavement, respectively. (a) Projects Having Longitudinal Cracking (b) Summary of Longitudinal Cracking Comparison 0 5 10 15 20 25 30 35 40 0 39 2 N o. o f P ai rs H>W H=W H<W Figure 4.2. Comparison of the length of wheel-path longitudinal cracking for HMA-WMA pairs based on the first-round distress survey results.

33 0 50 100 150 200 250 300 0.0 1.0 2.0 3.0 4.0 5.0 6.0 7.0 8.0 9.0 10.0 W he el -p at h Lo ng itu di na l C ra ck L en gt h, ft /2 00 ft Pavement Age, years HMA WMA Figure 4.3. Wheel-path longitudinal crack length versus pavement age for the first-round distress survey. Note: The number in parentheses indicates the number of HMA-WMA pairs in the wheel-path longitudinal crack length comparison. H=W (9) H=W (14) H=W (16) H<W (2) (a) HMA versus Sasobit (b) HMA versus Chemical (c) HMA versus Foaming (d) HMA versus Water-Based Foaming H=W (11) H=W (5) H<W (2) (e) HMA versus Water-Containing Foaming Figure 4.4. Breakdown comparison of the length of wheel-path longitudinal cracking between HMA and specific WMA technologies based on the first-round distress survey results.

34 (a) Comparison Between Chemical and Organic 1 6 0 0 2 4 6 8 10 N o. o f P ai rs Chemical>Organic Chemical=Organic Chemical<Organic (b) Comparison Between Chemical and Foaming 1 7 0 0 2 4 6 8 10 N o. o f P ai rs Chemical>Foaming Chemical=Foaming Chemical<Foaming Organic>Foaming (c) Comparison Between Organic and Foaming 0 7 0 0 2 4 6 8 10 N o. o f P ai rs Organic=Foaming Organic<Foaming Figure 4.5. Wheel-path longitudinal cracking comparisons among WMA additives in terms of crack length based on the first-round distress survey results. (a) Projects Having Wheel-Path Longitudinal Cracking 0 5 10 15 20 25 30 35 40 1 39 4 N o. o f P ai rs H>W H=W H<W (b) Summary of Cracking Comparison Figure 4.6. Comparison of the length of wheel-path longitudinal cracking for HMA-WMA pairs based on the second-round distress survey results.

35 0 50 100 150 200 250 300 0.0 1.0 2.0 3.0 4.0 5.0 6.0 7.0 8.0 9.0 10.0 Se co nd -R ou nd W he el -P at h Lo ng it ud in al C ra ck L en gt h, ft /2 00 ft Pavement Age, years HMA WMA Figure 4.7. Wheel-path longitudinal crack length versus pavement age for the second-round distress survey. Note: The number in parentheses indicates the number of HMA-WMA pairs in the wheel-path longitudinal cracking comparison. (a) HMA versus Sasobit (b) HMA versus Chemical (c) HMA versus Foaming H>W (1) H=W (8) H<W (2) H=W (14) H=W (17) H<W (2) (d) HMA versus Water-Based Foaming H=W (13) H=W (4) H<W (2) (e) HMA versus Water-Containing Foaming Figure 4.8. Breakdown comparison of the length of wheel-path longitudinal cracking between HMA and specific WMA technologies based on the second-round distress survey results.

36 Paired Ranking Analysis for Wheel-Path Longitudinal Cracking The material properties obtained from the field cores and extracted binders were used to determine potential signifi- cant determinants for wheel-path longitudinal cracking using paired ranking analysis. These material properties include the following: 1. Mixtures properties: dynamic modulus values, creep com- pliance values, and fracture properties at the intermediate temperature and low temperature including IDT strength, fracture work density, vertical failure deformation, and horizontal failure strain. 2. Binder properties: PG, G*sind, BBR m-value and stiff- ness, and fracture properties at temperatures of 41°F and 68°F including shear strength, fracture energy, and failure strain. First-Round Distress Survey Results Figure 4.10 presents a summary of the number of HMA- WMA pairs that show a correlation between the material properties and field wheel-path longitudinal cracking based on the first-round distress survey results. Detailed statistics of the paired comparison between HMA and WMA can be found in Appendix B. The IDT vertical failure deformation property shows the highest number (15 out of 17 HMA-WMA pairs) of qualitative correlations with wheel-path longitudinal crack- ing. High values of vertical failure deformation correlate with less wheel-path longitudinal cracking, indicating that a duc- tile mix is more resistant to wheel-path longitudinal cracking than a stiff mix. The horizontal failure strain levels (13 out of 17 HMA-WMA pairs) and mixture IDT strength at 68°F (12 out of 17 HMA-WMA pairs) also show strong potential to correlate with wheel-path longitudinal cracking. A high horizontal failure strain level correlates with less wheel-path longitudinal cracking; and a high IDT strength correlates with more wheel-path longitudinal cracking. Second-Round Survey Results Figure 4.11 presents a summary of the number of HMA- WMA pairs that show a consistent trend between the material properties and field wheel-path longitudinal cracking based on the second-round distress survey results. The vertical fail- ure deformation and horizontal failure strain results (17 out of 24 HMA-WMA pairs) provide the highest number of qualitative correlations with wheel-path longitudinal crack- ing followed by the mixture IDT strength at 68°F. These results are consistent with the findings from the first-round distress survey. 0 2 4 6 8 10 N o. o f P ai rs 0 4 3 Chemical>Organic Chemical=Organic Chemical<Organic (a) Comparison Between Chemical and Organic (b) Comparison Between Chemical and Foaming 0 6 1 0 2 4 6 8 10 N o. o f P ai rs Chemical>Foaming Chemical=Foaming Chemical<Foaming (c) Comparison Between Organic and Foaming 3 4 0 0 2 4 6 8 10 N o. o f P ai rs Organic>Foaming Organic=Foaming Organic<Foaming Figure 4.9. Wheel-path longitudinal cracking comparisons among WMA additives in terms of crack length based on the second-round distress survey results.

37 Statistical Predictive Models for Wheel-Path Longitudinal Cracking The PLS method was applied to develop a predictive wheel- path longitudinal cracking model. The following factors were considered for the model based on literature findings: • Mixture properties: IDT strength at 68°F; fracture work density at 68°F; mixture fracture energy at 68°F; dynamic modulus at 70°F and 1 Hz; in-place air voids; aggregate passing #4, #8, #200 sieve; and NMAS. • Binder properties: G*sind, binder fracture energy, and effective binder content. • Pavement structure: total HMA thickness and overlay thickness. • Climate, traffic, and pavement age parameters: room- temperature hours, AADTT, and pavement age. Table 4.1 contains predictor variables and the ranges of each independent variable measured during this project. Wheel-Path Longitudinal Cracking Propagation Model Equation (4.1) presents the model for predicting the length of wheel-path longitudinal cracking using the PLS method. Appendix G provides detailed methodology about the model Positive Negative 0 2 4 6 8 10 12 14 16 N o. o f P ai rs Mix IDT strength (68°F) Mix creep compliance (68°F) Mix horizontal failure strain (68°F) Mix vertical failure deformation (68°F) Figure 4.10. Number of HMA-WMA pairs that have consistent rankings between material property ranking and wheel-path longitudinal cracking ranking based on the first-round distress survey results. 0 4 8 12 16 20 24 N o. o f P ai rs Positive Mix IDT strength (68°F) Mix creep compliance (68°F) Mix horizontal failure strain (68°F) Mix vertical failure deformation (68°F) Negative Figure 4.11. Number of HMA-WMA pairs that have consistent rankings between material property ranking and wheel-path longitudinal cracking ranking based on the second-round distress survey results.

38 development. Five parameters were selected: total pavement thickness (+), IDT strength (+), in-place air voids (+), AADTT (+), and percentage passing the #200 sieve (-). The sign in the parentheses indicates the trend between the predictor vari- ables and responses. A positive trend indicates that high val- ues correlate with high levels of top-down crack distress and vice versa. A negative trend indicates that high values correlate with low levels of top-down crack distress and vice versa. (4.1)0.73402 0.00874 2.01589 0.39481 0.00149 1.314411 2 3 4 5= ( )− + + + + −Y e X X X X X where Y = field longitudinal cracking, ft/200 ft; e = base of natural logarithm, approximately 2.718; X1 = total pavement thickness, mm; X2 = IDT strength (68°F), MPa; X3 = in-place air voids, %; X4 = AADTT; and X5 = percentage passing the #200 sieve, %. The effects of individual predictor variables are in good agreement with the literature findings: (a) the pavements with a thicker pavement structure generally have a higher potential to develop top-down longitudinal cracking (Roque et al. 2010); (b) overlay mixtures with high IDT strength values could be related to high stiffness and high brittleness, and would therefore be more prone to top-down cracking; (c) the pavement with higher in-place air voids may have more top-down cracking (AASHTO 2008); (d) increased truck traffic load (AADTT) can lead to more crack propagation; and (e) within a specific range, a higher percent passing the #200 sieve could result in a more flexible and less crack sus- ceptible mixture (Schwartz et al. 2011). Figure 4.12 (a) shows the relationship between predicted and field-measured wheel-path longitudinal crack length. Predictor Variables Unit Range IDT strength, 68°F MPa 1.2-3.9 Work density, 68°F MPa 0.05-0.21 Dynamic modulus, 70°F, 1Hz MPa 706.3-8448.1 Mixture fracture energy, 68°C MPa 0.002-0.095 Air voids % 1.8-9.1 Percent passing #4 sieve % 45-82.2 Percent passing #8 sieve % 24.9-57.6 Percent passing #200 sieve % 2.8-11.9 NMAS mm 9.5-12.5 G*sin(phase angle) kPa 666.3-5170.6 Binder fracture energy MPa 0.5-15.5 Effective binder content % 6.7-14.4 Total pavement thickness mm 50.8-406.4 Overlay thickness mm 19.3-152.4 AADTT N/A 5-450000 Service life year 0.05-7 Table 4.1. Predictor variables and their ranges of wheel-path longitudinal cracking models. -2.0 0.0 2.0 4.0 6.0 -2.0 0.0 2.0 4.0 6.0 Fi el d M ea su re d Cr ac k (L n) , ft /2 00 ft Predicted Crack (Ln), ft/200 ft HMA WMA Line of Equality R2 = 0.85 SEE = 0.59 (a) (b) R2=0.6 SEE=0.99 -2 0 2 4 6 -2 0 2 4 6 Fi el d Cr ac k (L n) , ft /2 00 ft Validated Crack (Ln), ft/200 ft Validated Line of Equality Figure 4.12. Wheel-path longitudinal cracking statistical model development and validation: (a) relationship between predicted and field-measured longitudinal cracking and (b) validation of the longitudinal cracking model.

39 This model gives a R2 of 0.85, a standard error of the esti- mate of 0.59, and Mallow’s Cp of 6.0, indicating good pre- diction quality. Figure 4.12 (b) presents the validation of the crack propagation model using the LOOCV method. As shown, most of the validated data are located fairly close to the line of equality. The R2 value of 0.6 and standard error of the estimate of 0.99 illustrate fair validation of the field results. Wheel-Path Longitudinal Cracking Initiation Model The development of the crack initiation model is similar to that of the propagation model except that the crack initiation model requires additional BL regression analysis. The devel- opment of the initiation regression model uses 63 responses (including 15 with field cracks and 48 without field cracks). The optimum number of variables was determined to be five. The five predictor variables were selected using PLS regres- sion analysis based on the highest standardized coefficients (absolute values). These predictor variables are pavement age (+), percentage passing the #200 sieve (-), overlay thickness (-), fracture work density (-), and binder fracture energy (+). The sign in the parentheses indicates the trend between the predictor variables and the responses. The BL regression method also was used to develop a prob- abilistic model for crack initiation using the five predictor variables. Arbitrary values were assigned as follows: 0.02 for pavement sections without cracks (yi = 0.02) and 1.0 for pave- ment sections with recorded field cracks (yi = 1). The prob- ability model is shown in Equation (4.2), where P indicates the probability of the initiation of wheel-path longitudinal cracking; therefore, 1-P means the probability of no crack initiation. ˆ 1 1 1 (4.2) 3.51 0.003 0.105 0.0587 24.2 0.2151 2 3 4 5 P y e i X X X X X ( )= = + ( )− + − − − + where e = base of the natural logarithm, approximately 2.718; P = probability of initiation of top-down cracking, %; X1 = pavement age, year; X2 = percentage passing the #200 sieve, %; X3 = overlay thickness, mm; X4 = fracture work density (68°F), MPa; X5 = binder fracture energy (68°F), MPa; and yi = ith pavement section. The effects of the individual predictor variables are in good agreement with the findings in the literature: (a) a longer pave- ment age usually increases the probability of material deterio- ration, and thus the probability of crack initiation; (b) within a specific range, a higher percentage passing the #200 sieve would result in a more flexible and less crack-susceptible mixture (Schwartz et al. 2011); (c) a thick overlay delays the initiation of wheel-path top-down cracking (Dong and Huang 2014); (d) mixtures with higher fracture work density values may be more fracture-resistant (Wen 2013); and (e) higher binder fracture energy values, especially when associated with a higher degree of aging, could be related to mixtures with high levels of stiffness and brittleness, and thus have a higher potential for cracking. In fact, when revisiting the database, the research team found that only 8 out of 63 projects contained polymer- modified binder, which could indicate that the higher binder fracture energy values may be related to higher stiffness values and more aged binder. The probability of cracking for each project was esti- mated using the crack initiation model; Figure 4.13 pre- sents the results as the solid bars. Among the projects “with wheel-path longitudinal cracking,” shown in Figure 4.13 (a), 9 out of 15 pavement projects were predicted to have higher than 50 percent probability for crack initiation; further improvement would be needed for this model. In the “with- out top-down cracking” group, shown in Figure 4.13 (b), 46 out of 48 pavement projects were predicted to have less (a) (b) 0 5 10 15 20 5 1 2 76 1 2 6 N um be r o f P av em en t Se cti on s Probability Range, % Predicted Validated 0-25 26-50 51-75 76-100 0 10 20 30 40 37 9 2 0 34 11 2 1 N um be r o f P av em en t Se cti on s Probability Range, % Predicted Validated 0-25 26-50 51-75 76-100 Figure 4.13. Validation of wheel-path longitudinal crack initiation model: (a) with wheel-path longitudinal cracking and (b) without wheel-path longitudinal cracking.

40 than 50 percent probability for crack initiation, which is reasonable. To validate the model, the LOOCV method was used. Each sample data point was validated once during the LOOCV process. Figure 4.13 presents the results as the bars with grids. As the figure shows, the cross-validated data have almost the same probability range distribution as the pre- dicted data, indicating the reasonable prediction power of the model. In other words, it is expected that, when new vali- dation data are introduced, the model should still work well. Potential Significant Determinants for Wheel-Path Longitudinal Cracking Table 4.2 contains the identified potential significant deter- minants for wheel-path longitudinal cracking from two rounds of paired ranking analysis as well as the statistical model results. In the table, “+” means a positive relationship, that is, a higher value will lead to more longitudinal cracking; “-” means a negative relationship, that is, a higher value will lead to less longitudinal cracking. Properties in each category are listed sequentially based on their relative influence to longitudinal cracking. As seen, mixture IDT strength at 68°F was identified as a potential significant determinant by both the paired ranking and the modeling methods. The test method to obtain the IDT strength follows AASHTO T322. Other mixture proper- ties such as creep compliance, mixture vertical failure defor- mation, and mixture horizontal failure strain could also be potential significant determinants for wheel-path longitudi- nal cracking. Generally, mixture properties have a more direct relationship with field performance than binder properties and are thus preferred. 1st Round Ranking Mix horizontal failure strain, 68°F, (−) Mix vertical failure deformation, 68°F, (−) Mix IDT strength, 68°F, (+) Mix creep compliance, 14°F, (−) 2nd Round Ranking Mix horizontal failure strain, 68°F, (−) Mix vertical failure deformation, 68°F, (−) Mix IDT strength, 68°F, (+) Mix creep compliance, 14°F, (−) Statistical PLS Model, Crack Propagation Total pavement thickness, (+) Percentage passing the #200 sieve, (−) In-place air voids, (+) IDT strength, 68°F, (+) AADTT, (+) Statistical PLS Model, Crack Initiation Pavement age, (+) Binder fracture energy, (+) Overlay thickness, (−) Mix fracture work density, (−) Percentage passing the #200 sieve, (−) Table 4.2. Potential significant determinants for wheel-path longitudinal cracking.

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TRB's National Cooperative Highway Research Program (NCHRP) Research Report 843: Long-Term Field Performance of Warm Mix Asphalt Technologies compares material properties and field performance of warm mix asphalt (WMA) and control hot mix asphalt (HMA) pavement sections constructed at 28 locations across the United States. It explores significant determinants for each type of distress and potential practices regarding the use of WMA technologies.

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