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71 Chapter 3 presents field performance of the mixtures included in the field projects and corresponding laboratory performance. Kaseer et al. (2018c) provide additional details. 3.1 Pavement Distress Summary In order to tie the laboratory test results to field performance, pavement distress surveys were performed and field cores were procured (soon after construction and up to 3 years after construction). Table 22, Table 23, and Table 24 summarize the pavement distress surveys for the TX, IN, and WI field projects, including the quantity and severity of longitudinal, trans- verse, and alligator cracking for each of the test sections. No cracking was noted on any of the test sections in the NV and DE field projects, possibly because these mixtures were in service for a short period of time, and cracking distresses may take more time to appear. However, a few areas had visible signs of minor mix segregation in the DE test section with 0.41 RBR and 0.8% T2 plus 0.25% WMA, and some cracks started to initiate in the NV test section with 0.33 RBR and 2% T2. In Table 22, Table 23, and Table 24, and when comparing the quantity and severity of pave- ment distress of the asphalt mixtures with the field dose of recycling agent against the virgin and/or DOT control mixtures, the following conclusions can be drawn: â¢ For TX mixtures: The use of 2.7% recycling agent did not facilitate incorporating RAP and RAS compared to the virgin mixture, and the use of WMA additive in the DOT control mix- ture with 0.28 RBR and a lower production temperature was more effective than the use of a recycling agent. â¢ For IN mixtures: The use of 3% recycling agent did not facilitate incorporating RAP and RAS compared to the virgin mixture, and did not facilitate increasing the RBR from 0.32 to 0.42 compared to the DOT control mixture. â¢ For WI mixtures: All mixtures exhibited similar performance in terms of quantity and severity of cracking regardless of their composition, possibly because these mixtures were in service for a short period of time. 3.2 Field Core Results In addition to pavement distress surveys, field cores were procured from each test section soon after construction and up to 3 years after construction. I-FIT testing was conducted on these cores, and the results are presented in Figure 39, Figure 40, Figure 41, Figure 42, and Figure 43, with the error bars on each column representing Â± one standard deviation from the average value based on replicate measurements. Some FI values are missing for certain mixtures C H A P T E R 3 Field and Laboratory Performance of High RBR Mixtures
72 Evaluating the Effects of Recycling Agents on Asphalt Mixtures with High RAS and RAP Binder Ratios Distress Type Distresses Quantity and Severity per Test Section Virgin DOT Control (0.28 RBR) +0.5% WMA Rejuvenated (0.28 RBR) +2.7% T1 Transverse Crackinga 16.0 15.9 52.7 Longitudinal Crackinga 10.9 0.0 40.6 Alligator Crackingb â â â Summary Low-severity longitudinal and transverse cracking Low-severity longitudinal and transverse cracking Moderate-severity longitudinal and transverse cracking NOTE: â = not applicable. aTotal feet per 100 ft of test section. bPercentage of total wheel path. Table 22. Pavement distress summary for the TX field project (2 years after construction). Distress Type Distresses Quantity and Severity per Test Section Virgin DOT Control(0.32 RBR) Rejuvenated (0.42 RBR) +3% T2 Transverse Crackinga 0.8 1.4 118.4 Longitudinal Crackinga 1.0 0.5 4.5 Alligator Crackingb â 0.1 4.4 Summary Very minimalvisible cracking Very minimal visible cracking Significant amount of low-severity transverse and longitudinal cracking, and some alligator cracking NOTE: â = not applicable. aTotal feet per 100 ft of test section. bPercentage of total wheel path. Table 23. Pavement distress summary for the IN field project (2 years after construction). Distress Type Distresses Quantity and Severity per Test Section DOT Control (0.22 RBR) (PG 58-28) Recycled (0.31 RBR) (PG 58-28) Recycled (0.31 RBR) (PG 52-34) Rejuvenated (0.31 RBR) (PG 58-28) +1.2% V2 Transverse Crackinga 18.3 22.2 28.4 12.8 Longitudinal Crackinga â â â â Alligator Crackingb â â â â Summary Low-severity transverse cracking NOTE: â = not applicable. aTotal feet per 100 ft of test section. bPercentage of total wheel path. Table 24. Pavement distress summary for the WI field project (1 year after construction).
Field and Laboratory Performance of High RBR Mixtures 73 because these mixtures were very brittle and did not have post-peak displacement data available to allow determination of the inflection point, and thus FI approaches zero. Figure 39, Fig- ure 40, Figure 41, Figure 42, and Figure 43 demonstrate that all the recycled mixtures with high RBR and with the field dose of recycling agent exhibited lower FI values compared to the virgin and/or DOT control mixtures, indicating that using recycling agents at the low field doses did not adequately improve the cracking resistance of the recycled mixtures. Figure 39. FI results of TX field cores. Figure 40. FI results of NV field cores.
74 Evaluating the Effects of Recycling Agents on Asphalt Mixtures with High RAS and RAP Binder Ratios Figure 41. FI results of IN field cores. Figure 42. FI results of WI field cores. NV field cores were tested for UTSST, and the results are presented in Figure 44. The DOT control mixture at lower 0.15 RBR exhibited the highest CRIEnv value. The increase in RBR to 0.33 in the recycled control mixture resulted in a decrease in CRIEnv by approximately 75%. The effect of recycling agents in the rejuvenated mixtures at the field doses was retained after the first year of service, but after 2 years in service, the effectiveness of the recycling agent started to decrease.
Field and Laboratory Performance of High RBR Mixtures 75 Figure 43. FI results of DE field cores. Figure 44. UTSST CRIEnv for NV field cores.
76 Evaluating the Effects of Recycling Agents on Asphalt Mixtures with High RAS and RAP Binder Ratios 3.3 Comparison of Laboratory Results and Field Performance In order to evaluate the recycling-agent dose selection method developed in this study and facilitate proposing materials selection guidelines, the performance of field-test sections and UTSST and I-FIT results for corresponding laboratory-compacted LMLC and RPMLC speci- mens was compared in an effort to establish thresholds for determining acceptable mixture performance in terms of both low- and intermediate-temperature cracking resistance. Previous observations of a low-temperature cracking resistance index similar to CRIEnv indi- cated substantial correlation with field performance, particularly longitudinal and transverse cracking distresses, with details provided in Hajj et al. (2016). Acknowledging the dependency of both UTSST measurements and the field distresses on environmental conditions and specifically the aging or oxidation level, an exhaustive analysis was conducted to properly assess the rela- tionship between the CRIEnv of RPMLC specimens and crack density collected from pavement distress surveys at different in-service ages. Crack density was calculated as the measured linear longitudinal and transverse crack length divided by the area of each test section, excluding any construction joints, to normalize distress data for comparison with CRIEnv. RPMLC specimens were used for this comparison since more data were available with consis- tent correlation to field performance in both cold and warm climates. The RPMLC specimens were also LTOA before being tested in the UTSST to represent worst-case conditions for cracking resistance and an indiscriminate level of in-service aging. Table 25 provides details for the field-test sections considered in this effort, including some from MN not included in the overall study. Figure 45 presents a comparison between the CRIEnv of LTOA RPMLC specimens and their respective crack density. The horizontal line represents the threshold established based on the crack density that corresponds to the average MEPDG (AASHTO 2008) threshold for transverse cracking that delineates adequate (i.e., fair and better) and inadequate (i.e., poor) field perfor- mance for interstate and state routes. The vertical line denotes the proposed CRIEnv threshold to differentiate mixtures with inadequate and adequate low-temperature cracking resistance. In general, test sections with higher levels of cracking density exhibited lower values of CRIEnv after LTOA, and the general lack of measurements in the upper right and lower left corners supports the definition of CRIEnv and the proposed threshold developed based on these field projects. The circles on the plot represent the average values for CRIEnv and crack density, while horizontal and vertical whiskers represent minimum and maximum values. The circle in the upper left corner is the average value for the mixtures that exhibited inadequate performance, while the circle in the lower right corner is the average value for the mixtures that exhibited adequate field performance based on the crack density threshold of 0.046 mâ1. The intercept between the line connecting these two points and the threshold limit for significant cracking (crack density of 0.046 mâ1) results in a threshold of 38 for CRIEnv based on laboratory results for RPMLC specimens. In other words, a mixture with a CRIEnv below 38 after LTOA will likely exhibit significant cracking, as defined by a crack density greater than 0.046 mâ1. Using the same methodology, a threshold of 7 for FI was developed, as shown in Figure 46, for LMLC specimens after STOA. These data were used for this comparison since more data were available for both flexible and brittle mixtures, and STOA results provided greater differentia- tion among mixtures compared to LTOA results. Based on the comparison of laboratory test results and field performance, adequate perfor- mance in the field may be judged by laboratory tests on recycled asphalt mixtures with high RBR and recycling agents that should show similar or better performance than the DOT control mix- tures. Since the DOT control mixtures showed acceptable performance in the field, all recycled
Section ID Mix ID In-Service Age for Distress Data (Years) Crack Density (1/m)a Field Performance Conditionb FI of LMLC after STOA CRIEnv (kPa) of RPMLC after LTOA Mn_Olmsted-1 Recycled 0.2 RBR MIF (PG 58-34) (Elvaloy Modified) 5.1 0.018 Adequate (Good) â 51.9 Mn_Olmsted-2 MIF (PG 58-34) (Elvaloy Modified) 0.024 Adequate (Good) â 78.8 Mn_Olmsted-3 Canadian Blend (PG 58-28) 0.060 Inadequate (Poor) â 21.1 Mn_Olmsted-4 Arab Heavy/Arab Medium/Kirkuk Blend with REOB (PG 58-28) 0.128 Inadequate (Poor) â 15.4 Mn_Olmsted-5 Venezuelan Blend (PG 58-28) 0.016 Adequate (Good) â 101.4 TX-1 Virgin 2.1 0.074 Inadequate (Poor) 11.1 31.3 TX-2 DOT Control 0.28 RBR (PG 64-22) 0.046 Inadequate (Poor) 3.2 14.0 TX-3 Rejuvenated 0.28 RBR (PG 64-22) (2.7%) T1 0.275 Inadequate (Poor) 3.5 0.7 IN-C Virgin 2.1 0.005 Adequate (Good) 6.5 25.0 IN-E Rejuvenated 0.42 RBR (PG 58-28) (3%) T2 0.367 Inadequate (Poor) 4.2 1.0 IN-V DOT Control 0.32 RBR (PG 58-28) 0.005 Adequate (Good) 5.7 28.5 WI-1 Recycled 0.31 RBR (PG 52-34) 1.1 0.078 Inadequate (Poor) 14.1 40.7 WI-3 Rejuvenated (0.31 RBR) (1.2%) V2 0.035 Adequate (Fair) 9.2 25.0 WI-4 Recycled 0.31 RBR 0.061 Inadequate (Poor) 8.4 22.0 WI-5 DOT Control 0.22 RBR 0.050 Inadequate (Poor) 11.3 36.0 NOTE: â = not available. aMeasured linear longitudinal and transverse crack length divided by the area of respective test section, excluding any construction joints. bBased on information from Table 10-8 in Mechanistic-Empirical Pavement Design Guide (MEPDG): A Manual of Practice (AASHTO 2008): adequate (good), crack density < 0.033 mâ1; adequate (fair), crack density < 0.046 mâ1; inadequate (poor), crack density > 0.046 mâ1. Table 25. Summary of field distress data and CRIEnv and FI used to develop thresholds. Figure 45. Correlation of CRIEnv for LTOA RPMLC specimens with crack density (whiskers represent minimum and maximum observed values).
78 Evaluating the Effects of Recycling Agents on Asphalt Mixtures with High RAS and RAP Binder Ratios asphalt mixtures with recycling agents were directly compared to the DOT control mixtures in this study. Using DOT control mixtures as reference mixtures for determining acceptable mixture per- formance in terms of cracking resistance is an alternative if mixture thresholds are not avail- able since these mixtures showed adequate field performance and similar performance to the virgin mixtures. Virgin mixtures were not used as reference mixtures due to the use of differ- ent base binders than other mixtures. For most state DOTs, producing virgin asphalt mixtures without recycled materials is no longer a common practice, and the use of recycled materials, predominantly RAP, has become a general practice. In a report published by NAPA in 2017, out of 229 companies (with 1,146 production plants) surveyed in 2016, 98% reported using RAP in asphalt mixture production (Hansen and Copeland 2017). 3.4 Key Findings The key findings presented in this chapter are based on field performance of the mixtures included in the field projects and corresponding laboratory performance and include the following: â¢ Recycling-agent doses used in the field projects in this study were insufficient with aging. â¢ Field performance can be used to establish or verify thresholds for adequate mixture cracking performance or performance of recycled asphalt mixtures with high RBR, and recycling agents can be compared to that of DOT control mixtures. Figure 46. Correlation of FI for STOA LMLC specimens with crack density (whiskers represent minimum and maximum observed values).