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Suggested Citation:"Chapter 2. Literature Review." National Academies of Sciences, Engineering, and Medicine. 2023. Ruggedness of Laboratory Tests to Assess Cracking Resistance of Asphalt Mixtures. Washington, DC: The National Academies Press. doi: 10.17226/27421.
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Suggested Citation:"Chapter 2. Literature Review." National Academies of Sciences, Engineering, and Medicine. 2023. Ruggedness of Laboratory Tests to Assess Cracking Resistance of Asphalt Mixtures. Washington, DC: The National Academies Press. doi: 10.17226/27421.
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Suggested Citation:"Chapter 2. Literature Review." National Academies of Sciences, Engineering, and Medicine. 2023. Ruggedness of Laboratory Tests to Assess Cracking Resistance of Asphalt Mixtures. Washington, DC: The National Academies Press. doi: 10.17226/27421.
×
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Suggested Citation:"Chapter 2. Literature Review." National Academies of Sciences, Engineering, and Medicine. 2023. Ruggedness of Laboratory Tests to Assess Cracking Resistance of Asphalt Mixtures. Washington, DC: The National Academies Press. doi: 10.17226/27421.
×
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Suggested Citation:"Chapter 2. Literature Review." National Academies of Sciences, Engineering, and Medicine. 2023. Ruggedness of Laboratory Tests to Assess Cracking Resistance of Asphalt Mixtures. Washington, DC: The National Academies Press. doi: 10.17226/27421.
×
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Suggested Citation:"Chapter 2. Literature Review." National Academies of Sciences, Engineering, and Medicine. 2023. Ruggedness of Laboratory Tests to Assess Cracking Resistance of Asphalt Mixtures. Washington, DC: The National Academies Press. doi: 10.17226/27421.
×
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Suggested Citation:"Chapter 2. Literature Review." National Academies of Sciences, Engineering, and Medicine. 2023. Ruggedness of Laboratory Tests to Assess Cracking Resistance of Asphalt Mixtures. Washington, DC: The National Academies Press. doi: 10.17226/27421.
×
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Suggested Citation:"Chapter 2. Literature Review." National Academies of Sciences, Engineering, and Medicine. 2023. Ruggedness of Laboratory Tests to Assess Cracking Resistance of Asphalt Mixtures. Washington, DC: The National Academies Press. doi: 10.17226/27421.
×
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Suggested Citation:"Chapter 2. Literature Review." National Academies of Sciences, Engineering, and Medicine. 2023. Ruggedness of Laboratory Tests to Assess Cracking Resistance of Asphalt Mixtures. Washington, DC: The National Academies Press. doi: 10.17226/27421.
×
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Suggested Citation:"Chapter 2. Literature Review." National Academies of Sciences, Engineering, and Medicine. 2023. Ruggedness of Laboratory Tests to Assess Cracking Resistance of Asphalt Mixtures. Washington, DC: The National Academies Press. doi: 10.17226/27421.
×
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Suggested Citation:"Chapter 2. Literature Review." National Academies of Sciences, Engineering, and Medicine. 2023. Ruggedness of Laboratory Tests to Assess Cracking Resistance of Asphalt Mixtures. Washington, DC: The National Academies Press. doi: 10.17226/27421.
×
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Suggested Citation:"Chapter 2. Literature Review." National Academies of Sciences, Engineering, and Medicine. 2023. Ruggedness of Laboratory Tests to Assess Cracking Resistance of Asphalt Mixtures. Washington, DC: The National Academies Press. doi: 10.17226/27421.
×
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Suggested Citation:"Chapter 2. Literature Review." National Academies of Sciences, Engineering, and Medicine. 2023. Ruggedness of Laboratory Tests to Assess Cracking Resistance of Asphalt Mixtures. Washington, DC: The National Academies Press. doi: 10.17226/27421.
×
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Suggested Citation:"Chapter 2. Literature Review." National Academies of Sciences, Engineering, and Medicine. 2023. Ruggedness of Laboratory Tests to Assess Cracking Resistance of Asphalt Mixtures. Washington, DC: The National Academies Press. doi: 10.17226/27421.
×
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Suggested Citation:"Chapter 2. Literature Review." National Academies of Sciences, Engineering, and Medicine. 2023. Ruggedness of Laboratory Tests to Assess Cracking Resistance of Asphalt Mixtures. Washington, DC: The National Academies Press. doi: 10.17226/27421.
×
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Suggested Citation:"Chapter 2. Literature Review." National Academies of Sciences, Engineering, and Medicine. 2023. Ruggedness of Laboratory Tests to Assess Cracking Resistance of Asphalt Mixtures. Washington, DC: The National Academies Press. doi: 10.17226/27421.
×
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Suggested Citation:"Chapter 2. Literature Review." National Academies of Sciences, Engineering, and Medicine. 2023. Ruggedness of Laboratory Tests to Assess Cracking Resistance of Asphalt Mixtures. Washington, DC: The National Academies Press. doi: 10.17226/27421.
×
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Suggested Citation:"Chapter 2. Literature Review." National Academies of Sciences, Engineering, and Medicine. 2023. Ruggedness of Laboratory Tests to Assess Cracking Resistance of Asphalt Mixtures. Washington, DC: The National Academies Press. doi: 10.17226/27421.
×
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Suggested Citation:"Chapter 2. Literature Review." National Academies of Sciences, Engineering, and Medicine. 2023. Ruggedness of Laboratory Tests to Assess Cracking Resistance of Asphalt Mixtures. Washington, DC: The National Academies Press. doi: 10.17226/27421.
×
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Suggested Citation:"Chapter 2. Literature Review." National Academies of Sciences, Engineering, and Medicine. 2023. Ruggedness of Laboratory Tests to Assess Cracking Resistance of Asphalt Mixtures. Washington, DC: The National Academies Press. doi: 10.17226/27421.
×
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Suggested Citation:"Chapter 2. Literature Review." National Academies of Sciences, Engineering, and Medicine. 2023. Ruggedness of Laboratory Tests to Assess Cracking Resistance of Asphalt Mixtures. Washington, DC: The National Academies Press. doi: 10.17226/27421.
×
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Suggested Citation:"Chapter 2. Literature Review." National Academies of Sciences, Engineering, and Medicine. 2023. Ruggedness of Laboratory Tests to Assess Cracking Resistance of Asphalt Mixtures. Washington, DC: The National Academies Press. doi: 10.17226/27421.
×
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Suggested Citation:"Chapter 2. Literature Review." National Academies of Sciences, Engineering, and Medicine. 2023. Ruggedness of Laboratory Tests to Assess Cracking Resistance of Asphalt Mixtures. Washington, DC: The National Academies Press. doi: 10.17226/27421.
×
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Suggested Citation:"Chapter 2. Literature Review." National Academies of Sciences, Engineering, and Medicine. 2023. Ruggedness of Laboratory Tests to Assess Cracking Resistance of Asphalt Mixtures. Washington, DC: The National Academies Press. doi: 10.17226/27421.
×
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Suggested Citation:"Chapter 2. Literature Review." National Academies of Sciences, Engineering, and Medicine. 2023. Ruggedness of Laboratory Tests to Assess Cracking Resistance of Asphalt Mixtures. Washington, DC: The National Academies Press. doi: 10.17226/27421.
×
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Page 29
Suggested Citation:"Chapter 2. Literature Review." National Academies of Sciences, Engineering, and Medicine. 2023. Ruggedness of Laboratory Tests to Assess Cracking Resistance of Asphalt Mixtures. Washington, DC: The National Academies Press. doi: 10.17226/27421.
×
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Suggested Citation:"Chapter 2. Literature Review." National Academies of Sciences, Engineering, and Medicine. 2023. Ruggedness of Laboratory Tests to Assess Cracking Resistance of Asphalt Mixtures. Washington, DC: The National Academies Press. doi: 10.17226/27421.
×
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Suggested Citation:"Chapter 2. Literature Review." National Academies of Sciences, Engineering, and Medicine. 2023. Ruggedness of Laboratory Tests to Assess Cracking Resistance of Asphalt Mixtures. Washington, DC: The National Academies Press. doi: 10.17226/27421.
×
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Suggested Citation:"Chapter 2. Literature Review." National Academies of Sciences, Engineering, and Medicine. 2023. Ruggedness of Laboratory Tests to Assess Cracking Resistance of Asphalt Mixtures. Washington, DC: The National Academies Press. doi: 10.17226/27421.
×
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Suggested Citation:"Chapter 2. Literature Review." National Academies of Sciences, Engineering, and Medicine. 2023. Ruggedness of Laboratory Tests to Assess Cracking Resistance of Asphalt Mixtures. Washington, DC: The National Academies Press. doi: 10.17226/27421.
×
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Suggested Citation:"Chapter 2. Literature Review." National Academies of Sciences, Engineering, and Medicine. 2023. Ruggedness of Laboratory Tests to Assess Cracking Resistance of Asphalt Mixtures. Washington, DC: The National Academies Press. doi: 10.17226/27421.
×
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Suggested Citation:"Chapter 2. Literature Review." National Academies of Sciences, Engineering, and Medicine. 2023. Ruggedness of Laboratory Tests to Assess Cracking Resistance of Asphalt Mixtures. Washington, DC: The National Academies Press. doi: 10.17226/27421.
×
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Suggested Citation:"Chapter 2. Literature Review." National Academies of Sciences, Engineering, and Medicine. 2023. Ruggedness of Laboratory Tests to Assess Cracking Resistance of Asphalt Mixtures. Washington, DC: The National Academies Press. doi: 10.17226/27421.
×
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Suggested Citation:"Chapter 2. Literature Review." National Academies of Sciences, Engineering, and Medicine. 2023. Ruggedness of Laboratory Tests to Assess Cracking Resistance of Asphalt Mixtures. Washington, DC: The National Academies Press. doi: 10.17226/27421.
×
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Suggested Citation:"Chapter 2. Literature Review." National Academies of Sciences, Engineering, and Medicine. 2023. Ruggedness of Laboratory Tests to Assess Cracking Resistance of Asphalt Mixtures. Washington, DC: The National Academies Press. doi: 10.17226/27421.
×
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Suggested Citation:"Chapter 2. Literature Review." National Academies of Sciences, Engineering, and Medicine. 2023. Ruggedness of Laboratory Tests to Assess Cracking Resistance of Asphalt Mixtures. Washington, DC: The National Academies Press. doi: 10.17226/27421.
×
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Suggested Citation:"Chapter 2. Literature Review." National Academies of Sciences, Engineering, and Medicine. 2023. Ruggedness of Laboratory Tests to Assess Cracking Resistance of Asphalt Mixtures. Washington, DC: The National Academies Press. doi: 10.17226/27421.
×
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Suggested Citation:"Chapter 2. Literature Review." National Academies of Sciences, Engineering, and Medicine. 2023. Ruggedness of Laboratory Tests to Assess Cracking Resistance of Asphalt Mixtures. Washington, DC: The National Academies Press. doi: 10.17226/27421.
×
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Suggested Citation:"Chapter 2. Literature Review." National Academies of Sciences, Engineering, and Medicine. 2023. Ruggedness of Laboratory Tests to Assess Cracking Resistance of Asphalt Mixtures. Washington, DC: The National Academies Press. doi: 10.17226/27421.
×
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Suggested Citation:"Chapter 2. Literature Review." National Academies of Sciences, Engineering, and Medicine. 2023. Ruggedness of Laboratory Tests to Assess Cracking Resistance of Asphalt Mixtures. Washington, DC: The National Academies Press. doi: 10.17226/27421.
×
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Suggested Citation:"Chapter 2. Literature Review." National Academies of Sciences, Engineering, and Medicine. 2023. Ruggedness of Laboratory Tests to Assess Cracking Resistance of Asphalt Mixtures. Washington, DC: The National Academies Press. doi: 10.17226/27421.
×
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Suggested Citation:"Chapter 2. Literature Review." National Academies of Sciences, Engineering, and Medicine. 2023. Ruggedness of Laboratory Tests to Assess Cracking Resistance of Asphalt Mixtures. Washington, DC: The National Academies Press. doi: 10.17226/27421.
×
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Suggested Citation:"Chapter 2. Literature Review." National Academies of Sciences, Engineering, and Medicine. 2023. Ruggedness of Laboratory Tests to Assess Cracking Resistance of Asphalt Mixtures. Washington, DC: The National Academies Press. doi: 10.17226/27421.
×
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Suggested Citation:"Chapter 2. Literature Review." National Academies of Sciences, Engineering, and Medicine. 2023. Ruggedness of Laboratory Tests to Assess Cracking Resistance of Asphalt Mixtures. Washington, DC: The National Academies Press. doi: 10.17226/27421.
×
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Suggested Citation:"Chapter 2. Literature Review." National Academies of Sciences, Engineering, and Medicine. 2023. Ruggedness of Laboratory Tests to Assess Cracking Resistance of Asphalt Mixtures. Washington, DC: The National Academies Press. doi: 10.17226/27421.
×
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Suggested Citation:"Chapter 2. Literature Review." National Academies of Sciences, Engineering, and Medicine. 2023. Ruggedness of Laboratory Tests to Assess Cracking Resistance of Asphalt Mixtures. Washington, DC: The National Academies Press. doi: 10.17226/27421.
×
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Suggested Citation:"Chapter 2. Literature Review." National Academies of Sciences, Engineering, and Medicine. 2023. Ruggedness of Laboratory Tests to Assess Cracking Resistance of Asphalt Mixtures. Washington, DC: The National Academies Press. doi: 10.17226/27421.
×
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Suggested Citation:"Chapter 2. Literature Review." National Academies of Sciences, Engineering, and Medicine. 2023. Ruggedness of Laboratory Tests to Assess Cracking Resistance of Asphalt Mixtures. Washington, DC: The National Academies Press. doi: 10.17226/27421.
×
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Suggested Citation:"Chapter 2. Literature Review." National Academies of Sciences, Engineering, and Medicine. 2023. Ruggedness of Laboratory Tests to Assess Cracking Resistance of Asphalt Mixtures. Washington, DC: The National Academies Press. doi: 10.17226/27421.
×
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Suggested Citation:"Chapter 2. Literature Review." National Academies of Sciences, Engineering, and Medicine. 2023. Ruggedness of Laboratory Tests to Assess Cracking Resistance of Asphalt Mixtures. Washington, DC: The National Academies Press. doi: 10.17226/27421.
×
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Suggested Citation:"Chapter 2. Literature Review." National Academies of Sciences, Engineering, and Medicine. 2023. Ruggedness of Laboratory Tests to Assess Cracking Resistance of Asphalt Mixtures. Washington, DC: The National Academies Press. doi: 10.17226/27421.
×
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4 CHAPTER 2. LITERATURE REVIEW INTRODUCTION Cracking and durability issues of asphalt pavements have been primary concerns of DOTs the last two decades. Several modes of asphalt pavement cracking exist—fatigue, top- down, reflective, and thermal—and all are influenced by thermal loading, traffic loading, or a combination of both. Different laboratory cracking tests have been developed in the literature for these four modes of cracking, and some efforts have also been made to validate them. It is necessary to identify those efforts in terms of what was done and what is missing before any new validation initiative. Thus, the objective of the literature review is to document existing field validation efforts. As guided by the NCHRP 09-57A panel, the literature review process focused on four cracking tests: IDEAL-CT, DCT, IFIT, and OT. For each cracking test validation, the following information was assembled, if available, as described in the following sections: • Field test section descriptions, including pavement structure, location, existing pavement conditions for asphalt overlays, and so forth. • Traffic and climate information. • Asphalt mixture composition and other available mixture properties. • Lab cracking test data, field observation results, and their relationship. FIELD VALIDATION OF IDEAL-CT IDEAL-CT has been validated for assessing fatigue, reflective, top-down, and thermal cracking. Detailed discussion on each mode of cracking is provided as follows. IDEAL-CT for Fatigue Cracking Both the Federal Highway Administration’s (FHWA’s) accelerated loading facility (ALF) and the test sections on SH 15 in Texas were used to assess the relationship between the IDEAL-CT and fatigue cracking, as described below. FHWA ALF In 2013, 10 test lanes were constructed at the FHWA ALF in McLean, Virginia, to evaluate the fatigue performance of RAP and RAS mixes (Carvalho et al. 2015). The overall pavement structure was composed of a 100 mm (4 inch) asphalt layer, a 650 mm (26 inch) granular base, and the subgrade. The base layer and subgrade were the same for all lanes. The only difference among the 10 lanes was the surface asphalt mix type. The ALF testing was performed in the cooler seasons of the year, and the testing temperature of 20°C at a depth of 20 mm beneath the surface was controlled through radiant heaters when needed. All lanes were loaded with a 425 super-single tire wheel (14,200 lb load and 100 psi pressure) at 11 mph with a normally distributed wander in the lateral direction. The surface mixtures of ALF test sections were all 12.5 mm Superpave mixtures designed at an Ndesign of 65 gyrations. They were hot or warm mixed, with different binder types and RAP/RAS percentages. One 5 gallon bucket of plant mix from each test lane was obtained for the IDEAL-CT evaluation.

5 The IDEAL-CT testing was performed at a room temperature of 25°C with a 50 mm/min loading rate (Zhou et al. 2019). Three replicates of 150 mm diameter by 62 mm height specimens with 7±0.5 percent air voids were molded for each plant mix. Before the molding, each plant mix was conditioned in the oven for four hours at 135°C. Table 1 shows each ALF section’s asphalt mixture, field observation, and IDEAL-CT test information. The average CTIndex and coefficient of variation (COV) for each plant mix are tabulated as well. The fatigue data of two ALF test sections (Lanes 2 and 8) were unavailable during the study. Figure 1 shows a good correlation between the CTIndex values and the ALF passes to the first fatigue crack occurrence. The coefficient of determination R2 is about 0.87. The higher the CTIndex value, the better the fatigue cracking performance in the field. Table 1. FHWA ALF Experimental Design (Zhou et al. 2019). ALF Lane % Recycled Binder Ratio Virgin Binder Hot/Warm Mix No. of ALF Passes for First Crack Observed IDEAL-CT RAP RAS CTIndex COV (%) 1 0 0 PG 64-22 Hot mix 368,254 137.2 10.7 2 40 0 PG 58-28 Warm mix with water foaming No result 123.5 23.2 3 0 20 PG 64-22 Hot mix 42,399 45.2 7.9 4 20 0 PG 64-22 Warm mix with chemical additive 88,740 115.5 5.6 5 40 0 PG 64-22 Hot mix 36,946 37.5 21.6 6 20 0 PG 64-22 Hot mix 125,000 93.9 19.2 7 0 20 PG 58-28 Hot mix 23,005 38.0 19.6 8 40 0 PG 58-28 Hot mix No result 160.0 19.9 9 20 0 PG 64-22 Warm mix with water foaming 270,058 136.0 12.5 11 40 0 PG 58-28 Warm mix with chemical additive 81,044 69.5 23.9

6 Figure 1. Correlation between IDEAL-CT and FHWA ALF Full-Scale Fatigue Cracking (Zhou et al. 2019). Texas SH 15 Two field test sections on SH 15 in Texas were used to validate the IDEAL-CT for fatigue cracking (Zhou et al. 2019). A series of field test sections were constructed back-to-back on SH 15 close to Perryton, Texas, in October 2013. The original objective of these field test sections was to investigate approaches for improving the cracking resistance of asphalt mixes with RAP. It was a mill and inlay job. A 62.5 mm (2.5 inch) asphalt layer was milled and then replaced with 25.0 mm (1 inch) of dense-graded Type F mix and 38 mm (1.5 inch) of Type D surface mix. The Type F mix was used for the whole project. The focus of the test sections was on the Type D surface mixes. Two of these test sections were selected for validating the IDEAL-CT. The two sections experienced similar traffic loadings under the same climate conditions (dry, no-freeze zone) since they were back-to-back on SH 15. The only difference between the surface mixtures of the two SH 15 sections was the binder content: Section 1 contained 5.5 percent (optimum asphalt content [OAC]), and Section 2 contained 5.8 percent (OAC+0.3). Plant mixes were collected during the surface layer construction. Six field surveys have been conducted since the sections were opened to traffic. No rutting was observed on either test section. No cracks were observed in Section 1 until March 3, 2016, but significant fatigue cracking has been observed since then. Section 2, with a higher binder content, performed very well, and no cracking was observed. This result was expected since Section 2 had higher binder content. Three replicates of 150 mm diameter by 62 mm tall specimens with 7±0.5 percent air voids were molded for each plant mix. Before the molding, each plant mix was conditioned in the oven for four hours at 135°C. The IDEAL-CT was performed at a room temperature of 25°C with a 50 mm/min loading rate. Figure 2 and Figure 3 present the average CTIndex values of the two surface mixtures and their field cracking performances, respectively. The data in the two figures demonstrate that the ranking of the CTIndex values is consistent with the performance

7 ranking observed in the field. The higher the CTIndex value, the better the fatigue cracking performance in the field. Figure 2. IDEAL-CT Results of SH 15 Plant Mixes (Zhou et al. 2019). Figure 3. Fatigue Cracking Development Observed on SH 15, Texas (Zhou et al. 2019). IDEAL-CT for Reflective Cracking Both the LTPP Specific Pavement Studies-10 (SPS10) in Oklahoma and the test sections on US 62 in Texas were utilized to assess the relationship between the IDEAL-CT and reflective cracking, as described below. LTPP SPS10 in Oklahoma In the last decade, LTPP initiated SPS10: Warm Mix Asphalt (WMA) Overlay of Asphalt Pavements in many different climate zones. The SPS10 test sections were designed to capture

8 information on the performance of WMA and to compare their performance with hot mix asphalt (HMA). Note that WMA is defined by LTPP as asphalt mixes produced at a temperature below 275°F. Six test sections were constructed on SH 66 west of Yukon, Oklahoma, in November 2015. Before the 2 inch asphalt overlay, LTPP surveyed and recorded existing pavement distresses of the six test sections. All test sections exhibited a large amount of cracking except Section 400A62, but no transverse cracking occurred. Moreover, all six test sections experienced similar traffic loading under the same climate condition (wet, no-freeze zone). The overlay mixtures of SPS10 test sections on SH 66 were both HMA and WMA mixtures with different binder types, WMA additives, and RAP/RAS percentages, as listed in Table 2. Plant mix from each test lane was obtained for the IDEAL-CT. The IDEAL-CT test was performed at a room temperature of 25°C with a 50 mm/min loading rate. Three replicates of test specimens with 7±0.5 percent air voids were molded for each test section. Before the molding, each plant mix was conditioned in the oven for four hours at 135°C. To validate the IDEAL-CT for reflective cracking, Section 400A62 was excluded from this study since no cracks were found on the existing pavement. Thus, only five test sections (400A01, 400A02, 400A03, 400A61, and 400A63) were employed for the IDEAL-CT validation. In May 2018, researchers surveyed the pavement distresses of these test sections. Section 400A61 had 100 percent reflective cracking after 30 months of trafficking. Section 400A63 performed the best among these five test sections, and no reflective cracking was observed. Sections 400A01, 400A02, and 400A03 had less than 30 percent reflective cracking. Figure 4 shows a good correlation between CTIndex values and the field reflective cracking rate. The coefficient of determination R2 is about 0.99. Table 2. Asphalt Mixtures and Reflective Cracking Performance of LTPP SPS10 Test Sections on SH 66, Oklahoma (Zhou 2019). LTPP Section ID Asphalt Binder Mix Type HMA/ WMA WMA Additive WMA Dose Rate (%) Recyl. Agent (%) RAP (%) RAS (%) Refl. Crac. Rate (%) 400A01 PG 70-28 Superpave HMA NA NA 0 12 3 30.5 400A02 PG70-28 Superpave WMA Foam 2 0 12 3 27.6 400A03 PG 70-28 Superpave WMA Evotherm M1A 0.7 0 12 3 60.4 400A61 PG 64-22 Superpave WMA Evotherm M1A 0.7 11 12 3 100 400A62 PG 58-28 Superpave WMA Evotherm M1A 0.7 0 12 3 No existing cracking before overlay 400A63 PG 70-28 SMA WMA Evotherm M1A 1 0 NA NA 0

9 Figure 4. Correlation between IDEAL-CT and LTPP SPS10 Reflective Cracking Rate (Zhou 2019). Texas US 62 Two 1500 ft field test sections were constructed on eastbound US 62 close to Childress, Texas, on October 3, 2013 (Zhou et al. 2019). The original purpose was to evaluate the impact of RAP/RAS on pavement performance. The existing pavement had multiple overlays and severe transverse cracking before the milling and inlay. The mill/fill pavement design called for milling the top 200 mm (8 inch) asphalt layer and then replacing it with a 75 mm (3 inch) dense-graded Type B mix and 50 mm (2 inch) dense-graded Type D surface mix. The two test sections had the same Type B mix as the base course, but the Type D surface mixtures differed. The two sections experienced similar traffic loadings under the same climate conditions (dry, no-freeze zone). The virgin section had a Type D dense-graded mix with a PG 70-28 binder and an asphalt binder content of 5.4 percent. The RAP/RAS section was a Type D dense-graded mix with PG 70-28 binder and 5 percent RAP and 5 percent RAS. The total asphalt binder content for the RAP/RAS section was 5.7 percent, and recycled binder replacement was 23.6 percent from RAP and RAS. Table 3 summarizes the asphalt mixture information of each test section. Table 3. Surface Mixtures Used in the Texas US 62 Sections. US 62 Section Mixture Description Virgin Binder Grade Binder Content (%) RAP (%) RAS (%) Virgin Mix Dense-graded Type D PG 70-28 5.4 0 0 RAP/RAS Mix Dense-graded Type D PG 70-28 5.7 5 5 Reflective cracking caused major pavement distress for these two sections. Figure 5 shows performance survey results. Obviously, the virgin section performed much better. Similarly, each plant mix collected during construction was compacted to obtain three replicates of 150 mm diameter by 62 mm height specimens with 7±0.5 percent air voids. Before molding the specimens, each plant mix was conditioned in the oven for four hours at 135°C. The IDEAL-CT was performed at a room temperature of 25°C with a 50 mm/min loading rate.

10 Figure 6 presents the average CTIndex values of the two mixtures. The data indicate that the ranking of the CTIndex values is consistent with the reflective cracking performance ranking observed in the field. The higher the CTIndex value, the better the reflective cracking performance in the field. Figure 5. Reflective Cracking Development Observed on US 62, Texas (Zhou et al. 2019). Figure 6. IDEAL-CT Results of US 62 Mixes (Zhou et al. 2019). IDEAL-CT for Top-Down Cracking In 2015, a cracking group experiment included seven test sections on the National Center for Asphalt Technology (NCAT) test track, each with a different surface mix (West et al. 2021). The seven mixtures were intentionally designed to yield a range of field top-down cracking performances. Six of the seven mixtures (i.e., N1, N2, N5, N8, S5, and S6) were designed in accordance with the conventional Superpave requirements of AASHTO M 323 using an Ndesign of 80 gyrations. The mix design for Section S13 was unique in that it was a gap-graded, asphalt-

11 rubber mixture designed using the Marshall method, which involved 75 blows per side. Figure 7 shows the pavement structure of each section. From October 2015 to February 2021, most test sections accumulated 20 million equivalent single axle loads (ESALs). Sections N5 and N8 reached terminal serviceability in February 2020 after 16 million ESALs. Figure 7. Cross-Section of Cracking Group Test Sections on the NCAT Test Track (West et al. 2021). Table 4 summarizes the asphalt mixture information of each test section. The asphalt contents (ACs) of N2 and N5 were 5.4 percent and 5.1 percent, respectively. In addition, the as- constructed density levels for the two sections were intentionally varied for the experiment. Section N2 was compacted to a higher relative density target of 96 percent, and N5 was compacted to 90 percent. The other six sections had a target density of 92 to 93 percent of their respective maximum theoretical densities. The top-down cracking observation results of the NCAT test sections are listed in Table 4 as well. Since N5 and N8 were milled and overlaid in February 2020, the cracking data for these two sections had to be extrapolated by a sigmoidal function based on data prior to their removal from the experiment.

12 Table 4. Mixtures and Top-Down Cracking Performance of NCAT Test Sections (West et al. 2021). Test Track Section Mixture Description NMAS a (mm) Virgin Binder Grade RAP (%) RAS (%) Cracking (% of lane area) Feb. 2020 Feb. 2021 N1 Control 9.5 PG 67-22 20 0 11.2 44.5 N2 Control, Higher Density 9.5 PG 67-22 20 0 7.7 12.5 N5 Control, Low Density, Low AC 9.5 PG 67-22 20 0 21.1 47.4c N8* Control + 5% RAS 9.5 PG 67-22 20 5 70.8 99.3c S5 35% RAP, PG 58-28 9.5 PG 64-28 35 0 0.2 1.1 S6 Control, HiMAb Binder 9.5 PG 94-28 20 0 0 0.9 S13 Gap-Graded, Asphalt-Rubber 12.5 Not tested 15 0 0 0 a Nominal maximum aggregate size. b Highly modified asphalt. c Cracking results reported for Feb. 2021 for these sections were predicted based on the data before Feb. 2020. The IDEAL-CT specimens were prepared and conditioned in four distinct ways: • Some lab-mixed, lab-compacted (LMLC) specimens were subjected to short-term oven aging (STOA) according to AASHTO R 30 (at 135°C for 4 hours); the process is abbreviated as LMLC-STOA. • Some LMLC-STOA specimens were then treated to an additional eight hours of aging at 135°C in a loose mix condition prior to compaction. NCAT refers to the additional eight hours of aging at 135°C as the “critical aging” (CA) procedure described in Chen et al. (2020) and abbreviated as LMLC-CA. • Plant-mixed, lab-compacted (PMLC) specimens were reheated (RH) to the compaction temperature, a process abbreviated as PMLC-RH. • PMLC-RH specimens were then critically aged prior to compaction, a process abbreviated as PMLC-CA. Table 5 shows the IDEAL-CT results. These results are based on a minimum of five replicates. As expected, CTIndex results for each mixture decreased substantially with the critical aging procedure. It can also be seen that the CTIndex results for the LMLC-CA set are similar to the corresponding results of the PMLC-CA, indicating that the lab preparation of the mixtures provides results similar to plant-produced mixtures. The effect of specimen air void contents on the CTIndex can be seen by comparing the two sets of results for N2 and N5. For N2, the CTIndex results were substantially lower for specimens at 4 percent air voids than 7 percent air voids for each sample type and aging condition. For N5, the CTIndex was substantially higher for specimens at 10 percent air voids than 7 percent air voids. Overall, the effect of specimen air void content on CTIndex results is counterintuitive. Thus, only the results of 7 percent air voids were analyzed for the validation work.

13 Table 5. IDEAL-CT Results (CTIndex) of NCAT Test Sections (West et al. 2021). Test Section and Mixture Description LMLC-STOA LMLC-CA PMLC-RH PMLC-CA Avg. COV Avg. COV Avg. COV Avg. COV N1: Control 30.2 10% 7.3 13% 26.2 21% 8.8 9% N2: Ctrl, 5.4% AC, 7% Va 27.2 9% 10.3 17% 20.7 10% 10.8 18% N2: Ctrl, 5.4% AC, 4% Va 13.9 10% 6.1 13% 13.2 14% 5.1 18% N5: Ctrl, 5.1% AC, 7% Va 19.2 7% 6.5 17% 15.9 14% 7.6 12% N5: Ctrl, 5.1% AC, 10% Va 33.2 13% 11.8 11% 23.8 21% 8.6 12% N8: Control + 5% RAS 10.9 23% 2.8 28% 6.7 30% 2.4 23% S5: 35% RAP, PG 58-28 41.6 17% 10.7 17% 32.4 15% 16.3 9% S6: Control, HiMA Binder 80.8 16% 22.2 22% 32.9 11% 18.7 20% S13: Gap-Gr., Asphalt-Rubber 133.1 27% 63.4 19% 208.1 49% 68.4 19% Figure 8 shows the bar chart for the CTIndex results of the critically aged plant mix samples. The CTIndex ranking of the mixtures is consistent with the field top-down cracking performance of the test sections. For the critically aged set of PMLC samples, a CTIndex criterion of 15 appears to distinguish mixtures performing well from mixtures performing moderately based on their top-down cracking performance on the test track. The analysis of variance (ANOVA) indicated that some mixtures had statistically different CTIndex results. The Games-Howell post hoc pairwise comparison determined which mixtures differed statistically, as indicated by the letters down the middle of the chart. Mixtures that do not share a letter are significantly different at a 95 percent confidence level. It can be seen that the CTIndex result for the mixture from S13 is superior to all other mixtures and that the mixture from N8 is the worst, which is consistent with the top-down cracking performance on the test track. The pairwise comparisons of the CTIndex also statistically distinguished the mixtures with little to no cracking from those with a moderate amount of low-severity cracking. It is important to note that none of the Games-Howell groupings overlapped, which further indicates that the CTIndex effectively distinguishes the cracking resistance of mixtures.

14 Figure 8. Chart of Statistical Comparisons of CTIndex among Mixtures with Performance Groupings (West et al. 2021). Figure 9 shows the correlations of the CTIndex with the top-down cracking observed on the test track for the four sample preparation and aging condition sets. Each chart shows a strong correlation between the CTIndex and field top-down cracking performance. These results indicate that the CTIndex is a good indicator of top-down cracking resistance. The higher the CTIndex value, the better the top-down cracking performance in the field. Figure 9. Correlations of CTIndex with Field Performance for the Lab and Plant Samples Subject to Different Aging Conditions (West et al. 2021).

15 IDEAL-CT for Thermal Cracking In 2008, various test sections (or cells) were constructed at MnROAD (Johnson et al. 2009). Three cells (20, 21, and 22) were designed to evaluate thermal cracking, the most common distress in cold climates. These three cells had the same pavement structure thickness, base materials, and subgrade, but the asphalt-wearing course mixture varied. The three sections experienced similar traffic loadings under the same climate conditions (wet, freeze zone). The surface mixtures for the three sections were as follows: • Cell 20: PG 58-28 virgin binder and 30 percent non-fractionated RAP. • Cell 21: PG 58-28 virgin binder and 30 percent fractionated RAP split on the ¼-inch screen. • Cell 22: PG 58-34 virgin binder and 30 percent fractionated RAP split on the ¼-inch screen. MnROAD crews have been monitoring the three cells since the completion of construction in 2008. Figure 10 shows each cell’s thermal (transverse) cracking development history in both driving and passing lanes. Three observations can be made based on this figure: • Cell 22 performed much better than Cells 20 and 21, which is expected due to the softer virgin binder (PG 58-34) in Cell 22. • Traffic loading significantly impacted the development of thermal (transverse) cracking since the driving lane had more transverse cracking. • Cells 20 and 21 performed approximately equal.

16 (a) (b) Figure 10. Thermal Cracking Development History for Cells 20, 21, and 22: (a) Driving Lane, and (b) Passing Lane (Zhou et al. 2019). The plant mixtures of Cells 20, 21, and 22 were collected during construction. The IDEAL-CT tests were performed following ASTM D8225-19. Figure 11presents the average CTIndex values of the three plant mixtures. This figure indicates that Cell 22 has the highest CTIndex value and should perform the best, followed by Cells 21 and 20. Overall, the ranking of the IDEAL-CT results is consistent with the ranking of thermal cracking performance observed in the field. The higher the CTIndex value, the better the thermal cracking performance in the field.

17 Figure 11. IDEAL-CT Results of MnROAD Cells 20, 21, and 22 (Zhou et al. 2019). Summary of IDEAL-CT Validation Table 6 provides a summary of the IDEAL-CT validation results. The table shows that various field test sections on in-service pavements, test tracks, and an ALF can be used to validate the IDEAL-CT. All results indicate that the ranking of the IDEAL-CT results (CTIndex values) is consistent with the cracking performance ranking observed in the field, including fatigue cracking, reflective cracking, top-down cracking, and thermal cracking.

18 Table 6. Summary of IDEAL-CT Validation Results. Test Section No. of Sections Cracking Type Aging (before Sample Compaction) Asphalt Mixture Lab to Field Correlation FHWA ALF 8 Fatigue Cracking 135°C, 4 hr Superpave 12.5, HMA/WMA, different binders, different RAP/RAS percentages Good correlation, R2 = 0.87 SH 15, Texas 2 Fatigue Cracking 135°C, 4 hr Dense-graded Type D, 20% RAP, PG 58-28, AC 5.5% and 5.8% Consistent ranking between lab and field Oklahoma LTPP SPS10 6 Reflective Cracking 135°C, 4 hr Superpave 12.5, WMA, 12% RAP, 3% RAS, different binders, different WMA additives and percentages Good correlation, R2 = 0.98 US 62, Texas 2 Reflective Cracking 135°C, 4 hr Dense-graded Type D, 20% RAP, PG 70-28, 0 RAP/RAS vs. 5% RAP and 5% RAS Consistent ranking between lab and field NCAT Test Track, Top-Down Cracking 7 Top-Down Cracking STOA a, CAb Superpave 9.5 or gap- graded, different binders, different RAP/RAS percentages Good correlation, R2: 0.87 – 0.94 MnROAD 3 Thermal Cracking 135°C, 4 hr PG 58-28 or 58-34, fractioned or non- fractionated RAP Consistent ranking between lab and field a STOA according to AASHTO R 30. b CA plus an additional eight hours of aging at 135°C in a loose mix condition. FIELD VALIDATION OF DCT Many efforts have been made to validate DCT for thermal cracking. In one study, the DCT results were compared with fatigue cracking in the literature, as described below. National Pooled Fund Study: DCT for Thermal Cracking During Phase I of the national pooled fund study “Investigation of Low Temperature Cracking in Asphalt Pavements: National Pooled Fund Study 776” (Marasteanu et al. 2007), the research team surveyed and collected field cores from more than 15 pavement sections, including good and bad performing pavements. Asphalt overlays were not considered in this study to eliminate the effect of reflective cracking. Pavements containing a significant amount of RAP in the asphalt layers were not considered either. Finally, seven test sections in Minnesota, three in Illinois, and one in Wisconsin were identified and recommended for studying the relationship between DCT fracture energy and thermal cracking. The field cores were collected in 2006. Table 7 shows the test sections recommended during Phase I of the national pooled fund study. Most of these sections are in the wet, freeze zone. Table 8 shows the low pavement temperature at 50 percent reliability level values obtained from the LTPP database.

19 The asphalt mixture in the pooled fund study has very little or no RAP. The asphalt binder type used in the pavement surface mixture for each test section is listed in Table 9. One type of pavement distress—total length of transverse cracking—was assumed to be a good indicator of thermal cracking. Table 9 shows DCT and the field transverse cracking results. Note that DCT specimens were made from field cores. Figure 12 shows the relationship between DCT fracture energy and the field transverse cracking length. Table 7. Test Sections Recommended by the National Pooled Fund Study—Phase I (Marasteanu et al. 2007). State Section Performance (1 = Good) (5 = Bad) Age (Years to 2007) Pavement Structure IL I-74 2 15 1.5" AC + 15.5" base + 12" lime-stabilized subgrade MN CSAH-75 Section 2 4 10 2" AC + 2"AC + 2.5" recycled mx + 12 crushed base MN CSAH-75 Section 4 3 10 2" AC + 2"AC + 2.5" recycled mx + 12 crushed base MN Cell 3 3 14 6.3" AC + 4" crushed base MN Cell 19 4 14 7.8" AC + 28" Class 3 subbase MN Cell 33 3 6 4" AC + 12" crushed base MN Cell 34 1 6 4" AC + 12" crushed base MN Cell 35 4 6 4" AC + 12" crushed base IL US-20 Section 6 2 20 1.5" AC + 11.5" base IL US-20 Section 7 2 20 1.5" AC + 11.5" base WI STH-73 1 5 3" AC + 2" HMA base Note: CSAH = County State Aid Highway. Table 8. LTPP Low Pavement Temperatures at 50 Percent Reliability Level of the Test Sections (Marasteanu et al. 2007). Section Station Temp. (°C) IL I-74 Urbana, IL −16.4 MN CSAH-75 Section 2 Collegeville, MN −24.4 MN CSAH-75 Section 4 Collegeville, MN −24.4 MnROAD Cell 3 Buffalo, MN −23.8 MnROAD Cell 19 Buffalo, MN −23.8 MnROAD Cell 33 Buffalo, MN −23.8 MnROAD Cell 34 Buffalo, MN −23.8 MnROAD Cell 35 Buffalo, MN −23.8 IL US-20 Section 6 Freeport, IL −19.7 IL US-20 Section 7 Freeport, IL −19.7 WI STH-73 Stanley, WI −24.7

20 Table 9. Mixture Binder Types, DCT Fracture Energies, and Field Transverse Cracking Results of the Test Sections (Marasteanu et al. 2007). Section Binder Equivalence DCT Fracture Energy (J/m2) Length of Transverse Cracking (ft/500ft) IL I-74 AC-20 PG 64-34 199.7 1200 MN CSAH-75 Section 2 PG 58-28 PG 58-28 303.5 76 MN CSAH-75 Section 4 PG 58-34 PG 58-34 947.9 30 MnROAD Cell 3 120/150 PG 58-28 228.2 182 MnROAD Cell 19 PG 64-22 PG 64-22 203.6 547 MnROAD Cell 33 PG 58-28 PG 58-28 312.2 91 MnROAD Cell 34 PG 58-34 PG 58-34 380.1 5.5 MnROAD Cell 35 PG 58-40 PG 58-40 473.1 747 IL US-20 Section 6 AC 10 PG 58-28 319.3 84 IL US-20 Section 7 AC 20 PG 64-34 217.0 60 WI STH-73 PG 58-28 PG 58-28 375.3 0 Figure 12. Correlations of DCT Fracture Energy with Transverse Cracking Length (Marasteanu et al. 2007). During Phase II of the national pooled fund study (Marasteanu et al. 2012), the researchers updated the previous correlation plot, as shown in Figure 13. There is some difference in the data points between the two figures, but no details concerning the update were found in the report.

21 Figure 13. Updated Correlations of DCT Fracture Energy with Transverse Cracking (Marasteanu et al. 2012). According to Figure 13, a preliminary low temperature cracking specification was developed, and a minimum fracture energy of 400 J/m2 was suggested to protect against thermal cracking. Fracture energy in the range of 350–400 J/m2 was considered borderline and might be permissible on less critical projects in which a low to moderate degree of thermal cracking can be tolerated. A safety factor can be achieved for critical projects by specifying a minimum fracture energy of 600 J/m2. Furthermore, a thermal cracking specification was proposed for asphalt mix design (Marasteanu et al. 2012). Since the DCT test results presented in Figure 13 were based on field cores taken out of older pavements, a 15 percent increase in fracture energy was proposed in the pooled fund study to account for the fact that these requirements are specified for laboratory- mixed and laboratory-compacted mixtures with short-term aging. Specification limits for three levels of project criticality are provided in Table 10. Note that the specification applies to surface mixes only. Table 10. Recommended DCT Fracture Energy Thresholds (Marasteanu et al. 2012). Contents Project Criticality/Traffic Level Low <10M ESALs Moderate 10–30M ESALs High >30M ESALs Minimum Fracture Energy (J/m2)@low-temperature PG+10ºC 400 460 690

22 Cracking Performance Database from Four States: DCT for Thermal Cracking Buttlar et al. (2019) gathered a comprehensive array of field sections and assembled a summary of data from 52 projects having both DCT fracture energy results and field cracking measurements. The sections were from four different states—Illinois, Minnesota, Missouri, and Wisconsin—and provided a broader geographical view of the transverse cracking performance of the pavements. Further, the field sections included a variety of factors such as pavement layer configuration, binder type, aggregate source, etc. Table 11 shows the description of the field test sections. Further details can be found in other publications (Hausman and Buttlar 2002; Dave and Hoplin 2015; Bullar and Wang 2016). Table 12 shows the DCT fracture energy of field cores versus field transverse cracking results for the 52 sections. The age of the pavement section investigated at the time of coring and distress surveying is also listed in the tables. Note that the transverse crack length values include all severity levels. Table 11. Description of Field Test Sections (Buttlar et al. 2019). Section Additional Mixture and Pavement Configuration Details I-88 EB GTR PG 58-28 SMA, 33.9% ABR, 12.5 NMAS, lane mix I-88 EB GTR PG 46-34 SMA, 33.9% ABR, 12.5 NMAS, lane mix I-88 EB GTR PG 46-34 high ABR SMA, 46.8% ABR, 12.5 NMAS, lane mix I-88 EB ECR PG 58-28 SMA, 33.9% ABR, 12.5 NMAS, lane mix I-88 EB ECR PG 46-34 SMA, 33.9% ABR, 12.5 NMAS, lane mix I-88 EB ECR PG 46-34 high ABR SMA, 46.8% ABR, 12.5 NMAS, lane mix I-88 EB RMA PG 58-28 SMA, 33.9% ABR, 12.5 NMAS, shoulder mix I-88 EB RMA PG 46-34 SMA, 33.9% ABR, 12.5 NMAS, shoulder mix I-88 EB RMA PG 46-34 high ABR SMA, 47.0% ABR, 12.5 NMAS, shoulder mix TH10-PG 58-28 87.5 mm M/O CH10-PG 58-28 37.5 mm on existing HMA CH10-PG 58-28 37.5 mm M/O TH28-PG 58-34 75 mm M/O TH28-PG 58-34 112.5 mm M/O CH30-PG 64-34 150 mm M/O TH220-PG 58-28 75 mm M/O I-294 NB, North of Cermak Toll Mid-ABR (31%)—HMA, quartzite, PG 70-28 SBS, 50 mm surface TH9-PG 58-34 75 mm O/L on FDR TH9-PG 58-34 75 mm O/L on FDR WI STH 73 PG 58-28 Subbase stabilized with asphaltic base course, 50 mm milled HMA base, 75 mm surface I-90 WB Rt. 25 Mid-ABR (33%)—HMA, quartzite, PG 70-28 SBS, 45 mm surface TH6-PG 58-28 37.5 mm M/O TH27-PG 58-28 75 mm M/O Note: SMA = stone matrix asphalt; M/O = mill and overlay; ABR = asphalt binder replacement; O/L = overlay; SBS = styrene-butadiene-styrene; FDR = full-depth reclamation; and GTR = ground-tire rubber.

23 Table 11. Description of Field Test Sections (Buttlar et al. 2019) (Continued). Section Additional Mixture and Pavement Configuration Details TH27-PG 58-28 75 mm M/O TH210-PG 58-28 50 mm O/L on existing concrete MnROAD 33 PG 58-28 Silty clay subgrade (1994), 300 mm crushed granite base (class 5), 100 mm HMA surface (1999) US50_1 ABR (24.6%), PG 64-22, 12.5 NMAS, 50 mm HMA surface (2011) MnROAD 34 PG 58-34 Silty clay subgrade (1994), 300 mm crushed granite base (class 5), 100 mm HMA surface (1999) MnROAD 35 PG 58-40 Silty clay subgrade (1994), 300 mm crushed granite base (class 5), 100 mm HMA surface (1999) I35-PG 64-28 100 mm M/O on existing concrete MO 52_1 ABR (33.5%), PG 64-22, 12.5 NMAS, 50 mm HMA surface (2010) I-90 WB Rockford Low ABR (14%)—HMA, gravel, PG 76-22 GTR, 50 mm surface TH1-PG 58-34 100 mm O/L on FDR TH1-PG 58-28 37.5 mm O/L on existing HMA TH53-PG 58-28 37.5 mm M/O TH212-PG 70-34 100 mm SMA new construction I-90 EB near Newburg Rd. Mid-ABR (36%)—HMA, quartzite, PG 76-22 SBS, 50 mm surface US63_2 ABR (29.9%), PG 64-22, 12.5 NMAS, 50 mm HMA surface (2008) TH113-PG 58-28 37.5 mm O/L on existing concrete TH113-PG 58-34 125 mm O/L on FDR Taxiway E, Greater Peoria Regional Airport 150 mm AC overlay on 190 mm existing AC pavement (P201) and 510 mm aggregate base (P154), strip-type inlay system used for base isolation MN 75 2 PG 58-28 Sand-gravel subgrade (1955), 300 mm crushed base (Class 5), 70 mm recycle mix (32B), 50 mm recycle mix (42B), 50 mm HMA surface MN 75 4 PG 58-34 Sand-gravel subgrade (1955), 300 mm crushed base (Class 5), 62 mm recycle mix (32B), two 50 mm HMA lifts TH10-PG 64-28 100 mm M/O (sealed cracks) TH10-PG 64-28 100 mm M/O (cracks not sealed) US54_8 ABR (8.6%), PG 70-22, 12.5 NMAS, 50 mm HMA surface (2006) TH6-PG 58-34 37.5 mm on existing HMA TH6-PG 58-34 112.5 mm O/L on FDR TH2-PG 58-34 100 mm O/L on existing HMA MnROAD 19 PG 64-22 Silt clay subgrade constructed in 1992, crushed subbase (Class 3), 200 mm HMA (AC-20) MnROAD 03 PG 58-28 Silty clay subgrade constructed in 1992, crushed base (Class 5), 160 mm HMA (120/150) US54_7 ABR (0%), PG 64-22, 12.5 NMAS, 50 mm HMA surface (2003) IL I-74 (AC-20) Lime-stabilized subgrade, 390 mm 19 mm mix AC-20 base, 38 mm AC-20 surface Note: SMA = stone matrix asphalt; M/O = mill and overlay; ABR = asphalt binder replacement; O/L = overlay; FDR = full-depth reclamation; and GTR = ground-tire rubber.

24 Table 12. DCT Fracture Energy vs. Transverse Cracking Length of Test Sections (Buttlar et al. 2019). Section Test Temperature (°C) Fracture Energy (J/m2) Transverse Cracking (m/500 m) Age (years) I-88 EB ECR PG 46-34 −12 980 0 1 I-88 EB ECR PG 46-34 High ABR −12 905 0 1 I-88 EB ECR PG 58-28 −12 785 0 1 I-88 EB GTR PG 46-34 −12 2073 0 1 I-88 EB GTR PG 46-34 High ABR −12 1245 0 1 I-88 EB GTR PG 58-28 −12 785 0 1 I-88 EB RMA PG 46-34 −12 1001 0 1 I-88 EB RMA PG 46-34 High ABR −12 779 0 1 I-88 EB RMA PG5 8-28 −12 738 0 1 TH10-PG 58-28 (H) −24.2 212 273 2 CH10-PG 58-28 (F-1) 423 372 3 CH10-PG 58-28 (F-2) 423 162 3 CH30-PG 64-34 (L) 567 120 3 TH220-PG 58-28 (R) 183 78 3 TH28-PG 58-34 (K-1) 291 180 3 TH28-PG 58-34 (K-2) 227 174 3 I-294 NB, North of Cermak Toll −12 685 10 4 TH9-PG 58-34 (E-1) 271 54 4 TH9-PG 58-34 (E-2) 352 36 4 I-90 WB Rt. 25 −12 812 6 5 TH210-PG 58-28 (P) −24.8 293 202 5 TH27-PG 58-28 (J-1) 335 199 5 TH27-PG 58-28 (J-2) 272 216 5 TH6-PG 58-28 (C) −24.2 260 199 5 WI STH 73 PG 58-28 −24.7 375 0 5 I-35-PG 64-28 (M) 379 48 6 MnROAD 33 PG 58-28 −23.8 312 91 6 MnROAD 34 PG 58-34 −23.8 380 5.5 6 MnROAD 35 PG 58-40 −23.8 473 0 6 US50_1 −12 322 1 6 I-90 WB Rockford −12 642 0 7

25 Table 12. DCT Fracture Energy vs. Transverse Cracking Length of Test Sections (Buttlar et al. 2019) (Continued). Section Test Temperature (°C) Fracture Energy (J/m2) Transverse Cracking (m/500 m) Age (years) MO 52_1 −12 321 1000 7 TH1-PG 58-28 (A-2) −26.3 342 600 7 TH1-PG 58-34 (A-1) −26.3 408 493 7 TH212-PG 70-34 (Q) −20.7 1040 0 7 TH53-PG 58-28 (N) −25.7 397 432 7 I-90 EB near Newburg Rd. −12 659 0 8 Taxiway E, Greater Peoria Regional Airport −10 448 0 9 TH113-PG 58-28 (O-1) −23.7 182 499 9 TH113-PG 58-34 (O-2) −23.7 326 67 9 US-63_2 −12 272 1200 9 MN 75 2 PG 58-28 −24.4 304 76 10 MN 75 4 −24.4 948 30 10 TH10-PG 64-28 (G-1) −24.2 270 378 10 TH10-PG 64-28 (G-2) −24.2 238 294 10 TH6-PG 58-34 (D-1) −24.2 311 600 11 TH6-PG 58-34 (D-2) −24.2 352 24 11 US-54_8 −12 340 2 11 TH2-PG 58-34 (B) −24.4 449 356 12 MnROAD 03 PG 58-28 −23.8 228 182 14 MnROAD 19 PG 64-22 −23.88 204 547 14 US-54_7 −12 459 1 14 IL I-74 (AC-20) −16.4 200 1200 15 Figure 14 shows the relationship between DCT fracture energy (J/m2) and transverse cracking (m/500 m), with the diameter of the plot points (bubbles) representing the age of the asphalt mixture. Field Section I-88 GTR PG 46-34, having a fracture energy value of 2073 J/m2 and zero transverse cracking, is not shown in the plot. The pavement’s age directly relates to the reliability of the transverse cracking data (or the weight that the analyst should give to that data point). This finding implies that the smaller bubbles have a higher probability to bubble upward with further aging, while the larger bubbles become stabilized in terms of long-term aged fracture energy and field cracking level.

26 Figure 14. DCT Fracture Energy vs. Field Transverse Cracking (Buttlar et al. 2019). According to Figure 14, the thresholds for long-term aged, field-cored specimens were suggested to be 600 J/m2 and 400 J/m2. As seen in the figure, mixtures with fracture energies above 600 J/m2 are indeed found to have very low transverse cracking. Further analysis shows that only five of 30 sections having fracture energy values less than 400 J/m2 experienced zero cracking at the time of the survey. Conversely, for the asphalt mixtures in the very high fracture energy category of more than 600 J/m2, 14 of 15 sections exhibited zero cracking. Mixtures with a fracture energy range between 400 and 600 J/m2 exhibited some scatter due to many factors, such as different pavement ages, cracking severity levels, hybridization of cracking data (e.g., reflective cracking rather than true thermal cracking), etc. The thresholds 600 J/m2 and 400 J/m2 were for field cores with long-term aging. The thresholds for lab-compacted, short-term aged specimens are higher. This result validated the fracture energy thresholds recommended in the pooled funded study, as shown in Table 10. Illinois Tollway Test Sections: DCT for Multiple Modes of Cracking The plant samples of 14 different mixtures produced in 2018 on mainline and shoulder sections across the Illinois Tollway system were tested in this study (Buttlar et al. 2021). In addition, other existing Illinois Tollway sections were observed, and the field cores were taken from these sections and tested. Most of these existing sections were studied in previous projects, such as the following sections: • Ground-tire rubber test sections, Illinois Tollway I-88, a report published in 2017. • SMA test sections, I-294 and I-90, a report published in 2016. • RAS test sections, I-90 shoulder, a report published in 2012. Table 13 shows the test sections and the 14 mixtures overlaid in 2018. The first four mixtures (1844, 1835, 1824, and 1845) are friction-surface-type SMAs called Friction S. The three mixtures labeled 1818, 1834, and 1826 represent surface shoulder materials (Shoulder S.).

27 Finally, the last two sample IDs (1803 and 1807) represent shoulder binders, which appear below shoulder surface mixtures on the tollway. Table 14 shows the description of the existing test sections. Field cores were taken from these sections. Some cores are 6 inches deep, including the top and bottom lift mixtures. The asphalt mixture information for plant mix and field cores is presented in Table 15, Table 16, and Table 17. Table 13. Illinois Tollway Sections Overlaid in 2018 (Buttlar et al. 2021). Route Mile Post Location Mix. ID Mix Type Description of Performance Survey in 2019 I-355 12-22 Mainline 1844 SMA Friction S. Some reflective cracks I-88 93-103 Mainline 1835 SMA Friction S. Very low number of transverse cracking I-88 EB 76-91 Mainline 1824 SMA Friction S. Few or no cracks I-88 WB-105 Shoulder 1845 SMA Friction S. Some thermal cracking I-88 WB 76-91 Mainline 1836 SMA Surface Transverse Cracking, ~100 ft spacing I-88 103-113 Mainline 1840 SMA Surface Very low number of transverse cracking I-88 103-113 Mainline 1829 IL-4.75 Very low number of transverse cracking I-88 92-103 Mainline 1828 IL-4.75 Very low number of transverse cracking I-88 WB 79-91 Mainline 1823 IL-4.75 Transverse Cracking, ~100 ft spacing I-88 EB 76-91 Shoulder 1818 Shoulder S. Few or no cracks I-355 12-22 Shoulder 1834 Shoulder S. Some reflective cracks I-355 22-30 Shoulder 1826 Shoulder S. No distress I-88 103-113 Shoulder 1807 Shoulder Binder Hairline cracks I-88 92-103 Shoulder 1803 Shoulder Binder Few or no cracks

28 Table 14. Existing Sections for Coring (Buttlar et al. 2021). Route Lane Dir. Mile Post Range Description I-88 Inside lane—tangents EB 45.00–55.10 On rubblized jointed concrete pavement I-88 Inside lane—tangents EB 61.30–60.10 Control-SBS—located between the rubber sections I-90 Mainline—tangents WB 15.00–2.00 Gravel-aged SMA— construction joints; crack sealants I-90 Mainline EB 15.00–2.00 Diabase-aged SMA I-90 I-90 Ramps EB 17.80–16.50 High density block cracking I-294 Mainline NB 30.50–36.50 Quartzite mix—reflective cracking, rough ride—placed on jointed concrete I-88 Shoulder EB 45.00–55.10 Visually good performing I-88 Shoulder EB 55.10–60.00 Poor performing—transverse cracks, low severe block cracks. I-90 Shoulder WB 7.50–7.00 Poor performing— transverse and block cracks I-90 Shoulder WB 6.60–6.25 Poor Performing—severe transverse and block cracks I-90 Shoulder WB 6.25–5.25 Poor performing—3 ft interval transverse cracks and block cracking I-90 Shoulder WB 5.25–4.50 Poor performing—more transverse cracks than block cracks I-90 Shoulder EB 9.50–10.50 Good performing I-90 Shoulder WB 9.50–10.50 Poor performing—transverse cracks

29 Table 15. Asphalt Mixture Information of Plant Mix Overlaid in 2018 (Buttlar et al. 2021). Mix. ID Mix Type Base Binder Plan Grade ABR by RAP ABR by RAS NMAS 1844 N80 SMA Friction S. SBS 70-28 76-22 10.8 16.0 12.5 1835 N80 SMA Friction S. 46-34 +10% ECR 76-22 25.1 16.1 12.5 1824 N80 SMA Friction S. SBS 64-34 76-22 20.4 16.7 12.5 1845 N80 SMA Friction S. 46-34 +10.5% Lehigh 76-22 23.9 15.4 12.5 1836 N80 SMA Surface SBS 64-34 76-22 16.2 16.3 12.5 1840 N80 SMA Surface 58-28 +12% GTR 76-22 15.9 9.8 12.5 1829 N50 Dense IL-4.75 58-28 +12% GTR 76-22 17.8 9.3 4.75 1828 N50 Dense IL-4.75 46-34 +10% ECR 76-22 35.3 9.2 4.75 1823 N50 Dense IL-4.75 SBS 64-34 76-22 24.1 14.2 4.75 1818 N70 Dense Shoulder S. 64-22 64-22 20.4 0.0 9.5 1834 N70 Dense Shoulder S. 58-28 64-22 20.0 0.0 9.5 1826 N70 Dense Shoulder S. 46-34 64-22 27.6 18.1 9.5 1807 N50 Dense Shoulder Binder 46-34 64-22 34.4 14.0 19.0 1803 N50 Dense Shoulder Binder 58-28 64-22 26.5 16.6 19.0

30 Table 16. Asphalt Mixture Information of Field Cores, Top Lift (Buttlar et al. 2021). No. Location Construction Year Base Binder Mix. Type ABR by RAP ABR by RAS NMAS 1 I88-47E 2016 SBS 70-28 SMA Surface 11.6 19.8 12.5 2 I88-60.5E 2015 SBS 70-28 SMA Friction S. 14.8 20.7 12.5 3 I90-6.6W 2009 76-22+ GTR SMA Surface 13.9 0 12.5 4 I90-6.0E 2008 70-28+ GTR SMA Friction S. 16.3 0 12.5 5 I90-17.8E 2008 76-28+ GTR SMA Friction S. 16.0 0 19.0 6 I294-34N 2012 SBS 70-28 SMA Friction S. 15.5 16.2 19.0 7 I88-52E 2015 58-28 N70D Surface 19.1 19.6 9.5 8 I88-57E 2014 58-28 N70D Surface 22.8 17.8 9.5 9 I90-7.25W 2009 58-22 N70D Surface 16.7 20.1 9.5 10 I90-5.12W 2009 58-22 N70D Surface 24.4 0.0 9.5 11 I90-10E 2008 58-22 N70D Surface 24.0 0 9.5 12 I90-10W 2008 58-22 N70D Surface 16.2 0 9.5 Table 17. Asphalt Mixture Information of Field Cores, Bottom Lift (Buttlar et al. 2021). No. Location Construction Year Mix. Type Base Binder ABR by RAP ABR by RAS NMAS 1 I90-6.6W 2009 SMA Surface/Binder 76-22+ GTR 13.9 0 12.5 2 I90-6.0E 2008 SMA Binder 76-22+ GTR 15.3 0 12.5 3 I294-34N 2012 SMA Binder SBS 70-28 17.1 19.2 12.5 4 I90-7.25W 2009 N50 Binder 58-22 21.7 22.4 19.0 5 I90-6.06W 2009 N50 Binder 58-22 32.9 24.2 19.0 6 I90-5.12W 2009 N50 Binder 58-22 42.1 23.7 19.0 7 I90-4.75W 2009 N50 Binder 58-22 31.2 23.7 19.0 Figure 15, Figure 16, and Figure 17 show the DCT results for plant mixes and field cores from the top and bottom lift, respectively.

31 Figure 15. DCT Fracture Energy Result of Plant Mixes (Buttlar et al. 2021). Figure 16. DCT Fracture Energy Result of Field Cores, Top Lift (Buttlar et al. 2021). Figure 17. DCT Fracture Energy Result of Field Cores, Bottom vs. Top Lift (Buttlar et al. 2021).

32 Site visits to all sections in 2019 are summarized below. • Sections of 2018 overlaid mixtures: the mainline did not have considerable transverse cracking. Some reflective cracks were observed after the record cold winter of 2018– 2019. The shoulder with the 1845 mix began to show thermal cracking after the 2018–2019 harsh winter. • Ground-tire rubber test sections: all the mainline sections constructed in 2016 were performing very well (only a few isolated thermal cracks were observed). The control sections in between the rubber sections exhibited more thermal cracks than the GTR mainline sections. The dense-graded mix shoulders had frequent cracking. The SMA mix used on the shoulder (Evoflex RMA) showed extensive transverse cracking. • SMA test sections: the I-294 section constructed in 2012 showed many visible distresses and was starting to ride rough. This mix has been placed on jointed concrete pavement, and heavy truck traffic was observed. • RAS sections: the shoulders with RAP and RAS had many cracks, both thermal and blocking. The flowchart shown in Figure 18 outlines how to develop the DCT thresholds for Illinois tollways. An example for determining the DCT threshold for SMA friction surface mixtures is given in Figure 19. Figure 18. Steps in DCT Threshold Development (Buttlar et al. 2021).

33 Figure 19. Flowchart to Develop DCT Threshold for SMA Friction Surface Mixtures (Buttlar et al. 2021). The final recommended DCT thresholds for Illinois Tollway mixtures are presented in Table 18. A last consensus step was used to allow the final rounding of DCT thresholds based on practical considerations, such as knowledge of the ability of locally available materials to meet specification thresholds for various mix types, sustainability goals, and economic considerations. Table 18. DCT Thresholds at −12℃ for Illinois Tollway Mixtures (Buttlar et al. 2021). Mix. Type Category Existing (J/m2) Recommended (J/m2) SM A Friction Surface 750 775 Surface 700 700 Binder 650 650 Unmodified 500 500 D en se -g ra de d IL 4.75 450 450 Mainline Binder (Ndesign > 50) N/A 425 Mainline Binder (Ndesign = 50) N/A 450 Shoulder Surface (Ndesign ≤ 70) N/A 450 Shoulder Binders N/A 425

34 FHWA ALF Sections: DCT for Fatigue Cracking Ozer et al. (2018) used the same FHWA ALF plant mixes as described previously under the IDEAL-CT validation to assess the capability of the DCT test for fatigue cracking. The DCT test was conducted using ASTM procedures (ASTM D7313). Specimens were conditioned prior to testing in refrigerated chambers (Ozer et al. 2018). Tests were conducted at –12°C using crack mouth opening displacement (CMOD) at a rate of 1.0 mm/min (controlled by measuring displacement using knife points). A minimum of three replicates with 7±0.5 percent air voids specimens were fabricated for each plant mix with short-term aging. The number of ALF passes for the first crack observed in each lane were listed in Table 1. The relationship between the DCT fracture energy and the ALF passes is shown in Figure 20. Note that ALF passes for Lanes 2 and 8 were not available. A higher DCT fracture energy indicates better crack resistance. The overall correlation between the DCT fracture energy and the field fatigue cracking observation (shown in the insert to Figure 20) is weak. Figure 20. Relationship between DCT Fracture Energy and ALF Cycles (Ozer et al. 2018). Summary of DCT Validation Table 19 provides a summary of the DCT validation results. The results indicate that the DCT ranks mixtures reasonably according to expected relative field fatigue or transverse (thermal) cracking performance trends. Preliminary thresholds for different mixtures in some states have been recommended. Note that all the thresholds apply to lab or plant mixtures with short-term aging, although they were developed based on the analysis of field cores.

35 Table 19. Summary of DCT Validation Results. Test Section No. of Sections Cracking Type Aging Asphalt Mixture Lab to Field Correlation National Pooled Fund Study, Phase I & II 11 Transverse cracking Field core, long-term Superpave, dense- graded, no RAP/RAS R2 is not available, but DCT thresholds were recommended. Database from IL, MN, MO, and WIS 52 Transverse cracking Field core, long-term SMA, dense-graded, Superpave, different RAP/RAS percentages Previous DCT thresholds were validated, although R2 is not available. Illinois Tollway 26 Transverse cracking, block cracking Plant mix, short-term; field core, long-term SMA and dense- graded, different RAP/RAS percentages R2 is not available, but DCT thresholds were recommended for Illinois Tollway mixtures. FHWA ALF 8 Fatigue Cracking Plant mix, short-term Superpave 12.5, HMA/WMA, different binders, different RAP/RAS percentages Poor correlation, R2 = 0.37 FIELD VALIDATION OF IFIT IFIT is another cracking test DOTs are interested in. Field validation efforts in the literature are described below. FHWA ALF Sections: IFIT for Fatigue Cracking Ozer et al. (2018) used the same FHWA ALF plant mixtures described previously under the IDEAL-CT validation to assess the IFIT for fatigue cracking. The IFIT testing was conducted at a test temperature of 25°C with a 50 mm/min loading rate based on AASHTO TP124-16. A minimum of three replicates with 7±0.5 percent air voids specimens were fabricated for each plant mix with short-term aging (Ozer et al. 2018). The number of ALF passes for the first crack observed in each lane are listed in Table 1. The relationship between the flexibility index (FI) values (plant mix lab-molded samples) and the ALF passes is shown in Figure 21. Note that ALF passes for Lanes 2 and 8 were not available. In another study, field cores were recovered from these test lanes when the FHWA ALF testing was completed (Bennert et al. 2019). Due to the thickness of the lifts, the IFIT testing was conducted using the bottom lift of the field cores. This process helped reduce the potential for an aged asphalt gradient at the surface of the asphalt layer that may have created repeatability issues. Figure 22 shows the relationship between the FI values of field cores and the ALF passes.

36 Figure 21. Relationship between FI and ALF Passes (Ozer et al. 2018). Figure 22. Relationship between FI of Field Cores and ALF Passes (Bennert et al. 2019). Illinois Asphalt Overlay Sections: IFIT for Reflective Cracking Al-Qadi et al. (2017) constructed 12 asphalt overlay sections out of nine projects in the Chicago area, including four paved in 2013, two in 2014 (each project had two asphalt mixes), and three in 2015 (one project had two AC mixes). These sections contained either a single surface mix over the entire project or two mixes on a project, but different mixes by directions. Mixtures placed in 2013 and 2015 utilized total-recycle asphalt (TRA), which contains up to 60 percent ABR and 100 percent recycled aggregates. Distress surveys were conducted before construction and each spring, ending in 2017. There were two main families of pavements in this

37 study: (1) those pavements that were to be overlaid or milled down to bare jointed concrete pavement resulting in 2.25 to 3 inches of a new asphalt overlay over the concrete pavement; and (2) the other group of overlaid PCC pavement with much thicker combinations of new and preexisting asphalt overlays, in the range of 5.75 to 8.0 inches. These families were termed “thin” and “thick,” respectively. The thin-pavement family reflected cracks quicker and at higher severities than the thick-pavement family. The traffic speed limits varied from 30 to 55 mph in these studied sections. The two-way average daily traffic (ADT) volumes ranged from 1,700 for a local service road to 22,400 for a major arterial. Table 20 shows the asphalt mixture information for the 12 asphalt overlay sections. The mixtures have ABR ranging from 15 to 60 percent. Table 20. Asphalt Mixtures of Illinois Overlay Sections (Al-Qadi et al. 2017). Section ID Mixture Name Binder Grade RAP (%) RAS (%) ABR (%) Asphalt Content (%) A 26th Street/N50 TRA PG 52-28 51 4.6 60 6.7 B Harrison Street/N50 TRA PG 52-28 53 5.0 56 6.5 C Richards Street/N50 TRA PG 58-28 27 0 37 5.8 D Wolf Road/N70 Mix D PG 58-28 30 0 20 5.9 1S Crawford Ave./N70-30 PG 58-28 9.9 5.0 29 5.7 1N Crawford Ave./N70-15 PG 64-22 4.9 2.5 15 5.6 2E US-52 Section 1/N70-30 PG 58-28 20 3.1 30 5.5 2W US-52 Section 1/N70-30 PG 58-28 34 0 29 6.0 3 US-52 Section 2/N70-TRA PG 52-34 39 5.0 48 6.0 4 US-52 Section 3/N70-TRA PG 52-28 39 5.0 48 6.3 5W Washington Street/N70-30 PG 58-34 20 3.1 30 6.6 5E Washington Street/N70-30 PG 58-34 34 0 30 6.0 Distress survey data were collected on the sections using established distress criteria (Illinois DOT [IDOT] 2012). The rate was determined by normalizing the amount of cracking in 1,000 ln-ft of pavement. The data sets consisted of pre-construction, post-construction, and springtime surveys in 2014, 2015, 2016, and 2017. Major performance differences after the first and second winter were observed. FI values were determined using the plant mixes. The project on Wolf Road (Section D) did not have the plant mix taken for testing, resulting in a lack of FI data. Some other points were further reduced for consideration after exploring potential correlations to transverse cracking distress that could produce meaningful results. Figure 23 shows the relationship between the FI values and the transverse (reflective) cracking survey results. The FI values are consistent with expectations that the higher the FI, the less transverse cracking in the performance data. The data also show that the extent of transverse cracking in projects is closely related to the thin- or thick-pavement family for the projects in this study. Thus, within either the thin- or thick-pavement family, the resulting FI values reflect the amount of transverse cracking. The slope and trends of the relationship indicate that for surface mix, FI values in the 8 to 10 range provide the greatest benefit in reducing transverse cracking. Thus, the FI threshold of 8.0 was proposed to the IDOT.

38 Figure 23. Relationship between FI and Transverse (Reflective) Cracking (Al-Qadi et al. 2017). NCAT Test Track Sections: IFIT for Top-Down Cracking West et al. (2021) used the same asphalt mixtures as those described in the IDEAL-CT validation to assess the IFIT. Table 21 shows the IFIT results based on a minimum of five replicates (West et al. 2021). A higher FI indicates better crack resistance. Overall, the results follow the expected trends within each set sample type and conditioning method. As expected, critical aging causes a substantial decrease in FI results. IDOT currently requires one hour of short-term aging for mixtures containing low absorption aggregates and two hours of short-term aging for mixtures containing high absorption aggregates. Additionally, for surface mixtures only, IDOT uses a long-term aging protocol of three days at 95°C after IFIT specimens are cut and notched. IDOT’s current FI criteria for dense-graded mixtures are a minimum of 8.0 after short-term aging and a minimum of 5.0 after long-term aging. For SMA, the minimum FI is 16.0 after short-term aging and 10.0 after long-term aging. IDOT also has a separate criterion for a 4.75 mm mixture used for crack relief layers. Thus, comparisons of these results with the Illinois criteria must be cautious since the aging procedures are different.

39 Table 21. IFIT Results (FI) of NCAT Test Sections (West et al. 2021). Test Section and Mixture Description LMLC-STOA LMLC-CA PMLC-RH PMLC-CA Avg. COV Avg. COV Avg. COV Avg. COV N1: Control 4.16 23% 0.63 50% 3.58 8% 0.59 51% N2: Ctrl, 5.4% AC, 7% Va 2.24 21% 0.25 76% 1.46 25% 1.38 74% N2: Ctrl, 5.4% AC, 4% Va 2.65 31% 0.10 76% 1.86 13% 0.10 67% N5: Ctrl, 5.1% AC, 7% Va 1.37 13% 0.21 53% 1.34 16% 0.67 93% N5: Ctrl, 5.1% AC, 10% Va 4.02 18% 0.74 34% 2.69 29% 0.80 35% N8: Control + 5% RAS 0.43 44% 0.03 71% 0.39 18% 0.07 68% S5: 35% RAP, PG 58-28 5.21 22% 0.70 30% 6.27 10% 1.79 16% S6: Control, HiMA Binder 14.68 24% 3.43 20% 4.53 6% 3.77 16% S13: Gap-gr., Asphalt-Rubber 15.12 34% 5.15 21% 10.40 42% 4.34 18% The effect of specimen air void content on FI results is counterintuitive, which can be seen by comparing the two sets of results for N2 and N5. For N2, FI results were slightly higher for specimens at 4 percent air voids than 7 percent air voids for STOA and reheated mix samples but lower after critical aging. For N5, FI results were substantially higher for specimens at 10 percent air voids than 7 percent air voids for each sample type and aging condition. Thus, only the results of 7 percent air voids were analyzed for the validation work. Figure 24 shows the bar chart for the FI results of the critically aged plant mix samples. The FI ranking of the mixtures is consistent with the field performance of the test sections. The ANOVA indicated that some mixtures had statistically different FI results. The Games-Howell post hoc pairwise comparison determined which mixtures were statistically different from one another, as indicated by the letters down the middle of the chart. It can be seen from the pairwise comparisons that FI did not statistically distinguish the moderate performing mixtures from the poor performing mixtures due partly to the relatively high variability of some FI results. Also, the mixture from S5, which performed very well on the test track, had FI results that were not statistically grouped with the other well-performing mixtures (i.e., S6 and S13). Setting a preliminary FI criterion between the results for S5 and N2 seems reasonable; therefore, a minimum FI threshold of 1.5 for critically aged PMLC mixtures should provide good resistance to top-down cracking. Figure 25 shows the correlations of FI with the top-down cracking observed on the test track for the four sample preparation and aging condition sets. Each chart shows a strong correlation between the FI and field top-down cracking performance. These results indicate that the FI is a good indicator of top-down cracking resistance.

40 Figure 24. Chart of Statistical Comparisons of FI among Mixtures with Performance Groupings (West et al. 2021). Figure 25. Correlations of FI with Field Performance for the Lab and Plant Samples Subject to Different Aging Conditions (West et al. 2021). Missouri Test Sections: IFIT for Multi-Mode Cracking Field performance data for the 11 selected sections from the Missouri DOT (MoDOT) online Pavement Surface Evaluation and Rating (PASER) system were used in Buttlar’s analysis (Buttlar et al. 2020). Automatic Road Analyzer (ARAN) van video logs were used to delineate thermal cracks from block cracks. PASER scores were extracted from the MoDOT portal. The

41 field sections include those aged 5–16 years in the field. Table 22 presents the field performance measures available for these sections as of 2019. The Missouri climate differs fairly significantly from the northwest to southeast corners of the state, thus affecting pavement temperatures both at the surface and at depth. The field mixtures investigated were non-SMA mixtures and covered a wide range of RAP and RAS content levels, as listed in Table 23. Table 24 shows the FI values of the field cores from the 11 Missouri sections (Buttlar et al. 2020). Table 22. Field Cracking Performance of Missouri Test Sections (Buttlar et al. 2020). Section # Constr. Year PASER Brief Summary Distresses Observed in ARAN Images MO52_1 2010 4.0 Mainly joint reflective cracking US 54_8 2006 5.5 Block cracking developing US50_1 2011 6.5 Very little distress US63_2 2008 4.5 Dense block & thermal cracking US54_7 2003 7.5 Very little distress after 14 years MO 151 2010 4 Dense block & thermal cracking US 36 E 2011 5 Dense block & thermal cracking US 54 E 2010 5 Block cracking developing MO 94 2005 7.8 Very little distress after 14 years MO 6 W 2015 8.6 Very little distress US 61 N 2013 7.9 Very little distress Table 23. Binder and RAP/RAS Information of Missouri Test Sections (Buttlar et al. 2020). Section # Virgin Binder Grade Asphalt Content (%) ABR (%) ABR by RAP (%) ABR by RAS (%) MO52_1 PG 64-22 4.8 33.5 0 33.5 US 54_8 PG 70-22 5.6 8.6 8.6 0 US50_1 PG 64-22 5.0 24.6 24.6 0 US63_2 PG 64-22 5.6 29.9 19.9 10 US54_7 PG 64-22 6.2 0 0 0 MO 151 PG 64-22 4.7 30.6 15.9 14.7 US 36 E PG 64-22 5.1 24.7 24.7 0 US 54 E PG 70-22 5.7 11.8 11.8 0 MO 94 PG 64-22 5.6 0 0 0 MO 6 W PG 58-28 5.9 29.6 29.6 0 US 61 N PG 64-22H 5.3 29.6 29.6 0

42 Table 24. IFIT Results of Missouri Test Sections (Buttlar et al. 2020). Section # FI COV (%) MO52_1 0.6 51.4 US54_8 0.14 80.7 US50_1 1.4 51.6 US63_2 0.36 35.4 US54_7 1.85 37.6 MO151 0.3 80.2 US36 E 0.2 21.1 US54 E 0.6 33.8 MO94 0.8 91.9 MO6 5.4 61.5 US61 0.4 29.2 Figure 26 shows the relationship between the FI and the PASER deterioration rate, with the diameter of the plot points (bubbles) representing the age of the asphalt mixture. As expected, the higher FIs resulted in a lower deterioration rate. It is worth mentioning that except for the MO6 section, all sections yielded FI scores lower than 2.0. Since IFIT is very dependent on mixture aging, the size of the bubbles should be taken into consideration when the results are interpreted. The MO6 section (the blue bubble on the bottom right side of the plot) recorded the highest FI, meaning the cracking potential is expected to be the lowest based on the IFIT cracking assessment. However, this section is the youngest among the studied sections, and the FI might considerably decrease as the section further ages. US54_7, MO94, and US50_1 were the next-best performing sections. The PASER deterioration rates for these sections were relatively low. The correlation between the PASER deterioration rate and FI is shown in Figure 27. Figure 26. FI vs. PASER Deterioration Rate and Aging Years (Buttlar et al. 2020).

43 Figure 27. Correlation between FI and PASER Deterioration Rate (Buttlar et al. 2020). Table 25 summarizes the parameters used to develop the FI threshold. Using the above approach and parameters, the FI thresholds were determined and then adjusted based on practical considerations and stakeholder discussions that relied on a consensus process. The final FI threshold recommendations for Missouri non-SMA mixtures are presented in Table 26. Note that the thresholds apply to lab or plant mixtures with short-term aging, although they were developed based on the analysis of field cores. Table 25. Parameters Used for the FI Threshold Development (Buttlar et al. 2020). Parameter High Criticality (HC) Medium Criticality (MC) Low Criticality (LC) PASER Det. Rate 0.25/year 0.3/year 0.4/year Reliability 95% 87% 68% FI Baseline Score 2.5 1.6 0.8 Aging effect on FI, Surface 400% for all categories Aging effect on FI, Non-surface 300% for all categories

44 Table 26. Recommended FI Thresholds for Mainline and Shoulder, non-SMA Mixtures (Buttlar et al. 2020). Category Position in Pavement Criticality FI Mainline Shoulder a SL H 14 8 b SL M 8 4 c SL L 4 3 d NSL H 7 5 e NSL M 5 2 f NSL L 2 1 Note: SL = Surface Lift; NSL = Non-surface Lift; H = High; M = Medium; L = Low. Summary of IFIT Validation Table 27 provides a summary of the IFIT validation results. The results indicate that the IFIT correlates well with field cracking performance, including fatigue cracking, reflective cracking, and top-down cracking. Thresholds for different mixtures in some states (e.g., Missouri non-SMA mixtures [Table 26]) have been recommended. IDOT’s current FI criteria for dense- graded mixtures are a minimum of 8.0 after short-term aging and a minimum of 5.0 after long- term aging. For SMA, the minimum FI is 16.0 after short-term aging and 10.0 after long-term aging. IDOT also has a separate criterion for a 4.75 mm mixture used for crack relief layers. Additionally, the NCAT study indicated that a minimum FI threshold of 1.5 for critically aged PMLC mixtures is adequate to have a good resistance to top -down cracking at the test track. Table 27. Summary of IFIT Validation Results. Test Section No. of Sections Cracking Type Aging Asphalt Mixture Lab to Field Correlation FHWA ALF 8 Fatigue cracking Plant mix, Short- term, Field core, Long-term Superpave 12.5, HMA/WMA, different binders, different RAP/RAS percentages Fair/good correlation R2: 0.68–0.83 Illinois Asphalt Overlays 12 Transverse (reflective) cracking Plant mix, Short-term Dense-graded, different binders, different RAP/RAS percentages Fair/good correlation R2: 0.59–1.0; FI thresholds were recommended. NCAT Test Track, Top-Down Cracking Experiment 7 Top-Down cracking STOAa, CAb Superpave 9.5 or gap- graded, different binders, different RAP/RAS percentages Good correlation, R2: 0.76–0.89 Missouri 11 Multi-Mode cracking Field core, Long-term Non-SMA, different RAP/RAS percentages Poor correlation R2 = 0.20 a STOA according to AASHTO R 30. b STOA plus an additional eight hours of aging at 135°C in a loose mix condition.

45 FIELD VALIDATION OF OT The OT has been adopted by the Texas Department of Transportation (TxDOT) and New Jersey Department of Transportation (NJDOT). Field validation efforts in the literature are described below. FHWA ALF Sections: OT for Fatigue Cracking Ozer et al. (2018) used the same FHWA ALF plant mixes as described previously under IDEAL-CT validation to assess the OT for fatigue cracking. Ozer et al. (2018) fabricated OT specimens for each plant mix with short-term aging. The test was conducted by following Tex-248-F and using the asphalt mixture performance test (AMPT) with a deviation from the standard test temperature. Tex-248-F specifies a test temperature of 25°C (77°F); however, the ALF test sections were tested at 20°C (68°F). The OT testing was conducted at 20°C (68°F) to match the test section temperature. Test specimens were fabricated to be 76 mm (3 inch) wide by 38 mm (1.5 inch) thick and 150 mm (6 inch) in length. The loading was a cyclic triangular waveform to a constant maximum displacement of 0.6 mm (0.025 inch). The sliding block reaches the maximum displacement and returns to its initial position in 10 s (1 cycle). The test is run until a 93 percent reduction of the maximum load occurs when measured from the first opening cycle. If a 93 percent reduction is not reached within 1200 cycles, the machine automatically turns off. According to the standard method of calculating the number of cycles to failure, only one of the asphalt mixtures (Lane 3) achieved a 93 percent reduction in load. All the other lanes went 1200 cycles before the machine turned off. Three other failure criteria were used to check sensitivity to the change in recycled content and binder grade, as presented in Figure 28. The criteria are defined as follows: • Criterion 1 is defined as cycles to failure corresponding to the horizontal asymptote on a plot of percent change in load reduction with change in cycles. • Criterion 2 is defined as cycles to failure corresponding to the horizontal asymptote on a plot of percent reduction of load with total cycles. • Criterion 3 is the number of cycles to failure at 80 percent instead of 93 percent. Criteria 1 and 3 showed a reasonable correlation between the OT cycles and the ALF passes, while Criterion 2 did not show any meaningful trend. The number of ALF passes for the first crack observed in each lane are listed in Table 1. The relationship between the OT cycles (plant mix lab-molded samples) and the ALF passes is shown in Figure 28. Note that ALF passes for Lanes 2 and 8 were not available.

46 Figure 28. Relationship between OT and FHWA ALF Passes (Ozer et al. 2018). Additionally, Bennert et al. (2019) tested field cores recovered from these test lanes when the FHWA ALF study was completed. The OT testing was conducted on the bottom lift of the field cores to reduce the potential for an aged asphalt gradient at the surface of the asphalt layer. Figure 29 shows the relationship between the OT (field cores) and the ALF passes. Figure 29. Relationship between OT (Field Cores) and ALF Cycles (Bennert et al. 2019).

47 NCAT Test Track Sections: OT for Top-Down Cracking West et al. (2021) used the same asphalt mixtures as those described in the IDEAL-CT validation to assess the OT. Table 28 shows the OT results based on a minimum of four replicates (West et al. 2021). For the parameter crack progression rate β, a lower number indicates better cracking resistance. TxDOT recently established a preliminary balanced mix design (BMD) criterion for a maximum cracking progression rate (i.e., β) of 0.45 applicable to most mix types, including SMA, Superpave, and other dense-graded mixtures. A lower maximum criterion of 0.40 has been proposed for crack attenuating mixtures (CAM) and thin overlay mixtures (TOM). These preliminary criteria apply to short-term conditioned, lab- produced mixtures and reheated plant mix samples. Table 28. OT Results (β) of NCAT Test Sections (West et al. 2021). Test Section and Mixture Description LMLC-STOA LMLC-CA PMLC-RH PMLC-CA Avg. COV Avg. COV Avg. COV Avg. COV N1: Control 1.00 9% 2.34 29% 0.88 32% 2.08 16% N2: Ctrl, 5.4% AC, 4% Va 0.84 28% 2.04 35% 0.60 16% 2.03 11% N5: Ctrl, 5.1% AC, 10% Va 0.90 25% 2.38 20% 0.85 7% 2.96 11% N8: Control + 5% RAS 2.31 22% 3.25 5% 3.54 10% 3.43 4% S5: 35% RAP, PG 58-28 0.55 12% 2.04 19% 0.60 14% 1.54 22% S6: Control, HiMA Binder 0.42 3% 0.89 22% 0.95 38% 1.07 13% S13: Gap-gr., Asphalt- Rubber 0.40 20% 0.57 13% 0.32 2% 0.48 9% Table 28 indicates that the general trends are logical. Within each set of mix sample type and aging conditions, the β for mix N8 is the highest, and the β for mix S13 is the lowest. For each mixture, the β increased after critical aging, except for the plant mix samples (N8). Figure 30 shows the bar chart for the OT β results for the critically aged plant mix samples. In the figure, OT-TX β was used to differentiate from OT-NCAT β (West et al. 2021). The OT β parameter does a very good job distinguishing the mixtures’ cracking resistance. For this study, a β value of about 1.75 is a good criterion to separate excellent cracking resistance (i.e., little to no cracking on the test track) from moderate cracking resistance of the critically aged PMLC mixture. The ANOVA indicated that the mixtures had a statistically significant effect on the β parameter. The Games-Howell post hoc pairwise comparison was then conducted to determine which mixtures were statistically different from one another. The letters A, B, C, D, and E down the middle of the chart indicate the results of the Games-Howell comparisons. Mixtures that do not share a letter are significantly different at the 95 percent confidence level. In this analysis, the gap-graded asphalt-rubber mix in S13 was superior to all other mixtures. The result indicates that the OT β can be used to discern the cracking resistance of asphalt mixtures. Figure 31 shows the correlations of OT β with the top-down cracking observed on the test track for the four sample preparation and aging condition sets. Each chart shows a strong correlation between the OT β and field top-down cracking performance. These results indicate that OT β is a good indicator of top-down cracking resistance.

48 Figure 30. Chart of Statistical Comparisons of OT β among Mixtures with Performance Groupings (West et al. 2021). Figure 31. Correlations of OT β with Field Performance for the Lab and Plant Samples Subject to Different Aging Conditions (West et al. 2021). Texas In-Service Road Sections: OT for Fatigue Cracking Field validation was conducted using distress surveys of 17 pavement sections monitored and documented under TxDOT Research Project 0-6658, Collection of Materials and Performance Data for Texas Flexible Pavements and Overlays. Most pavement sections are overlaid sections (Garcia et al. 2017). Distress surveys were conducted at nominally six-month intervals to document the conditions and performance of these sections. During the distress surveys, four different cracking distresses were documented: alligator, block, transverse, and longitudinal cracking. The distress severity of each field section was then ranked either low, moderate, or high. The performance of these field section mixtures was divided into good, satisfactory, and poor categories based on their service lives, distress severities, pavement structures, traffic, and climate conditions. This validation work did not provide detailed

49 information about the pavement structure and the location (or climate) for each test section. Table 29 lists the test sections and the corresponding performance categories. The traffic and mix information of these sections is shown in Table 30. The plant mixtures from these test sections were sampled during the construction stage (Garcia et al. 2017). Three replicates of OT specimens were fabricated in the lab for each test section. The air voids of these lab specimens were 7±1.0 percent. Field cores were collected around 5 years after construction. The performance of the sections and the OT result of the lab specimens (initial) and field cores are shown in Figure 32. Error bars for the initial results show the standard deviations for the OT tests of lab specimens. The data labels provide the average relative densities of the field cores. Most field cores had a relative density between 95 percent and 97 percent, especially for the well-performing sections. The relative densities of the field cores from the satisfactory and poor performing sections varied substantially. Figure 32a shows that almost all the good performing sections except Section 5 have a number of cycles larger than the proposed limit (300). Similarly, all sections that performed poorly have a number of cycles smaller than the proposed limit. The number of cycles was 1000 for field cores of Sections 6, 2, 3, and 16 because if a 93 percent reduction was not reached within 1000 cycles, the machine automatically turned off. The OT result difference between the lab specimens and the field cores may be partially due to the asphalt layers’ oxidation (aging) and densification. Figure 32b shows that almost all the good performing sections except Section 5 had a crack progression rate β smaller than the proposed limit (0.45). Similarly, all sections that performed poorly had a β larger than the proposed limit. Although for the well-performing sections the results from the lab specimens and the field cores are similar, there are differences for the poorly performing sections. These differences may be partially due to aging and densification.

50 Table 29. Texas Field Test Sections (Garcia et al. 2017). Section ID Age (Months) Type of Cracking Distress General Performance Alligator Block Transverse Longitudinal 1 44 None None None None Good 2 44 None None None None Good 3 43 None None None None Good 4 36 None None None None Good 5 44 None None None None Good 6 43 None None None None Good 7 31 None None Low None Satisfactory 8 31 None None Low None Poor 9 36 None None Moderate None Poor 10 31 Low None Low None Poor 11 49 Moderate None Low None Satisfactory 12 58 Low None Moderate None Poor 13 59 Low None Low Low Poor 14 59 Moderate None Low Low Poor 15 47 None None None None Good 16 36 Low None Low None Satisfactory 17 36 None None Low None Satisfactory

51 Table 30. Traffic and Mixture Information of Texas Sections (Garcia et al. 2017). Section ID Construction Year ADT Truck Volume, % Mix Type Binder Grade RAP % RAS % 1 2011 3007 5.5 SMA-D PG 70-28 20 0 2 2011 612 — SMA-D PG 70-28 0 0 3 2011 4837 3.2 SMA-D PG 70-28 10 0 4 2012 2103 22.3 SMA-D — 23 0 5 2011 4600 17.9 SMA-D PG 70-28 0 0 6 2012 337 2.0 SMA-D — 18 0 7 2013 579 14.3 CMHB-F PG 64-22 20 0 8 2013 372 12.8 CMHB-F PG 64-22 20 0 9 2013 343 16.0 Type-C PG 64-22 20 0 10 2013 — — CMHB-F PG 70-22 20 0 11 2012 3288 1.0 Type-C PG 64-22 20 0 12 2011 1545 4.2 Type-C PG 64-22 20 0 13 2011 4127 7.8 Type-C PG 64-22 20 0 14 2012 4270 4.0 Type-C PG 64-23 20 0 15 2012 929 12.0 TOM PG 76-22 0 0 16 2013 3952 13.9 TOM PG 76-22 0 0 17 2013 2620 4.4 TOM PG 76-22 0 0

52 (a) (b) Figure 32. Field Performance vs. OT Results: (a) Number of Cycles and (b) Crack Progression Rate β (Garcia et al. 2017). Summary of OT Validation Table 31 provides a summary of the OT validation results. The results indicated that the OT correlates well with field cracking performance, including fatigue cracking, top-down cracking, and other types of cracking. The β parameter is a good indicator of a mixture’s cracking resistance. It is more discerning and more repeatable than cycles to failure. The effect of air voids on test results is not counterintuitive, as with some other cracking tests. A β value of about 1.75 appears to be a good criterion to separate excellent cracking resistance (i.e., little to no cracking on the NCAT Test Track) from moderate cracking resistance of the critically aged PMLC results. TxDOT recently established a preliminary BMD criterion for the maximum cracking progression rate (i.e., β) of 0.45 applicable to most mix types, including SMA, Superpave, and other dense-graded mixtures. A lower maximum criterion of 0.40 has been proposed for CAM and TOM. These preliminary criteria apply to short-term conditioned, lab-produced mix and reheated plant mix samples.

53 Table 31. Summary of OT Validation. Test Section No. of Sections Cracking Type Aging Asphalt Mixture Lab to Field Correlation Texas In-Service Road 17 Transverse, alligator, and longitudinal cracking Plant mix, short-term; field core, long-term SMA, Dense-Graded, CMHB, Different Binders, Different RAP Percentages R2 is not available, but thresholds were recommended. FHWA ALF 8 Fatigue cracking Plant mix, short-term Superpave 12.5, HMA/WMA, Different Binders, Different RAP/RAS Percentages Fair correlation R2 : 0.67–0.76. NCAT Test Track, Top- Down Cracking 7 Top-down cracking STOAa, CAb Superpave 9.5 or Gap- Graded, Different Binders, Different RAP/RAS Percentages Good correlation R2: 0.76–0.91. a STOA according to AASHTO R 30. b STOA plus an additional eight hours of aging at 135°C in a loose mix condition. SUMMARY AND CONCLUSIONS This chapter reviewed and documented the past field validation efforts of the four laboratory cracking tests: IDEAL-CT, DCT, IFIT, and OT. Table 32 presents an overall summary of the field validation efforts. Based on the information presented in this chapter, the following observations and conclusions are offered: • Overall, all four cracking tests have been validated to some extent. Among these tests, the IDEAL-CT, IFIT, and OT have strong or good relationships with traffic-related cracking, such as fatigue, reflective, and top-down cracking, while the DCT ties more closely to thermal cracking. This observation is important since the desire is to test asphalt mixtures for general cracking resistance rather than have a separate test for each type of cracking. Consequently, the number of field test sections required can be significantly reduced. • IDEAL-CT and IFIT are counterintuitively sensitive to air voids. Thus, attention to specimen air voids should be exercised when validating these cracking tests. • Most DCT validation and threshold development efforts were based on long-term aged field cores. To circumvent the impracticalities associated with requiring long- term aging of mixtures in the lab, the effect of aging was calibrated into the DCT thresholds for short-term aged and lab-produced specimens.

54 Table 32. Summary of Validation Results of the Four Cracking Tests. Test Test Sections Cracking Type Materials and Aging Condition Validation Result IDEAL-CT FHWA ALF Oklahoma LTPP-SPS10 Texas SH 15 Texas US 62 MnROAD 2008 NCAT Test Track Fatigue, reflective, top- down, and thermal cracking; both traffic and thermal related Plant mixes with short-term or critical aging Good correlation with traffic- related cracking types with high R2; thresholds recommended DCT FHWA ALF Pooled Fund Study— Thermal Cracking Database (IL, MN, MO, and WIS) Illinois Tollway Mainly transverse (thermal or reflective) cracking; more thermal related Mainly field cores with long-term aging Fair correlation, but most R2 not available; thresholds recommended for Missouri non- SMA and Illinois Tollway mixtures IFIT FHWA ALF Illinois Overlay Sections NCAT Test Track Missouri Field Sections Fatigue, reflective, top- down, and thermal cracking; both traffic and thermal related Plant mixes with short-term or critical aging; Field core with long-term aging Good correlation with traffic- related cracking types with relatively high R2; thresholds recommended OT FHWA ALF NCAT Test Track Texas In-Service Roads Fatigue, reflective, top- down, and thermal cracking; both traffic and thermal related Mainly plant mixes with short-term or critical aging Good correlation with traffic- related cracking with high R2; thresholds recommended

Next: Chapter 3. Assessment of the Availability of Materials and Performance Data of Field Sections Identified in NCHRP 09-57 »
Ruggedness of Laboratory Tests to Assess Cracking Resistance of Asphalt Mixtures Get This Book
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 Ruggedness of Laboratory Tests to Assess Cracking Resistance of Asphalt Mixtures
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Cracking and durability issues of asphalt pavements have been primary concerns of departments of transportation the last two decades. Several modes of asphalt pavement cracking exist—fatigue, top-down, reflective, and thermal—and all are influenced by thermal loading, traffic loading, or a combination of both.

NCHRP Web-Only Document 389: Ruggedness of Laboratory Tests to Assess Cracking Resistance of Asphalt Mixtures, from TRB's National Cooperative Highway Research Program, documents existing field validation efforts for these four modes of cracking.

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