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Ruggedness of Laboratory Tests to Assess Cracking Resistance of Asphalt Mixtures (2023)

Chapter: Chapter 5. Conclusions and Recommendations

« Previous: Chapter 4. Identification of Alternative Field Sections and Recommendations for Validating Cracking Tests
Page 87
Suggested Citation:"Chapter 5. Conclusions and Recommendations." 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 87
Page 88
Suggested Citation:"Chapter 5. Conclusions and Recommendations." 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 88

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87 CHAPTER 5. CONCLUSIONS AND RECOMMENDATIONS This chapter presents the research team’s conclusions, recommendations, and future research suggestions. CONCLUSIONS Based on the information presented in this report, the research team offers the following conclusions: • A significant amount of field validation work has been done on the four laboratory cracking tests: IDEAL-CT, DCT, IFIT, and OT. Overall, 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 is tied more closely to thermal cracking. This observation is critical for future field validation of cracking tests. A test once validated for traffic-related cracking (e.g., fatigue cracking) is applicable to other traffic-related cracking (e.g., reflective cracking). Consequently, only two types of field sections—one for traffic-related cracking and the other for thermal cracking—are needed. This finding significantly reduces the number of field sections required for validating cracking tests. • For all nine MnROAD field sections, the performance data (transverse cracking and fatigue cracking), climate, pavement structure, traffic, and plant mixes are available, but raw materials for the nine sections are not available. This situation is also problematic for most of the 40 LTPP field sections. After a thorough review process, 12 LTPP field sections were identified that have adequate raw materials available for validating laboratory cracking tests. • After incorporating the LTPP SPS10 sections, a total of 36 alternative field sections were identified in this study. For the 36 alternative field sections, the performance data (fatigue, top-down, and transverse cracking), pavement structure, climate, traffic, raw materials, and plant mixtures are all available. • Going forward, it is important to note that without the original 12 and 36 alternative LTPP sections, this work would not be possible. Thus, future field trials should provide for adequate materials storage, both in terms of volume and material conditions. Likewise, it is important for agencies to consider long-term performance data, including traffic, climate, pavement structure, and pavement condition ratings. RECOMMENDATIONS Based on the assembled information, the research team makes the following recommendations: • Candidate field sections: A total of 48 candidate field sections, including the originally and newly identified field sections, are recommended. The sections listed in Table 56 are for validating traffic-related cracking tests, and the sections in Table 57 are for thermal cracking tests. The 48 candidate field test sections have all the attributes needed for validating the cracking tests. Furthermore, they are well dispersed around the United States in different climate zones under different traffic conditions.

88 • Candidate cracking tests: The three levels of laboratory cracking tests presented in Table 58 for field validation, depending upon available funding, are still valid to provide a path forward for field validation. • Steps for validating candidate cracking tests: The goal of validating candidate cracking tests is twofold: (1) to finalize laboratory cracking tests for traffic-related cracking and thermal cracking, respectively, and (2) to establish corresponding performance-related acceptance criteria. A three-step, hybrid validation approach described in Chapter 4 is recommended: collection of asphalt materials, PPLC specimens for validation, and LPLC specimens for the development of acceptance criteria. • National effort to catalog state activities where test sites and test sections are being constructed: It is fortunate for this research effort that the LTPP SPS10 sites are available to provide the opportunity for this validation effort. However, that function was not their intended use, and eventually a sufficient number of LTPP sites will not be available to perform research such as the validation of other cracking tests or models. Information on pavement performance, structural design, asphalt mixture components, traffic, climate, etc., should be made available to agencies interested in long-term behavior of pavement structures. FUTURE RESEARCH After the completion of ruggedness evaluation, assessment of availability of materials and performance data of existing field sections, and identification of alternative field sections, the next step is to validate the traffic-related cracking tests and thermal cracking tests using the candidate field sections recommended from this study. Additionally, laboratory round-robin tests should be conducted to establish precision and bias after the field validation effort.

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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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