Ruggedness of Laboratory Tests for Asphalt Mixture Cracking Resistance (2022) / Chapter Skim
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4 Research Approach Introduction The research was conducted in two phases. Phase I included finalizing the selection of eight cracking tests for the ruggedness testing, consisting of the seven candidate cracking tests originating from NCHRP 09-57 and one new cracking test developed after the conclusion of NCHRP 09-57, and developing an experimental design of the ruggedness testing for all selected cracking tests following ASTM E1169.
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Research Approach 5 number of OT cycles to failure, the better the cracking resistance of asphalt mixtures. However, the number of cycles is a highly variable cracking parameter.
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6 Ruggedness of Laboratory Tests for Asphalt Mixture Cracking Resistance (a) Draw middle line.
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Research Approach 7 AASHTO T 321-17: BBF The BBF test has been used to determine the fatigue life of asphalt mixtures for more than a half century. Fatigue failure has been traditionally defined as the load cycle at which the specimen exhibits a 50% reduction in stiffness relative to the initial value.
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8 Ruggedness of Laboratory Tests for Asphalt Mixture Cracking Resistance fundamental relationship between damage and material integrity can be used to analyze fatigue characteristics of asphalt mixtures and to predict fatigue behavior when combined with failure criterion, linear viscoelastic properties of asphalt mixtures, and pavement response models. This test was discussed in the 2015 workshop of NCHRP 09-57, but it was not selected.
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Research Approach 9 Indirect Tensile Nflex Factor Test West et al.
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10 Ruggedness of Laboratory Tests for Asphalt Mixture Cracking Resistance IDT Specimen DimensionsIDT Specimen and Fixture Figure 6. IDT test specimen and configuration (dimensions in millimeters)
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Research Approach 11 Figure 8. Correlation between the Nflex factor and fatigue cracking of FHWA-ALF (West et al., 2017)
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12 Ruggedness of Laboratory Tests for Asphalt Mixture Cracking Resistance (coring/cutting/gluing) , AMPT setup, and a typical test result.
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Test Standard Test Configuration Cracking Parameter Test Temperature No. of Specimens Specimen Preparation and Instrumentation Test Variability Equipment Cost Sample Preparation, Testing, and Analysis Time Adoption by States/FHWA DCT (monotonic test)
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14 Ruggedness of Laboratory Tests for Asphalt Mixture Cracking Resistance design with two levels, seven factors, and eight replicated runs. In addition, when selecting the test factors and their high and low levels, the experimental design for each cracking test described in the NCHRP 09-57 final report served as the basis for this research.
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Research Approach 15 SCB-LT The SCB-LT, in general, is a monotonic test, but it involves eight loading-unloading steps before the actual monotonic loading until failure. Unlike the DCT, specimen preparation for the SCB-LT does not require drilling two holes but rather splitting a circular specimen into two SCB specimens (Figure 11)
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16 Ruggedness of Laboratory Tests for Asphalt Mixture Cracking Resistance SCB-FI The SCB-FI test is also a monotonic test. The specimen preparation for the SCB-FI is like that for the SCB-LT test except for the specimen thickness (Figure 12)
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Research Approach 17 diameter and 120-mm height is cut into two equal circular test samples 57 mm thick. ese samples are cut along the central axis into two equal semicircular samples.
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18 Ruggedness of Laboratory Tests for Asphalt Mixture Cracking Resistance IDEAL-CT The IDEAL-CT is a simple monotonic test. The specimen preparation (Figure 14)
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Research Approach 19 BBF The BBF test is a cyclic fatigue test that has been used to characterize fatigue performance of asphalt mixtures for more than 6 decades. Preparing one beam specimen (Figure 16)
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20 Ruggedness of Laboratory Tests for Asphalt Mixture Cracking Resistance No. Factor Standard Value High Level Low Level 1 Specimen height 50 mm 56 mm (Std.+6 mm)
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Research Approach 21 Selection of Test Materials and Specimen Preparation Test Material Selection Asphalt mixtures are complex and may be composed of asphalt binders, aggregates, RAP/RAS, rejuvenators, and additives. The bulk properties (e.g., dynamic modulus and flow number)
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22 Ruggedness of Laboratory Tests for Asphalt Mixture Cracking Resistance DCT Specimen Preparation Sixteen DCT specimens were prepared for each of the three mixtures -- 12.5-mm SMA, 12.5-mm Superpave, and 9.5-mm Superpave -- following the ASTM D7313-20 guidelines and the high and low levels of each ruggedness factor (Table 3)
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Research Approach 23 and the high and low levels of each ruggedness factor (Table 7)
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24 Ruggedness of Laboratory Tests for Asphalt Mixture Cracking Resistance A replicated eight-run process (a total of 16 runs) is most often used to evaluate the ruggedness of asphalt mixture property tests.
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Research Approach 25 for Conducting Ruggedness Tests and developed experimental designs for the ruggedness evaluation of the eight cracking tests. Specifically, a balanced PB fractional factorial design with two levels, seven factors, and eight replicated runs (a total of 16 runs)
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