Field Validation of Laboratory Tests to Assess Cracking Resistance of Asphalt Mixtures: An Experimental Design (2016) / Chapter Skim
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NATIONAL COOPERATIVE HIGHWAY RESEARCH PROGRAM Responsible Senior Program Officer: Edward T Harrigan August 2016 C o n t e n t s Background, 1 objective, 1 Research Approach, 1 selection of Asphalt Cracking tests, 2 Refinement of the selected Cracking tests, 9 ILs to Define Precision of the selected Cracking tests, 12 experimental Design for Field Validation of the selected Cracking tests, 13 summary, 25 FIeLD VALIDAtIon oF LABoRAtoRy tests to Assess CRACkIng ResIstAnCe oF AsPhALt MIxtuRes: An exPeRIMentAL DesIgn This digest summarizes key findings of research conducted in NCHRP Project 09-57, "Experimental Design for Field Validation of Laboratory Tests to Assess Cracking Resistance of Asphalt Mixtures," by the Texas A&M Transportation Institute, Texas A&M University, College Station, Texas.
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2the webinars, (4) developing a cracking test reference booklet tailored for the workshop participants, and (5)
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3• Test variability: Cracking tests based on monotonic loading [e.g., indirect tension (IDT) , semi-circular bend (SCB)
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4IDT Low- temperature cracking AASHTO T322: Dt and tensile strength test (monotonic tests)
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5IDT Low- temperature cracking AASHTO T322: Dt and tensile strength test (monotonic tests)
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6S-VECD Bottom-up fatigue and top-down cracking AASHTO TP107 (cyclic tests)
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7S-VECD Bottom-up fatigue and top-down cracking AASHTO TP107 (cyclic tests)
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8and the modified Overlay test for top-down cracking. Thus, a total of 12 cracking tests, as categorized in Table 2, were discussed at the workshop.
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9ReFIneMent oF the seLeCteD CRACkIng tests Ruggedness testing The main purpose of the proposed ruggedness testing is to identify those factors that significantly influence the cracking resistance measurements of each specific cracking test method and to estimate how closely these factors need to be controlled. Basically, the ruggedness test is a sensitivity test on variables of a test method rather than the materials under test.
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10 table 4 Proposed ruggedness testing variables for selected cracking tests. Test Name Test Standard Test Configuration Specimen Geometry Test Variability Ruggedness Testing Variables Standard Factor High Level Low Level Tolerance DCT ASTM D7313 (monotonic test)
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11 table 4 Proposed ruggedness testing variables for selected cracking tests. Test Name Test Standard Test Configuration Specimen Geometry Test Variability Ruggedness Testing Variables Standard Factor High Level Low Level Tolerance DCT ASTM D7313 (monotonic test)
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12 of homogeneous material prepared for the ILS. The ILS plan summarized below and described in detail in Chapter 3 of the project final report was developed following ASTM E691-14: Standard Practice for Conducting an Interlaboratory Study to Determine the Precision of a Test Method.
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13 mary of specific experimental designs for thermal, reflection, bottom-up fatigue, and top-down cracking, respectively. Chapter 4 of the project final report proposes two D-optimal experiment designs (i.e., Design 1 and Design 2)
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14 A full factorial design with these three factors consists of 24 factor-level combinations, given in Table 7. D-optimal designs select a subset of runs from Table 7, maximizing the D-efficiency (i.e., minimizing the generalized variance of main effects' estimates)
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15 minimized) among all the designs that are subject to the same constraints.
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16 table 10 Four types of field experimental test facilities in the United States. Items APT Full-Scale Test Tracks Full-Scale Test Roads In-Service Pavements Examples FHWA-ALF, LouisianaALF, CalTrans-heavy vehicle simulator (HVS)
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17 date the capability of the selected thermal cracking tests for differentiating the performance of these experimental test sections. More test sections lead to a more precise estimation of the factor effects.
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18 and summarizes an experimental design for field validation of reflection cracking tests. Reflection Cracking Mechanism and Influential Factors Reflection cracking arises from the movement of cracked or jointed substrate below the pavement surface layer, which causes cracks to be transmitted through the surface layer.
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19 be located below 40°N to avoid confounding with thermal cracking. A total of three overlay mixes and two different overlay thicknesses are considered in the experimental matrix.
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20 experimental Design for Validating Bottom-up Fatigue Cracking tests This section briefly discusses bottom-up fatigue cracking mechanisms and associated influential factors and summarizes an experimental design for field validation of tests for bottom-up fatigue cracking. Bottom-Up Fatigue Cracking Mechanism and Influential Factors Bottom-up fatigue cracking is the result of the application of repetitive traffic loads to a pavement surface, initiating a crack where a critical tensile strain occurs at the bottom of the asphalt layer; continued traffic loading eventually causes these cracks to propagate upward through the entire asphalt layer.
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21 table 17 Field experimental design factors identified for bottom-up fatigue cracking. Key Factor Variation Level Climate 1)
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22 and documented all potential existing field test sections for validating top-down cracking tests in this section as well. Top-Down Cracking Mechanism and Influential Factors The mechanisms for top-down cracking are not as well defined as for the other types of cracking discussed.
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23 lower solar radiation and lower temperatures. There is a decreasing gradient to aging with layer depth, which consequently reduces crack resistance and makes it easier for top-down cracking to occur.
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24 will likely take place on sections with high overall stiffness. With this in mind, it is assumed that topdown cracking sections will consist of thick asphalt sections [likely 150 mm (6 inches)
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25 cracking tests. This digest first summarized the cracking test selection process and identified the cracking tests selected for field validation.
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Transportation Research Board 500 Fifth Street, NW Washington, DC 20001 These digests are issued in order to increase awareness of research results emanating from projects in the Cooperative Research Programs (CRP)
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