FHWA > HfL > Technology Partnerships > ABCD Final Report > Asphalt Binder Cracking Device Interlaboratory Study 
Asphalt Binder Cracking Device to Reduce LowTemperature Asphalt Pavement Cracking: Final ReportAsphalt Binder Cracking Device Interlaboratory StudyFor the ABCD ILS, each laboratory received instructions and the ABCD test procedure to review before receiving the ABCD unit and binder samples. After a few practice tests, each laboratory performed 3 ABCD runs of 4 specimens each (a total of 12 specimens) on each of the 3 binder grades. Average ABCD cracking temperature and strain jump for each binder and each laboratory are presented in tables 3 and 4 and figures 3 and 4. ABCD strain jump (e) at fracture may be converted into the fracture stress of the asphalt binder (σ_{ƒ}) as follows: σ_{ƒ} = (K) ε•E_{ABCD}•A_{ABCD}/A_{binder} where
To use the ABCD for accurate strength measurement, each ring should be calibrated for loadstrain relationship. The ABCD rings used in this ILS were not calibrated. The precision of ABCD strain jump results may be improved when calibrated ABCD rings are used. For easy comparison, the Yaxis scales of figures 3 and 4 are kept the same for all three binders. Before determining the precision of the test, ASTM C802 requires the operator to identify and remove erratic data by plotting variance versus lab, as shown in figures 5 and 6. Even though Lab 1 (EZ Asphalt laboratory) was the only laboratory with significant prior experience with ABCD testing, many labs produced lower variance for the ABCD test (meaning the results of three runs of one sample are similar). There are quite few noticeably large variance values. However, it is not clear if they are erratic data. Since the number of participating laboratories (23) was significantly larger than the recommended minimum (10), the effects of few data with the large variance values could be insignificant. Data analysis was performed without removing these data, and the precision estimates of ABCD test results would be conservative ones. The statistical summary of the ABCD ILS results is presented in table 5. The ABCD cracking temperatures of three binders were significantly lower than the PG lowtemperature grade since ABCD tests evaluated the lowtemperature cracking potential of asphalt binder only. The addition of mineral aggregates in the asphalt binder would raise the cracking temperature. For all three binders, the withinlab variances of the ABCD cracking temperatures were similar and independent of the cracking temperature. The betweenlab variance for the mediumstiffness binder is lowest (s^{2} = 1.19), followed by the lowstiffness binder (s^{2} = 1.87) and the highstiffness binder (s^{2} = 2.58). The lowstiffness binder seemed to deform easily during the trimming, transportation, and handling steps, resulting in larger variances than the mediumstiffness binder. The highstiffness binder was extremely stiff at room temperature, making trimming unusually difficult and contributing to the large betweenlab variance. Two SBSmodified binders (PG 7028 and PG 7622) exhibited much larger strain jump than the unmodified highstiffness binder (PG 88+6). The fracture strengths of the low, medium, and highstiffness binders were estimated to be 6.5 MPa (943 psi), 6.3 MPa (914 psi), and 3.3 MPa (479 psi), respectively. The withinlab and the betweenlab variances of the strain jump seemed larger for the binders with a larger strain jump. The SBSmodified binders, which showed about twicelarger strain jump than the unmodified binder, also had twice or more withinlab and betweenlab variances. The precision estimates of ABCD tests are given in table 6. When a single operator runs the ABCD test twice on the same sample, the acceptable range of two test results should be less than 2.69 ºC (4.84 ºF), 15.50 με, and 2.43 MPa (352.4 psi), for the ABCD cracking temperature, strain jump, and fracture strength, respectively. When two different operators at two different laboratories perform ABCD tests on the same sample, the acceptable range of two test results should be less than 3.85 ºC (6.93 ºF), 20.39 με, and 3.20 MPa (464.1 psi) for the ABCD cracking temperature, strain jump, and fracture strength, respectively.
Figure 3. ABCD ILS Results: Average ABCD cracking temperatures. Figure 4. ABCD ILS Results: Average strain jump. Figure 5. ABCD ILS Results: Withinlab variance of ABCD cracking temperature. Figure 6. ABCD ILS Results: Withinlab variance of strain jump.
^{a}These values represent the 1S and D2S limits described in ASTM Practice C 670. PDF files can be viewed with the Acrobat® Reader®

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Updated: 09/02/2011 