Asphalt Binder Cracking Device to Reduce Low-Temperature Asphalt Pavement Cracking
For the ABCD ILS, data from 23 laboratories were used. With very limited experience with the ABCD equipment and test procedure, all participating laboratories were able to complete the ABCD ILS without major difficulty. Ten laboratories also provided data for the BBR Critical Temperature ILS.
The precision estimates for the ABCD test and the BBR critical temperature were determined and are presented in tables 6 and 11, respectively. The standard deviations of the ABCD cracking temperature, strain jump, and fracture strength for the single-operator ABCD tests were 0.95 °C (1.71 °F), 5.48 με, and 0.86 MPa (125 psi), respectively. The standard deviations of the ABCD cracking temperature, strain jump, and fracture strength for the multilaboratory ABCD tests were 1.36 °C (2.45 °F), 7.21 με, and 1.13 MPa (163.9 psi), respectively. The standard deviations of the BBR critical temperature for single-operator and multilaboratory testing were 0.44 °C (0.79 °F) and 0.75 °C (1.35 °F), respectively, when the critical temperatures were determined by interpolation. When extrapolation was used, the standard deviations of the BBR critical temperature for single-operator and multilaboratory tests were 0.68 °C (1.22 °F) and 1.25 °C (2.25 °F), respectively. Interpolation is the common case in BBR testing where the test results from two adjacent grading temperatures bracket the specification limit values (300 MPa [43.51 ksi] creep stiffness and 0.300 m-value). Extrapolation is the case where the BBR test results from two adjacent grading temperatures do not bracket the limit values. The BBR critical temperature precision is better than the ABCD cracking temperature precision. However, it should be pointed out that the BBR critical temperature alone cannot estimate the proper cracking temperature of asphalt binder. A strength test must be performed and combined with the BBR test results. Then, the precision of the resulting cracking temperature by BBR would be similar to that of ABCD cracking temperature.
The No-Trim ABCD experiment, performed with a limited number of binders, showed that the trimming and lubrication of the silicone mold in the current ABCD procedure can be eliminated. Based on these finding, a revised ABCD test procedure was developed that did not have steps for trimming the sample and lubricating the silicone mold. The results of the revised ABCD test procedure would have the same precision level for the ABCD cracking temperature and would improve the precision of the strain jump for the single-operator test. Multilaboratory precision of the ABCD cracking temperature and the strain jump would be significantly improved with the revised ABCD test procedure.