A Simplified Protocol for Permanent Deformation Characterization of Asphalt Concrete

Permanent deformation (PD; or rutting) is one of the major distresses in flexible pavements. To predict PD in asphalt concrete, repeated and recovery load tests are usually conducted in the laboratory. The full-blown repeated load permanent deformation (RLPD) is time-consuming, limiting its use in research programs and developing correlations. Therefore, a quicker yet reliable procedure is needed for use in performance prediction programs. This paper presents a simplified and quicker procedure to obtain PD model parameters. It is illustrated using labo-ratory tests on field specimens. The procedure uses one specimen, compared with three spec-imens in the full-blown RLPD test, to be tested at two temperatures, the highest and lowest in the RLPD test, under the same conditions as in the RLPD test. The results of any intermediate temperature are obtained from the calibrated model. Two approaches are presented for ana-lyzing the test results: the power equation in the AASHTOWare program, and the construction of a master curve. In the full-blown testing program with three specimens and three temper-atures, the master curve approach fitted the results better than the power law. In the simplified procedure, the fitting of the two approaches is almost identical. Results obtained from tests conducted on six mixes show (1) testing one specimen at the highest temperature only and extrapolating the results overpredicts the material behavior at intermediate and low temperatures, and (2) the master curve from the simplified procedure compares very well with the one from the full-blown RLPD program.