Characterization of Crack Growth Rate of Sulfur-Extended Asphalt Mixtures Using Cyclic Semicircular Bending Test

Abstract

Characterizing crack propagation of asphalt mixtures is helpful for optimizing mixture design and predicting cracking performance of asphalt pavements. This paper explores a new method based on the cyclic semicircular bending (SCB) test to characterize crack growth rate and evaluate fatigue cracking resistance of asphalt mixtures. For characterizing crack growth rate, the difficulty is the measurement of crack length during testing. A digital image correlation (DIC) was used to track the crack propagation during the test, which was used to establish a correlation curve with the corresponding crack mouth opening displacement (CMOD) measurements. Four sulfur-extended asphalt (SEA) mixtures with different dosages of sulfur were evaluated with the proposed cyclic SCB test. The results of the test fitted well to the Paris law function, and the Paris law coefficients of SEA mixtures were identified. They were also consistent with the test results from the monotonic SCB test and horizontal strain field of the crack tip characterized using the DIC. The cyclic SCB test showed substantially lower coefficients of variance in terms of the number of cycles to failure compared with other traditional fatigue tests such as the bending beam fatigue test and the Texas overlay test. Regarding the effects of sulfur, test results showed that a low level of sulfur addition, such as 15%, softens asphalt binder to the stage where more damage can be induced in a controlled-stress mode of loading, while extra sulfur would act as fillers to stiffen the asphalt binder when the dosage was greater, such as 3%–45%.