Evaluation of Rheological Properties and Field Applications of Buton Rock Asphalt

Abstract Buton rock asphalt (BRA) is a type of natural asphalt found in Buton Island, located at southeast of Sulawesi Island of Indonesia. Because of different situations during its sedimentation process, the content of bitumen in the rock varies. The BRA used in this study contained about 20 % of bitumen by weight, with loose, black fine particles. A laboratory testing program was carried out in this study to evaluate the effects of the BRA on both the asphalt binder and asphalt concrete mixture. In the first part, a commonly used asphalt binder in China for pavement construction was used as the control binder sample. Specimens containing 0, 25, 50, 75, and 100 % of BRA, by weight of the Pen60/80 binder, in addition to the base Pen60/80 binder, were subjected to penetration test, ring and ball softening test, and the dynamic shear rheometer (DSR) test to assess their rheological properties. All tests were performed on original asphalt binders as well as short-term aged asphalt binders after the rolling thin film oven test (RTFOT). Test results showed that, with increasing BRA content, the binder’s penetration decreased, softening point increased, dynamic viscosity at 60°C increased, and complex modulus increased. The incorporation of BRA in the binder also changed the viscoelastic property of the asphalt binder. For all binders, with increasing testing temperature, the elastic portion of the binder stiffness decreased; however, the rates of decrease were different for different combinations of binders. Within the temperature range of the testing, the BRA modified asphalt binder retained a more elastic portion than the unmodified binder did. The trend was more significant at higher temperatures. From testing on samples subjected to RTFOT, BRA can improve the binder’s ability in resisting aging. Furthermore, BRA was more effective in affecting the rheological properties when its content was more than 50 % of the weight of the Pen60/80 asphalt binder. It is therefore recommended that, during a paving operation, the BRA optimal content should be about 2.0 to 2.5 % of the total weight of the asphalt concrete mixture or more. In the second part of the testing, asphalt concrete mixture samples were prepared with the Pen60/80 asphalt binder and with binders containing 50 and 100 % of BRA by weight of the Pen60/80 binder (BRA: Pen60/80 = 0.5:1 and BRA: Pen60/80 = 1:1, respectively). For comparison purpose, styrene-butadiene-styrene (SBS) modified asphalt concrete mixture samples were also prepared and were subjected to the same tests. Results from the rutting tests indicated that the BRA modified asphalt concrete mixtures had better rutting performance as compared to the control asphalt concrete mixture sample. The immersion Marshall test and the freeze-thaw splitting tensile test were performed on the samples to evaluate the influences of the BRA and SBS on water stability of the various asphalt concrete mixtures. Results showed that the BRA modified asphalt concrete mixture had similar water stability as the SBS modified asphalt concrete samples and both were better than unmodified asphalt concrete mixture. The fatigue life of the BRA modified asphalt concrete mixture was longer than that of the unmodified and the SBS modified asphalt concrete mixture samples, as determined by the semi-circular bending test.