Estimation of Reclaimed Asphalt Pavement (RAP) characteristics using simple indicative tests

The design of hot recycled asphalt mixes with high RAP content, say more than 25%, as per existing guidelines is complex compared to the conventional Hot Mix Asphalt (HMA) design. This is due to the fact that the mix design requires the properties of bitumen in the RAP material and hence, it involves using solvents to recover the bitumen and testing of the recovered bitumen using sophisticated equipment. Considering the issues associated with bitumen recovery procedure that were reported in the literature and the practicalities involved in testing the recovered bitumen, the present study aims to identify indices that can reasonably estimate the RAP characteristics without the need to recover the bitumen. For this purpose, two tests namely, the Fragmentation test and Cohesion test that were proposed by the RIlEM Technical Committee 237-SIB committee for RAP classification for cold mix design were evaluated. These two tests can be conducted using conventional apparatus used for quality control tests that are available at most of the field laboratories. Fragmentation test was carried out on six different RAP sources and at three different conditioning temperatures (5 degrees C, 20 degrees C, and 40 degrees C). Cohesion test was carried out on RAP from five different sources at five conditioning temperatures (70 degrees C, 100 degrees C, 140 degrees C, 170 degrees C, and 190 degrees C). The test results suggest that the index derived from fragmentation test (S (frag)) correlated well with the physical properties of recovered bitumen such as penetration, softening point, and complex shear viscosity. Further, the index was able to estimate the difference in % of fines in black and white curves. The sensitivity of the air voids and Indirect Tensile Strength (ITS) of the Marshall specimen (S (air voids) and S (ITS)) obtained from the cohesion test correlated well with bitumen content and bitumen type respectively.