Characterizing RAP binder properties through impact resonance testing of asphalt mixtures

Determining properties of the binder in recycled asphalt pavement (RAP) is an essential step in any mix design requiring inclusion of high RAP content. Today's common practice in determination of RAP binder properties is through extraction and recovery of the binder and conducting necessary mechanical and rheological tests on the recovered binder. This process is lengthy, time consuming, and expensive, while requiring the use of chemical solvents, a deterrent to reducing adverse effects of chemicals on the environment. There is also the possibility of change in binder properties because of the use of the chemical solvents or if any amount of solvent is left in the residue after binder recovery. An approach is proposed for determination of binder properties through nondestructive testing of laboratory compacted mix specimens with RAP and binders with known engineering properties. To prove this concept, a large number of impact resonance tests were conducted on various mixes made with different binder grades as well as made with 100% RAP mixes. The tests were conducted on gyratory compacted cylindrical specimens of asphalt concrete, in the longitudinal mode, and at a range of temperatures between 3°C and 35°C. Data capturing was through the use of an accelerometer. The collected data was reduced for interpretation in the frequency domain using Fast Fourier Transform (FFT). The results indicate the potential of the proposed concept and feasibility of the approach in determining binder properties including the RAP binder. A practical method is proposed for determination of binder properties based on mixture testing, and recommendations are suggested on the next steps that need to be taken to complete the process.