Evaluation of ageing in asphalt cores using low-field nuclear magnetic resonance

This paper introduces an innovative methodology for estimating the ageing of asphalt concrete cores without extracting the binder. Asphalt concrete samples at different ageing stages (unaged, 3-month and 6-month aged) and with different percent air voids (4%, 7% and 10%) were analysed with low-field nuclear magnetic resonance (NMR). The transverse relaxation time T-2 and relative hydrogen index (RHI) obtained from NMR measurements were related to the viscosity of the asphalt binder. The samples were analysed during cooling from 70 degrees C to room temperature, showing increase in viscosity with decreasing temperature. There was a clear trend indicating higher viscosities in samples that were aged for a longer period and samples with higher percent air voids. The RHI and T-2 values obtained from low-field NMR measurements and the viscosity data calculated from measurements using a dynamic shear rheometer were correlated to develop a model that relates viscosity with RHI.