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

Abstract

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 T₂ 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°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 T₂ 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.

Keywords::

• asphalt
• nuclear magnetic resonance
• viscosity
• ageing
• T₂
• relative hydrogen index
• dynamic shear rheometer

Acknowledgements

This work was supported by the Qatar National Research Fund (QNRF) under Grant National Priority Research Program project NPRP 5-506-2-203 to Texas A&M University at Qatar. All statements are those of the authors and do not represent QNRF. The authors acknowledge Mohammed Sadeq for providing the DSR data.

Notes

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^3. Email: [email protected]