Determining the effect of ageing of nano-clay modified bitumen using atomic force microscopy

This study investigates the effects of ageing simulation on the physical properties of nano-clay modified bitumens (NCMBs). Bitumen with penetration grade 60/70 is modified with 0, 2 and 4% nano-clay, and the consistency of the samples is characterized using the penetration, softening point, and viscosity tests before and after aging. Atomic force microscopy (AFM) is used to evaluate the surface roughness and tip deflection of the modified bitumens. The results of the consistency tests revealed that the incorporation of nano-clay up to 4% NC resulted in increased hardness of the modified bitumen, and all modified bitumens were affected by ageing; the results for surface roughness and tip deflection showed a similar trend and 2NCMB exhibited the lowest roughness and highest tip deflection. However, the results of consistency tests and AFM for ageing sensitivity of the bitumens are different, indicating that the addition of nano-clay has an effect on the modified bitumen but not on the unmodified bitumen. There is a high correlation between the results of consistency tests, surface roughness and tip deflection, which implies that AFM is able to identify any changes in the fluidity of the bitumen. However, the correlation between tip deflection and penetration is very weak.