Examination of physical property degradation due to severe short-term ageing and effect of hydrated lime as antioxidant in asphalt mixture

Abstract

If the short-term ageing (SA) level of asphalt mixture is intense before paving, the pavement service life will be reduced due to the highly stiffened binder from the starting time of service. However, since how much the ageing damage is induced by the severe SA is not known, this study was initiated to examine the physical property degradation of the binder in the SA treated mixes. Four SA times (1, 2, 4 and 8 h) at 160°C and 180°C were used for 3 mixes: a dense-graded HMA mix with a normal binder (PG64-22), the same mixes including a hydrated lime (HL; 1.5% by wt. of mix) and a polymer stabiliser (KL; 1.5% by wt. of binder). Increasing patterns of absolute viscosity (AV) and stiffness (G*/sin δ) due to ageing were found to follow the form of exponential function. They were highly increased in 2 h (h) SA, but exceedingly increased in 4 h and longer SA at 180°C. These AV and stiffness increase resulted in DSR critical temperature (CT) escalation and degradation of bending beam rheometer (BBR) CT. The AV, G*/sin δ, DSR CT and BBR CT of the normal mixes were found to have a very high correlation (R²> 0.98) with large-molecular size (LMS) ratio (%) of gel-permeation chromatography. The binder AV and G*/sin δ of HL and KL mixes were estimated using LMS. In comparison of binder ageing level of mixes with and without HL or KL, it was found that both HL and KL retarded the ageing, but HL more significantly, for longer SA time at higher temperature. Therefore, it was evidenced that the use of HL in the HMA mix should be a highly beneficial choice for preserving durable pavement.

Keywords:

• asphalt
• short-term ageing
• hydrated lime
• GPC
• absolute viscosity
• large-molecular size