Awam, Pusat Pengajian Kejuruteraan
(2018)
Evaluation of laboratory Short-term ageing and rutting Characterisation of bitumen and Asphalt mastics /Noor Halizah Binti Abdullah.
PhD thesis, Universiti Sains Malaysia.
Abstract
In Malaysia, the most prevalent form of surface distress is top down cracking due to
repeated loading accelerated by bitumen ageing. Ageing also causes structural and
functional failures in asphalt pavement. According to international laboratory
standards (ASTM D2872), short-term ageing is simulated by conditioning the
bitumen in the rolling thin-film oven (RTFO) test. However, several researchers
reported some discrepancies between the results obtained from the RTFO and field
ageing. This thesis presents a short-term ageing procedure that was developed using
response surface method, to determine the corresponding ageing duration and
temperature that best mimicked ageing that took place during asphalt production in
the Malaysian asphalt mixing plant. The optimization procedure suggested ageing
protocols equivalent to conditioning at 170°C over a 132 minutes duration which
corresponded to the measured bitumen properties recovered from site. Ageing
duration and temperature were significant factors affecting the physical and
rheological properties of short-term aged bitumen. Rheological characterisation
indicated that bitumen viscosity increased with ageing severity and improved rutting
resistance of bitumen. The stiffening effects were found to be dependent on bitumen
type, ageing temperature and duration, and test temperature. The rheological master
curves of bitumen and asphalt mastics were described using the two springs, two
parabolic creep elements and one dashpot (2S2P1D) Model. This model was found to accurately describe the rheological properties of both unaged and aged bitumen and
asphalt mastics. The cumulative shear strain showed slightly higher magnitudes of
recoveries for 60/70 penetration grade bitumen obtained from Quarry B compared to
80/100 penetration grade bitumen from Quarry A and B. Meanwhile, asphalt mastics
prepared using 60/70 base bitumen incorporating 60% hydrated lime always showed
higher recoveries. Short-term ageing generally reduced non-recoverable compliance
(Jnr) and increased percentage recovery (R) of the bitumen and asphalt mastics.
Based on the comparison between rutting indicators, good correlations were found
between Superpave rutting parameter (G*/sin δ) and Jnr for both bitumen and asphalt
mastics. Hydrated lime filler always registered greater rutting resistance compared to
asphalt mastics prepared using ordinary Portland cement. The activation energy (AE)
of asphalt mastics tested between 45 to 65°C indicated a reduction in AE with higher
frequency, while higher filler content and ageing increased AE. These findings were
also similar for samples tested at temperatures ranging from 5 to 35°C. AE was
found to be influenced by bitumen type, filler type, filler content, frequency and
temperature range. It was concluded that the standard RTFO procedure was unable to
simulate the actual short-term ageing that occurs on site. Ageing improved rutting
resistance and hydrated lime showed higher stiffening effects compared to ordinary
Portland cement.
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