Investigation of mechanisms of top-down fatigue cracking of asphalt pavement

This paper presents the results of pavement temperature measurements with depth over a year obtained with a setup emulating the heat flow on a pavement with 305 mm (12 in.) of hot mix asphalt (HMA) and 152 mm (6 in.) of aggregate base. Several findings related to top-down fatigue cracking (TDFC) in Hawaii were obtained from these measurements. It was observed that pavement temperatures near the surface, which were both the lowest and the highest in the HMA depending on the time of day, were rarely below 20°C, and thus, that most cracking in Hawaii occurs at higher temperatures. It was also observed that passing rains can cause sudden temperature drops of the order of 15°C within short periods (15 min). HMA moduli estimated using measured temperature profiles indicate that high temperature gradients may lead to inverted moduli profiles that when loaded cause the highest tensile and shear strains to occur near the surface, and that these may be a main reason for TDFC in the state. The simulated stresses and strains under high temperature gradients also indicate they may be conducive to delamination problems related to large horizontal shear strains generated near the surface and combined with nearly vertical but small tensile strains at the layer interface. The observation that cracking suddenly and consistently stops under overpass bridges and immediately resumes after them provides strong evidence consistent with the findings of the stress/strain distributions generated from profiles with high surface temperature and high temperature gradients potentially causing TDFC. The paper provides recommendations for further study.

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Towards the Use of Waste Pig Fat as a Novel Potential Bio-Based Rejuvenator for Recycled Asphalt Pavement

Materials ◽

10.3390/ma13041002 ◽

2020 ◽

Vol 13 (4) ◽

pp. 1002

Author(s):

Nader Nciri ◽

Taesub Shin ◽

Namho Kim ◽

Arnaud Caron ◽

Hanen Ben Ismail ◽

...

Keyword(s):

Low Temperature ◽

Asphalt Pavement ◽

Fatigue Cracking ◽

Recycled Asphalt ◽

Excellent Thermal Stability ◽

Temperature Performance ◽

Aged Asphalt ◽

Ft Ir ◽

Low Temperature Performance ◽

The Impact

This article presents a novel potential bio-based rejuvenator derived from waste pig fat (WPF) for use in recycled asphalt applications. To achieve this purpose, the impact of different doses waste pig fat (e.g., 0, 3, 6, and 9 wt.% WPF) on the reclaimed asphalt pavement binder (RAP-B) performance is investigated. The unmodified and WPF-modified asphalts are characterized by means of Fourier-transform infrared spectroscopy (FT-IR), thin-layer chromatography–flame ionization detection (TLC-FID), scanning electron microscopy (SEM), atomic force microscopy (AFM), thermogravimetric analysis (TGA), and differential scanning calorimetry (DSC). Physico-rheological properties of asphalt blends are assessed through Brookfield viscometer, softening point, penetration, and dynamic shear rheometer (DSR) tests. TLC-FID data highlighted that incremental WPF addition into RAP-B restored its original balance maltenes-to-asphaltenes ratio; finding which was supported by FT-IR analysis. SEM disclosed that WPF has a great compatibility with the aged asphalt. AFM observations showed that grease treatment induced a decline in surface roughness (i.e., bee structures) and a rise in friction force (i.e., para-phase dimension) of RAP binder. TGA/DSC studies revealed that the bio-modifier not only possesses an excellent thermal stability but also can substantially enhance the binder low-temperature performance. Empirical and DSR tests demonstrated that WPF improved the low-temperature performance grade of RAP-B, reduced its mixing and compaction temperatures, and noticeably boosted its fatigue cracking resistance. The rejuvenation of aged asphalt employing WPF is feasible and can be an ideal approach to recycle both of RAP and waste pig fats.

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