The December issue of the World of Petroleum and Bitumen
WPB: Surface raveling is a prevalent functional issue that affects the longevity of bituminous pavement. To investigate this phenomenon, a comprehensive pavement study was carried out over a 36-month period on a major district road (MDR) in Telangana State, India. Field cores were extracted from the Bituminous Concrete (BC) pavement surface and subjected to laboratory testing for detailed analysis.
At the outset, the bulk specific gravity (Gmb) of the core samples was measured. Initially, one month after construction, the Gmb values were found to be between 91.1% and 92.9% of the maximum specific gravity (Gmm), with the binder content recorded at 5.4%. By the end of three years, due to traffic-induced compaction, the field density had increased to a range of 94.1% to 95.3% of Gmm. Concurrently, the binder content had dropped to 4.5%, primarily because fine aggregates had been displaced, leading to raveling.
Further analysis of the BC cores revealed a change in aggregate gradation, reflecting the loss of fine particles. Examination of the bitumen binder properties extracted from the samples showed a similarity to bitumen aged artificially using the pressure ageing vessel (PAV), indicating that four years of service life resulted in significant ageing.
To evaluate the ageing gradient within the pavement layers, the field cores were divided into two sections: the upper and lower slices. Bulk density measurements were performed on both sections, and bitumen was separately extracted from the top and bottom slices to determine binder content. Laboratory tests assessed the extracted bitumen for non-recoverable creep compliance (Jnr) and binder fatigue life (Nf).
Results demonstrated that the upper slice had a higher Gmb, lower Jnr, and reduced Nf compared to the lower slice. These differences were attributed to more severe oxidative ageing in the upper layer, as it is directly exposed to environmental factors. Additionally, the binder content in the top layer was notably lower due to raveling on the pavement surface.
The study concluded that increasing the compaction level of the BC layer to 94% of Gmm, instead of 92%, can help mitigate binder ageing and prolong the service life of bituminous pavements.
By Bitumenmag
Bitumen, Asphalt, Study, Article
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