Abstract
The production process of Hot Mix Asphalt (HMA) causes a short term aging (STA) to asphalt binder due to the heating of both asphalt binder and aggregates before mixing together. Laboratory protocols are followed to simulate the STA conditions for both asphalt binders and asphalt mixtures. STA protocols expose asphalt binders or asphalt mixtures to specific aging temperature for a specific period of time to produce stiffening that is similar to that of actual production conditions. Successful construction of HMA in cold season/regions may require elevating the production temperature of HAM to achieve proper compaction of HMA layers. Producing HMA mixtures at elevated temperatures may cause further increase in the binder stiffness and negatively affect the future field performance of asphalt pavements. This negative affect can be even worse especially if it is coupled with extended exposer time increase. This study aims to investigate effect of elevated production (mixing and STA) temperatures and exposure time on the stiffening of binders and asphalt mixtures. The binder experiment involved aging of two Performance Graded (PG) binders (PG 76-16 and PG 64-22) at two different temperatures and aging durations. The asphalt mixture experiment involved the STA of asphalt mixtures produced in the laboratory at mixing and STA temperatures 25°F above standard practice and aging time 2 and 4 hours longer than standard practices. The effect of different aging times and temperatures was investigated by running viscosity tests on binders and dynamic modulus |E*| and Indirect Diametrical Strength (IDT) tests on asphalt mixtures. The results showed that increasing the mixing and STA temperatures by 25°F seems to have no significant effect on the asphalt mixture properties while doubling the standard STA time seems to have a significant effect on binder and asphalt mixture properties.
Highlights
Short term aging of asphalt binders refers to the hardening of asphalt that occurs during mixing, storing, transporting and placement operations
On the other hand for Hot Mix Asphalt (HMA), the short term aging in the field is simulated in the laboratory using the Short Term Oven Aging (STOA) procedure which involves heating a loose mix in a forced draft oven for 4 hours at a temperature of 135°C (275°F) [4]
Most studies have focused on long term aging, this study focused only on the effects of short term aging conditions on the laboratory behavior of asphalt binder and mixtures
Summary
Short term aging of asphalt binders refers to the hardening of asphalt that occurs during mixing, storing, transporting and placement operations. The 2015 Shell Handbook recommends that the best practices for providing coating viscosity while limiting aging due to elevated temperatures is to use the minimum temperatures necessary to attain required coating viscosities [2] It acknowledges the practice of mixing hot mix asphalt (HMA) at elevated temperatures to address the need for maintaining adequate lay down temperatures under conditions of low ambient temperatures and long hauling distances. This leads to paving operations that are halted, delayed or shut down during the winter months To overcome these delays and waste associated with constructions shut downs, contractors have proposed that hot mix asphalt be produced at higher than prescribed temperature as long as compaction densities or target air voids and binder contents are achieved in the field. The combined effect of elevated temperature and longer exposure time may cause excessive short term aging and adversely affect the performance of the pavement
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