Performance of ethanol and ethanol-NaHCO3 based foamed WMA mixtures for low emission asphalt technology

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Department of Civil, Environmental, and Geospatial Engineering


The foaming techniques implemented in Warm Mix Asphalt (WMA) have been highly recognized to aid in the production of eco-friendly asphalt mixtures. However, to a certain extent, the application of this technology is limited by its defects in moisture sensitivity and rutting resistance. Prior to this, the WMA mixtures were prepared using ethanol and ethanol-NaHCO3 foamed binders and were tested to evaluate their moisture susceptibility, rutting potential, crack resistance and thermal cracking potential. The mixture samples were prepared based on the mixture design for a 9.5 mm nominal maximum aggregate size. The designed traffic level was less than 3 million Equivalent Single-Axle Loads (ESALs). Nano-hydrated lime was incorporated during the preparation of the sample as a filler material. The foamed WMA mixtures were prepared at three different temperatures: 80 °C, 100 °C and 120 °C; meanwhile, the control Hot Mix Asphalt (HMA) sample was prepared at 155 °C and 145 °C. For the purpose of incorporating the temperature losses during the foaming process, the foamed binders were produced at a temperature higher than the production temperatures by approximately 20 °C. Overall, the results show that 1% and 3% ethanol-foamed WMA mixtures are found to have a comparable or better performance than the control HMA mixture, especially for the samples prepared at 120 °C. The addition of nano-hydrated lime contributed to the increase on the adhesive and cohesive characteristic of mixtures; hence, improving the resistance to moisture damage. Regardless of the contents of the foaming agent and production temperatures, most of the foamed WMA mixtures prepared using a combination of foaming agents have comparable thermal cracking characteristics as the control HMA mixture. The resistance to rutting of foamed WMA mixtures increased with the increase in the production temperatures. The sample prepared at 120 °C is found to have much lower or comparable rut depths to the control HMA mixture. However, the combination of ethanol with 1% NaHCO3 was optimal for these foamed WMA mixtures prepared at 80 °C to obtain a good long-term performance.

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Construction and Building Materials