Moisture resistance and compactibility of asphalt concrete produced in half-warm mix asphalt technology with foamed bitumen

- We evaluated a fine asphalt concrete mix with foamed bitumen compacted at 95 °C.
- The foam mix with 2.5% Fischer-Tropsch wax performed similarly to HMA.
- Moisture resistance testing procedure was significant to obtained results.
- The air void content had an effect on all of the measured properties of the mixes.

Current regulations regarding emissions, as well as the efforts focused on reducing energy intensity of building materials production create a need for implementing new road construction technologies. Particular attention is being paid to the lowering of asphalt concrete production temperature, which is about 160 °C. In response to this need warm mix asphalt (WMA) technologies have been developed which allow producing asphalt mixes at temperatures about 20-30 °C lower than those of conventional methods. However, it was only after half warm mix asphalt (HWMA) was introduced that the mixing temperature of asphalt concrete with foamed bitumen could be reduced by as much as 60 °C. Asphalt pavements constructed with HWMA may have a reduced service life and lower resistance to environmental factors (e.g. water). This paper presents the results from the tests with one freeze cycle and from the moisture sensitivity analysis conducted for the low-temperature asphalt concrete (AC 8) with foamed bitumen and the control mix produced according to conventional hot mix asphalt technology. It was found that the modification of 50/70 bitumen (before foaming) with the addition of 2.5% FT synthetic wax had a beneficial effect on the properties of asphalt concrete mixes under investigation. The ITSR indices were compared having been determined in accordance with procedures based on European and AASHTO standards that are widely used in Poland. The analysis was extended to include the compactibility evaluation of low-temperature bituminous mixes and the impact of air voids on the mechanical parameters. The foamed asphalt concrete modified with 2.5% FT wax was found to satisfy the requirements for moisture resistance determined during the test with one freeze cycle.

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