Aging of bituminous mixes for rap simulation

The use of reclaimed asphalt pavement (RAP) has gained considerable importance due to increasing environmental concerns and the search of more economic ways in road paving. Although a large amount of RAP is produced each year, only a part of it can be recycled in a suitable way. The efforts have been towards increasing the RAP content, and if possible, making complete use of RAP in road pavement construction. There have been many studies conducted on the aging of bitumen and compacted bituminous mixes, however the effects of aging conditions on the loose bituminous mixture to simulate RAP has not been examined in detail. As part of a research project on hot mix asphalt recycling, the effect of temperature, aging duration, humidity, oxygen concentration, and sample thickness on loose asphalt aging for the production of RAP was investigated. Bituminous mixture was aged in the forced draft oven in a special aging box and representative samples of asphalt were taken at defined time intervals for rheological tests. Hyperbolic-like curves were observed for rheological properties of bitumen versus aging duration. Asphalt aging was shown to be not only affected by the temperature, oxygen content, aging duration, and humidity but also the presence of trace substances in the air. No effect of layer thickness on the bitumen aging was found.