Kenta HARUKAWA

Study on Utilization of Substandard Reclaimed Asphalt Pavement for Recycled Asphalt Mixtures

Osamu TAKAHASHI

Asphalt mixture recycling has carried on a full-scale operation since the 1980s. The ratio of recycled asphalt mixtures to total asphalt mixture production has been increasing year by year, reaching a high level of more than 70% in recent years. On the other hand, the quality of reclaimed Asphalt pavement (RAP) deteriorates due to repeated reuse of the asphalt mixtures. As a result, substandard RAP which does not meet quality standards, increases in Japan. Under these circumstances, it is necessary to effectively utilize the substandard RAP in order to maintain the current recycling status in the asphalt industry.
To use the substandard RAP with a high mixing ratio of 60%, the present investigated a rejuvenation mixing method focusing on curing time and curing temperature of rejuvenated old asphalt and a mix design method focusing on the validity of old asphalt. The recycled asphalt mixtures using the substandard RAP (substandard recycled mixtures) were assessed with evaluation of cracking resistance and rutting resistance.
In order to investigate the mixing method, the curing time and curing temperature were changed after adding the rejuvenator to the substandard RAP. The direct tensile tests were conducted for the produced substandard recycled mixtures.
On the investigation of a design method, the direct tensile tests and the wheel tracking tests were conducted for the substandard recycled mixtures which were designed by introducing the concept of effective degree of the old asphalt. In this design procedure, the RAP was classified into two types, effective one and ineffective one, and the effective degree of the old asphalt was controlled by changing the ratio of the two types.
The test results showed that it was difficult to use the substandard RAP at high mixing ratios in the recycled mixture by devising the rejuvenation mixing method only. However, the concept of the effective degree of old asphalt was valid for the mix design method.