Tomoya IWASAKI

Study on the Method of Recycling Old Asphalt in Consideration of Repeated Recycling

Osamu TAKAHASHI

In Japan, recycling of asphalt mixtures has been continuously conducted to realize a recycling-oriented society. The production ratio of recycled mixture to the total mixture has been increasing year by year and has reached a high level of more than 70% in recent years. On the other hand, the quality of recycled aggregate has deteriorated due to repeated recycling, and the amount of substandard recycled aggregate that does not meet quality standards is increasing. In order to maintain the current reclaimed ratio, it is necessary to effectively use non-standard recycled aggregate as a material in the reclaimed mixture, and it is necessary to study a method of repeated reclamation of old asphalt in the future.
The current quality standard uses needle penetration as an index of softness, and the method of restoring needle penetration, which has decreased due to deterioration, to the same level as new asphalt by using a reclaiming additive is widely used. However, it is known that excessive or repeated use of naphthenic reclaiming additives, which are commonly used in Japan, may restore the softness of the old asphalt, but the bonding force connecting aggregate particles is not sufficiently improved, and pavements constructed with the reclaimed asphalt mixture are prone to cracking at an early stage. Pavements constructed with the recycled asphalt mixture are known to be prone to cracking at an early stage. In this study, we investigated a method to recycle the old asphalt considering repeated use by using a special additive for recycle, which is a polymer that improves the properties of asphalt in addition to the commonly used additive for recycle.
Nine types of polymers with different physical properties were used as additives, and the regeneration effects of the different polymers were evaluated. It was confirmed that the regeneration effect differs depending on the physical properties of the additives and the blending ratio, and that a high recovery effect can be obtained by blending the additives in an appropriate combination. The effect of the additives for composite regeneration during repeated degradation and regeneration was confirmed to be different from that of the normal regeneration method, as the addition of polymers in an appropriate manner restored fatigue fracture resistance. In addition, it was confirmed that excessive addition of polymers during repeated regeneration resulted in a decrease in properties, and knowledge was obtained regarding the amount of polymer to be blended during repeated regeneration.
These results indicate that the regenerative effect can be improved by adding specific polymers to common naphthenic additives, and that the amount of polymers can be adjusted for repeated reclamation.