Tomoki TAKEZAKI

Study on the Effect of Quality and Mixing Ratio of Recycled Aggregate on Cracking Resistance of Recycled Asphalt Mixture


Osamu TAKAHASHI

In recent years, more than 70% of asphalt mixtures produced are recycled asphalt mixtures, and the mixing ratio of recycled aggregate is also becoming higher. This high production ratio and mixing ratio has resulted in the repeated reuse of recycled aggregate, which has led to a decline in quality and an increase in the amount of substandard recycled aggregate that does not meet quality standards. Therefore, there is a need to effectively utilize substandard recycled aggregate as a material for recycled mixture. 
In this study, we investigated the effective use of substandard recycled aggregate as a material for recycled asphalt mixtures by changing the mixing ratio for each quality of recycled aggregate. The recycled mixture was prepared by combining three levels of recycled aggregate quality and four levels of recycled aggregate mixing ratio with two types of recycled additives, and the effects on the crack resistance of the recycled mixture were evaluated by direct tensile tests. As a result, the following findings were obtained.
(1) Recycled asphalt mixture using recycled aggregate with a needle penetration of 13(1/10mm) in the old asphalt at a mixing ratio of 60% recovered to a level equivalent to that of the recycled asphalt mixture using recycled aggregate with a needle penetration of 20(1/10mm).
(2) Recycled asphalt mixture using 30% recycled aggregate with a needle penetration of 8(1/10mm) in the old asphalt will recover to the same level as the recycled asphalt mixture using recycled aggregate with a needle penetration of 20(1/10mm).
(3) The recycled asphalt mixture after service is considered to be more susceptible to deterioration than the new asphalt mixture.