Effect of rejuvenator and mixing methods on behaviour of warm mix asphalt containing high RAP content

Rejuvenators are normally used in the hot in plant or hot in place recycling process of asphalt pavement. The use of rejuvenators in recycling RAP in warm mix asphalt (WMA) remains very limited. This study was carried out to investigate the use of a rejuvenator which was normally used for HMA, in producing WMA containing RAP. Laboratory tests were done on the binder rheological properties and the mechanical behaviours of the mixtures. Mechanical behaviours of WMA with RAP mixtures produced by the rejuvenator were compared with that of a control HMA and other WMA-RAP mixtures produced by using Evotherm WMA additive. Tests were carried out on resilient modulus, indirect tensile strength, semi-circular bending test, and four-point bending fatigue test. Results showed that it is possible to produce WMA by adding RAP and by using rejuvenators. WMA adding RAP mixtures produced with the rejuvenator performed better than WMA adding RAP produced with Evotherm additive in fatigue cracking resistance. The study further investigated the effect of different mixing methods of the rejuvenator with the binder on the mechanical properties of the WMA adding RAP mixtures. The study found that when the content of the RAP is lower than 50%, the mechanical behaviour of mixtures did not significantly change regardless of different mixing methods. However, when the content of the RAP is 50% or higher, adding the rejuvenator directly into the RAP significantly improved the moisture resistance of WMA RAP mixtures. For overall results, adding the rejuvenator into RAP was found more effective than adding the rejuvenator into the hot bitumen before mixing.