Warm mix asphalt (WMA) has gradually become more popular in the roading industry, because, compared to hot mix asphalt (HMA), WMA can bring numerous benefits, such as lower energy consumption, lower emissions, and greater ability to incorporate a high proportion of reclaimed asphalt pavement (RAP) in the mixtures. Incorporating RAP in WMA can increase the sustainability benefits and enhance the performance of WMA. This study investigated the performance of WMA by adding RAP in different proportions, from 0 up to 70% by mass of WMA. The performance of mixtures was compared with a control HMA. One type of binder, 80/100 penetration grade, and two types of additives were use: a chemical warm mix additive and a rejuvenator, namely, Evotherm and SylvaroadTM RP1000, respectively. Tests were done on the binder’s viscosity and the mechanical performance of mixtures such as moisture resistance, fatigue cracking, and rutting resistance. In this study, the semi-circular bending test was investigated to further study its applicability in asphalt pavement testing. Results from laboratory tests showed that the two additives reduced the viscosity of the binder. Mixtures with the chemical additive (Evotherm) performed better than other mixtures in terms of moisture resistance. Only the WMA mixture with the Sylvaroad rejuvenator showed a higher number of cycles to fatigue failure than the control HMA. For rutting resistance, the increase in RAP proportion greatly improved the performance of WMA mixtures. WMA without RAP had a lower number of cycles to reach maximum rut depth than the HMA. All WMA-RAP mixtures showed considerably better rutting resistance than the HMA. The study of semi-circular bending test showed that the notch depths from 5 to 15 mm are suitable for 100 mm diameter samples. The indirect tensile strengths yielded by the semi-circular test and those from the indirect tensile method could be convertible.