Recently, the excessive quantity of waste polyethylene terephthalate (WPET) creates a significant environmental concern globally. One way to reuse WPET is in the pavement industry as secondary materials. Nevertheless, based on works of literature review on the use of WPET in asphalt materials, inconsistent findings were reported with an increase and decrease in mechanical properties. To overcome this issue, gamma radiation has been utilized on the WPET. This study investigated the effect of using non-irradiated and irradiated WPET on some engineering properties of asphalt mixes. Marshall Samples incorporating a various amount of WPET (Plastiphalt); 0, 0.5, 1.0, 1.5, 2.0 and 2.5 by weight of total aggregates were tested based on Marshall Stability (MS), indirect tensile strength (ITS), and resistance to moisture damage. The results of x-ray diffraction (XRD) on the irradiated WPET showed that the degree of crystallinity had increased. The results of Marshall Stability (MS) showed an enhancement with increasing WPET content up to 2.0 for the plastiphalt mixes. Marshall Quotient, and ITS show a decreasing trend with increasing WPET amount for the plastiphalt mixes. Furthermore, results on moisture damage resistance indicated that indirect tensile strength and Marshall Stability ratios were marginally increased for plastiphalt mixes compared to the reference mixture (0 WPET). Comparing the moisture sensitivity tolerance results for the WPET modified mixes shows that irradiated WPET plastiphalt mixes had a better outcome than non-irradiated WPET plastiphalt mixes. © Published under licence by IOP Publishing Ltd.