Semi-flexible pavement surfacings are constructed from impregnating highly flowable cementitious grouts into the voids of open-graded asphalt wearing course layers. Semi-flexible surfacings offer superior load bearing and rutting resistance performance when compared to either conventional or polymer modified hot mix asphalts. On the other hand, when semi-flexible surfacings are used as part of a flexible pavement construction, they offer an economic alternative to concrete construction. In this laboratory investigation, the properties and performance of semi-flexible mixes containing three types of cementitious grouts (a control grout, a grout containing regular waste polyethylene terephthalate (PET) and a grout containing gamma-irradiated waste PET) were investigated and compared to the performance of a conventional hot mix asphalt (HMA). Test results showed that the properties of semi-flexible control specimens comprising 100 cementitious grout can be matched by specimens containing 2.75 regular PET as partial replacement to the cement. When gamma-irradiated PET is used, the cement replacement content can be increased to 4.75 whilst maintaining properties comparable to the control grout. It was thus argued that gamma-irradiation is a useful tool for enhancing product sustainability. The laboratory produced semi-flexible specimens were evaluated for the degree of grout impregnation, Marshall stability, indirect tensile strength, thermal expansion, moisture resistivity, and fuel resistivity. The results were compared directly to those obtained from testing conventional HMA specimens. All three semi-flexible mixtures exhibited superior performance compared to the HMA mixture in terms of Marshall stability, indirect tensile strength, resistance to moisture damage and resistance to fuel spillage. © 2021 Elsevier Ltd