The resilient modulus (MR) of unbound materials is a required input in most of the mechanistic-based pavement analysis and design process and has a significant effect on the projected pavement performance in the mechanistic– empirical pavement design guide programme or AASHTOWare DARwin. The Iowa Department of Transportation (DOT) recently acquired a servo-hydraulic dynamic loading materials test system known as the Nottingham asphalt tester (NAT). The Iowa DOT NAT is a hybrid servo-hydraulic machine designed for testing not only hot-mix asphalt performance properties but also unbound materials’ MR (although this has not been verified so far). The primary objectives of this research are to update and verify the capacity of the Iowa DOT hybrid NAT for testing unbound material’s MR through a detailed laboratory testing programme and regression analyses using non-linear stress-dependent models.