Evaluation of the hot mix asphalt (HMA) design process in Turkey within the framework of contemporary approaches and improvement recommendations

Road transport, the most common mode of transport in our country and around the world, is constantly expanding due to increasing population and transport demand. However, it has been observed that pavements designed using the empirical Marshall method, which is widely used in road pavements, cannot adequately address performance issues such as permanent deformation and cracking, especially under high traffic loads. This situation has highlighted the need for performance-based mix design methods. The aim of this study is to propose an alternative design method that includes basic performance tests suitable for our country's conditions by examining existing performance-based approaches and, in particular, the performance tests used in balanced mix design. In this context, performance tests found in the literature and their place in mixture design were first researched, and applications in different countries were examined. Subsequently, the equipment and tests used in Superpave and balanced mixture design (e.g., wheel track, cracking, and moisture damage tests) were technically evaluated and compared with current Turkish applications. Furthermore, the current regulations in the Highway Technical Specifications, the harmonisation efforts with European standards, and the experimental studies conducted in the laboratory environment were evaluated. The study concluded that the Marshall method, which is still widely used in our country, is insufficient in solving performance problems, but that more reliable and durable pavements can be obtained if selected basic performance tests are integrated into the design process. In particular, experiments such as the Hamburg Wheel Mark Test, SCB (Semi-Circular Bending Test) and TSR (Tensile Strength Ratio) were found to offer a practical and applicable solution in BSK design. The outputs of this study will contribute to the transition to performance-based approaches in BSK design in Turkey, shed light on specification revisions for relevant authorities, and provide a methodological basis for academic studies. Thus, it is aimed to take an important step towards the design of more economical, durable, and reliable road pavements.