The mechanical behaviour of uncompacted asphalt mixtures is still not well understood, threatening directly to the pavement practices such as control of mixture's workability and segregation. This situation may become even worse due to the gradually increasing complexity and advances in paving materials and technologies. This study adopts a slump flow test based on concrete technology and a Discrete Element (DE)-based numerical tool to investigate the mechanical behaviour of uncompacted asphalt mixture from a microstructural point of view, particularly focusing on the bituminous binder effects. The combined experimental and numerical analysis indicates that bitumen distinctly influences the contact interactions within the mixture and thus its macroscopic flow, which can be physically interpreted as a combined effect of lubricated friction and bonding force. Additional case studies demonstrate that the DE model is capable of simulating the flow response of asphalt mixtures under changed particle contact conditions and driven force.