Development of A balanced mix design approach for stone Matrix asphalt mixtures

Stone Matrix Asphalt (SMA) has been widely used as a durable, high-quality mixture for primary roads. With the growing interest in incorporating innovative materials into SMA designs, developing effective and reliable mix design methodologies has become essential to ensure durability, sustainability, and cost-effectiveness. While performance tests have gained national acceptance for asphalt mix design and balanced mix design (BMD) methods have been adopted in many states for hot mix asphalt (HMA), SMA has not been fully considered with the BMD implementation. This study aimed to develop a BMD approach for SMA, incorporating both SMA-specific volumetric parameters and performance requirements. To achieve this, a new approach was developed based on BMD methods outlined in the American Association of State Highway and Transportation Officials (AASHTO) standards MP 46 and PP 105. It combined the advantages of Approaches A, which focused on the volumetric parameters to form the stone-on-stone structure, and Approach B, which allowed adjustments to binder content based on performance test results. The approach was demonstrated using two mix designs: one with traprock (a typical aggregate specified for SMA) and the other with steel slag (a commonly used innovative material) as coarse aggregates. The results indicated that the SMA with traprock met the performance requirements based on the initial volumetric design. However, the initial volumetric design for the SMA mixture with steel slag yielded insufficient cracking resistance. After conducting performance tests at multiple binder levels, a balanced binder content range was determined that met both cracking and rutting resistance criteria.