Nano-size effect of environmentally friendly ulexite powder as a bitumen additive in stone mastic asphalt

Various additives are used to increase resistance against permanent deformation of bituminous mixtures. These additives improve pavements by modifying the bitumen or being easily added to the mixture. Stone Matrix Asphalt (SMA), in addition to additives, enhances properties such as rutting resistance, durability, and stability with its high bitumen ratio and high coarse aggregate content. In this study, the environment-friendly ulexite mineral, which is abundantly available worldwide, was added to 50/70 penetration bitumen in various ratios and in nano/micron particle sizes to improve engineering properties. Penetration, softening, and elastic recovery experiments were carried out to check the suitability of the produced modified bitumen. SMA with a suitable modified bitumen was prepared. Subsequently, Marshall stability and flow tests were performed under SMA wear layer design criteria, and the compliance of ulexite-modified SMA samples with the Turkish Highway Technical Specifications (HTS) was investigated. Ulexite minerals of three different sizes (−25μ, −45μ, and −75μ) were added in varying proportions (3.50%, 4.50%, 6.00%, and 7.50%) to the bitumen, and the most suitable ratio was determined to be 7.5% within the HTS limit values. It was decided that ulexite powder with nano-size (Ulexite −25μ) provided the best SMA mixture with a Marshall stability of 1331 kgf.