Investigation of Using Ulexite as a Filler in Various Combinations in Stone Mastic Asphalt Mixtures

Ulexite is one of the most commonly used minerals in boron elements. Especially with the increase in infrastructure investments, new raw materials and new asphalt mixtures with higher performances than traditional asphalt mixtures are needed against the deterioration caused by increasing traffic loads. Stone mastic asphalt (SMA), one of the asphalt mixture types, is preferred due to some superior performances. It is important for mixture performance because the filler material ratio in SMA mixtures is higher than in other hot-mix asphalt (HMA) types. In this study, the influence of ulexite in SMA mixtures was examined by Marshall, indirect tensile strength (ITS), resilient modulus, and moisture sensitivity (modified Lottman) tests using ulexite and basalt in various combinations as filler, providing that the optimum bitumen ratio remained constant. It resulted in increased stability, ITS, and resilient modulus values by a maximum of 8%, 25%, and approximately 79% compared with the control mixture, respectively. In addition, using ulexite provided significant improvements in SMA performance by increasing the resistance to water damage by 13%. Based on the results of the tests, the combination of 4.5% ulexite and 5.5% basalt is recommended for the best SMA performance.