Evaluation of the impact factors on the leaching risk of steel slag and its asphalt mixture

In recent years, there has been an increasing interest in steel slag asphalt mixtures. Steel slag has good mechanical properties, but there is a risk of leaching of heavy metal elements during the steel slag stockpiling process and after paving asphalt pavement. Therefore, this work firstly investigated the effect of different influencing factors on the leaching concentration of heavy metal elements during the steel slag stockpiling process and analyzed the leaching mechanism by microstructure. Then, the gray relational analysis method was adopted to compare the magnitude of the effects of asphalt type, grade type, binder content and temperature on the leaching concentration of heavy metal elements in steel slag asphalt mixes. The results showed that the leaching concentration of heavy metal elements from steel slag increased rapidly due to the acid rain effect. With the formation of CaSO4 crystals to fill the micro-pores on the steel slag surface, the leaching concentration of heavy metals slowed down. Cu is the element with the largest leaching risk coefficient. The increase of specific surface area and the decrease of pH value will increase the leaching risk of heavy metals in steel slag. The leaching risk of steel slag was significantly reduced after it was prepared into asphalt mixes. The main influencing factor for the leaching risk of heavy metal elements from steel slag asphalt mixes is the type of grading, the secondary factors are temperature and asphalt content. Considering the high temperature environment common in asphalt pavements during use, it is recommended to use dense-graded asphalt mixtures in areas of high temperatures.