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Purpose: To solve the serious problems of high production, large stockpiles, and low utilization in industrial solid wastes. Method: Hot-braised steel slag(SS),a by-product of steel making,and phosphogypsum(PG), a by-product of the phosphorus chemical industry, were taken to prepare inorganic water stability layers for highway engineering as the main raw materials, together with a certain proportion of natural aggregates (NA) and silicate cement (PC), based on the design idea of multi-solid waste synergistic utilisation. Properties such as unconfined compressive strength,splitting strength,bulk stability,and scouring resistance were determined,then the mechanism of the hydration process was characterized by X-ray diffraction (XRD), Fourier transform infrared (FT-IR), and scanning electron electron microscopy (SKM) . Result; Proper amount of phosphogypsum helps the generation of ettringite to fill the voids, whereas excess dosage makes gypsum adhereto the surface of the steel slag and reduces the bonding force between the aggregates. Especially,Consisting of 6%PG(^0. 30 mm) + 6%PC(^0. 30 mm) + 32%SS (0. 30 -- 4. 65 mm) + 40%NA(4. 65 -- 20. 00 mm) + 22%SS(4. 65 -- 20. 00 mm),layer MW-2 satisfied the high-heavy highway strength criteria, with a solid waste zutilization to 60%. [ABSTRACT FROM AUTHOR]