Abstract: Modified concrete was prepared by adding different amounts of iron and aluminium slag into mortar. Compression tests, computed tomography (CT) scans and electron microscope scans were carried out to investigate the mechanical properties and fine structural characteristics of the ferric-aluminum slag doped concrete. The results showed that the compressive strength and modulus of elasticity of the concrete specimens showed an increasing and then decreasing trend with the increase in the amount of ferric-aluminum slag, and the optimum amount of Fe-Al slag was determined to be 15%. The modifying effect of ferric-aluminum slag promoted the secondary hydration reaction of cement mortar, resulting in a reduction of Ca(OH)₂ content and an increase of hydrated calcium silicate (C-S-H) content in the concrete, which eventually caused the closure of cracks between the aggregates and improved the overall mechanical properties of the material.