The global growth of concrete is a strong indication of the urgent need for sustainable construction materials to reduce carbon footprints and reuse industrial waste. In this work, we study the combined effect of mixing two industrial by-products, silica fume and mill scale. The concrete mixes were prepared with combined substitution levels of 0, 20, 25, and 30%. Fresh properties were evaluated by slump, flow table, and compaction factor tests. Hardened performance was studied by compressive, flexural, splitting tensile, and non-destructive ultrasonic pulse velocity (UPV) tests. The long-term chemical durability of the combinations was studied by exposure for 91 days to magnesium sulfate (MgSO₄), sulfuric acid (H₂SO₄), and NaCl conditions. The performance of the trial indicated that a moderate replacement level of 20% is optimum for the fresh properties, resulting in the highest slump and flow values due to paste modification and improved particle packing. The result of non-destructive testing showed that the mix with 25% replacement achieved the highest UPV, which means the microstructure was highly dense and the interfacial transition zone was improved. The modified mixes exhibited better resistance against the mass loss of sulfuric acid when exposed to aggressive chemical environments than the control mix. The maximum acid resistance was found to be highest in the 30% substitution due to the decreased reserves of Ca(OH)₂. The 25% mix showed the best microstructural density and steady long-term development of compressive strength under sulfate and marine conditions. However, the high replacement (30%) resulted in a high dilution of cement clinker and a major decrease in mechanical performance and workability. The study shows that, in general, a replacement rate of 20% to 25% provides a good compromise between environmental sustainability and waste management, on one hand, and good mechanical performance and chemical durability, on the other, concerning modern concrete architecture.