This study investigates the employment of copper slag and fly ash with hydraulic binders lime and ground granulated blast furnace slag (GGBS) to bolster the base layer of flexible pavements. By leveraging these industrial by-products, the research seeks sustainable advancements in pavement engineering. Laboratory tests evaluated compaction characteristics, unconfined compressive strength (UCS), and durability, examining their influence on pavement performance. The results indicated that mixes with copper slag and fly ash significantly improve mechanical and durability properties. For instance, mixtures with a 2% lime and 9% GGBS content achieved a UCS of 7.19 MPa after 28 days of curing, surpassing traditional base materials. Durability tests confirmed the mixes’ resilience, with a less than 5% loss in dry weight after durability cycles, well within acceptable limits for base and subbase applications. This research validates the hypothesis that integrating copper slag and fly ash in base layers not only mitigates industrial waste but also elevates pavement quality, making it a viable approach for sustainable and robust road construction.