This paper presents the fresh and hardened concrete properties with fly ash (FA) and copper slag (CS). M30 grade of concrete has been designed with a constant water–cement ratio as 0.4. Twenty four concrete mixtures are arrived by cement is partially replaced by FA from 0 to 30% with 10% increment and natural sand is replaced by CS from 0 to 100% at 20% increment. The compressive strength of the concrete was verified at 3, 7, 14, 28, 56, and 90 days curing periods. Five reinforced concrete (RC) beams of size 150 mm × 250 mm × 3200 mm were cast based on the optimum mix proportion and flexural behavior of RC beams was monitored by a four‐point bending test. From the experimental results, compressive strength, and flexural strength were increased for concrete with 30% FA and 80% of CS because the smaller surface area of CS per unit volume is exposed with a large quantity of concrete matrix and workability of concrete also increased.