This research aims to evaluate the impact of calcium carbonate powder (CCP) and superplasticizer admixtures on the mechanical properties of concrete, with the objective of improving performance and durability. Eight concrete mixes were designed with varying water-to-cement (W/C) ratios and different additive concentrations. The results showed that the addition of CCP reduces concrete workability (slump), but the use of superplasticizers significantly compensates for this reduction, thereby improving workability. Regarding compressive strength, a significant improvement was observed with the addition of 2.5% CCP, where the strength reached 58.0 MPa when CCP was combined with a superplasticizer, confirming the synergistic effect of the superplasticizer in increasing concrete density and strength. For flexural strength, data indicate that CCP acts as a fine filler enhancing cohesion. In 70 cm beams, the average flexural load increased from 11.2kN for the reference mix to 15.2kN with the addition of 2.5% CCP (W/C 0.45), and reached 24.5kN when using 5.0% CCP with 1.8% superplasticizer (W/C 0.45). For 50 cm beams, the average flexural load increased from 23.7kN for the reference mix to 30.1kN with 2.5% CCP (W/C 0.45), and registered 26.0kN when using 5.0% CCP with 1.8% superplasticizer (W/C 0.45). Overall, the research indicates that the incorporation of CCP, especially at 2.5%, whether with or without superplasticizers, achieves optimal mechanical performance for concrete..................... Keywords:........... Calcium carbonate powder, Superplasticizers, Mechanical and physical properties, Compressive strength, and Flexural strength.