One of the main challenges in today's construction industry is improving the performance of concrete while reducing costs and minimizing its environmental impact. An effective approach to address this challenge is the use of alternative and mineral additives in concrete mixtures. Limestone powder, due to its abundance in the northwest region of the country, accessibility, and affordability, serves as an optimal local material for partially replacing sand in concrete mix designs. On the other hand, pozzolanic additives, such as diatomite powder, enhance mechanical properties and durability of concrete by increasing pozzolanic reactions, making them widely applicable in the concrete industry. The impact of these materials on concrete performance depends on their independent or combined usage. However, most previous studies have focused on the effects of these materials individually, with limited exploration of their combined influence. This research aims to investigate both the independent and combined effects of limestone powder and diatomite powder on the mechanical properties of conventional concrete. The findings can provide practical solutions for producing high-quality, sustainable concrete, optimizing mix designs, and expanding the application of these proposed materials. For this purpose, a reference mix design (B1) and 15 additional mix designs were developed. These included varying proportions of the two proposed materials: limestone powder as a partial replacement for sand, and diatomite powder as a concrete additive at levels of 0%, 10%, 15%, and 20%. Specifically, in three mixes (B2, B3, B4), only diatomite powder was used, in three others (B5, B9, B13), only limestone powder was utilized, and in the remaining nine mixes, both materials were combined. The study measured slump, water absorption during curing, compressive strength, and tensile strength for all 16 concrete mixtures. Results showed an increase in both compressive and tensile strength across all samples. However, the highest compressive strength was achieved in mix B11, which included 10% diatomite powder as an additive and 15% limestone powder as a partial sand replacement. For the 28-day, 90-day, and 180-day samples of mix B11, the compressive strength increased by 60%, 48%, and 45%, respectively.