Concrete remains a fundamental material in modern construction due to its durability, versatility, and structural reliability. Its performance is largely governed by compressive strength and density, which determine suitability for load-bearing applications and long-term serviceability. Aggregates, constituting 60–80% of concrete’s volume, significantly influence these properties. While crushed granite aggregates are conventionally favored for their high strength, specific gravity, and angular morphology, alternative materials such as seashell aggregates are gaining attention for potential sustainability and cost benefits. This study provides a comparative evaluation of concrete properties using seashell and granite aggregates, examining their effects on compressive strength, density, and overall material behavior. Experimental results highlight differences in mechanical performance attributable to aggregate type, offering insights for sustainable material selection and optimized concrete design in structural applications.