This study evaluates concrete mixtures in which 5%, 10% and 20% of the 0–4 mm fine aggregate fraction is volumetrically replaced by olive pit biochar and discusses their practical implications for applications in concrete plants. Four mixes were produced using conventional CEM II/A-L cement, natural coarse aggregates and standard plasticizing and superplasticizing admixtures. Compressive strength, splitting tensile strength and static modulus of elasticity were measured at 7 and 28 days. All biochar-modified concretes achieved strength levels within the range of conventional structural concrete classes commonly used for building and general infrastructure slabs, with 28-day compressive strength reductions of about 6–14% and a systematic decrease in stiffness as biochar content increased. The 10% replacement level provided the most favourable compromise, combining the highest splitting tensile strength with an adequate modulus for general structural and precast applications. Overall, the results show that olive pit biochar can be integrated into conventional concrete production with limited adjustments, offering a promising route towards lower-carbon concrete applications.