The construction industry is a major contributor to global CO₂ emissions, with Portland cement production alone responsible for 5–8% of the total, primarily due to its clinker-intensive process. To reduce this environmental impact, the partial replacement of clinker with supplementary cementitious materials (SCMs) has gained significant attention. Calcined clay, due to its high pozzolanic reactivity, availability, and low-carbon profile, is emerging as a key SCM in sustainable binder development. This study reports the findings from an experimental program assessing the mechanical and time-dependent behavior of structural concretes incorporating a commercially available blended cement, formulated with 7% calcined clay. This percentage reflects a realistic industrial substitution level defined by production constraints and the technical-operational criteria of the cement manufacturer. Four fluid-consistency (class F) concretes were studied: two reference strength classes targeting fck,28 = 25 and 40 MPa, and two polypropylene macrofibre-reinforced concretes (3 and 6 kg/m3) designed to meet fct,fl,28 = 3.5 MPa. Standardized tests were performed at 7, 28, 90 and 120 days to evaluate compressive strength, tensile strength, modulus of elasticity, flexural behaviour, and drying shrinkage. All concretes met or exceeded the specified performance targets. Indirect tensile strength at 28 days ranged from 3.1–3.9 MPa, and the elastic modulus developed within 30–39 GPa. Increasing fibre dosage notably enhanced post-cracking residual capacity, supporting crack-control-oriented design. Overall, the results support the feasibility of low calcined-clay substitution for structural concretes while quantifying the mechanical and serviceability-related contributions of polypropylene macrofibres.