Limestone Calcined Clay Cement‑based rubberized self‑compacting concrete: Fresh, mechanical, durability, and embodied‑carbon assessment

This study presents the development and comprehensive evaluation of Limestone Calcined Clay Cement-based rubberized self-compacting concrete (RubSCC-LC³), where crumb rubber (CR) is added as a sustainable partial volumetric substitution for sand. Five concrete mixtures were produced with CR contents of 0 %, 10 %, 20 %, 30 %, and 40 %, targeting an optimal balance between fresh performance, mechanical behavior, and environmental impact. The fresh properties were evaluated through slump flow, V-funnel, U-box, and L-box. All mixtures satisfied EFNARC criteria, indicating good workability, viscosity, and passing ability. Notably, slump flow diameter ranged from 655 mm (0 % CR) to 680 mm (40 % CR), while V-funnel flow time ranged from 11.5 s to 10.2 s, reflecting excellent flowability due to optimized superplasticizer dosage and the rheological advantages of the LC³ binder. L-box ratios ranged from 0.88 to 0.94, confirming consistent passing ability. In terms of mechanical performance, compressive strength at 28 days decreased from 67.5 MPa (0 % CR) to 34.7 MPa (30 % CR), and 25.2 MPa (40 % CR). Similarly, flexural strength declined from 7.78 MPa (0 % CR) to 5.74 MPa (30 % CR), and 4.94 MPa at 40 % CR. Splitting tensile strength reduced from 4.50 MPa to 2.53 MPa. Despite these reductions, all mixes up to 30 % CR maintained mechanical performance within structural application ranges. The elastic modulus dropped from 31.5 GPa (0 % CR) to 8 GPa (40 %), while Poisson’s ratio increased significantly (0.21–0.27), indicating improved ductility. Density decreased from 2250 to 1960 kg/m³ with increasing CR content, while water absorption, permeable voids, and water penetration depth increased with replacement (1.99 to 3.88 %, 4.84 to 9.36 %, and 0.4 mm to 100 mm). This reflects higher water transport pathways. Conversely, chloride‑ion penetrability remained very low at higher CR content. Moreover, the bulk electrical resistivity increased from ∼4 to > 10 kΩ·m as CR increased, while thermal conductivity decreased markedly (1.542 to 0.479 W/m·K), evidencing enhanced insulation potential. A cradle-to-gate carbon footprint reduced from 355.9 kg CO₂ eq/m³ (0 % CR) to 39.6 kg CO₂ eq/m³ (40 % CR), highlighting the synergistic environmental benefits of LC³ and recycled rubber. These findings confirm that RubSCC-LC³, particularly at 10 % −30 % CR, offers an optimal combination of mechanical integrity, workability, and environmental benefit for sustainable construction applications.