Low-carbon calcined clay-based engineered cementitious composites with hybrid fibers: mechanical performance, shrinkage control, and microstructural insights

This study investigates the development of low-carbon, engineered cementitious composites (ECC) incorporating calcined clay (CC), silica fume (SF), calcium sulphoaluminate cement (CSC), and hybrid PVA-PP fibers. The influence of water-to-binder (w/b) ratio (0.16–0.25), CSC dosage (5–15%), and curing conditions on workability, mechanical properties, shrinkage behavior, and microstructure was systematically evaluated. Reducing the w/b ratio significantly improved mechanical performance, with compressive strength decreasing from 52.43 MPa at w/b = 0.16 to 39.75 MPa at 0.25 and flexural strength declining from 15.98 MPa to 10.25 MPa. Improved performance occurred at w/b = 0.19, balancing strength and workability. Wet curing further enhanced performance, achieving 56.43 MPa compressive strength and 15.86 MPa flexural strength under T50-wet48 conditions. Tensile strength reached 7.76–9.21 MPa. CC-ECC exhibited substantially higher shrinkage (−3147 με) than SF-ECC (−854 με), while CSC induced expansion up to 3054 με, compensating shrinkage through self-stressing. Microstructural analysis confirmed dense hydration products supporting durability.