Mechanical behaviour and fibre reinforcement mechanism of engineered cementitious composites (ECC) based on limestone calcined clay cement (LC3)

Traditional concrete is characterized by high carbon emissions and inherent brittleness, while excellent toughness and low carbon are the keys to the improvement of cement-based materials. A new generation of greener and high-ductility engineered cementitious composites (ECC) using limestone calcined clay cement (LC 3 ) has gradually developed. This study systematically investigates the effects of different limestone calcined clay (LC 2 ) replacement ratios (0 %, 30 %, 45 %, 60 %) for cement on the mechanical, micro design and fibre-to-matrix interfacial behaviour of ECC to conduct a comprehensive performance analysis. Results indicate that as the LC 2 replacement increases, the 28-day compressive strength and ultimate tensile strength of ECC show a decreasing trend, with maximum reductions of 33.5 % and 31.4 %. However, the strain capacity of ECC under tension significantly improves by 78.2 %, accompanied by a denser multiple microcracking pattern. Micromechanical analysis reveals that with increasing LC 2 replacement, the fracture toughness of matrix decreases but the pseudo strain hardening strength index increases to 1.634, ensuring stable strain hardening behaviour. The chemical bonding strength between a single fibre and matrix significantly weakens with higher LC 2 replacement. The maximum pullout strength reduces by up to 62.7 % at an embedded depth ranges from 6 mm to 2 mm, which effectively promotes fibre slip rather than rupture. Ecological assessment demonstrates that LC 2 replacing cement can significantly reduce the embodied energy and carbon emissions of ECC. Thus, the toughening and energy saving mechanisms of LC 3 -ECC have been explored through a multi-scale investigation, providing a theoretical and practical foundation for its engineering applications.