Engineered cementitious composites with nano calcium carbonate and corona waste mask fibers for sustainable 3D printing applications

Engineered cementitious composites (ECC) are ductile cement-based materials developed to overcome the brittleness of conventional concrete by exhibiting strain-hardening behaviour and improved crack control under tensile loading. The use of waste polypropylene fibres obtained from discarded COVID-19 face masks offers a sustainable approach to enhancing ECC performance, while nano calcium carbonate (NCC), a comparatively economical nanomaterial, improves particle packing and interfacial bonding in cementitious systems. This study examines the combined influence of NCC and modified corona waste mask fibres (CWMF) on the fresh, physical, and mechanical properties of 3D printed cement-based mortar, with NCC incorporated in the range of 0-4% by weight of cement. The results show that increasing NCC content reduces fluidity but significantly improves the buildability of the mixes. The dry density of the 3D printed specimens increased up to an optimum NCC content of 3% and decreased thereafter, while water absorption exhibited a similar trend. Mechanical properties evaluated at the designated test age indicate that compressive, flexural, and splitting tensile strengths attained optimum values at 3% NCC. At this NCC level, the 3D printed specimens consistently demonstrated superior mechanical performance compared to conventionally cast samples, indicating the effectiveness of NCC-CWMF modified mixes for 3D concrete printing applications.