A Critical Review on Synergistic Integration of Nanomaterials in 3D Printed Concrete: Rheology to Microstructure and Eco-Functionality

The use of nanomaterials (NMs) in 3D printing concrete (3DPC) has shown significant advancements in enhancing both fresh and hardened properties. This review finds that their inclusion in printable concrete has altered the rheological properties of the mix by promoting thixotropy, extrudability, and buildability while simultaneously refining the microstructure to enhance mechanical strength. Additionally, the photocatalytic properties of nano-TiO₂ enable self-cleaning ability and assist pollutant degradation, whereas carbon-based materials improve electrical conductivity, thereby facilitating the development of innovative and multifunctional structures. NMs mitigate anisot-ropy by filling voids, creating crack-bridging networks, and reducing pore intercon-nectivity, thereby improving load distribution and structural cohesion in printed structures. Integrating topology optimisation with 3DPC has the potential to enable ef-ficient material usage. Thus, it enhances both sustainability and cost-effectiveness. However, challenges such as efficient dispersion, agglomeration, energy-intensive production processes, high costs, and ensuring environmental compatibility continue to hinder their widespread adoption in concrete printing. This paper emphasises the need for optimised NM dosages, effective dispersion techniques, and standardised testing methods, as well as sustainability considerations, for adapting NMs in concrete printing.