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. Studies further highlight that these additives impart functional properties, such as the photocatalytic activity of nano-TiO2, which enables self-cleaning ability and assists pollutant degradation. At the same time, carbon-based materials enhance electrical conductivity, thereby facilitating the development of innovative and multifunctional structures. Such incorporation also mitigates anisotropy by filling voids, creating crack-bridging networks, and reducing pore interconnectivity, thereby improving load distribution and structural cohesion in printed structures. Integrating topology optimisation with 3DPC has the potential to enable efficient 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 article 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.