Waste Marble Powder Valorisation in 3D-Printable Cement-Based Composites ^†

Freeform architecture and precision material placement make 3D printing particularly useful when architectonic issues, such as complex or highly variable geometries, are demanding. Three-dimensional printable cementitious-based composites (3DPCCs) are very challenging from the point of view of engineering properties, namely, in the fresh state, where pumpability, extrudability, and buildability should co-exist. The mixture design must meet these requirements. Thus, the aggregate content in the mixture is significantly reduced, and the dosage of cement and supplementary cementitious materials (SCMs) is increased. Additionally, white cement formulations are popular due to colour requirements for architectural or design purposes. Thus, high dosages of fine powder materials needed for 3DPCCs is an environmental concern from a long-term perspective.

The use of locally available additions is a key factor in saving energy, reducing cost, and decreasing CO₂ emissions in the production of 3DPCCs. The partial replacement of white Portland cement with SCMs can be beneficial considering economic, technical and environmental aspects, particularly the valorisation of industrial wastes, such as marble powder.

The current work evaluated the incorporation of waste marble powder (MP), from a local company, into 3DPCCs for product design purposes. MP was ground (GMP), and fundamental characterisation was performed to check its compatibility with the cement. Afterwards, a mixture composition study was performed, including performance-based laboratory testing for 3DPCC fresh property assessment, based on standard and novel protocols, including a systematic choice of parameters and identifying their threshold values for printability mixtures. Several printable mixtures were reached with GMP cement replacements ratios between 0 and 50%. Specimens presented an attractive finish and colour properties. The mechanical performance complies with typical values for cement-based materials, and, as expected, GMP incorporation decreased the mechanical strength. In particular, the current work provides insight into the concept of 3D printing using local materials, including specific waste, contributing in an integrated way to a circular economy, reducing landfills, and reducing cement dosage.