Use of waste marble powder as a cement substitute in three-dimensionally printable mortars

The potential of Tunisian marble waste as a sustainable partial substitute for cement in mortars for three-dimensional printing (3DP) for construction applications was explored. Marble powder (MP) generated from cutting and finishing processes was characterised through X-ray diffraction, X-ray fluorescence, scanning electron microscopy, thermogravimetric analysis and particle size analyses, confirming its predominantly calcitic composition, fine granulometry and thermal stability. A total of 12 mortar mixtures were formulated by varying the water-to-fines and sand-to-fines ratios, with a fixed 15% MP as cement replacement. Printability was assessed using a robotic extrusion system, while fresh and hardened properties were evaluated through tests for setting time, buildability, compressive strength and flexural strength. The results indicated that the use of MP delayed setting and reduced the bulk density, which is beneficial for lightweight applications. Despite its chemical inertness, the fine particle size of MP enhanced packing density, leading to up to 19% higher early compressive strength, while only slightly reducing the flexural strength. Microstructural observations revealed dense calcium silicate hydrate networks and well-integrated marble particles without deleterious phases. Although the printed specimens exhibited lower strength than moulded ones owing to interlayer weaknesses, their overall performance was suitable for additive manufacturing. These findings indicate MP to be a promising, eco-friendly mineral additive for low carbon dioxide, high-performance cementitious materials suitable for 3DP.