(Re)carbonation: A new opportunity for sustainable 3D-printed concrete

3D-printed concrete (3DPC) is an innovative production technique that has the potential to reduce material consumption in construction compared to in-situ formwork or prefabricated elements. However, its sustainability is debated because printable concrete has a higher carbon footprint than ordinary concrete. 3DPC also shows faster carbonation - a natural process in which cementitious materials absorb CO 2 from the atmosphere. When the corrosion of steel reinforcement is not a concern - as in most unreinforced 3DPC - fast carbonation can serve as a form of (re)carbonation that partially mitigates the material's footprint and should be included in life-cycle assessments. This study evaluates this potential through a case study on Tor Alva, a 30 m 3D printed tower in the Swiss Alps. By defining the minimum CO 2 uptake of the printable concrete using thermodynamic simulations, the rate of carbonation measurements and dynamic life cycle assessments, it was possible to determine a positive reduction on the carbon footprint of the 3DCP used in the tower of approximately 4.1 tCO 2eq (21%) over a time horizon of 50 years. The findings highlight the need to consider carbonation coefficients when assessing 3DPC's long-term sustainability and provide a completely new perspective on its environmental impact. In this context, print path planning becomes a unique tool for 3D printing to optimized for (re)carbonation, while keeping durability in check.