3D Printable Mortars with Different Recycled Concrete Powders as Fillers (2024-09)¶

3D Printing in construction hold great opportunities to tackle long-lasting challenges such as high waste generation and lack of automatization. However limited solutions to lower the high cement content of printable mix-tures have been proposed. An interesting prospect is the use of recycled concrete powders (RCP) as cement replacement. RCPs are commonly discarded from the production of recycled aggregates from concrete wastes, but these fine particles can be employed as fillers in cementitious mixtures. Yet, properties of recycled materials are dependent on their origin, and recycled powders will consequently differ in their compositions and effect on concrete. Understanding the character of each RCP is decisive to determine an adequate mix design for 3D Printing with lower cement content, while meeting technical requirements. This research investigated the use of RCPs from two origins to replace 50% of Portland Ce-ment in printable mortars. Their effect in rheological behavior was evaluated by an adapted green strength test. Mechanical performance was evaluated through uniaxial compressive testing at 7 and 28 days. The Life Cycle Assessment meth-odology was used for environmental analysis of the mortars. The results show that rheological behavior varied considerably due to the different physical prop-erties of each powder, with RCPs causing increase or decrease in yield stress. A loss on mechanical performance of mortars occurred with both powders. Finer adjustment of mix design could however solve these issues, and thus ensure the use of RPCs as candidates in the formulation of low cement 3D printable mix-tures. Finally, the results of Life Cycle Assessment support the use of RCPs as an environmentally viable option for printable mortars.