Recycled brick aggregates in one-part alkali-activated materials: Impact on 3D printing performance and material properties

This study investigates the printability of one-part brick powder-based alkali-activated materials (AAMs) containing end-of-life brick particles as aggregate. The novel formulation showcases promise for 3D printing of small to medium-sized building blocks, reminiscent of a Lego-type system, capitalising on the rapid setting time inherent to one-part AAMs. The effect of replacing up to 50% by weight of natural aggregate with brick aggregate on the fresh properties of brick powder-based alkali-activated materials, including slump measurements, flowability, setting time, open time and green strength were investigated. In addition, the flexural and compressive strength of the 3D printed mixtures were determined and compared to those of cast specimens. The buildability and microstructure were also examined. The results showed that incorporating high porous and rough brick aggregate to replace natural aggregate is beneficial in improving the mixtures’ slump, which is essential for retaining the shape of the printed layers. However, it decreased the flowability, setting time and open time when incorporating up to 50% brick aggregate. The green, flexural and compressive strengths were increased with increasing brick aggregate content up to 50% due to enhancing interlock between the binder and brick aggregate, and the better compaction because of the absorption properties of brick aggregate. The mechanical results revealed the better performance of 3D printed specimens than the cast specimens. Moreover, the incorporation of brick aggregate enhanced the buildability of the mixtures showcasing their potential in advancing 3D printing capabilities.