Valorising excavated low-grade waste clay in limestone calcined clay cement system for 3D printing applications

Limestone calcined clay cement (LC3) presents a suitable low-carbon cementitious material for large-scale 3D printing due to its long open time. This study investigates the impact of substituting up to 100 % natural aggregate with recycled brick aggregates (BA) on the engineering properties, durability and printing properties of LC3. BA's rough surface and irregular shape reduced the workability of the LC3 mixtures even though the water absorption of BA was compensated for by adding extra water. The mechanical strength increased significantly in the presence of BA of around 36 %–62 %. Moreover, incorporating BA was found to boost the hydration and allowed it continue due to the presence of additional water in its microstructure. The water absorptions of LC3 prepared with up to 70 % replacement level of aggregates with BA were comparable to the reference mix, while a 100 % replacement level increased the water absorption by around 9 %. In contrast, incorporating BA improved the freeze-thaw resistivity by up to 25 %. Moreover, it was found that incorporating BA improved the layer quality of 3D-printed filaments. The results of this study present a breakthrough in the recycling of brick aggregates in LC3 systems for both cast and 3D printing applications, which will help develop a more environmentally friendly mixture with high engineering performance. • Brick aggregates enhance LC3's mechanical strength and freeze-thaw durability. • Up to 70 % BA inclusion maintains water absorption comparable to reference mixes. • BA acts as an internal curing agent, improving hydration and long-term performance. • VMAs ensure shape retention and buildability for 3D-printed LC3 mixtures. • Recycled bricks offer a sustainable solution for low-carbon construction materials.