Effect of recycled brick powder with various particle features on early-age hydration, water state, and rheological properties of blended cement paste in the context of 3D Printing

Partially replacing cement with recycled brick powder (RBP) in 3D printing concrete (3DPC) is an effective way to reduce carbon footprint and resolve the construction and demolition waste disposal problems. Understanding the impact of RBP on the rheological parameters of 3DPC is of utmost importance, given its critical role in ensuring the requisite printability. Here, three types of RBPs with various particle features were prepared by mechanical grinding, and their effects on several rheological parameters of cement-RBP pastes were characterized by hydration kinetic and water state distribution. Results show that incorporating RBP increases the growth rate of static yield stress due to the nucleation effect in the first 2 h. The initial static yield stress and thixotropy of cement-RBP pastes are governed by morphology effect and Debye length, while the mean interparticle distance and water lubrication effect under shear process play the dominant role in dynamic yield stress. RBP can promote the evolution of structural build-up and thixotropy of cement paste, all of which have a significant positive impact on filament shape retention and structural stability of 3DPC.