# A Novel Approach to Optimize the Rheology and Buildability of 3D-Printed Magnesium Phosphate Cement Composites Using Carbonated Recycled Aggregate

## TL;DR

This study shows how adding carbonated recycled aggregate to 3D-printed cement composites improves their stability and sustainability.

## Contribution

A novel method using carbonated recycled aggregate to enhance the rheology and buildability of 3D-printed magnesium phosphate cement composites.

## Key findings

- CRA increased static yield stress and storage modulus of the composites.
- CRA content over 15% resulted in solid-like behavior with a phase angle under 45°.
- Structural deformation decreased due to CRA's rough surface promoting uniform stress transfer.

## Abstract

Controlling structural deformation is essential for the structural stability of 3D-printed cement composites. In this paper, carbonated recycled aggregate (CRA) was incorporated into 3D-printed magnesium phosphate cement composites (MPCCs) to control rheology and improve buildability. Experimental results show that CRA increased the static yield stress from 2210.96 to 6238.18 Pa and the storage modulus. When the incorporation of CRA was more than 15%, the phase angle was less than 45°, indicating predominantly solid-like behavior. Additionally, due to the higher porosity, the compressive strength and flexural strength of 3D-printed MPCCs decrease with the increasing CRA content; however, the decline tendency becomes significantly more pronounced when CRA content exceeds 10%. Structural deformation decreased from 14.39% to 6.91%, attributed to the rough surface of CRA, which promotes more uniform stress transfer during stacking. This study demonstrates a simple upcycling route that improves the printing stability and sustainability of 3D-printed magnesium phosphate cement composites (MPCCs).