Rheology of fiber-reinforced mortar for 3D printing construction: Effect of recycled hybrid powder and polyethylene fiber

Green recycled hybrid powder (RHP) was proved to partly replace cement to prepare 3D printable mortar, which can recycle the demolition waste and reduce carbon emissions. In this study, different contents of RHP and polyethylene fiber (PE fiber) were selected to prepare 3D printable RHP mortar (3DPRM). The initial rheological parameters, including dynamic yield stress, plastic viscosity, static yield stress and thixotropy, as well as the rheological parameters varying with time were investigated. Besides, the early-age hydration of RHP paste was studied to reveal the influence mechanism on rheological properties. The experimental results show that the dynamic yield stress, plastic viscosity and thixotropy as well as their time-varying properties were all increased with RHP replacement. The static yield stress of 3DPRM with 30 % RHP had the most significant enhancement, which was 416.5 % increased after resting for 20 min, showing the great buildability enhancement potential of RHP. The addition of PE fiber (6 mm and 12 mm) increased the rheological parameters of 3DPRM, among which the increase ratio of initial dynamic yield stress was 60 %-195 %. However, the increase ratio with time for dynamic/static yield stress of 3DPRM with PE fiber was lower than that without PE fiber, indicating that PE fiber had great effect on the extrudability but small effect on buildability of 3DPRM. The energy intensity, carbon emission and cost of RHP were 65.27 %, 66.57 % and 12.5 % lower than that of cement, illustrating the sustainable contribution of RHP for construction industry. The results can be used to guide the printability design of 3D printable mortar containing RHP and PE fiber.