A Comprehensive Study on the Valorization of Recycled Concrete Aggregates in 3D-Printable Cementitious Systems (2025-05)¶

This study analyzes the incorporation of recycled concrete aggregate (RCA) in 3D printable mixture designs using both traditional Portland cement systems and white cement systems. A comprehensive range of testing methods was employed, including rheological assessments through flow table tests, rheometer flow curve analysis, three-interval thixotropy testing (3ITT), and Vicat tests. Mechanical and durability properties were evaluated via compressive strength tests, water absorption and sorptivity tests, drying shrinkage tests, freeze-thaw tests, and wetting-drying tests. To explore the microstructural and physical characteristics and their relationships with mechanical performance, scanning electron microscopy (SEM) analysis was conducted. Results indicated that incorporating RCA led to a stickier mixture that hindered spreading ability and reduced open-time performance during 3D-printing operations. Static yield stress was more significantly affected by RCA than dynamic yield stress and viscosity, impacting the overall flow properties. Despite these challenges, high-strength mortar designs with compressive strengths of approximately 70 MPa were achievable through careful adjustment of mixture design parameters. Mixtures containing RCA exhibited higher water absorption and sorptivity rates than those with natural aggregates (NA), along with greater shrinkage and slightly higher strength loss under wet-dry conditions and freeze-thaw cycles. However, the negative impacts of RCA were minimal and deemed negligible, suggesting its potential for effective use with appropriate adjustments. Notably, the use of RCA in 3D-printable mixtures did not present any issues during the printing process or after hardening, indicating promising prospects for high-value-added applications in advanced 3D additive manufacturing.