Performance Evaluation of Cement-Based Composites Incorporating Recycled Concrete Aggregates Suitable for Three-Dimensional Additive Manufacturing

Abstract

This study analyzes the effect of the recycled concrete aggregate (RCA) incorporation into 3D printable mixture designs using both traditional Portland cement 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. The 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. The results indicated that incorporation of RCA led to a stickier mixture, which limited the spreading ability and reduced open-time performance during 3D-printing operations. The use of RCA has affected the static yield stress more than the dynamic yield stress and viscosity. Despite these challenges, high-strength mortar designs with compressive strengths of approximately 70 MPa were achieved through careful adjustment of mixture design parameters. The 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, it was evaluated that it was possible to minimize these negative impacts of the use of RCA with appropriate adjustments. Notably, the use of RCA in 3D-printable mixtures did not show any problems during the printing process or after hardening, indicating promising prospects for high-value-added applications in advanced 3D additive manufacturing.