Potential of Reusing 3D Printed Concrete (3DPC) Fine Recycled Aggregates as a Strategy towards Decreasing Cement Content in 3DPC

Abstract

This paper explores the new potential strategy of using fine recycled aggregates (fRA) derived from waste 3D printed concrete (3DPC) as a substitute for cement in additive manufacturing. This study hypothesizes that fRA can optimize mixture design, reduce cement content, and contribute to sustainable construction practices. Experimental programs were conducted to evaluate the fresh and hardened properties, printability window, and buildability of 3DPC mixes containing fRA. Mixes with replacement rates of cement with fRA by 10 vol%, 20 vol%, 30 vol%, 40 vol%, and 50 vol% were produced. A comprehensive experimental protocol consisting of rheological studies (static and dynamic yield stress), dynamic elastic modulus determination (first 24 h of hydration), flexural and compressive strengths (2 d and 28 d), and an open porosity test was performed. The obtained results were verified by printing tests. In addition, an economic and environmental life cycle assessment (LCA) of the mixes was performed. The results indicate that up to 50 vol% cement replacement with fRA is feasible, albeit with some technical drawbacks. While fRA incorporation enhances sustainability by reducing CO2 emissions and material costs, it adversely affects the printability window, green strength, setting time, and mechanical properties, particularly in the initial curing stages. Therefore, with higher replacement rates (above 20 vol%), potential optimization efforts are needed to mitigate drawbacks such as reduced green strength and buildability. Notably, replacement rates of up to 20 vol% can be successfully used without compromising the overall material properties or altering the mixture design. The LCA analysis shows that reducing the cement content and increasing the fRA addition results in a significant reduction in mix cost (up to 24%) and a substantial decrease in equivalent CO2 emissions (up to 48%). In conclusion, this study underscores the potential of fRA as a sustainable alternative to cement in 3D printed concrete.

Influence of Residue Soil on the Properties of Fly Ash–Slag-Based Geopolymer Materials for 3D Printing

“…Ordinary Portland cement (OPC) is the most commonly used binder material, and its extraction and production processes are associated with high energy consumption and significant CO 2 emissions [ 12 , 13 , 14 ], exacerbating global warming issues. Therefore, in the quest to develop cleaner, greener, and more sustainable 3D printing materials, recent research trends have tended towards the use of low-carbon, green binder materials, in order to reduce cement use and carbon dioxide emissions [ 15 , 16 ]. Compared to OPC, geopolymers have been widely accepted as green binders due to their superior mechanical and durability properties [ 17 , 18 ].…”