A study on material design for selective cement activation 3D printing
Developing a strong and sustainable concrete mix suitable for additive manufacturing and underwater application
G. Schouten (TU Delft - Civil Engineering & Geosciences)
B. Šavija – Graduation committee member (TU Delft - Materials and Environment)
Sandra Nunes – Mentor (TU Delft - Concrete Structures)
Andries Koopmans – Mentor (Coastruction)
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Abstract
The increasing urgency of global warming and resource depletion demands more sustainable construction methods capable of reducing material use. Additive manufacturing (AM), in particular selective cement activation (SCA), offers such potential; however, its adoption remains limited due to challenges in mechanical performance and shape accuracy. Current SCA systems, including the custom-built printer used in this study, often exhibit low strength and require high water dosages to compensate, resulting in excessive penetration depth and thereby a loss of detail in the product.
This research aims to develop a concrete mix suitable for printing reef-like structures using SCA by optimising both strength and shape accuracy. Eighteen mix designs were investigated through small-scale mechanical testing, including compression and bending. Additionally, four different curing regimes were tested. Shape accuracy was evaluated using a visual grading method applied to complex printed geometries. Key mix parameters—particle-size distribution, cement-to-aggregate (C/A) ratio, binder composition, and additives—were systematically studied to identify their influence on water penetration behaviour and resultant print quality.
The results show that increasing the C/A ratio and adjusting the PSD significantly improve mechanical performance, while cellulose ether considerably enhances shape accuracy when applied within a narrow dosage range. A ternary binder of 90% ordinary Portland cement (OPC), 5% calcium sulphate (CS), and 5% calcium aluminate cement (CAC), combined with a C/A ratio of 0.4 and 0.25% cellulose ether, produced the most favourable balance between strength and geometric accuracy. This final mix design increased bending strength from 0.37 MPa to 1.62 MPa and compressive strength from 0.38 MPa to 1.15 MPa without sacrificing shape accuracy.
Overall, the study advances the understanding of material design for SCA-based 3D concrete printing and highlights sustainable binders and improved layer compaction methods as key directions for continued development. At the same time, it underscores that the recommended mix design is not universal but must be tailored to the specific requirements of the intended application.