Evaluation of Alkali-Activated Limestone Calcined Clay Mortars for 3D Concrete Printing Applications (2025-08)¶

Limestone calcined clay (LC2) has gained significant attention as a supplementary cementitious material (SCM) due to its ability to reduce energy consumption and mitigate the carbon footprint associated with ordinary Portland cement (OPC). The combination of limestone and calcined clay enables the partial replacement of OPC while maintaining strength and durability. However, its use as an SCM is typically limited to a maximum 50% reduction in OPC utilization. This limitation restricts the full potential of LC2 in sustainable construction. To overcome this constraint, alkali activation offers a promising alternative by enhancing the binding properties of LC2, allowing it to function as a standalone binder rather than just an SCM. Alkali-activated materials (AAMs) have shown superior mechanical properties, durability, and sustainability compared to traditional cementitious binders. Additionally, their potential application in 3D concrete printing (3DCP) is of particular interest, as 3DCP is revolutionizing the construction industry by reducing construction time, labour costs, and material wastage. However, for effective integration into 3DCP, binders must exhibit tailored rheological properties, including controlled flowability, buildability, and setting time. The development of sustainable and cost-effective materials for 3DCP applications is, therefore, an urgent need. This study aims to develop and optimize alkali-activated LC2 mortars for 3DCP applications. Various binder formulations were designed by modifying the alkalinity of the system using different dosages of sodium hydroxide, sodium silicate, and hydraulic lime. The selection of these alkaline activators was based on their ability to enhance the dissolution of aluminosilicates present in calcined clay, leading to the formation of a geopolymer-like binding matrix. The impact of different activator concentrations on setting time, workability, and printability was systematically evaluated. The study involved multiple experimental investigations to assess the suitability of alkali-activated LC2 binders for 3DCP. Flowability tests were conducted to determine the ease of material extrusion and its ability to retain shape upon deposition. Additionally, rheological tests were performed to measure yield stress, viscosity, and thixotropic behaviour, which are crucial parameters for ensuring the structural integrity of 3D-printed layers. Mechanical properties, including compressive and flexural strength, were also evaluated to confirm the material’s performance. To validate the practical feasibility of the developed formulations, printing trials were carried out using a 3D concrete printer. The printability of different mixtures was assessed based on their deformation resistance and extrusion consistency. The most promising formulations demonstrated a balance between flowability and buildability, making them suitable for large-scale 3D printing applications. The findings of this study contribute valuable insights into the development of sustainable, alkali-activated binders for 3DCP. By maximizing the potential of LC2 through alkali activation, this research paves the way for cost-effective, environmentally friendly construction materials. The integration of such materials into 3DCP technology holds immense potential for advancing the future of sustainable infrastructure.