A research team has identified a simple way to significantly improve layer adhesion in 3D concrete printing (3DCP). The process is based on the use of lithium silicate between the print layers – a material that is already known and widely used in the construction industry.
In recent years, 3D concrete printing has established itself as a construction method in which concrete is applied layer by layer through a nozzle – similar to the FFF process used in plastic printing. While complex structures can be realized with this method, the mechanical strength suffers at the interfaces between the individual layers. This is because the bottom layer has often already set too much by the time the next layer is applied.
The new method involves applying an aqueous solution of lithium silicate directly to the previously printed layer. This solution penetrates up to six millimetres deep into the concrete. There, the silicate reacts with the calcium hydroxide present to form calcium silicate hydrate (C-S-H), which compacts the pores in the material and stabilizes the interfaces between the layers.
In laboratory tests, the researchers were able to show that both the adhesion between the layers and the compressive and tensile strength of the test specimens increased significantly. The porosity decreased measurably and the proportion of larger pores (>1 mm) was reduced from two percent to just 0.3 percent. This indicates a more homogeneous microstructure.
The low cost factor is particularly noteworthy: the additional material application is around one US dollar per square meter. Another advantage is the environmental compatibility of the process – lithium silicate is VOC-compliant and not classified as a hazardous substance.
There is still a lack of commercial 3D concrete printers that can apply the material automatically. However, the implementation of such systems should be technically straightforward. Further details can be found in the scientific paper “Surface treatment of 3DPC interlayers with silicate-based solution for enhanced interfacial bonding“.
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