Evaluation of a soil for 3D printing on earth stabilized with cement, metakaolin and filler
3D printing. Additive Manufacturing. Earth construction. Constructability.
Earth construction is one of the oldest and most widespread vernacular building techniques, because it is an ecological, sustainable, affordable material that can be manufactured with locally sourced materials, reducing the impact of greenhouse gases for the house-building industry. In this context, the aim of this work is to analyse a type of regional soil classified as sandy-silt and check its suitability for the 3D printing process, by stabilizing it with Portland cement and using chemical additives to provide the pumpability required for printing. The cement was then replaced by metakaolin and limestone filer, with the aim of providing the mixture for 3D printing in raw earth-cement (3DTC) with a volume of paste suitable for the printing system, but with low Portland cement contents. The experimental program started with an initial empirical analysis of mixtures, with the aim of obtaining a 3DTC mixture with a consistency compatible with the extrusion method of the printer used, and thus defining the contents of chemical additives and the water/dry material ratio. The number of layers that could be built in a single batch and that were compatible with the material and the printing system was then determined. After 3DTC printing in block format, dimensional analyses were carried out to assess the constructability of the 3DTC process adopted, compressive strength and flexural tensile strength tests of small pieces extracted from the 3DTC blocks, and the axial compressive strength of 3DTC blocks. Among the mixtures analyzed, it was possible to build 3DTC blocks with cement consumption of 113.60 kg/m³ and 152.78 kg/m³ in the T15%C and T20%C mixtures and make them printable with cement reduction levels of 82% and 76%, respectively, compared to the reference mixture (REF) which used only cement and raw earth in a 1:1 ratio by mass. The reference 3DTC block had the highest compressive strength (19.8 MPa) of the three mixtures analyzed, due to the high cement content present in the mixture. The T15%C and T20%C mixtures reached strengths of 3.1 MPa and 3.0 MPa, respectively, which makes the 3DTC mixtures suitable for masonry construction.