Realization of a reinforced SPI façade : Direction-dependent material properties and durability assessment

The additive manufacturing method Selective Paste Intrusion (SPI) describes a particle-bed binding technology which uses cement paste to bind thin layers of aggregate. SPI allows to produce components complex in shape without needing support structures, e.g. façade elements. Façade elements should also be lightweight and translucent, but they subject to high flexural loads which means they need to be reinforced. They are also exposed to severe weathering and need to be correspondingly durable. Reinforced elements must therefore have sufficient concrete cover to ensure load transfer into the concrete and sufficient resistance to corrosion. This preliminary study investigates the material properties (compressive/flexural strength and E-modulus) of SPI components produced using a large scale printer and a CEM II/A-S cement as binder. The compressive strength and E-modulus values showed an isotopic behaviour. The flexural strength exhibited an anisotropic behaviour but only in one direction by a load introduction parallel to the layers. In addition, the durability properties concerning reinforcement corrosion due to chlorides were determined. A durability assessment was carried out to provide information on the required concrete cover in combination with selected reinforcement materials. The chloride migration coefficients of SPI material were comparable to those of casted concrete of the same binder type and w/c-ratio. A dependence on the ratio of test direction to printing direction could be determined. For the realisation of low concrete covers the use of reinforcement with a high C_crit value is expedient. Summarized this study showed that SPI is suitable for the production of durable, reinforced, filigree façade elements when the printing direction, exposure direction, reinforcing materials and concrete cover are coordinated.