The selective paste intrusion (SPI) describes a selective binding, additive manufacturing method. SPI bonds thin layers of aggregate by cement paste locally. Currently, SPI can achieve higher compressive strength, durability, and easier unpacking behavior compared to other selective binding methods suitable for the production of concrete structures. Particle-bed based methods not only achieve much higher surface resolutions than depositing (extrusion)-based additive manufacturing methods but also have no restrictions in freedom of form. However, the mechanical performance of SPI components strongly depends on the void content between the individual layers and thus the penetration behavior of the cement paste. This paper presents direction-dependent measurements of the strength and durability of SPI-printed components compared to casted specimens with the same mixing composition. The results show compressive strength values between 70 and 78 MPa after 7 d, flexural strength of 1/10 without reinforcement, a high freeze-thaw resistance, no detectable carbonation after 182 days of exposure under ambient CO2-conditions, and after 28 days under increased CO2 content of 2 vol % as well as low chloride penetration resistances. All tests showed in almost all cases no dependency on the layer orientation.
Keywords: 3D printing; additive manufacturing; cement; cementitious material; durability; fine-grain concrete; particle-bed; particle-bed binding; selective binding; selective paste intrusion; strength.