Effect of aleuropelite content on fresh and hardened properties of 3D-printable multi-binder composites

The object of research is a 3D-printable blended mixture with aleuropelite content. The effect of the aleuropelite dosage and viscosity modifier type on the technological properties and structure formation strength of 3D-build printable mixtures has been investigated. Method. Two types of 3D-built printable mixtures have been used. Their mix design was regulated by the kind of viscosity modifier (metakaolin and combined modifier based on xanthan gum + liquid glass) and dosage of the aleuropelite. Two squeezing tests were used to evaluate the fresh mixture's extrusion ability and shape retention. A high compression speed test using a constant plate speed of 5 mm/s was implemented as the system's behavior in the extrusion process. The squeezing test was conducted with a constant strain rate of 0.5 N/s and was implemented as the system's behavior in the multi-layer casting process. The compressive strength was measured according to Russian Standard GOST 10180-2012 «Concrete. Methods for determining strength from control samples». The SEM-microscopy methods were used to evaluate the microstructure and hydrate phase composition. Results. The plasticity and shape retention of 3D-built printable mixtures depend on aleuropelite content in a binder. The fresh 3D-printable mixtures with 20-30 % aleuropelite dosage in the binder had a plastic yield value of 0.8–1.6 kPa and structural strength of 1.2–5.5 kPa. The strength of 3D-build printable concrete depends on the combination of viscosity modifier type and aleuropelite content in a binder. The combination of metakaolin and aleuropelite as highly active aluminosilicate modifiers causes a high compressive strength (46–56 MPa and 37–65 MPa at seven days and 28 days after production, respectively). The combination of the aluminate phase of metakaolin and aleuropelite in the mix determines the acceleration of the hydration phase formation. The technologically acceptable plasticity shape retention and high strength of 3D-build printable mixtures must be based on hydration process control.