Influence of rheology modifying admixtures on the buildability of 3D printing cement-based mortars

The use of rheology modifying admixtures (RMA) is widely extended in 3D printing with cement-based materials (CBM). Nanoclays (NC) produce a thixotropic effect, while viscosity modifying admixtures (VMA) enhance extrudability of CBM. This study investigates 3D printable cement- based mortars buildability combining NC and VMA. Rheology, fresh mechanical properties and hydration kinetics of CBM were assessed, identifying the effects of RMA on buildability and hydration mechanisms. It was found that critical strain (γcrit) remained constant for each mixture over time. VMA increased mortars’ deformability while NC showed a stiffening effect, improving dimensional stability and buildability. When NC and VMA were combined, the shear stiffening effect of NC dominated, although larger amounts of superplasticiser were required, delaying the development of mechanical properties. A transition from fresh plastic behaviour into a rigid state was related to setting and initial hardening after 90 min. Physical mechanisms such as flocculation produced stiffening at earlier ages.