Effects of nano clays and fiber on rheological and mechanical properties of 3D printable cement-based mortars

Despite the many advantages of 3D printing (3DP), it is less adapted to construction. Finding the right materials and evaluating their properties are still the main barriers to implementing this novelty in construction. In this study, Sepiolite (SEP) and Nano-Montmorillonite (NM) Nano-clays are investigated as rheological modifiers in pre-designed cement-based mortar tailored for 3D concrete printing (3DCP) modified with fly ash (FA) to fulfill sustainability. Moreover, Polyamide (PA) fiber addition is evaluated as reinforcement. Experiments were carried out to assess effect of the addition of NM and SEP at rates of 0.5% and 1% (by weight of binder amount), and PA fiber at rates of 0%, 0.05%, 0.125%, and 0.150% (by weight of binder amount), on the properties of printable concrete. In total, five different mix designs were either extruded manually using a caulk gun or printed using a robot, depending on the type of the experiment. Additionally, concrete samples were cast for some of the experiments to evaluate the effect of printing on the properties of the mortar. Based on the obtained results, PA fiber with a content ratio of 0.15% improved interlayer bonding and reduced slump flow loss progress as well. Moreover, the addition of 1% NM/SEP decreased workability as expected, but improved buildability, appearance, and interlayer bonding. Replacing 20% of cement by FA enhanced rheological characteristics, but weakened buildability and accelerated the slump flow loss trend.