3D printable cement-based composites reinforced with Sisal fibers: Rheology, printability and hardened properties

Reinforcement of cement-based systems is one of the main unsolved issues for 3D printing technology (3DP). The use of short fibers is a promising way to improve cement-based systems fresh and hardened strength, overcoming this limitation. Among natural fibers, Sisal fibers (SF) can be an excellent option, due to their irregular cross-section morphology, water retention capacity and high Young modulus. In this study, fresh and hardened properties of 3D printable cement-limestone filler mortar reinforced with 1 % volumetric fraction (VF) of 6.5 mm SF and 0.5, 1 and 1.5 % VF of 13 mm SF was assessed. Fresh state mortar rheology was evaluated using flow table test (FT), Self-weight cone-penetration (WCP), Displacement-controlled cone-penetration (DCP) and fresh squeeze tests (SQT). 3DP was evaluated on mortars using a manual extruder and a 3D cartesian robotic printer. Hardened physical and mechanical properties were tested, comparing the effect of 3DP and SF reinforcement on conventional and 3D printed specimens. It was observed that SF slightly modified mortars’ rheology and cohesiveness, while SF improved fresh mechanical behavior and enhanced flexural strength and toughness index ( I T ) on hardened state, due to SF alignment produced by 3DP. Water capillarity and open porosity was also modified by 3DP, due to particle squeezing and fiber´s alignment during extrusion. Higher VF and longer fibers reduced robotic printability and produced discontinuities and pumping blockage, showing limits for SF addition. • Sisal fiber (SF) of 13 and 6.5 mm length were added to 3D printable mortars. • SF increased shear yield stress and mechanical properties in fresh state. • Ram and screw system 3D printing methods were used and in both SF were aligned. • SF and 3D printing process increase apparent density and reduce open porosity. • Aligned SF increased flexural strength and toughness index of 3D printable mortars.