Effect of polypropylene fibres on the workability parameters of extrudable cementitious materials

3D Concrete Printing (3DCP) has aa potentiality to produce complex, geometries and can modify the details rapidly using a printer integrated with a pump and nozzle. From the earlier studies on 3DCP, it is distinguished that the rheological behaviour of the material, printing direction, and printing time may have significant effects on the overall structural behaviour of the printed structure. The layered concrete may create weak joints in the specimens and reduce the load bearing capacity in terms of compressive, tensile and flexural strength that requires stress transfer across or along these joints The present study focuses on the examination of the effect of adding polypropylene (PP) fibres on the failure behaviour of print mortar on printed concrete, on different print directions. The Silica Fume (SF) based control mix was used in the analysis with fibre addition in different mass fraction of binder ranging from 0.5% to 3.0%. Those mixes were designated after the detailed fresh property analysis and control cementitious specimens without fibre inclusion were also printed for comparison. The specimens were collected in different orientations from manual extruded concrete blocks and tested for mechanical properties. For the materials tested, it is found that the mechanical properties such as compressive and flexural strength of extruded samples are governed by its printing directions. The mixes with 1.0% and 0.5% PP fibre addition exhibit the better performance in terms of flexural strength and 0.5% PP mix can be considered as the optimum fibre content with respect to the compressive strength.