Effect of Metakaolin, Fly Ash and Polypropylene Fibres on Fresh and Rheological Properties of 3D Printing Based Cement Materials

Abstract

The aim of this paper is to investigate the effect of mix composition such as the percentages of metakaolin (MTK) and fly ash (FA) on the fresh and rheological properties and also the percentage of polypropylene fibres. Several tests were used to determine the rheological properties such as the flow table test, the cylindrical slump test and penetrometer test. The estimated yield stress values were then calculated from the results of cylindrical slump test and the fresh density of mortar. The extrusion of layers for 3D printing was carried out using a controlled air pressure gun. This tool made it possible to test the extrusion of each mortar mix directly after mixing by producing several layers on top of each other. The use of MTK had a significant effect on the fresh and rheological proprieties. It was observed that replacing cement with MTK led more cohesive and dry mixes and therefore difficult to extrude. Using a combination of FA and MTK has increased the yield stress, cohesion, reduced the penetration and improved the shape stability and printability. It also reduced bleeding and segregation. Finally, adding more polypropylene fibres reduced the workability by improving the cohesion with a denser fibre network and reduced the penetration. Thus led to an increase in the yield stress and a reduction of the fresh properties. Good relations were observed between the fresh and rheological properties.