3D printing of fibre cement-based materials: fresh and rheological performances

Abstract

The aim of this paper is to investigate the effect of different mix composition on fresh and rheological properties of a printable mortar. For the mix design, two binders such as fly ash (FA), and silica fume (SF) were used with cement and sand for a water/binder ratio of 0.50. Polypropylene fibres (PP), superplasticizer (SP), and viscosity modifying agents VMA (Diutan gun and nano-clay) were used in the investigation. The results show that adding 24% of fly ash and 8% Silica fume increased the yield stress, cohesiveness, and improved the structure homogeneity and stability which appeared to be an advantage to print layers. Indeed it reduced the fluidity, bleeding and the blockage of layers. Additionally, it also improved the passing ability through the extruder and showed a greater resistance to penetration. The addition polypropylene fibres (0.2% to 0.6%) led to a higher yield stress, and cohesiveness of the mix. This is led to a stable mortar and kept the shape of layer under its own weight and sustained weight of successive layers. The incorporation of PP fibres reduced the time gap. Furthermore, high dosage of fibres can create more difficulties to extrude layers and led more drainage phenomenon which increased the stiffening of the mix. PP fibres might be efficient to print layers due to their small length and diameter which resulted in a dense and efficient network. VMAs cause an important loss of workability and time gap which influenced the passing ability of the mix through the extruder. However a high dosage of SP increased also bleeding and segregation and may affect the stability and shape of the printable layers. Good correlations existed between slump flow results, penetration results and also yield stress.