Digital fabrication of eco-friendly ultra-high performance fiber-reinforced concrete

A 3D-printable ultra-high performance fiber reinforced concrete (3DP-UHPFRC) has been developed recently by the authors. This material shows high compressive and flexural strengths accompanied by deflection-hardening behavior, which allows digital fabrication of thin structures with noticeable reduction/elimination of conventional steel bars. However, the high cement content of the developed 3DP-UHPFRC (840 kg/m3) limits the material's environmental sustainability. This paper reports the development of an eco-friendly 3DP-UHPFRC by replacing high volume of the cement component of the mixture with fly ash (FA) and/or ground granulated blast-furnace slag (S). Three printable eco-friendly mixtures were prepared in which 60% of the cement was replaced by either 60% FA (S0F60) or 60% S (S60F0) or 30% FA and 30% S (S30F30). All mixtures had 30% silica fume (SF) content, by mass of binder. The fresh properties (i.e., extrudability, buildability, workability, and rheological parameters), the hardened properties (i.e., anisotropic compressive and flexural strengths), and the environmental impacts (i.e., global warming potential (GWP)) of the eco-friendly mixtures were measured and the results were compared with those of the control mixture made with SF but no FA or S (S0F0). The printable eco-friendly mixtures developed in this research have significantly higher environmental sustainability while retaining mechanical performance comparable to the 3DP-UHPFRC. A material efficiency index (MEI) was proposed to compare suitability of the eco-friendly mixtures against the control mixture. The MEI simultaneously considers multiple performance criteria including mechanical and rheological properties, and GWP. The order of MEIs of the mixtures was: S60F0 > S0F0 > S30F30 > S0F60.