Properties of additively manufactured geopolymer incorporating mineral wollastonite microfibers

• Mineral wollastonite microfiber is a low-cost and sustainable reinforcement for 3DCP. • At 10% replacement of wollastonite, the static yield stress and thixotropy were enhanced. • At 10% replacement of wollastonite, the flexural strength was enhanced. • At 10% replacement of wollastonite, the compressive strength was not changed. Integration of reinforcement in the 3D concrete printing (3DCP) process is a major challenge. As a possible solution, the addition of short synthetic/metallic fibers directly to a fresh mixture before extrusion has been investigated in previous studies. However, the use of natural/inorganic microfibers such as wollastonite as reinforcement for 3DCP has received less attention. Wollastonite is substantially cheaper and more environmentally friendly than synthetic/metallic fibers. To fill this knowledge gap, this study reports a systematic approach to enhance the flexural strength of a 3D-printed geopolymer by the addition of wollastonite microfiber. The effect of different replacement levels of wollastonite (0, 5, 10, 15, 20, and 30% by weight of sand) on setting time and mechanical properties of several mixtures were evaluated to identify the optimum wollastonite content. The printing performances, rheological properties, and mechanical strengths of the optimum mixture were then evaluated and compared with the control mixture (without wollastonite). The results showed that at 10% replacement level, the static yield stress and thixotropy property of the mixture were enhanced, which is desirable for the superior printability of the mixture. In addition, the flexural strength of the mixture incorporating 10% wollastonite was superior to the control mixture, whereas the compressive strength was not changed. The use of mineral wollastonite microfibers as a low-cost and environmentally friendly reinforcement for 3DCP is experimentally established in this study.