The effect of fillers on the fresh and hardened properties of 3D printed geopolymer lattices

This work analyzed the effect of particle fillers on the rheology of geopolymer-based inks and on the microstructure and mechanical properties of lattices fabricated by Direct Ink Writing and subjected to different curing and firing temperatures. Adding particle fillers effectively improved the printability of the pure geopolymer ink; ground geopolymer filler was the most effective. In particular, it increased the yield strength and storage modulus, speeded up the recovery after extrusion and expanded the working window. The mechanical response of the lattices did not increase with the addition of fillers nor with increased curing temperature and time; curing at 80°C for 1 day was the best compromise between strength and time. The filler influenced the mechanical properties of lattices as a function of the firing temperature. Samples without fillers had a maximum strength of 34 ± 3 MPa after firing at 300°C, whereas those containing sand were damaged by the treatment; samples containing ground geopolymer were the most stable up to 1000°C.