Fabrication and mechanical properties of metakaolin-based geopolymer composites reinforced with auxetic fabrics

This work presents a novel experimental study on the use of auxetic fabrics as the main reinforcement in geopolymer composites, aiming at higher energy dissipation in impact demanding applications. For this, a potassium-based geopolymer was reinforced with an auxetic fabric consisting of basalt fiber fillings positioned between helical auxetic yarns (HAY) made of a thermoplastic polyester core, and a stiffer liquid-crystal polymer wrap, which dispersed the load demands into several single elements having different capabilities. The composites were investigated under quasi-static flexural and tensile loadings, in both longitudinal and transverse directions. The latter showed increased mechanical strengths, up to 26 MPa in tension, and 12.8 MPa in flexural strength. Each fiber portion was tested in tension separately, reaching flexible (core) and stiffer (wrap and basalt) responses, whereas HAYs displayed combined performances due to a suitable auxeticity effect, that is, a negative Poisson's ratio. The pullout investigation justified the cracking and delamination of the composites, due to its cyclic lateral area modification, which created a load demand much higher than what the brittle geopolymer can sustain in this type of solicitation. Thermogravimetric analyses helped to predict the use of such configurations under thermal exposure, pointing out that the geopolymer material could be a suitable thermal barrier to prevent sudden degradation of the fabric under these conditions.