Implications of Yarn Impregnation in the Bond and Tensile Behaviour of Textile-Reinforced Mineral-Bonded Composites: An Overview

In the development of textile reinforced composites with inorganic matrices, the interfacial bond between the yarns and the mineral matrix, regardless of its nature (e.g. cementitious, natural hydraulic lime, geopolymer) and application, plays a key role. Depending on the intended application of the composite system (Textile Reinforced Concrete (TRC) is generally devised for new lightweight structures, whereas Textile Reinforced Mortar (TRM) is intended for retrofitting purposes), the tensile performance of the composites is governed by the formation and development of diffuse crack patterns, which ultimately control the ductility. In this paper we review the experimental approaches, mainly developed in the last decade, to improve the interfacial bonding between multifilament yarns and mineral matrices while maintaining the inorganic nature of the composite. The most effective solutions consisted of silica coating of AR glass yarns in TRM systems, which induced a significant improvement of the bond due to fibre functionalisation. In the field of TRC, a promising technique is the impregnation of carbon yarns with cementitious or geopolymer suspensions, which could simultaneously improve the monolithic behaviour of the yarns and the chemical bond with the cementitious matrix. These techniques compete against the more established polymer impregnation, i.e. epoxy, which, while improving the bond with mineral-bonded matrices (e.g. cement or lime based fine-grained concrete) in TRC/TRM and preventing telescopic failure, has the significant disadvantage of degrading at moderate temperatures, exposing the structural element to the risk of premature failure.