Permeation of water and gases through cracked textile reinforced concrete

Textile reinforced concrete (TRC) is a high-performance, cement-based composite consisting of fine-grained concrete and textile reinforcement, the latter usually consisting of glass or carbon multi-filament yarns. When subjected to tensile loading, TRC shows pronounced strain hardening behaviour accompanied by multiple cracking. The superior mechanical performance of TRC can be used very efficiently in the strengthening and repair of structural elements made of reinforced concrete or other traditional materials. The durability of restored structures with such TRC layers depends directly on the resistance of TRC to the transport of fluids and gases into and through the repair material. In this experimental study the effects of multiple cracking on the permeation of water and gases through TRC are investigated.For permeability testing special equipment was developed to facilitate in situ measurement of the water and gas transport properties of cracked TRC at chosen strain levels under uniaxial tensile loading. Further parameters of the study were the fineness and coating of the yarns comprising the textile reinforcement. In the case of uncoated textile, an increase in the fineness of the yarns as well as the residual strain led to a considerable increase in water absorption. The permeation of oxygen and water through cracked TRC correlated with the induced strain and the crack characteristics, i.e. the number of cracks and crack width. The crack pattern itself depended on the choice of the particular textile reinforcement. The influence of imposed strain on the permeation of water in cracked TRC was described by a simple model based on Hagen–Poiseuille’s Law. Furthermore, the effect of self-healing phenomena on the transport properties of TRC was investigated. The self-healing of fine cracks led to a very pronounced reduction in the transport rates over time.